Book of Abstracts

International Symposium "Metal-Hydrogen Systems. Fundamentals

and Applications"

Moscow, Russia July 19-23, 2010 Chemistry Department Lomonosov Moscow State University

MH International Steering Committee E.Akiba Japan H.Jonsson Iceland V.E.Antonov Russia  R.Kirchheim Germany R.C.Bowman, Jr. USA  M.Mintz Israel R.Cantelli Italy  S.V.Mitrokhin Russia M.Fichtner Germany  D.Noreus Sweden H.Figiel Poland  D.K.Ross UK D.Fruchart France  T.Sakai Japan Y.Fukai Japan  V.A.Somenkov Russia E.McA.Gray Australia  T.Udovic  USA M.Gupta France  V.A.Yartys Norway B.Hauback Norway  K.Yvon Switzerland B.Hjörvarsson Sweden  A.Züttel  Switzerland C.M.Jensen USA

ISC Honorary Members B.Baranowski Poland  G.Sandrock  USA T.B.Flanagan USA L.Schlapbach  Switzerland I.R.Harris UK  Q.D.Wang China H.Ishikawa Japan  S.Suda Japan J.Y.Lee Korea  A.C.Switendick USA Y.Q.Lei  China  H.Wipf Germany A.Percheron‐Guegan  France H.Züchner  Germany J.J.Reilly USA

Local Organizing Committee V.V.Lunin Chairman, MSU S.V.Mitrokhin Vice‐chair, MSU V.E.Antonov ISSP RAN B.M.Bulychev MSU S.A.Nikitin MSU O.A.Petrii MSU V.A.Somenkov Kurchatov RSC  V.N.Verbetsky MSU

Symposium Proceedings will be published in in a Special Supplement issue of the Journal of Alloys and Compounds.

The Guest Editors V.A. Yartys S.V. Mitrokhin V.E. Antonov V.N. Verbetsky

Symposium is held with the support of Russian Foundation for Basic Research and Moscow city Government

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Contents Plenary lectures 3 Invited and Keynote Lectures 7 Oral Presentations 32 Poster Presentations 122 Author Index 395

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Plenary Lectures

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Metal Hydride, the Material which Lead Success of Hybrid and Coming Fuel Cell Vehicle. The Key Material and Technologies for the Current

and Future Power Train.

K. Hirose Toyota Motor Corporation

Mobility is a very important desire of human being and automobile can provide freedom for the people to move unlimitedly on the land. Oil has been main fuel to propel automobile since it started. However we are now facing to move off from this valuable high energy density fuel because of the global worming problem which automobile need to reduce carbon emissions and volatility of oil price which lead the economical instabilities Automobile companies are accelerating the development of reducing and non oil power train system such as hybrid vehicle, electric vehicle and fuel cell vehicle. Hybrid vehicles have shown the great success in the alternative power train which is reducing every day use of precious oil. The success of hybrid vehicle is due to the proper use of NiMH battery for RESS (Rechargeable Eversible Storage System). Metal hydride improved the battery capacities and output drastically. The output property of hybrid battery was the real driver for the success of Prius and other strong hybrid. And NiMH battery will likely be continuing to be used for the hybrid power train since output density and compactness are important for HV. Other new power trains which is close to the commercialization is Fuel Cell Vehicles. Vehicles development has been finalizing to go into the commercialization. September 2009 major seven auto manufactures announced they are going to make the hydrogen fuel cell vehicle into the commercialization in 2015. Cost reduction and infrastructure are the two main issues to be solved. However for the future wide penetration of fuel cell is heavily due to the availability of cheap easy hydrogen storage system even manufactures are currently working high pressure tank systems. Current high pressure system requires expensive carbon fiver and limit the design flexibilities by its cylindrical shape. So that hydrogen storage is the most desirable technologies for this innovation for the future. In the presentation status of the various hydrogen storage systems are explained and

current challenge and future scope will be discussed. In addition the priority performances for the vehicle manufactures are discussed

especially whether volumetric or gravimetric density is more important. From the point of vehicle manufactures volumetric density is more important because of the compactness of the fuel tank is very important for the vehicle design flexibility, and customer’s convenience.

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Aluminum hydride as a hydrogen and energy storage material: past, present and future

J. Graetz1, J. Reilly1, V.A. Yartys2, J.P. Maehlen2, B.M. Bulychev3, V.E. Antonov4,

B.P.Tarasov5, I.E. Gabis6 1Energy Science and Technology Department, Brookhaven National Laboratory, Upton, New York, USA

2Institute for Energy Technology, Kjeller, NORWAY 3Department of Chemistry, Lomonosov Moscow State University, Moscow, RUSSIA

4Institute of Solid State Physics, Russian Academy of Sciences, Chernogolovka, RUSSIA 5Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, RUSSIA

6V.E. Fock Institute of Physics, Saint-Petersburg University, St. Petersburg, RUSSIA Email: graetz@bnl.gov

Aluminum hydride (AlH3) is a metastable, crystalline solid at room temperature that has a volumetric hydrogen density (148 g H2/L) greater than twice that of liquid hydrogen and a gravimetric hydrogen density that exceeds 10 wt.%. It also exhibits a low heat of reaction (7 kJ/mol H2) and rapid hydrogen evolution rates at low temperature (<100°C). Military research programs on aluminum hydride date back to the 1960’s when independent groups in the United States and the Former Soviet Union first synthesized the crystalline form of α-AlH3. Over the past half century it has been used as an explosive, a reducing agent, a solid rocket propellant, a hydrogen source for portable power systems and for the deposition of Al films. The recent renaissance in hydrogen storage research for automotive applications has generated renewed interest in AlH3 due to its lightweight and low decomposition temperature. Over the years, research groups from around the globe have led efforts to tackle the key challenges that limit the widespread use of aluminum hydride. Considerable work has been focused on studying the structure, thermodynamics and kinetics of α-AlH3 and the other polymorphs (α’, β and γ-AlH3) to better understand decomposition pathways and H2 release rates. A number of groups have developed methods to kinetically stabilize alane by growing larger crystallites and applying surface coatings to inhibit spontaneous decomposition, while other groups, interested in enhancing low temperature decomposition, have investigated ways to destabilize AlH3 by incorporating catalysts. The need for a new, low cost method to synthesize AlH3 has led to many interesting hydrogenation and regeneration studies with a number of groups investigating AlH3 and Al hydrogenation at high pressures, while others have focused on low-pressure options using chemical or electrochemical routes to reform the hydride from the elements. A review of past, present and future research on aluminum hydride will be presented. This will include conventional and unconventional synthesis routes (e.g., microcrystallization. batch and continuous methods), structure and thermodynamics of the four main polymorphs, decomposition kinetics (e.g., as a function of crystallite size, catalysts and surface coatings), regeneration routes and high-pressure hydrogenation experiments.

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Conversion Materials for Hydrogen Storage and Electrochemical Applications - Concepts and Similarities

M. Fichtner

Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology, P.O. Box 3640, D-76021 Karlsruhe, Germany

Email: m.fichtner@kit.edu In classical hydrogen storage materials based on transition metal alloys hydrogen atoms are sitting at the interstities of the metal alloy leading to a very high volumetric density of the hydrogen. However, the gravimetric storage capacity is comparably low, due to the high mass of the transition metal atoms of the framework. The discovery that also complex hydrides may reversibly desorb and absorb hydrogen [1] led to the development of a new class of materials where H exchange is performed and studied on the basis of reversible solid state reactions in reactive nanocomposites where several solid hydride phases may be involved in the hydrogenation or dehydrogenation transition. Many of these hydride materials and reaction systems consist of light metal atoms and there is the perspective to not only achieve high volumetric densities but also high gravimetric capacities for hydrogen. Chemical bonding of the hydrogen by polarized covalent bonds is a distinctive feature of these systems. This paradigm change from intercalation to conversion materials has opened a new research field where chemical reactions of solids are investigated at the nanoscale. Diffusion in the solid, the role of dopants, properties and stabilization of grain boundaries, and new intermediate and metastable phases in the transition are of major importance in such systems.[2] Electrochemical storage in batteries and supercapacitors is currently based on insertion systems where Li is intercalated in host structures, oxides and carbon for example. Most of the materials have layered structures, olivine or perowskite structures. The storage density is limited, however, and it is a great challenge to achieve energy densities which are comparable to those of a hydrogen storage material because the energy density would have to be improved by a factor of 5 or more. An alternative approach which has a high potential to increase energy densities considerably is making use of several oxidation or reduction steps in a conversion so that more than one electron can be transferred by an active electrode element. Again, this may be possible by solid state conversion reactions which occur in reactive nanocomposites based on metal hydrides, oxides, fluorides or chalkogenides. Examples will be presented for anode and cathode systems which are based on the conversion principle and the state of the art will be discussed. Strategies for improving the performance and cyclic life time will be presented and discussed. It will be shown that there are similar scientific questions and challenges in both the development of H storage materials and batteries. References

1. B. Bogdanovic J. Alloys Compd., 253-254 (1997) 1 2. M. Fichtner, Intern. Symposium on Metal Hydrogen Systems (MH 2004), Krakow, Poland

(2004)

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Invited and Keynote Lectures

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Metallic Hydrides as Efficient Electrode Materials in Advanced Batteries

M. Latroche, J. X. Zhang, L. Lemort, C. Georges and F. Cuevas

CMTR- ICMPE, UMR 7182, CNRS, 2-8 rue Henri Dunant, 94320 Thiais, France Email: michel.latroche@icmpe.cnrs.fr

The storage of hydrogen for either stationary or mobile applications is becoming more and more important in view of the foreseen 'hydrogen-driven-economy'. Numerous intermetallic compounds can reversibly store hydrogen at ambient pressures following two different ways: via solid gas or electrochemical reactions. For about two decades, most commercial rechargeable Ni-MH batteries employ LaNi5-based compounds that exhibit excellent properties as negative electrodes [1]. However, they exhibit low capacities (only 1.2 wt.% hydrogen). To improve their weight capacities, such LaNi5-type compounds can be alloyed with MgNi2-type phase leading to so-called superlattice alloys [2,3] that are now used as electrodes. However, real breakthrough will not be achieved without getting rid of heavy rare earths elements. Therefore, the search for new metal hydrides has focused on Mg-rich alloys, since pure Mg has a very high reversible storage capacity (7.6 wt.%). Extremely sluggish sorption kinetics prevents practical application of MgH2 as a storage medium, but Mg-M (M=Sc,Ti) alloys have recently proven [4,5] to be viable reversible hydrogen storage media. They were shown to have extremely high reversible electrochemical storage capacities up to more than 5 wt.%, with discharge kinetics far superior to those of pure MgH2. Finally, the conversion reaction between Mg or Ti hydrides and lithium metal will be foreseen as a possible route for new negative electrodes for Li-ion batteries [6,7]. References 1. T.K. Ying, X.P. Gao, W.K. Hu, F. Wu and D. Noréus. Intern. J. of Hydrogen Energy, 31 (2006) 525. 2. T. Kohno, H. Yoshida, F. Kawashima, T. Inaba, I. Sakai, M. Yamamoto and M. Kanda, J. Alloys Compd., 311 (2000) L5. 3. M.-A. Petit-Férey, F. Cuevas, M. Latroche, B. Knosp and P. Bernard, Electrochimica Acta, 54 (2009) 1710. 4. W.P. Kalisvaart, M. Latroche, F. Cuevas and P.H.L. Notten, J. Solid State Chem., 181 (2008) 1141. 5. S. Srinivasan, P.C.M.M. Magusin, W.P. Kalisvaart, P.H.L. Notten, F. Cuevas, M. Latroche, R.A. van Santen, Phys. Rev. B, 81 (2010) 054107. 6. Y. Oumellal, A. Rougier, G. A. Nazri, J-M. Tarascon and L. Aymard, Nature Materials, 7 (2008) 916. 7. Y. Oumellal, A. Rougier, J-M. Tarascon and L. Aymard, Journal of Power Sources 192 (2009) 698.

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Hydrides as Negative Electrode for Li-ion Batteries. New Opportunities for Metal Hydrides and Li-ion Technologies

from Micrometrics to Nanometric Size Range. 1Y. Oumellal, 1W. Zaïdi, 1A. Rougier, 2J. Zhang, 2F. Cuevas, 2M.Latroche, 3J-L Bobet.

and 1*L. Aymard 1 : LRCS, UMR CNRS 6007, 100 rue Saint leu Amiens, France

2 : ICMPE, CNRS UMR 7182 2-8 rue Henri Dunant, 94320 Thiais, France. 3 : ICMCB-CNRS UPR 9048, 33608 Pessac France

* corresponding author Email: luc.aymard@u-picardie.fr

Limited fossil energy ressources and global warming push to the development of alternative energy sources, conversion devices and storage systems. Regarding mobile applications, the success of technologies such as Electric Vehicle (EV), Hybrid EV or Fuel Cell (FC) is strongly dependent on the improvement of storage capacities, kinetics, and density of energy. In this context, new concepts must appear. Herein, the use of metal hydrides (MH) for Li-ion technology coupling the advantages of high weight capacity of MH electrodes with the high energy density of Li-ion batteries has been recently proposed as a promising concept for mobile applications.

As an exemple, the MgH2 optimized electrode shows a large reversible capacity of 1480 mAh/g (four times that of conventional Li/C electrodes) at an average voltage of 0.5 V vs. Li+/Li° which is suitable for the negative electrode in such batteries. In addition, the polarization shows the lowest value (0.2 V vs Li+/Li°) ever reported for conversion electrodes. The discharge electrochemical reaction results in the formation of a composite made of Mg embedded in a LiH matrix, which on charging converts back to MgH2. Though quite attractive, limitations of the performances of the MgH2 electrode due to slow hydrogen diffusion appear at high cycling rates. Capacity fading due to the large volume variation of the electrode (83%) during charge/discharge is also a key issue. To overcome these limitations, decreasing of the hydride particle size from micrometric to nanometric range as well as the use of catalytic nano additives is proposed.

The extension of the conversion reaction MHx + x Li+ + x e- ↔ M + x LiH to other hydrides has been experimentally confirmed for TiH2, NaH, TiNiH, LaNi4.25Mn0.75H5 and Mg2NiH3.7 hydrides. Better performances are expected for low-weight metallic systems with fast kinetic hydrogenation properties. The use of such hydrides is currently under investigation. Note than for TiH2 new conversion mecanism via the formation of TiH2-x fcc solid solution and metastable phases can be observed.

References 1. Y. Oumellal, A. Rougier, G.A. Nazri, J-M. Tarascon and L. Aymard “Metal hydrides for Li-ion batteries”. Nature materials 7 ( 2008) 916 2. Y. Oumellal, A. Rougier, J-M. Tarascon and L. Aymard*. “2LiH + M: (M=Mg, Ti): New concept of negative electrode for rechargeable lithium-ion batteries” Journal of Power Sources 192 (2009)6

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Surface-Modified Advanced Hydrogen Storage Alloys for Hydrogen Separation and Purification

M. Lototsky1, M. Williams1, Y. Klochko1 and V.A. Yartys2 1South African Institute for Advanced Materials Chemistry, University of the Western Cape, Bellville,

South Africa Email: mlototskyy@uwc.ac.za

2Department of Energy Systems, Institute for Energy Technology, Kjeller, Norway

Applications of metal hydrides (MH) offer promising solutions in addressing the problem of hydrogen recovery from the process gases. Selectivity of reversible hydrogen interaction with hydride-forming materials allows development of simple and efficient systems for hydrogen extraction from gaseous mixtures and its fine purification. The main problem of this approach is in a deterioration of the hydrogen sorption performances caused by impurities of active gases. This presentation summarises collaborative activities of South African and Norwegian groups in the development and characterisation of the advanced surface-modified materials on the basis of AB5- and AB-type hydrogen storage alloys. Activation performance and poisoning tolerance of the H-storing alloys were shown to be significantly improved by their surface modification using fluorination and / or electroless deposition of single- or mixed-metal coatings on the basis of Platinum Group Metals, Pd and / or Pt [1–5]. Synthesis route significantly influenced surface morphology and kinetics of hydrogenation. Hydrogen absorption rate, after long-term pre-exposure to air was shown to be increased in ~100 times for the surface-modified materials, as compared to the unmodified alloy. Most importantly, we demonstrated feasibility of application of the surface-modified MH for the efficient hydrogen separation from gas mixtures (H2 + CO/ CO2/H2O). Sequential fluorination – functionalization – Pd encapsulation technique dramatically increased the poisoning resistance of the modified materials as compared to the unmodified ones where a significant deterioration of the H absorption kinetics took place after poisoning by CO2 and / or CO. Surface-modified materials were characterised by the kinetic studies in a running-flow regime, elemental (AAS) and phase-structural (SR XRD) analysis, high-resolution SEM (morphology of the coatings), specific surface area studies (BET), element surface distribution (micro-PIXE). Observed improvements were credited to the promotion of the hydrogen spillover phenomenon using fluoride as a high surface area scaffolding and Pd as a unique catalytic mantle. The approach undertaken has the potential in tailoring of the new classes of highly efficient and robust composite H storage materials. This work is supported by South Africa – Norway Programme for Research Cooperation (project # 180344), ESKOM Holdings Ltd., and South African Department of Science and Technology within HFCT RDI Strategy (Project KP8-S02). References

1. Patent application PCT/IB2008/054893 (2008), South Africa. 2. Patent ZA 2008/09123 (2009), South Africa. 3. M. Williams, M. V. Lototsky, V. M. Linkov, A. N. Nechaev, J. K. Solberg, V. A.Yartys,

Int. J. Energy Research, 33 (13) (2009) 1171-1179. 4. M. Williams, A.N. Nechaev, M.V. Lototsky, V.A.Yartys, J.K.Solberg, R.V.Denys,

C.Pineda, Q.Li, V.M.Linkov, Mater. Chem. Phys., 115 (2009) 136–141. 5. M.Williams, M.V.Lototsky, A.N.Nechaev, V.A.Yartys, J.K.Solberg, R.V.Denys,

V.M.Linkov, South African Journal of Science (manuscript MS 6360; in press).

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Effect of Mg on Structure and Thermodynamics of La-Mg-Ni Hydrides Synthesised by Hydrogen Metallurgy and Studied by in

Situ Diffraction

R.V. Denysa,b and V.A. Yartys a,c b Institute for Energy Technology, Kjeller, Norway

bPhysico-Mechanical Institute / National Academy of Sciences of Ukraine, Lviv, Ukraine c Norwegian University of Science and Technology, Trondheim, Norway

Email: rdenys@ipm.lviv.ua

Despite the electrochemical properties of the La-Mg-Ni alloys are widely Ternary La-Mg-Ni intermetallics of AB3 and A2B7 types are important in advancing the Ni-MH batteries. studied, however, little is known about influence of the Mg La substitution on the structural, thermodynamic and hydrogen sorption properties. The mechanism of the hydrogenation process and the crystal structures of the formed hydrides (deuterides) were studied in this work by SR XRD (at Swiss-Norwegian Beam Lines, ESRF) and by NPD (at Swiss Spallation Neutron Source SINQ). The single phase samples of the La1-xMgxNi3 (x=0-0.67) and La2-yMgyNi7 (y=0-0.25) intermetallic alloys were prepared by powder metallurgy. Magnesium strongly affects crystal structures, H storage capacities, and thermodynamics of the La-Mg-Ni-based hydrides. La replacement by Mg proceeds in an ordered way, only within the Laves type layers of the hybrid crystal structures, which are built from the altered MgZn2- and CaCu5-type slabs. Mg influences structural features of the hydrogenation process and determines various aspects of hydrogen interaction with the La-Mg-Ni intermetallics causing: (a) change of the mechanism of the hydrogenation from anisotropic to isotropic one; (b) increase of the reversible hydrogen storage capacity (the highest reversible capacity was reached when 50% of La was substituted by Mg in the MgZn2-type slabs); (c) improvement of the resistance against hydrogen-induced amorphisation; (d) substantial decrease of the stability of the hydrides. Instead of a strong unilateral anisotropic expansion with H atoms filling the Laves-type slabs observed for LaNi3 and La2Ni7 [1], in the “isotropic” structures of the Mg-substituted compounds both LaNi5 and La1-xMg1+xNi4 layers become occupied by H [2]. Powder metallurgy techniques were successfully applied in this work to synthesise nanostructured La-Mg and La-Mg-Ni H storage alloys. These included RBM in hydrogen followed by cycling of hydrogen absorption and desorption [3]. Hydrogen metallurgy (HM) route yielded the LaMg12 and La2Mg17 intermetallic compounds synthesized from LaH2 and MgH2 via the mechanism of cooperative phase transformation at low temperatures being 400° C below the decomposition temperature for the individual LaH2 [4]. This demonstrates a profound potential of HM in synthesis of hydrogen-storing IMC. References 1. V. A. Yartys, et al. Z.Kristallogr. 223 (2008) 674–689. 2. R.V. Denys, et al. Journal of Solid State Chemistry, 181 (4) (2008) 812-821. 3. R.V. Denys, et al. Acta Materialia, 57 (13) (2009) 3989-4000. 4. R. V. Denys, et al. Acta Materialia, 58 (7) (2010) 2510-2519.

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Thermodynamic Optimization of the System Pd-Rh-H-D-T

J.-M. Jouberta and S. Thiébautb a Chimie Métallurgique des Terres Rares, ICMPE, CNRS, 2-8 rue H. Dunant, F-94320 Thiais, France

bCEA/DAM/Valduc, F-21120 Is sur Tille, France Email: joubert@icmpe.cnrs.fr

The Calphad method is a semi-empirical technique for the modelling and calculation of phase diagrams based on the description of the Gibbs energies of the different phases. The phase equilibrium in multi-component systems may be predicted by extrapolation when lower order systems (binaries, ternaries…) have been correctly modelled by fitting the parameters describing the Gibbs energies to the available experimental data (phase diagram and thermodynamic data). The Calphad method has been used to model the quinary system Pd-Rh-H-D-T. Indeed Pd and Pd-Rh alloys are considered for hydrogen and isotope storage. The constituting binary systems have been first described. Not only experimental phase diagrams but also thermodynamic properties such as calorimetric measurements and pressure-composition curves are well reproduced by adjusting the parameters describing the Gibbs energy of the fcc phase [1]. In order to describe Rh-H systems, a new equation of state of hydrogen gas has been obtained allowing to describe analytically its Gibbs energy and molar volume as a function of pressure [2]. The binary systems can be combined and used to predict any kind of parameters in the quinary system e.g. isotope separation factor or plateau pressure as a function of Rh or isotope concentration. References 1. J.-M. Joubert, S. Thiébaut, J. Nucl. Mater., 395, (2009), 78-88. 2. J.-M. Joubert, Int. J. Hydrogen Energy, 35, (2010), 2104-2111.

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Hydrogen in Nanostructured Materials

R. Andrievski Institute of Problems of Chemical Physics, Russian Academy of Sciences, Chernogolovka, Russia

Email: ara@icp.ac.ru

Curently the nanostructured approach based on the use of nanostructural advantages becomes more and more wirespread. It is characterized by the size of fundamental structure components (grains, phase inclusions, layers, etc.) being in the range from 1-2 nm to about of 100 nm. As applied to hydrogen materials these features seem to be very important both in the synthesis processes and physical-chemical properties. This review is mainly devoted to the structure and properties of hydrogen nanostructured materials [1,2]. Attention is focused on the effect of crystalline size on absorption/desorption properties of the Me – H2 systems such as the Pd – H2, TiFe – H2, Mg2Ni – H2, Mg – H2 systems and so on. Structural features and some physical properties of nanocrystalline and amorphous hydrides studied by different independrnt characterization methods are considered and discussed in details. Some aspects still to be clarified are pointed. References 1. R.A. Andrievski, Materials Science Forum, 555 (2007) 327-334. 2. R.A. Andrievski, Physics – Uspechi, 50 (2007) 691-704.

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Structure and Bonding in Metal Borohydrides

Y. Filinchuk1, R. Černý2, D. Ravnsbæk3, B. Richter3, T.R. Jensen3, D. Chernyshov1, V. Dmitriev1 and H. Hagemann4

1Swiss-Norwegian Beam Lines at ESRF, Grenoble, France 2Lab. Crystallography, Univ. of Geneva,

Switzerland 3Dept. of Chemistry and iNANO, Aarhus University, Denmark 4Dépt. de Chim. Phys., Univ. of Geneva, Switzerland

Email: yaroslav.filinchuk@esrf.fr Here we present new borohydrides, new forms of some known compounds, their structure and transformations, and rationalize the observations in terms of different bonding schemes between metal atoms and the borohydride groups. We reveal different structure-forming units (cation and anion) and different extents of ionicity/covalency (related to the change transfer from cations to anions), and group the compounds accordingly. --- Pressure and temperature evolution of MBH4 series (M = Li-Rb) reveals largely ionic bonding between M and BH4. A reduction in the number of the repulsive H…H contacts is responsible for the transition from the cubic to the ordered LT/HP phase, while their compression primarily determines the compressibility [1]. The structures are the result of close packing of the tetrahedral BH4 group in the M-atom environments, with coordination numbers varying from 4 to 8. The stereochemical role of the anisotropic anion can be generalized to a concept of anion-centred complexes. --- Bimetallic borohydrides involving alkaline and transition metals contain cation-centred complexes, where a d-metal atom is strongly bound to the BH4 groups. More electropositive s-metal atoms donate electrons, stabilizing the cation-centred complex anions. M[Sc(BH4)4], M = Li-K contain mononuclear, M[Zn2(BH4)5], M = Li, Na contain dinuclear, and Na[Zn(BH4)3] – polynuclear d-metal complexes. --- BH4 groups in cation-centred complex anions can be combined with other ligands, as demonstrated by the first heteroleptic (heteroligand) complex in K[Zn(BH4)Cl2]. --- The anion- and cation-centred complexes may combine in the same compound, leading to at first sight complicated compositions: Li4Al3(BH4)13 = [(BH4)Li4] + 3[Al(BH4)4] [2]. --- Monometallic borohydrides involving less electropositive metals reveal a pronounced covalency of the M...BH4 interaction, leading to a totally new chemistry. This includes unprecedented open zeolite-like frameworks, dense interpenetrated frameworks etc. New results will be presented for Mg(BH4)2, Mn(BH4)2 and Y(BH4)3 systems and the underlying building principles and the bonding scheme will be proposed. The results show that the BH4 group serves as a directional ligand and this class of borohydrides resembles metal-organic frameworks (MOFs). Thus, the principles of coordination chemistry apply, radically changing the established views on the chemistry of metal borohydrides.

Structure-stability relations and synthetic approaches will be discussed, and the ways towards a design of new borohydrides-based systems will be suggested. References 1. O. Babanova, A. Soloninin, A. Stepanov, A. Skripov, Y. Filinchuk, J. Phys. Chem. C, 114, (2010), 3712-3718. 2. Lindemann I., Ferrer R.D., Dunsch L., Filinchuk Y., Hagemann H., D'Anna V., Černý R., Schultz L., Gutfleisch O. submitted.

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15

Hydrogen Diffusion and Partial Reversibility of Transition Metal- Doped Magnesium Hydrides

D. Moser1 D. J. Bull1, K. Ross1 and D. Norèus2

1 University of Salford, The Crescent, Salford, Manchester M5 4WT 2 University of Stockholm, S-10691, Stockholm, Sweden

MgH2 is hydrogen-dense but normally has a rutile structure, which is too stable and has a hydrogen diffusion rate that is too low for practical applications [1]. At pressures of several GPa, MgH2 has been predicted to form a CaF2 structure [2]. When a small fraction of the magnesium atoms is replaced by transition metal atoms such as Ti, this cubic phase remains stable when the high GPa synthetic pressure is released. The ordered form of this new phase has a typical composition Mg7TiH16 [3]. The nature of the change in the metal-hydrogen bonding as compared to that in conventional MgH2 and TiH2 is discussed. Density Functional Theory calculations show a weakening in the force constants of the Ti-H and Mg-H bonds which can be directly related to the FCC structures of TiH2 and MgH2. Consideration of the structural similarities of the three FCC systems leads to a better understanding of the formation process of the new ternary compounds [4]. The presence of two non-equivalent types of tetrahedral site with different force constants, as predicted by a vibrational analysis, suggests a two-step hydrogenation/dehydrogenation process. Subsequent gravimetric measurements allow us to investigate the reversibility of incompletely dehydrogenated samples and these results show the fast kinetics of desorption and the associated reordering of the MgH2- TiH2 environment is demonstrated by XRD structural analysis. Comparison with theTiHx system is also interesting in terms of hydrogen diffusion inside the host lattice [5, 6]. This aspect of the system has been investigated with Quasi Elastic Neutron Scattering. A rapid drop in the elastic scattered intensity, as measured on IN10 at the ILL Grenoble, has been measured in the 100-400 K temperature range. Assuming a model with only long range diffusion on the H2 (Td4Mg) sites, an activation energy of E = 0.075 eV is obtained. If this partial reversibility could be optimised with respect to TM selection and substitution level, it would demonstrate an important breakthrough for storing hydrogen in magnesium hydrides. References 1. J. Topler, H. Buchner, H Saufferer, K. Knorr, W. Prandl, J. Less-Comm Me. 88 (1982) 397-404. 2. P. Vajeeston, P. Ravindran, A. Kjekshus, H. Fjellvеg, Phys. Rev. Lett. 89 (2002) 175506. 3. D. Kyoi, T. Sato, E. Rennebro, N. Kitamura, A. Ueda, M. Ito, S. Katsuyama, S. Hara, D. Noreus, T. Sakai, J. Alloy Compd. 372 (2004) 213. 4. D. Moser, D.J. Bull, T. Sato, D. Norйus, D. Kyoi, T. Sakai, N. Kitamura, H. Yusa, T. Taniguchi, W.P. Kalisvaart and P. Notten, J Mater. Chem., 19, (2009) 8150-8161 5. U. Kaess, G. Majer, M. Stoll, D.T. Peterson, R.G. Barnes, J. Alloys Compd. 259 (1997) 74-82 6. H. Wipf, B. Kappesser, R. Werner, J. Alloys Compd, 310 (2000) 190-195

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A Comprehensive Study of Ammonia Borane by Anelastic Spectrosopy: Hydrogen Dynamics, Structural Phase Transitions, Isotope Effects and Nanoconfinement

R. Cantelli Università di Roma "La Sapienza", Rome, I-00185, ITALY

Email: Rosario.Cantelli@roma1.infn.it

Ammonia borane, NH3BH3, has a very interesting hydrogen content of 19% wt and moderate dehydrogenation temperatures (less than 100 °C). However, the rates of H2 release at temperatures below 85 °C need to be increased, borazine formation must be prevented and regeneration must be made more energy efficient for applications in fuel cells. An anelastic spectroscopy study of NH3BH3 displayed the presence of thermally activated relaxation processes at about 100 K (for a sample vibration frequency of ~1 kHz), due to the dynamics of a very mobile species with pre-exponential factors of the relaxation rate typical of hopping of atoms or atom clusters. From a comparative analysis of our results with NMR data and theoretical estimates, the measured processes were attributed to the torsional and rotational motions of the NH3 and BH3 groups of the ammonia-borane complex.[1] These two relaxation processes are present also in the partially deuterated and in the perdeuterated sample. Recently, on studying the effects of isotope substitutions we observed a very intense thermally activated process around 70 K in NH3BD3 and ND3BD3. From the features of the relaxation curves as a function of temperature we attributed that process to the n-fold relaxation of the B-N axis around its average orientation. A secondary peak in the low temperature shoulder was ascribed to an extensional relaxation of the BN bond caused by the hopping of N between two close and energetically equivalent sites along the axis. In the ND3BH3 those motions seem to be coupled.[2] A systematic study of the structural phase transition occurring around 220 K in NH3BH3 and in its deuterated anologues was also performed by combining anelastic spectroscopy and differential scanning calorimetry. The transition is accompanied by a latent heat which denotes a 1st order character and by a temperature hysteresis of the elastic and anelastic properties. In the deuterated samples the enthalpy variation is reduced and the transition is shifted towards higher temperatures. Moreover, the coexistence region between the low- and high-temperature phases is very narrow (a fraction of K). Quantitative kinetic measurements yield a time constant τ of ~16 minutes for the transformation of the orthorhombic into the tetragonal phase in NH3BH3 and an increase of τ in the deuterated compound, showing a drastic isotope slowing down of the transformation kinetics. Recently it was reported that artificial assembling of ammonia borane consisting in the infusion of NH3BH3 into mesoporous silica scaffolds increases the desorption rates of hydrogen and decreases both the contamination of hydrogen from borazine and the dehydrogenation enthalpy. We studied to which extent the basic physical properties of ammonia borane are modified when this compound is dispersed as a single monolayer inside porous silica channels. In particular we showed that the infiltration of NH3BH3 completely suppresses the structural phase transition occurring in bulk NH3BH3.[3]. Those results provided evidence that nano-confining drastically affects the thermodynamic properties of the starting material. The occurrence of different electronic and lattice interactions in nano-confined hydrogen storage systems could provide an alternative approach to modify the physical features of other bulk hydrogen storage materials to obtain enhanced dehydrogenation and rehydrogenation properties. References 1. A. Paolone, O. Palumbo, P. Rispoli, R. Cantelli, T. Autrey, Journal of Physical Chemistry C 113 (2009) 5872. 2. A. Paolone, O. Palumbo, P. Rispoli, R. Cantelli, T. Autrey, A. Karkamkar, Journal of Physical Chemistry, submitted. 3. A. Paolone, O. Palumbo, P. Rispoli, R. Cantelli, T. Autrey, A. Karkamkar, Journal of Physical Chemistry C 113 (2009) 10319

17

Classical Diffusion of Interstitial Hydrogen Revisited

A. Blomqvist, G. K. Pálsson, C. Moysés Araújo, R. Ahuja and B. Hjörvarsson Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

Email: Andreas.Blomqvist@fysik.uu.se Diffusion of hydrogen is often envisioned as an over barrier jump in a static potential. Here we show that a much more complicated view on the dynamics and the energy landscape emerges when the underlying mechanism of the interaction and the diffusion in the lattice is considered. The absorption of hydrogen is associated with self-trapping in a local strain field, caused by changes in the electronic structure and the elastic response of the lattice. This local strain field is commonly referred to as a small-polaron. The polaron has an influence on the potential energy landscape and will therefore influence the diffusion of hydrogen and its isotopes. At low temperatures, the polaron follows the hydrogen atom and the diffusion process can be viewed as the diffusion of the combined proton-polaron quasi-particle. As the temperature is increased, the residence time of the proton decreases and eventually becomes shorter than the response time of the lattice. This process can be described as a proton-polaron unbinding, as the local strain field can not be formed during the short residence time of the proton. Our ab initio molecular dynamics simulations of hydrogen isotopes in Nb agree well with the experimentally observed increase in diffusion at elevated temperatures [1]. The results from these calculations allowed us to unambiguisly identify the onset of the un-binding process and to pinpoint the two main types of diffusion. The unbinding of the intersitial proton and the polaron, in combination with the identification of the underlying diffusion mechanism, calls for a revision of the conceptual framework of diffusion of interstitial hydrogen as well as light interstitials in general. References 1. T. Eguchi and S. Morozumi, Nippon Kinzokugakkaishi 41, 795 (1977).

18

Hydrogen-Related Properties of Metal and Alloy Nanoparticles

M.Yamauchi Catalysis Research Center, Hokkaido University, Japan

Email: yamauchi@cat.hokudai.ac.jp Hydrogen storage in metal exhibits many advantages, i.e., compactness, moderate working condition, safe storage, etc. For practical usage, higher-density storage and lowerworking temperature and pressure are required. As a new hydrogen storage media, we notice metal and alloy nanoparticles. Because nanoparticles have large surface area to whole volume and peculiar electronic states, they are expected to show unique properties as hydrogen storage media. In our study on 2.6 nm palladium nanoparticles, it is found that critical temperature of two-phase region of solid solution of palladium and hydrogen and palladium hydride is reduced by ca. 200 K, which is attributed to the different energetic stability and a large degree of structural freedom in nanometer-sized hydrides.(see Figure 1).[1-3] Taking into it account that hydride of nanoparticles have large extent of disorder, we tried to use hydrogen as an agitator for structural control of alloy nanoparticles. It is noted that some metals, which is inert to hydrogen storage in the bulk, become to absorb hydrogen with decrease of their size less than 100 nm in diameter. We examine structural control of nanoparticles by hydrogen charging treatment at relatively low temperatures. For example, FePt alloy nanoparticles, which usually show ferromagnetic characters after thermal treatment at ca. 550 °C, became roomtemperature ferromagnet after hydrogen charging treatment at 280 °C.[4] Mechanism for structural change of alloy nanoparticles were examined by in-situ XRD measurements by using SOR. Further, application of alloy nanoparticles to photocatalysis will be presented. Motional properties of hydrogen atoms absorbed in palladium nanoparticles were investigated by solid NMR and neutron scattering measurements. Both measurenents gave data that demostrate excitation of tunneling of hydrogen with particle-size dependence. References 1.M. Yamauchi, H. Kobayashi, H. Kitagawa, ChemPhysChem, 10, (2009), 2566-2576. 2.H. Kobayashi, M. Yamauchi, H. Kitagawa, Y. Kubota, K. Kato, and M. Takata, J. Am. Chem. Soc., 130(6), (2008), 1828-1829. 3.M. Yamauchi, R. Ikeda, H. Kitagawa, M. Takata, J. Phys. Chem. C, 112, (2008), 3294- 3299 . 4.M. Nakaya, M. Kanehara, M. Yamauchi, H. Kitagawa, T. Teranishi, J. Phys. Chem. C, 111, (2007), 7231-7234.

19

Inhibition of Hydrogen Chemisorption on Uranium Surfaces by Traces of Water Vapor

N. Shamir

Physics Dept., Nuclear Research Centre – Negev, P. O. Box 9001, Beer-Sheva 84190, Israel Email: noah.shamir@gmail.com

Traces of about 1-2% water vapor are sufficient to inhibit hydrogen dissociation and chemisorption on uranium surfaces, under low pressure exposures, at room temperature. The efficiency of the inhibition increases with temperature in the range of 200 – 400 K. The inhibition effect is also influenced by the extent of residual strain of the sample, with increasing inhibition efficiencies exhibited by a less strained surface. O2, in contrast to H2O, is not an inhibitor to surface adsorption and dissociation of hydrogen. Three types of mechanisms are discussed in order to account for the above inhibition effect of water. It is concluded that the most probable mechanism involves the reversible adsorption of water molecules on hydrogen dissociation sites causing their ‘‘blocking’’.

20

Principles of So-Called d-Metal Catalyst Interfaces for Very Fast Hydrogenation Kinetics of Magnesium

G. Girard, D. Fruchart, O. Fruchart, S. Miraglia, L. Ortega, N. Skryabina+ Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France

daniel.fruchart@grenoble.cnrs.fr It is well known that to form easily MgH2 Mg, fast absorption/desorption kinetics can be achieved when two main properties are developped that are : 1 – micro- to nano crystallite sizing Mg with a huge density of defects, 2 - deposit of so-called catalyst nanoparticles (metals, oxydes, etc) onto the surface of micrometric Mg grains. In practice, both processes can be installed parallel, e.g. using energetic ball milling (BM) procedure. In order to better model the chemical and crystalline aspects of interface created between a so-called catalyst metal and magnesium, allowing high hydrogenation/dehydrogenation kinetics, perfectly built monocrystalline interface layers were deposited by using the fine technique of Laser Ablation Deposit. We selected Nb metal to interface the Mg layer, since Nb (with almost same number of valence electron and same crystal structure than TiVCr alloys practically used in factory*) was early demonstrated of the best so-called catalytists to activate Mg,. Also, Nb as one element is easier to deposit than a multinary TiVCr, besides we had interstingly probed Nb/Mg interface from BM by using in-situ neutron diffraction experiments, thus revealing the “H-door” effect of Nb particle on Mg. So a multilayered Mo/Mg/Nb/Pd/Mo/Al2O3 “nano tank” was designed for which synthesis and characterisation procedures of the deposit will be described in detail.. Hydrogen was charged in the Mg-layers via the Pd-made nano-layers forming a pipe. In fact, the nanotank was fairly hydrogenated in smart conditions (8 bars H2 pressure at RT), thus forming Pd, Nb and Mg hydrides. The texture and crystal structure of the whole system was characterised before and after hydrogenation by using many techniques such as RHEED, AFM, conventional XRD, grazing incidence, texture etc. Then the hydrogenated system was studied all along during a dehydrogenation cycle, using an efficient in-situ XRD facilities, temperature being monitored from RT up to 300°C, then maintained during a few hours while primary vacuum was applied on the chamber. The resulting steps of the dehydrogenation process fully agree with both the thermal stability of MgH2 and thermodynamics of the Nb-H (p,c,T) phase diagram. During the hydrogen transfer process at desorption, MgH2 is thermally destabilised, and hydrogen atoms are readily trapped by Nb via the crystal interface (in practical by particles accreted by BM onto the surface) of MgH2/Mg grains, e.g. by energetic ball-milling. Thus, under the thermodynamical conditions orthorhombic β-NbH0.89 is formed, such hydride exhibiting very poor hydrogen mobility. Thus after a slight hydrogen release, the niobium hydride transforms to the cubic superstructure α’-NbH0.80, where the presence of a noticeable density of vacancies allows high hydrogen dynamics. Then, the late hydride transforms to α-NbH0.20, the limit of solid solution, for a complete hydrogen evacuation through the Nb-door-interface. So, we conclude on one of the driving principles of hydrogenation/dehydro-genation of Mg powders when accreting a transition metal type as so-called catalysts (here Nb, but practically TiVCr alloys), that can be immediately extended to neighbour d-elements (Ti, V, Ta; etc). The present analysis is adressed as well to other type catalysts for which during BM occurs H-reduction via MgH2 of non-metal additives to metal nano-particles.

21

The Thermodynamics and Hydrogen Sorption Mechanism of Borohydrides

A. Züttel, R. Gremaud, S. Kato, A. Borgschulte, A. Remhof, Ph. Mauron, S.-I. Orimo EMPA Materials Sciences & Technology, Div. Hydrogen & Energy, Dübendorf, Switzerland

Email: andreas.zuettel@empa.ch The stability of complex hydrides is investigated based on the enthalpy of formation of the elemental hydrides and the intermetallic compounds involved in the reaction. The equilibrium hydrogen pressure for the absorption and desorption reaction is calculated. The mechanism for the hydrogen absorption and desorption in complex hydrides is not known yet. In the conventional view the complex hydride with a general formula of Mx+[TH4-]x

(M = Li, Na, Mg, Ca…; T = Al, B, N and x is the stoichiometry) releases Hto form MHx + x·TH3 [1]. The stability of the AlH3 < BH3 < NH3, therefore, alanates decompose into hydrogen and aluminum while boranates tend to liberate beside hydrogen also B2H6 and the ammonium spontaneously decomposes into NH3. Therefore, the thermodynamics i.e. stability and kinetics is calculated based on the intermediate products identified.

Fig. 1 Absorption (top) and desorption (bottom) mechanism for borohydrides. The stability of the TH4- is determined by the localization of the electron on the T-atom. As a consequence the stability of the complex hydride strongly depends on the electronegativity of the cation. However, this approach is only able to describe the stability of the forth hydrogen atom in the anion. The stability of the neutral and “hypothetical” TH3

is also determining the equilibrium pressure of the complex hydride. The appearance or the induced creation of intermediate products in the hydrogen desorption reaction is a possibility to destabilize the complex hydrides and to facilitate the reversible hydrogen absorption. References 1. Andreas Züttel, Andreas Borgschulte and Shin-Ichi Orimo, « Tetrahydroborates as new hydrogen storage materials », Scripta Materialia, Volume 56, Issue 10, May 2007, Pages 823-828 2. Shin-Ichi Orimo, Yuko Nakamori, Jennifer R. Eliseo, Andreas Züttel and Greg Jensen, « Complex Hydrides for Hydrogen Storage », Chemical Reviews, October 2007, Volume 107, Number 10, 4111-41

22

Effect of Interstitial Elements and/or Pressure on the Magnetic Properties of Some Iron Rich Intermetallic Compounds

O. Isnard1, Z. Arnold2, C.V. Colin1, V. Paul-Boncour3, M. Guillot4, J. Kamarád2

1Institut Néel, CNRS / Université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France

2Institute of Physics AS CR v.v.i., Na Slovance2, 182 21, Prague 8, Czech Republic 3Chimie Métallurgique des Terres Rares, ICMPE, CNRS et Université Paris Est, 2-8 rue H. Dunant, 94320

Thiais Cedex, France 4Laboratoire National des Champs Magnétiques Intenses CNRS / Université Joseph Fourier 38042 Grenoble

Cedex 9, France The purpose of this contribution is to present new results on the effect of hydrogen insertion on the intrinsic magnetic properties of iron rich containing phases in particular YFe2(H,D)4.2 and some RFe11TiH compounds. The YFe2(H,D)4.2 compounds are found to displays a giant (H,D) isotope effects on most of the physical properties, namely the magnetic properties are significantly affected [1-3]. To go deeper into the understanding of the H or D influence on the itinerant electron metamagnetic character of Fe magnetism, we have compared the effects of hydrostatic pressure up to 12 kbar on Curie temperature TC, spontaneous magnetization MS and magnetization curves of both YFe2H4.2 and YFe2D4.2 polycrystalline samples. We observed not only remarkable decrease of both TC and MS with increasing pressure but these experiments enabled us to determine the pressure dependence of the metamagnetic transition between a ferromagnetic (FM) and an antiferromagnetic (AFM) structure of the Fe sublattice. Insertion of H and D are found to induce remarkably different pressure dependant magnetic behaviours on YFe2. We have also investigated the influence of hydrogen on the magnetic properties of the RFe11Ti series of compounds [4,5]. Here, high magnetic field studies up to 23T are presented to analyse the magnetocrystalline anisotropy thus revealing the occurrence of unusual behaviour in the magnetization curves of some compounds (i.e. R=Pr). The effects of H insertion on the exchange interactions and other magnetic properties are also presented. The resulting magnetic phase diagrams are discussed in the light of neutron scattering studies and earlier published data. 1. V. Paul-Boncour, M. Guillot, G. Wiesinger, G. André, Phys. Rev. B, 72 (2005) 174430 2. T. Leblond, V. Paul-Boncour, F. Cuevas, O. Isnard, J.F. Fernandez International J. of Hydrogen Energy 34 (2009) 2278– 2287 3. V. Paul-Boncour T. Mazet, J. Appl. Phys., 105 (2009) 013914 4. C. Piquer, F. Grandjean, O. Isnard, G.J. Long J. Phys. Condens. Matter. 18 (2006) 221 5. O. Isnard, M. Guillot J. Optoelect. and Advanced Materials 10 (2008) 744-749

23

Nuclear Magnetic Resonance Studies of Atomic Motion in Borohydrides

A.V. Skripov Institute of Metal Physics, Urals Branch of the Academy of Sciences, Ekaterinburg, Russia

Email: skripov@imp.uran.ru Light metal borohydrides M(BH4)n are considered as promising materials for hydrogen storage. While the volumetric and gravimetric hydrogen densities in these compounds are high, the stability of the borohydrides with respect to thermal decomposition and the slow sorption kinetics remain the major drawbacks for their practical use. Elucidation of the complex structures and hydrogen dynamics in these materials may give a key to improving their hydrogen-storage properties. This work presents a review of the dynamical properties of light metal borohydrides. It is based mainly on recent experimental results obtained by the nuclear magnetic resonance (NMR) group at the Institute of Metal Physics (Ekaterinburg). NMR appears to be especially effective technique for studies of atomic motion in this class of materials. In contrast to traditional metal hydrides, the measured nuclear spin-lattice relaxation rates in borohydrides do not contain any significant contributions not related to atomic motion (such as the conduction-electron contribution in metallic systems). This allows us to trace the atomic jump rates in borohydrides over the range of eight orders of magnitude (104 – 1012 s-1). Another important feature of these studies is that different nuclei (1H, 11B, 7Li, 23Na, …) can serve as NMR probes of atomic motion, complementing each other. Two basic types of atomic jump motion are known to exist in M(BH4)n: the reorientational motion of BH4 groups and the translational diffusion of cations (M) or anions (BH4). At low temperatures (80 – 400 K), the NMR data are usually governed by the reorientational motion of BH4 groups [1,2]. We will discuss the activation energies of this motion in different borohydrides (LiBH4, NaBH4, KBH4 and various crystallographic modifications of Mg(BH4)2) and the changes in the jump rates at the phase transition points. We will also demonstrate a relation between the motional parameters and the structural features of borohydrides. The translational diffusion on the NMR frequency scale becomes important in some borohydrides above 400 K [3]. We will focus on the discussion of the jump rates of different diffusing species. The motional parameters derived from our NMR measurements will be compared to those obtained by other techniques, such as quasielastic neutron scattering. References 1. A.V. Skripov, A.V. Soloninin, Y. Filinchuk, D. Chernyshov, J. Phys. Chem. C, 112 (2008) 18701-18705. 2. O.A. Babanova, A.V. Soloninin, A.P. Stepanov, A.V. Skripov, Y. Filinchuk, J. Phys. Chem. C, 114 (2010) 3712-3718. 3. A.V. Soloninin, A.V. Skripov, A.L. Buzlukov, A.P. Stepanov, J. Solid State Chem., 182 (2009) 2357-2361.

24

Developing Novel Materials and Methods for Hydrogen Storage Ragaiy Zidan

Savannah River National Laboratory, Aiken, SC 29808 USA Email: Ragaiy.Zidan@srnl.doe.gov

Novel materials and methods for hydrogen storage are presented. Aluminum hydride (alane) is one of the most attractive hydrogen storage materials. However, the impracticality of using very high hydriding pressure (105 bars) or costly chemical methods to form alane has precluded alane from being used for hydrogen storage. In this work we present a cycle that uses electrolysis and catalytic hydrogenation of spent aluminum. Our method is aimed at avoiding the impractical high hydrogen pressure and the formation of stable by-products, when chemical rout is used. A reversible cycle to form alane electrochemically using NaAlH4 or LiAlH4 in THF or ether has been successfully demonstrated. To complete the cycle, the starting alanate can be regenerated by direct hydrogenation of the dehydrided alane and the alkali hydride (NaH or LiH).1,2 The process was recently enhanced by the use of an electo-catalytic additive, increasing the yield and improving the efficiency. Electrochemical formation of aluminum hydride adducts has also been demonstrated. Novel separation methods of alane from solution were developed. Alane produced by the electrochemical method was characterized using thermogravimetric analyzer, XRD and Raman spectroscopy. In addition, our work involves the development of novel hydrogen storage systems, complex and alkali metal fullerene nanocomposites. We demonstrated reversible hydrogen interaction with these composites.3,4 A series of desorption/absorption experiments indicates these nanocomposites can be cycled with minimal loss in hydrogen storage capacity. Particular attention is paid to the lithium fulleride nanocomponsite and includes the hydrogen cycling of various C60:LiH stoichiometries, of which the 1:6 ratio has the largest hydrogen content (see Figure).

Figure. Formation of Li-C60-Hx composite for hydrogen storage.

The 1:6 lithium fulleride material was found to store up to six hydrogen atoms per Li atom, indicative of the formation of a unique hydrogen storage matrix. Efforts to determine structure and mechanistic characteristics of the fullerene hydride composites using, MAS NMR, XRD, Raman, PCT, are conducted. References 1. R. Zidan. Aluminum Hydride (Alane) Chapter 9- Handbook of Hydrogen Storage: New

Materials for Future Energy Storage, WILEY-2010. Edited by M. Hirscher. 2. R. Zidan, B. L. Garcia-Diaz, C. S. Fewox, et al. Chem.Comm., 3717–3719 (2009). 3. P. A. Berseth, A. G. Harter, R. Zidan, et al. J. Nano Letters, Vol. 9, No. 4, (2009). 4. M. Wellons, P. Berseth, R. Zidan. Nanotechnology 20 204022 (2009).

25

Synthesis of Mg-Ti Alloys with HCP, FCC, BCC Structures and Their Hydrides with FCC Structure

Kohta Asano, Hirotoshi Enoki, Etsuo Akiba National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

Email: k.asano@aist.go.jp Mg and Ti metals have a hexagonal close packed (HCP) structure at ambient temperatures and Ti metal has a body centered cubic (BCC) structure above 1155 K. In the reported binary phase diagram of the Mg-Ti system, solubility of each metal to another is less than 2 at.% and intermetallic compounds are not found. Synthesis of a Mg-Ti alloy using the melting method has not been successful because the difference in melting points between Mg (923 K) and Ti (1943K) is significant and Mg markedly vaporizes during melting process. However, we have successfully synthesized Mg-Ti alloys with a BCC structure by means of ball milling of Mg and Ti [1-4]. In the field of thin film Mg-Ti HCP thin films were prepared by the sputtering method [5,6]. Bulk Mg-Ti alloys which have HCP and face centered cubic (FCC) structures have also been synthesized by means of ball milling by the authors [3,7,8]. In the present work, firstly, the synthesis process of Mg-Ti BCC alloys by means of ball milling was studied. During milling, Mg and Ti were deformed mainly by the basal plane slip and the twinning deformation, respectively. The BCC phase was found after dissolution of Mg in Ti [4]. It was found that the mechanical properties of Mg and Ti metals affect the ball milling process of Mg-Ti powder mixtures. Mg is readily deformed by addition of Li because the non-basal slips are activated [9]. We have confirmed that Li added Mg reacted with Ti much faster than pure Mg [10]. Crystal structure of milled products plastically deformed during ball milling. The dynamic energy given by the milling balls, i.e., the mass of milling balls, affects the compressive stress to the raw materials. Based on this hypothesis, using various weights of milling balls we have successfully synthesized Mg-Ti HCP, FCC and BCC alloys [3]. Hydrogenation of Mg-Ti HCP, FCC and BCC alloys which were prepared by means of ball milling has been carried out. Mg-Ti FCC hydrides were synthesized from Mg80Ti20 HCP, Mg50Ti50 FCC and Mg50Ti50 BCC alloys [3]. The FCC hydride phase synthesized from Mg50Ti50 BCC alloy under a hydrogen pressure of 8 MPa at 423 K had a chemical formula of Mg42Ti58H177 (H/M = 1.77 or hydrogen content of 4.7 mass%) [2]. This FCC hydride phase was also synthesized by milling of MgH2 hydride and Ti metal [11]. References 1. E. Akiba, S. J. Choi, H. Enoki, Y. Tsushio, Collected Abstracts of Int. Symp. on Metal-Hydrogen Systems (MH2002), (2002) p.115. 2. K. Asano, H. Enoki, E. Akiba, J. Alloys Compd. 478 (2009) 117-120. 3. K. Asano, H. Enoki, E. Akiba, J. Alloys Compd. 480 (2009) 558-563. 4. K. Asano, H. Enoki, E. Akiba, J. Alloys Compd. 486 (2009) 115-123. 5. D.M. Borsa, R. Gremaud, A. Baldi, H. Schreuders, J.H. Rector, B. Kooi, P. Vermeulen, P.H.L. Notten, B. Dam, R. Griessen, Phys. Rev. B 75 (2007) 205408-1-9. 6. S. Bao, K. Tajima, Y. Yamada, M. Okada, K. Yoshimura, Appl. Phys. A 87 (2007) 621-624. 7. G. Liang, R. Schulz, J. Mater. Sci. 38 (2003) 1179-1184. 8. W.P. Kalisvaart, P.H.L. Notten, J. Mater. Res. 23 (2008) 2179-2187. 9. S. Ando, H. Tonda, Mater. Trans. JIM 41 (2000) 1188-1191. 10. K. Asano, H. Enoki, E. Akiba, Mater. Trans. 48 (2007) 121-126. 11. K. Asano, E. Akiba, J. Alloys Compd. 481 (2009) L8-L11.

26

"High-Density Hydrogen Storage" and “Lithium Super(Fast)-Ionic Conduction” in Metal Borohydrides

Shin-ichi Orimo Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan

Email: orimo@imr.tohoku.ac.jp Complex hydrides with the (BH4)– anion, so-called metal borohydrides, are conventionally expressed as M(BH4)n (n: valence of metal M), which shows ionic bonding between the Mn+

cation and the (BH4)– anion. These hydrides have been attracting great interest as potential candidates for advanced hydrogen storage materials because of their high hydrogen densities [1]. One of the metal borohydrides, Li(BH4), exhibits another novel property, that is, lithium super(fast)-ion conduction (more than 1×10−3 S/cm over 390 K [2]), which was observed during attempts to clarify the microwave absorbing mechanism [3, 4]. The ion conductivity of Li(BH4) jumps by three orders of magnitude at approximately 390 K due to its structural transition from the low temperature (LT) phase to the high temperature (HT) phase. The HT phase of Li(BH4) can be stabilized by addition of lithium halides, resulting in the enhanced ion conductivity at room temperature (RT) [5-8]. Recently we have also reported another conceptual study and remarkable results that Li2(BH4)(NH2) and Li4(BH4)(NH2)3 with combinations of the (BH4)– and (NH2)– anions show ion conductivities four orders of magnitude higher than Li(BH4) even at RT, due to being provided new occupation sites for lithium ions [9]. These studies not only demonstrate an important direction in which to search for higher ion conductivity in complex hydrides but also greatly enlarge material variations of solid electrolytes for improving safety and energy-density of lithium-ion batteries. References 1. S. Orimo, Y. Nakamori, J.R. Eliseo, A. Züttel, C.M. Jensen, Chem. Rev., 107, (2007), 4111-4132. 2. M. Matsuo, Y. Nakamori, S. Orimo, H. Maekawa, H. Takamura, Appl. Phys. Lett., 91, (2007), 224103(1)-(3). 3. Y. Nakamori, S. Orimo, T. Tsutaoka, Appl. Phys. Lett., 88, (2006), 112104(1)-(3). 4. M. Matsuo, Y. Nakamori, Y. Yamada, S. Orimo, Appl. Phys. Lett., 90, (2007), 232907(1)-(3). 5. H. Maekawa, M. Matsuo, H. Takamura, M. Ando, Y. Noda, T. Karahashi, S. Orimo, J. Am. Chem. Soc., 131, (2009), 894-895. 6. M. Matsuo, H. Takamura, H. Maekawa, H-.W. Li, S. Orimo, Appl. Phys. Lett., 94, (2009), 084103(1)-(3). 7. H. Oguchi, M. Matsuo, J.S. Hummelshøj, T. Vegge, J.K. Nørskov, T. Sato, Y. Miura, H. Takamura, H. Maekawa, S. Orimo, Appl. Phys. Lett., 94, (2009), 141912(1)-(3). 8. T. Ikeshoji, E. Tsuchida, K. Ikeda, M. Matsuo, H.-W. Li, Y. Kawazoe, S. Orimo, Appl. Phys. Lett., 95, (2009), 221901(1)-(3). 9. M. Matsuo, A. Remhof, P. Martelli, R. Caputo, M. Matthias, Y. Miura, T. Sato, H. Oguchi, H. Maekawa, H. Takamura, A. Borgschulte, A. Züttel, S. Orimo, J. Am. Chem. Soc., 131, (2009), 16389-16391.

27

Nanoconfining Metal Hydrides: Impact on Thermodynamics, Kinetics and Reversibility of Hydrogen Sorption

P. Adelhelm, J. Gao, P. Ngene, R. Bogerd, S. Tatiparti, K.P. de Jong, and P.E. de Jongh

Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University Sorbonnelaan 16, 3584 CA Utrecht, the Netherlands

P.E.deJongh@uu.nl Hydrogen as an energy carrier is expected to play an important role in a future more sustainable society, especially for mobile applications. However, a requirement is the safe, efficient and compact on-board storage of hydrogen. Reversible storage in metal hydrides is promising, but at the moment no known materials system fulfills all requirements regarding hydrogen content, release temperature, and reversibility simultaneously. Binary light metal hydrides generally are thermodynamically too stable, while in addition boronhydrides, alanates and other complex systems contain multiple phases, causing reversibility issues due to phase segregation.

A general approach to the preparation of hydrogen storage materials is high energy ball milling, which decreases the crystallite size and allows the addition of catalysts. In an alternative approach we study the effect of nanosizing the metal hydrides (<10 nm), and supporting or confining them in a porous matrix. This is not only expected to improve the kinetics, but can potentially also change the thermodynamics of the systems1. Furthermore, nanoconfinement can benefit the reversibility by limiting macroscopic phase segregation upon cycling, while the addition of carbon can also lead to better mechanical stability and thermal management.

Nanoconfined materials such as Mg(Ni), NaH, NaAlH4 and LiBH4 were prepared by solution impregnation and/or melt infiltration of nanoporous carbon matrices.2 Structural characterisation by N2 physisorption, XRD, solid state NMR, EXAFS and electron microscopy demonstrated that in many cases high loadings of active materials could be confined in the porous matrices. We will discuss in detail the impact on the hydrogen sorption properties for a few selected examples. For the Mg(Ni) system the melt infiltration allows very efficient mixing of Mg, carbon and Ni on a nanoscale, leading to low hydrogen release temperatures and mixed phases. Particularly interesting is also NaH/C for which not only the kinetics are clearly enhanced (for instance allowing partial reloading of the NaH/C system at 1 bar H2 pressure and room temperature), but also under 1 bar pressure some H2 is released 200 oC below the equilibrium decomposition temperature of bulk NaH.3 Finally for the NaAlH4/C system we discuss in detail the impact of the carbon matrix, not only on the structure of the NaAlH4 and the kinetics of hydrogen release, but also how the nanoconfinement leads to a shift in the thermodynamics of the equilibrium 3NaAlH4↔Na3AlH6 +2Al+3H2.4 References 1. R.W.P. Wagemans et al. J. Am. Chem. Soc. 127 (2005) 16675. 2. P.E. de Jongh et al. Chem. Mater. 19 (2007) 6052 3. P. Adelhelm, K.P. de Jong, P.E. de Jongh, Chem. Comm., (2009), 6261. 4. J. Gao et al. J. Phys. Chem. C, 114 (2010), 4675.

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Nanophase Aspects of Hydrogen Storage Materials - a Theoretical Study

P. Vajeeston, P. Ravindran, H. Fjellvåg Center for Materials Science and Nanotechnology, Department of Chemistry, University of Oslo, Box 1033

Blindern N-0315, Oslo, Norway Email: ponniahv@kjemi.uio.no

It is anticipated that physical and chemical properties of nano-phase materials are different from the bulk materials. Upon reducing the particle size beyond a certain range (called critical size), most of the atoms will be exposed to the surface. It is at this region where the properties of the material begin to differ drastically from that of the bulk materials. In the hydrogen storage technology numerous studies have been focused on improving the problematic sorption kinetics, including mechanical ball milling and chemical alloying. However, it is found that these methods can only improve the absorption and not the desorption kinetics, possibly because even the smallest particle sizes (20 nm) obtainable by these methods still primarily display bulk desorption characteristics. From our theoretical simulations we have found that most of the complex hydrides are having critical particle size below 2 nm range.[1,2,3] The calculations also suggest that one can reduce the decomposition temperature and increase the sorption kinetics of potential hydrogen storage materials including borohydrides. In this talk we are going to discuss how one can find the critical particle size of hydrides using density functional theory and how it can influence the physical, chemical, and mechanical properties of the chosen material. Moreover, we will also discuss the changes in the properties of such nano-particles when they are filled in carbon scaffolds. References 1. P. Vajeeston, P.Ravindran, and H.Fjellvåg, Nanotechnology 19, 275704 (2008). 2. P. Vajeeston, P.Ravindran, and H.Fjellvåg, Nanotechnology 20, 275704 (2009). 3. P. Vajeeston, P.Ravindran, and H.Fjellvåg, (submitted to Phys. Rev. B)

29

Thermodynamics of Nano-Cluster Complex Hydrides Using First-Principles Density Functional Theory

E. H. Majzoub1, F. Zhou2, V. Ozolins2 1Center for Nanoscience and Department of Physics and Astronomy, University of Missouri, St. Louis

2Materials Science and Engineering, University of California, Los Angeles

The equilibrium plateau pressure of a metal hydride at a given temperature is a characteristic thermodynamic quantity, and determines the application and engineering required for a hydrogen storage system. While recent interest has focused on complex metal hydrides such as NaAlH4 and Ca(BH4)2, these compounds are not as easily tunable as the interstitial metallic hydrides through alloying with other metal atoms, due to the strongly ionic character of the cohesive energy. However, the complex hydrides are superior on a wt.% hydrogen basis, and are the preferred materials for vehicular transport. In order to address thermodynamic tunability, we investigate these materials at the nano-scale, where the ratio of surface to bulk atoms impacts the energetics. Recent theoretical work by Wagemans et al. [1] and others indicate that small clusters of MgH2, for example, can significantly lower the desorption enthalpy with respect to bulk. Small metal or hydride clusters may be incorporated into nanoporous frameworks such as metal organic frameworks (MOFS), block co-polymer (BCP) templates, or nanoporous hard carbons, for example, to prevent agglomeration and perhaps even improve tunability through particle/surface interactions. We present theoretical results for desorption energetics of free nano-clusters of NaAlH4 as a function of temperature and pressure. Prototype geometries for the clusters were generated using a well-validated electrostatic ground state approach to a global optimization of the cluster total energy using a recently developed non-conventional Monte Carlo random walk in energy space. First-principles density functional theory applied to the prototype clusters was used for full free energy calculations of the clusters and decomposition products. Results will be discussed with relation to recent experimental work on incorporation of complex hydrides in nanoporous framework materials, and the importance of the surface chemistry of the frameworks. References 1. R.W.P. Wagemans, J.H. van Lenthe, P.E. de Jongh, A.J. van Dillen and K.P. de Jong, J. Am. Chem. Soc. 127 (2005) 16675-16680.

30

Reaction Mechanism and Kinetics of MgH2/Borohydrides Based Reactive

Hydride Composites M. Dornheim, U. Bösenberg, C. Pistidda, C. Bonatto Minella, R. Gosalawit, I. Saldan, K.

Suarez, M. Peschke, G. Barkhordarian, T. Klassen, R. Bormann Institute of Materials Research, Materials Technology, GKSS-Forschungszentrum Geesthacht GmbH,

Geesthacht, Germany Email: Martin.Dornheim@gkss.de

Reactive Hydride Composites like combinations of MgH2 with M(BH4)x (M being Li, Na or Ca) show significantly reduced values of reaction enthalpies as well as improved ab- and desorption kinetics compared to the pure borohydrides. Furthermore, due to their high reversible gravimetric storage capacities of up to 11 wt.% they are interesting candidates for future hydrogen storage applications. However, in spite of the significantly lowered value of reaction enthalpy and thus a high thermodynamic driving force for desorption hydrogen release still takes place at temperatures above 250°C only. In this presentation, an overview will be given on reaction mechanisms, thermodynamic properties and sorption behaviour of the nanocrystalline RHCs: 2LiBH4+MgH2, 2NaBH4+MgH2 and Ca(BH4)2+MgH2. The progress in the optimisation of reaction kinetics reached so far will be described. Function and suitability of additives as potential catalysts on hydrogen ab- and desorption will be discussed. References 1. G. Barkhordarian et al., J. Alloys and Compds. 440 (2007) L18-L21, 2. M. Dornheim et al., Scripta Materialia 56 (2007) 841-846.

31

Properties of Metal Hydrides Under High Pressure Studied Using Synchrotron Radiation X-Rays

A. Machida Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo, Japan

Email: machida@spring8.or.jp Synchrotron radiation (SR) x-rays enable us to investigate the structural and electronic properties of metals that change often dramatically on hydrogenation and/or dehydrogenation. Metal hydrides have been investigated with a focus on hydrogen-metal bonding and hydrogen-hydrogen interaction for their densified states realized under high pressure. Application of pressure results in contraction of the metal lattice and decrease in the interatomic distances. The nature of hydrogen-metal bonding state would change significantly and becomes to be clearly detectable. Another aspect of high pressure effect is direct hydrogenation of metals. The chemical potential of hydrogen increases steeply with increaseing pressure. Consequently, the hydrogen dissociation into metal is enhanced. Novel hydrides would be prepared by direct hydrogenation of metals with hydrogen-fluid chemically actived at high temperature and high pressure. New Energy and Industrial Technology Development Organization (NEDO), Japan, launched a five years project (FY2007-FY2011), Advanced Fundamental Research on Hydrogen Storage Materials. As one branch group of the project, we have been conducting high-pressure experiments on metal hydrides using SR X-rays at SPring-8 to clarify the hydrogen-metal interactions. My talk will cover the lates results on the SR studies of the structural, electronic, and magnetic properties of metal hydrides under high pressure. (1) Pressure-induced structural and electronic transitions of rare-earth metal hydrides [1- 8] and transition metal hydrides [9,10], (2) Pressure-induced magnetic transition of iron hydride [10], (3) Hydrogenation process of aluminum at high temperature and high pressure [11-13]. References 1. A. Machida et al., Solid State Commun.,138 (2006) 436. 2. A. Machida et al., Phys. Rev. B 76 (2007) 052101. 3. A. Ohmura et al., Phys. Rev. B 73 (2006) 104105. 4. T. Kume et al., Phys. Rev. B 76 (2007) 024107. 5. A. Ohmura et al., J. Alloys and Compds 446-447 (2007) 598. 6. T. Kume et al., J. Phys. Conference Series 121 (2008) 042011. 7. A. Machida et al., to be submitted. 8. Y. Sakurai et al., to be submitted. 9. N. Hirao et al., poster presentation in MH2008. 10. N. Hirao et al., to be submitted. 11. H. Saitoh et al., Appl. Phys. Lett. 93 (2008) 151918. 12. H. Saitoh et al., Appl. Phys. Lett. 94 (2008) 151915. 13. H. Saitoh et al., J. Alloys and Compds, in press.

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Oral Presentations

33

Electrochemical Properties of Ti45Zr38-xNi17+x (0≤x ≤8) Quasicrystals Produced by Rapid-Quenching

Akito Takasaki*, Chihiro Kuroda*, Sang-Hwa Lee** and Jae-Yong Kim**

*- Departtment of Engineering Science and Mechanics, Shibaura Institute of Technology, Japan **- Department of Physics, Hanyang University, Korea

Email (corresponding author): takasaki@sic.shibaura-it.ac.jp

Ti-Zr-Ni icosahedral (i) quasicrystal phases, which have a new type of translational long-range order and display non-crystallographic rotational symmetry, are believed to possess a large number of tetrahedral interstitial sites in their quasilattices [1], so that the i phase alloys are attractive as one of hydrogen storage materials. One of the authors has recently investigated electrochemical hydrogenation/dehydrogenation properties of Ti45Zr38Ni17 amorphous and i phase electrodes synthesized by mechanical alloying (MA) and subsequent annealing, and reported that the maximum discharge capacity for the i phase electrode at room temperature (298 K) was about 24 mAh/g at current density of 15 mA/g, while that for the amorphous one with identical composition was about 6 mAh/g, much lower than that for the i phase electrode [2]. However, even the measured discharge capacity for the i phase is very low if we compare with the theoretical charge capacity (795 mAh/g for Ti45Zr38Ni17 i phase electrode) estimated from its chemical composition, so that it is thought that some hydrogen atoms located at the interstitial sites in the quasilattice were strongly bound with neighbouring atoms. Furthermore, because MA is a dynamic processing, the i phase powder generally appeared together with a Ti2Ni type crystal phase (fcc structure). This means that the measured discharge capacity for the i phase electrode includes the one for the Ti2Ni crystal phase. An accurate measurement of discharge capacities for pure i phase is needed, and if one can reduce the chemical interaction between hydrogen and neighbouring atoms in the interstitial sites of the quasilattice, higher discharge capacities are also expected for the i phase electrodes. In this study, we attempted to produce Ti45Zr38-xNi17+x (0≤x ≤8) i phase ribbons by rapid-quenching, measured their electrochemical properties by a three-electrode cell (KOH solution) at room temperature, and investigated the effect of substitution of Ni for Zr on the electrochemical properties. All the ribbons were mostly the i phase after rapid-quenching, although substitution of Ni for Zr also produced very small amount of Laves phase. The discharge capacity increased with increasing amount of Ni substituted for Zr. The maximum discarge capacity obtained was about 90 mAh/g for Ti45Zr30Ni25. An activation process, which was needed for the powders after MA, was not necessary for one after rapid-quenching. The discharge performance for the i phase electrodes after substitution of Ni for Zr was stable against the charge/discharge cycle (until 15 cycles), and the i phase structure was also stable even after the 15th charge/discharge cycle.

References 1. P.C. Gibbons, and K.F. Kelton, in Physical Properties of Quasicrystals, ed. Z.M. Stadnik, (Springer, 1999) pp.403. 2. A. Takasaki, W. Zając, T. Okuyama, J.S. Szmyd, J. Electrochem. Soc., 156 (2009), A521.

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Hydrogen Storage for Stationary and Portable Electricity Supply E.MacA. Graya, C.J. Webba, S.L.I. Chanb and J. Andrewsc

aQueensland Micro- and Nanotechnology Centre, Griffith University, Nathan 4111, Brisbane, Australia bSchool of Materials Science and Engineering, University of New South Wales, Kensington 2052, Sydney,

Australia cSchool of Aerospace, Mechanical and Manufacturing Engineering, RMIT University

Bundoora 3083, Melbourne, Australia Email: E.Gray@griffith.edu.au

Potential applications of storage-guaranteed renewable-energy systems range from stationary remote telecoms and single dwellings, to farms and whole communities for whom connection to the electricity grid is too expensive or otherwise infeasible, to portable systems for remote industrial, military, humanitarian and emergency purposes. The key requirements of continuity-guaranteed energy storage technology are: low self-discharge, safety, reliability, longevity and, for portable applications, relatively high energy density. Batteries are almost universally used in this niche at present. An advantageous system configuration for electricity generation can be based around photovoltaic (PV) primary energy coupled to a PEM electrolyser, hydrogen storage subsystem and PEM fuel cell. The load is supplied directly with PV primary energy whenever possible, with any excess of supply over load being diverted to the electrolyser and used to generate hydrogen for storage. When the load exceeds the available PV power, the fuel cell supplies the deficit using stored hydrogen. In contrast to an automotive hydrogen storage tank, in which the absorption-desorption sequence is steady desorption of the major part of the tank capacity followed by a steady and controlled refill, in a renewable-energy system the hydrogen storage may switch between absorption and desorption thousands of times each year in response to the supply and load fluctuating many times per day, and on day/night (for PV primary energy), weather- and climate-related cycles. Furthermore, the use of a PEM electrolyser and fuel cell necessitates hydrogen absorption and desorption at pressures of order a few bar. In this paper we consider the requirements for hydrogen storage in a metal hydride (MH). Based on the above system concept, we show that the energy density of the entire storage sub-system, including electrolyser and fuel cell, can be competitive with or even much better than the best Li-ion batteries. We consider the thermodynamics and efficiency of the MH storage tank and show that (i) the efficiency of MH storage is very high if waste heat from the fuel cell is used to desorb hydrogen from storage and (ii) any forseeable fuel cell generates enough heat to desorb the hydrogen it needs. We also consider the significance of pressure hysteresis, first in relation to energy loss, which we show to be insignificant compared to likely heat losses, and second, in the relationship between the hydrogen pressure and the “state of charge” of the MH tank. This must be accurately known at all times but is difficult and/or expensive to measure via the difference between integrated flow in and out over many thousands of small flow episodes. We consider an important factor, namely that the actual performance of a partially-cycled MH storage bed is inevitably subject to microhysteresis, i.e. the execution of minor loops in the pressure-composition plane as relatively small aliquots of hydrogen are added and withdrawn in response to fluctuations in the balance between available primary energy and load. The interplay of mass flow, heat flow and hysteresis breaks down the simple relationship between hydrogen pressure and global hydrogen content.

35

A MgH2 Tank – PEM-FC Coupling

P. de Rango, S. Garrier, Ph. Marty*, C. Dupuis**, A. Chaise, D. Fruchart, S. Miraglia

Institut Néel et CRETA, CNRS - UJF, BP 166, 38042 Grenoble cedex 9, France *LEGI - INPG, BP 53, 38041 Grenoble cedex 9, France

**McPHy Energy, 26190 La Motte-Fanjas, France Email: patricia.derango@grenoble.cnrs.fr

Optimised ball-milled magnesium hydride (BM MgH2) powders exhibit very fast

sorption kinetics. Presently, high quality batches of several kg are produced at industrial scale [1]. However, due to the marked exothermicity at hydrogen absorption and to the poor thermal conductivity of BM MgH2 powders, the tank loading time is limited by the efficiency of heat extraction. Combining ENG with MgH2 to form compressed composite leads to improve drastically the thermal conductivity in the radial direction of the resulting compacts [2]. Moreover, compacting the composite using a die increases markedly the volumetric hydrogen storage capacity.

A 1.8 kg containing MgH2 tank was designed accordingly to the performances of MgH2 compacts. The tank was tested in various experimental conditions. The load time was found strongly dependent of the cooling efficiency using air flow pipes. At maximum cooling rate, the tank has stored more than 1.1 Nm3 hydrogen within 30 min. The loading process appeared independent of both initial temperature and H2 pressure. At desorption, the maximum hydrogen flow was found fully proportional to the thermal power of a heating system (25 Nl/mn at 1.5 kW). The specific-energy was up to 270 Wh/kg with a system energy-density of 42 g/l. The tank was connected to a Helion PEM-FC which intlet pressure is 0.12 MPa. Then at H2 flow rate of 12 Nl H2/min., 1.2 kWe electric power was delivered for 65 min. The maximum power regime was reached in less than 1 min. and then the tank anticipated very fastly power needs, without H2 gas buffer supply. Interestingly, the high temperature metal hydride tank was found auto-adaptive to demands. In fact, MgH2 reacts in fullfilling equilibrium (P,T) conditions, only temperature was set at a equilibrium point determining a required outlet pressure. No mass flow or pressure monitor were needed to connect tank and FC. References 1. P. de Rango, A. Chaise, J. Charbonnier, D. Fruchart, M. Jehan, Ph. Marty, S. Miraglia, S.

Rivoirard, N. Skryabina, J. Alloys and Comp., 446-447 (2007) 52-57. 2. A. Chaise, P. de Rango, Ph. Marty, D. Fruchart, S. Miraglia, R. Olivès, S. Garrier, Int. J. Hydrogen Energy, 34 (20), (2009) 8589-8596.

36

Hydride Fuel Cells: from Solid to Liquid Fuel G.L.Soloveichik

General Electric Global Research, Niskayuna, USA Email: soloveichik@ge.com

Fuel cells have generally higher efficiency and less emissions than other power generators. Proton exchange membrane fuel cells (PEMFC) are considered as the most suitable for mobile applications. In addition, reversible (regenerative) fuel cells are of great interst for energy storage. However, hydrogen, which has been proposed as a clean energy carrier for fuel cells, is hard to produce and store, needs expensive new infrastructure, and has safety and public acceptance issues. Several attempts have been made to replace hydrogen as a fuel for fuel cells with more energy dense hydrides. Metal hydride fuel cells (MHFCs) are able to store hydrogen in the form of a metal hydride within the cell thus eliminatign the problem of hydrogen storage. The cell can be refueled celectrochemically (regenerative mode) or chemically by reaction with hydrogen. Unfortunately, only intermetallic hydrides with low hydrogen content (about 2 wt. %) could be used in MHFCs. Direct borohydride fuel cell (DBFC) is based on oxidation of NaBH4 dissolved in alkaline electrolyte and has higher OCV (1.64 V vs. 1.23 V for PEMFC) and higher energy density. However, DBFCs produce hydrogen as a byproduct and regeneration of the reaction product borax, NaBO2, is questionable. Both MHFCs and DBFCs do not require expensive platium group metal catalysts but could be easily poisoned by CO2, which should be scrubbed. A new concept of a regenerative fuel cell using high energy density organic hydrides (DOFC) has been proposed.1,2 The projected fuel cell works as follows. A hydrogenated organic liquid carrier is fed to the anode of a PEM fuel cell where it is electrochemically dehydrogenated, generating electricity, while air oxygen is reduced at the cathode to water. Dehydrogenated organic hydride, for example, aromatic hydrocarbon, is stored in a separate tank. To recharge the flow battery, the reactions are reversed and the organic liquid is electrochemically re-hydrogenated, or rapidly replaced with the hydrogenated form at a refueling station. Separation of energy conversion (fuel cell) from energy storage (a storage tank) lets the system energy density be close to the energy density of organic hydride (up to 1350 Wh/kg). System flexibility allows for usage in mobile and stationary energy applications, including renewable energy sources. Three novel components are needed to make the proposed DOFC concept practical: a reversible organic liquid hydride with low dehydrogenation energy, an electro(de)hydrogenation catalyst(s), and a low humidity proton exchange membrane. Preliminary data on development of new organic carriers and electrocatalysts will be presented. Advantages and disadvantages of these three types hydride fuel cells will be considered and compared with other methods for energy storage.

This material is based upon work supported as part of the Center for Electrocatalysis, Transport Phenomena, and Materials for Innovative Energy Storage, an Energy Frontier Research Center funded by the U.S. Department of Energy, Office of Science, Office of Basic Energy Sciences under Award Number DE-SC0001055. References 1. G. L. Soloveichik, J.-C. Zhao, US Patent Application 20080248345 (2008). R. H. Crabtree, Energy & Environmental Science, 1, (2008), 134-138.

37

Optical Hydrogen Sensor Based on the Elastic Clamping Effect

V. Palmisano, A. Baldi, M. Slaman, H. Schreuders and B. Dam Department of Chemical Engineering, Delft University of Technology, Delft, The Netherlands

Email: vpalmis@few.vu.nl The development of fast, reliable and cheap hydrogen sensors is crucial for the social acceptance of hydrogen as a clean energy carrier. There are four important parameters related to the performance of a hydrogen detector: reliability, sensitivity, response time and lifetime. Hydrogen sensors based on fiber optics allows working in explosive environments thanks to the possibility of separating the sensing point from the electrical read-out. Following the discovery of the switchable mirror effect [1] we developed an optical hydrogen detector [2] based on the change in the optical reflectance of a thin layer of Mg0.7Ti0.3 upon hydrogenation. The fiber optic hydrogen detector represents a unique combination of small dimensions, low cost and safety, however it only indicates whether the hydrogen pressure is above or below a certain threshold level. We have shown that the thermodynamics of hydrogen absorption of thin Mg layers is strongly influenced by the chemical nature of the “cap” layer and that plateau pressures can be increased by a factor 300 respect to bulk Mg [3]. We exploit this effect in order to engineer a multistep sensor made by a thin film multilayer. To be able to detect different ranges of hydrogen concentrations the multilayer consists of various Mg layers sandwiched between different buffer materials. In particular we show a multilayer which can distinguish three ranges of hydrogen pressure: between 30 and 200 Pa; between 200 and 10000 Pa; higher than 10000 Pa. Another way to tune the equilibrium pressure is by varying the Mg thickness of clamped Mg thin films: we use this effect in order to make a device with a continuous measurement range between 200 and 4000 Pa. The device consists of a wedge of Pd-capped Mg: the hydrogen pressure is measured by the lateral progression of the portion of the film which undergoes the M-H transition. The clamping effect may also be exploited in multifiber hydrogen sensors by depositing the capped Mg wedge on a bunch of fibers. The main problem associated with the use of Pd-capped Mg layers is the low reproducibility upon cycling due to alloying at the interface between Mg and Pd [4]. Mg shows low hydrogenation kinetics at room temperature. To solve these inconveniency we are exploiting Mg alloys as alternative sensing materials. Furthermore, research of clamping materials with a Young modulus higher than Pd allows us to extend the measurement range. References 1. J.N. Huiberts, R. Griessen, J.H. Rector, R. J. Wijngaarden, J.P. Dekker, D.G. de Groot, N.J. Koeman, Nature 380, 231 (1996). 2. M. Slaman, B. Dam, M. Pasturel, D.M. Borsa, H. Schreuders, J.H. Rector, and R. Griessen, Sensors and Actuators B 123, 538 (2007). 3. A. Baldi, M. Gonzalez-Silveira, V. Palmisano, B. Dam, and R. Griessen, Phys. Rev. Lett. 102, 226102 (2009). 4. Baldi A, V. Palmisano, M. Gonzalez-Silveira, Y. Pivak, M. Slaman, H. Schreuders, B. Dam, and R. Griessen, Appl. Phys. Lett. 95 071903 (2009).

38

Magnetocaloric Effects in Y1-xRxFe2-yMy(H,D)4.2 Compounds (R= Gd, Tb, Er; M=Al)

V. Paul-Boncour1, T. Mazet2, M. Phejar1, O. Isnard3, C.V. Colin3

1Chimie Métallurgique des Terres Rares, ICMPE, CNRS et Université Paris XII, 2-8 rue H. Dunant, 94320 Thiais Cedex, France

2 Institut Jean Lamour, Département P2M, Nancy Université, UMR 7198, BP 70239, 54506 Vandœuvre-lès-Nancy Cedex, France

3Institut Néel, CNRS et université Joseph Fourier, BP 166, 38042 Grenoble Cedex 9, France Y1-xRxFe2(H,D)4.2 compounds (R= Gd, Tb, Er) display a giant isotope effect (H,D) on the magnetic transition temperature (TM) between a ferromagnetic (FM) and an antiferromagnetic (AFM) structure on the Fe sublattice [1]. This first order transition exhibits an itinerant electron metamagnetic behaviour. The FM-AFM transition temperature TM is very sensitive to the volume change, the (H,D) isotope content and the application of an external or internal field. The investigation of the magnetocaloric properties of YFe2D4.2 compound has shown an entropy variation at the transition (TM = 84 K, –ΔSM = 10.83 J.K-

1.kg-1 for a field variation of 5 T) close to that of Gd [2]. These compounds are interesting since they form a new family showing promising magnetocaloric properties. Their magnetic and magnetocaloric properties can be tuned by the chemical substitution of Y and Fe atoms but also by D for H substitution. The influence of the substitution of R for Y and Al for Fe has been investigated using magnetic and neutron diffraction measurements. Both types of substitution induce different changes on the magnetic structure. The aim of this study is to increase both the transition temperature and the magnetic entropy variation, in the purpose of magnetic refrigeration applications. References 1. V. Paul-Boncour, M. Guillot, G. Wiesinger, G. André, Phys. Rev. B, 72 (2005) 174430 2. V. Paul-Boncour, T. Mazet, J. Appl. Phys., 105 (2009) 013914

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V-W Alloy Membranes for Hydrogen Purification H.Yukawa1, T.Nambu2, M.Matsumoto3, M.Morinaga1

1Department of Materials Science and Engineering, School of Engineering, Nagoya University, Japan 2Department of Materials Science and Engineering, Suzuka National College of Technology, Japan

3Department of Mechanical Engineering, Oita National College of Technology, Japan Email: hiroshi@numse.nagoya-u.ac.jp

Mass production of high purity hydrogen gas is necessary for the future clean energy systems. Hydrogen permeable membranes are important materials for hydrogen separation and purification technologies. Nb- and V-based alloys are ones of the most promising materials for hydrogen permeable membranes because of their lower cost and higher hydrogen permeability than currently used Pd-based alloys. However, there is a still large barrier to the practical application due to their poor resistance to hydrogen embrittlement. Recently, a concept for alloy design of Nb-based hydrogen permeable membrane has been proposed [1]. Following this concept, Nb-based alloys with high hydrogen permeability and strong resistance to hydrogen embrittlement have been designed and developed. For example, designed Nb-5mol%W alloy possesses more than 4 times higher hydrogen permeability than Pd-26mol%Ag alloy without showing any hydrogen embrittlement [2]. In this study, the concept is further applied to V-based alloys. The mechanical properties of pure vanadium in hydrogen atmosphere are investigated by the in-situ SP test method in hydrogen atmosphere at 637~773K. It is found that the ductile to brittle transition occurs drastically at the hydrogen concentration around H/M=0.23. These results suggest that the resistance to hydrogen embrittlement will be improved by reducing the hydrogen concentration less than this critical value. For this purpose, the alloying effects on the hydrogen solubility and the resistance to hydrogen embrittlement are investigated for V-based alloys. The hydrogen solubility is found to decrease by the addition of tungsten into vanadium. For example, V-5mol%W alloy absorbs only 0.2 (H/M) of hydrogen even in the hydrogen pressure of 0.3MPa at 773K. On the other hand, the hydrogen fluxes, J, through the membrane are measured by the conventional gas permeation method at 673~773K. It is evident that V-5mol%W alloy possesses more than 7 times higher permeability than Pd-26mol%Ag alloy without showing any evidence of hydrogen embrittlement, as shown in Fig.1. References 1. H. Yukawa, T. Nambu, Y. Matsumoto, N. Watanabe, G.X. Zhang, and M. Morinaga,. Materials Transactions, 49 (2008), 2202-2207. 2. N. Watanabe, H. Yukawa, T. Nambu, Y. Matsumoto, G.X. Zhang, and M. Morinaga, J. Alloys and Compounds, 477 (2009), 851-854.

40

Hydrogen Permeation through the Pd-V/Nb-Pd Composite Membranes:

Surface Effects and Thermal Degradation

V.Alimova, Y.Hatanob, A.Busnyuka, M.Notkina and A.Livshitsa a Bonch-Bruevich University, St. Petersburg, Russia

Email: livshits@mail.axon.ru b Hydrogen Isotope Research Center, University of Toyama, Japan

Email: hatano@ctg.u-toyama.ac.jp The hydrogen transport through Group 5 metals occurs with a much higher speed than through Pd and its alloys. Therefore the composite membranes based on Group 5 metals are capable of H2 separation with the high speed and infinte selectivity at a reasonable cost. The composite Pd2μm-V100μm-Pd2μm and Pd2μm-Nb100μm-Pd2μm membranes were investigated with the test stand which allowed measuring the H2 permeation in the pressure range from 10-5Pa to 0.5MPa. The SEM, EDAX and GD-profiler were used for analyses. Due to the wide pressure range the purely diffusion- and purely adsorption rate limited regimes of permeation could be observed in one experiment with one and the same membrane sample at the different states of Pd surface: from the surface fully saturated by carbonaceous species to the atomically clean surface. At usual pressures (P>0.1 MPa), the surface contaminations decreased the permeation by a factor of around 2 as that is typically observed. However the permeation experiments at lower pressures demonstrated that an orders-of-magnitude change in the probability of H2 molecule sticking is actually hidden behind this relatively small effect. The membranes with the contaminated surface could be recovered by the exposure to O2 at (300–400)°C. The composite V/Nb based membranes demonstrated the large permeation flux at higher pressures (150 sccm/cm2 at 0.4 MPa) confirming that they are the promising means of H2 separation. On the other hand, an extremely high permeation probability was observed at lower pressures in the case of clean Pd surface: more than 10% of incident H2 molecules permeated at P<0.1 Pa. The latter allows developing an effective membrane pump that could be applied for D/T processing in fusion devices. The membrane heating at temperature higher than 500oC resulted in an irreversible degradation. It is demonstrated that the permeation behavior at the reversible degradation caused by the surface contaminations and at the irreversible thermal degradation is quite different. The physico-chemical mechanisms behind it are discussed with taking intoaccount the results of SEM and concentration profile analyses.

41

Hydrogen-Palladium Temporary Gradient Material. Form Changes Laws and Nature of the Phenomenon

M.Goltsova and E.Lyubimenko

Physics & Metallurgy Department Donetsk National Technical University, Donetsk, Ukraine Email: goltsova@fem.dgtu.donetsk.ua

Hydrogen atom dissolved in metal crystal lattice and any concentrational nonhomogeneties of hydrogen distribution in metal proceed in appearance, rearrangements and relaxation of internal stresses. Such stresses induced by hydrogen were called “hydrogen concentrational gradient stresses”. The phenomenon was called “hydrogen elasticity phenomenon” by the analogy with thermoelasticity one. In dependence of experimental conditions or metal exploitation conditions hydrogen elasticity phenomenon can be developed in a form of different mechanical or diffusional effects. To study mechanical hydrogen elasticity phenomenon manifestation there was planned and constructed a new hydrogen-vacuum device (HVD-4), which could make possible to investigate a hydrogen elastic deformation of metals (on the example of palladium) at Т>150 ОС, i.e. in the wider region of α–solid solutions of hydrogen in palladium. The palladium plate under investigation was preliminary covered on the one side with copper, and then fixed by its one butt-end in a holder of HVD-4 by such a way, that a plate side covered with copper was upside. An other butt-end of the sample was free. Quartz window was used for “in situ”observation of the sample free-end behaviour during saturation with gaseous hydrogen. A bend value was measured by cathetometer up to ± 5 mm (precision accuracy ±0,02 mm). Electric furnace was used to heat the sample, and a manometer with accuracy 1,5 was used for gaseous hydrogen pressure measurement. For registration of bend changes Samsung videocam was connected to the cathetometer and videodata fixed were then analysed in Pinnacle Studio computer programmes second by second and frame by frame. Accuracy of frame-by-frame analyzes was 1/25 s. Thanks to such experimental technique we fixed a beginning stages of palladium plate bend under gaseous hydrogen loading, i.e., the processes which take seconds to be realized. We investigated palladium plate behavior when saturated with hydrogen in a wide temperature interval (110-350оС) and under different hydrogen pressure values. Mainly the laws fixed in the temperatures higher 150oC are the same as registered in <150oC but there is a principle difference. At the temperatures higher than 300oC the palladium plate bending is completely reverse. The main result: the palladium plate reversible bending induced by hydrogen is almost 2 times above than that induced only by mechanical loading in the region of palladium elasticity. And there was no plastic deformation induced by hydrogen bending! We should underline that this experimentally fixed fact show fundamental difference between behavior of hydrogen gradient material and pure metal under mechanical load. In the report we’ll observe the experimental results in details, as well as discuss the nature of phenomenon. The results are useful for hydrogen palladium membrane technology as well as for hydrogen sensors production.

42

Novel Behaviour in Aluminium Hydride at High Pressures S. P. Besedin1,2, A.P. Jephcoat3,4, A.V.Irodova2

1A.V.Shubnikov Institute of Crystallography RAS, Russia, email: stasb@crys.ras.ru , 2 Russian Research Centre “Kurchatov Institute”, Russia, 3Diamond Light Source UK, 4University of Oxford, UK

The trivalent aluminium hydrides AlH3 and AlD3 were studied experimentally at high pressures in a diamond anvil cell (DAC) by means of Raman scattering, synchrotron X-ray powder diffraction and visual observations of optical transmission. We observe that under compression at P ≈ 53 GPa the α-phase of AlD3 is transformed into a new phase as indicated by powder XRD and Raman scattering. The phase transition appears first order and the specific volume jump equals approximately that observed by Goncharenko et. al in AlH3 [1]. However the transition we observe takes place 10 GPa lower in pressure than that reported in [1] and the structures of the high-pressure phases in AlD3 and in AlH3 appear different. The isotope effect on the equation of state of the α-phase was determined with sufficiently good accuracy and found to be small, so that difference in the vibrational energy cannot be responsible for the difference in the phase transition pressures between the isotopes. Instead it appears dependent on the experimental conditions. In our case, the phase transition was stimulated by the visible laser light used for Raman scattering measurement. This is an essential point indicating strong electron – phonon coupling in the α-phase, which in turn mediates the onset of a martensitic transformation otherwise hindered due to slow kinetics. In the new, photo-induced phase, the aluminium atoms form a lattice with a monoclinic unit cell over which a long-period superstructure is developed when pressure is varied. Our results suggest that aluminium hydride exhibits greater diversity in its phase diagram than reported previously [1] or than has been predicted a priori [2,3]. Transformation kinetics appear to have significant impact on the behaviour of the compound. References 1. I.N. Goncharenko, M. I. Eremets, M. Hanfland, J.S. Tse, M. Amboage, Y. Tao, I.A. Troyan, Phys. Rev. Lett., 100, (2008), 045504 2. P. Vajeeston, P. Ravindran, H. Fjellvag, Chem. Matter., 20, (2008), 5997-6002 3. C. Wolverton, V. Ozolins, M. Asta, Phys. Rev. B, 69, (2004), 144109

43

The Elastic Fields Generated byal Hydride Particle on a Free Surface of a Metal and their Effect on its Growth

Y. Greenbaum, D. Barlam, R.Z. Shneck and M.H. Mintz The formation of a metal hydride is associated with a large increase of volume relative to the parent metal and therefore in large strain energies. Effects of elastic energy on the hydriding of metals are revealed in the microstructural evolution and kinetics of hydride growth on free surfaces. We study the elastic fields set up by hydride particle growing at a free surface of metal with cubic symmetry, with and without an oxide layer. Three stages along the microstructural evolution on the surface of some hydride forming metals exposed to hydrogen at constant pressure were experimentally observed and explained, based on the theoretical calculations of the elastic fields are suggested: (a), A hydride particle at the free surface generates regions of tensile and compressive hydrostatic stress in the surrounding matrix. This may induce a preferred nucleation of new hydrides and formation of clusters of hydrides precipitates, that is indeed observed experimentally. (b) Clustering, on the other hand, may contribute to the cease of growth due to competition on hydrogen. In addition, as the particle grows, changes in the stress fields may retard further diffusion from the surface and be another contribution to the cease of growth. (c) A growing hydride increases the stress in the oxide layer and may finely break it. Then the elastic energy per unit volume drops to its minimum value and the growth may accelerate. This formation of a "growth center" is favored for that hydride precipitate that grow alone and not in a cluster.

44

New Fundamental Experimental Studies on Mg(BH4)2 and Other Borohydrides

H.Hagemann1, V. D’Anna1, J.P. Rapin2, R. Černý2, Y. Filinchuk3, K. Kim4, D. Sholl4 and

S.F. Parker5 1Dépt. de Chim. Phys and 2Lab. Crystallography, Univ. of Geneva, Switzerland, 3Swiss-Norwegian Beam

Lines at ESRF, Grenoble,France, 4Georgia Inst. Technol., Atlanta, USA and 5ISIS, Rutherford Appleton Lab., UK.

Email: hans-rudolf.hagemann@unige.ch Magnesium borohydride with a theoretical hydrogen content of 14.8% has received much interest in view of potential hydrogen storage applications. In this series of studies, we adress fundamental properties of this and related compounds combining various experimental and theoretical methods. We have prepared highly pure (>99%) Mg(BH )2 by recrystallization of 95% pure Mg(BH4)2 obtained from the reaction of MgH2 and E 3NBH3.

4t

Deuterium-hydrogen exchange is observed in solid -Mg(BH4)2 starting at temperatures as low as 132 °C (405K), a much lower temperature than previously reported for LiBH4. About 95% deuterium substitution was achieved after exposing Mg(BH4)2 for 72 hours to 50 bar of D2 at 172 °C. The system LiBH4 – Mg(BH4)2 has been studied by temperature dependent in-situ synchrotron diffraction. This system appears to present an eutectic, no other phase than LiBH4 and Mg(BH4)2 was observed. The crystal structure of Mn(BH4)2 [1] is not as complex as the crystal structure of Mg(BH4)2 [2], but the two structure present some similarities. Both compounds were studied using IR, Raman and INS experiments. The vibrational spectra for both compounds are quite similar, with frequencies shifted to lower energies for Mn(BH4)2. The vibrational density of states as obtained from periodic DFT calculations shows a good agreement with the INS data and allows to assign the observed spectra. Further NMR studies on Mg(BH4)2 are reported separately [3]. References 1. R. Černý, N. Penin, H. Hagemann,Y. Filinchuk J. Phys. Chem. C, 113, (2009), 9003-9007. 2. Y. Filinchuk, R. Černý, H. Hagemann, Chem. Mat., 21, (2009), 925-933. 3. O.A. Babanova, A.V. Soloninin, A.V. Skripov, Y. Filinchuk, H. Hagemann, Abstract no xxx,MH2010.

45

Raman and X-ray High Pressure Investigations on Terbium and Dysprosium Trihydrides

M. Tkacz1, T. Palasyuk1, S. Saxena2

1Institute of Physical Chemistry PAS, Warsaw, Poland 2CeSMEC, Florida International University, Miami, USA

Email: tkaczm@yahoo.com

Recently an increasing attention to rare earth trihydrides has been noted due to the h.c.p. to f.c.c. structural phase transition which was observed for the first time during X-ray diffraction study of ErH3 under high pressure. In this contribution we will present results of high-pressure study of X-ray and Raman effect in TbH3 and DyH3. The following study has been aimed at the better understanding of the mechanism of the structural phase transition and confirmation of the earlier predictions of the transition pressures in those systems. Like other rare earth trihydrides previously investigated both these trihydrides undergo a structural phase transition from initial hexagonal to cubic structure. The pressures of transition, estimated from the EDXRD patterns taken during pressure increase, are about 5 and 5.5 GPa respectively. A disappearance of Raman modes has been observed in a certain pressure range above the pressure of the structural phase transition for each trihydride as a result of the symmetry restrictions due to h.c.p. to f.c.c. changes. The pressures of transition, compressibility, and lattice parameters of terbium and dysprosium trihydrides have been determined and compared with other trihydrides of the lanthanide family. Results of molar volume vs pressure for DyH3 are presented in Figure below.

16,5

18,0

19,5

21,0

22,5

24,0

0 5 10 15 20 25 30 35

hexagonal DyH3B0= 82 GPaB0

/= 5.1Vmole= 23.2 cm3

cubic DyH3B0= 119 GPaB0

/= 1.9Vmole= 21.4 cm3

Pressure (GPa)

Mol

ar v

olum

e (c

m3 )

46

The Effect of Film Thickness on the Thermodynamics of the Hydrogen-

Vanadium Thin Films System. J. Bloch1, B. Pejova2, J. Jacob, B. Hjörvarsson

Department of Physics, University of Uppsala, Box 530, SE-75121, Uppsala, Sweden 1Permanent address: Nuclear Centre-Negev, P.O.Box 9001, Beer-Sheva, Israel

2Permanent address: Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, Skopje,

R Macedonia. Email:bjorgvin.hjorvarsson@fysik.uu.se

The absorption of hydrogen in thin V(001) films under pressures of 1-104 Pa H2 and at temperatures between 350 and 530 K was studied as a function of film thickness between 50 and 5 nm using in situ electrical resistivity measurements. The critical temperatures for the order-disorder transitions taking place in the V-H system are decreased with decreasing film thickness. At 370 K, the high-concentration (ε-VH) phase disappears as the thickness of the film is reduced from 50 to 10nm and the low-concentration (β-VH) phase follows when the film thickness is farther decreased to 5 nm. The critical temperature for the β-VH formation is decreased by 50 K when the film thickness is reduced from 50 to 10 nm. At 530 K the difference in solubility of H in the α-phase of V films down to 10 nm is small but it increases for lower temperatures. At low concentrations the heat of solution in the 10 nm film is somewhat lower than in the bulk, but around H/V=0.07, the values of ΔHH in the film approach those of the bulk. The values of ΔSnc

H of the film are rather close to those of the bulk. Significant difference is found in the pressure-resistivity isotherms above the maximum of the residual resistivity, ΔRmax. For the 10 nm film, in contrast to the 50 nm film, a minimum is located just beyond ΔRmax for the whole temperature range but the difference between the maximum and minimum starts to decrease above 420 K. This results in, by extrapolation, the vanishing of the maximum around 520 K. We suggest that this effect is the result of additional interstitial sites which become available for the H atoms in the lattice of the V film.

47

The Effect of Hydrogen on the Electrical Resistivity of Iron-Vanadium Alloy Thin Films

J. Bloch1, B. Pejova2, J. Jacob, O. Levy1,S. Curtarolo3,4, B. Hjörvarsson Department of Physics, University of Uppsala, Box 530, SE-75121, Uppsala, Sweden

1Permanent address: Nuclear Centre-Negev, P.O.Box 9001, Beer-Sheva, Israel 2Permanent address: Institute of Chemistry, Faculty of Science, Sts. Cyril and Methodius University, Skopje, R

Macedonia. 3Department of Mechanical Engineering and Materials Science,Duke University, Durham, NC 27708, US

4 Department of Materials and Interfaces, Weizmann Institute of Science, Rehovot, Israel

Email: bloch@bgu.ac.il

The interaction of thin (10 nm) films of FexV1-x alloys (x=0, 0.1 and 0.5) with hydrogen gas under pressures between 1-104 Pa H2 and at temperatures between 310 and 473 K was studied using in situ electrical resistivity measurements. Films were deposited on MgO substrates and oriented along the (001) direction. At 310 K and low hydrogen concentrations the excess resistivity increases with the hydrogen concentration following the modified Nordheim equation, similar to the behaviour of pure vanadium films. The results indicate that the H solubility is considerably reduced as the content of iron in the alloy is increased. For higher temperatures, however, the residual resistivity decreases with increasing hydrogen pressure right from the first addition of hydrogen to the system. This behavior has not been reported before for thin H absorbing films. It is highly unusual since under low pressure hydrogen is expected to dissolve into interstitial sites within the metal (or alloy) crystal lattice generating scattering centers for the conduction electrons, thus increasing the resistivity. This resistivity decrease in FexV1-x alloys becomes larger as the iron concentration in the alloy, x, increases and with increasing temperature. This effect may be explained by a hydrogen induced structural change of the alloy. In the temperature range in which the system was studied, between 300 and 550K, there are three possible phases: an iron rich solid solution with vanadium as a substitutional solute, a vanadium rich solid solution with iron as a substitutional solute, and the σ phase with structure type D8b

(space group P42/mnm) with 30 atoms per unit cell. The electrical resistivity of the σ phase is expected to be higher than the pure metals since the iron and vanadium atoms are randomly distributed between the five different Wyskoff sites, degrading the lattice periodicity. The same is true for the iron and vanadium rich disordered solutions. High-throughput combinatorial ab initio computations based on Density Functional Theory for the Fe-V system predict two stable structures with compositions of Fe3V and V3Fe. Both structures are ordered and are expected to decrease the electrical resistivity of the system. The kinetics of the reaction was followed by the time dependence changes of the residual resistivity upon changing of the hydrogen pressure. Two stages can be distinguished: a fast short initial part and a much slower subsequent process in which the resistivity changes direction. The results are explained according to the suggested mechanism.

48

Di-Vacancies and the Hydrogenation of Mg-Ti Films with Short-Range Chemical Order

H. Leegwater1, H. Schut1, L. Ravelli2, W. Egger2, A. Baldi3, B. Dam3, and S.W.H. Eijt1 1Department of Radiation, Radionuclides and Reactors, Faculty of Applied Sciences, Delft University of

Technology, Delft, The Netherlands 2Institut für Angewandte Physik und Messtechnik, Universität der Bundeswehr München, Neubiberg,

Germany 3Department of Chemical Engineering, Faculty of Applied Sciences, Delft University of Technology, Delft,

The Netherlands Email: s.w.h.eijt@tudelft.nl

Mg-Ti(-H) films have an intriguing microstructure [1]. While Ti and Mg are immiscible metals on a macroscopic scale, co-deposition of Mg and Ti by magnetron sputtering leads to Mg-Ti films with a coherent structure, as indicated by X-ray and electron diffraction studies, and a very high degree of intermixing of the Mg and Ti. We obtained direct evidence [2] for the partial chemical segregation of as-deposited and hydrogenated Mg1-

yTiy films (0≤ y ≤ 0.30) into nano-scale Ti and Mg domains using some of the unique features of positron annihilation methods [2-4]. These enabled us to monitor the hydrogenation of Mg domains exclusively, owing to the large difference in positron affinity for Mg and Ti. The electron momentum distribution broadens significantly [3] upon transformation to the MgH2 phase over the whole compositional range [2], revealing the similarity of the metal-insulator transition for rutile and fluorite MgH2. This is quite remarkable given the complex overall optical and electronic properties observed in these nanoscale intermixed metal hydride films, consisting of insulating MgH2 and metallic TiH2

phases. The stabilization of the fluorite phase is thought to occur via elastic coupling of MgH2 to the nanoscale TiH2 domains. Positron lifetime studies show first time evidence for the presence of di-vacancies in the as-deposited and hydrogenated Mg-Ti metal films [2]. In conjunction with the relatively large local lattice relaxations we deduce to be present in fluorite MgH2, these may induce the fast hydrogen sorption kinetics in this cubic MgH2

phase.

References 1. A. Baldi, R. Gremaud, D.M. Borsa, C.P. Baldé, A.M.J. van der Eerden, G. L. Kruijtzer, P.E. de Jongh, B. Dam and R. Griessen, Int. J. Hydrogen Energy 34 (2009) 1450-1457. 2. H. Leegwater, H. Schut, W. Egger, A. Baldi, B. Dam, and S.W.H. Eijt, Appl. Phys. Lett. (accepted). 3. S.W.H. Eijt, Phys. Stat. Solidi (c) 6 (2009) 2561-2565. 4. S.W.H. Eijt, R. Kind, S. Singh, H. Schut, W.J. Legerstee, R.W.A. Hendrikx, V.L. Svetchnikov, R.J. Westerwaal, and B. Dam, J. Appl. Phys. 105 (2009) 043514.

49

Structure and Hydrogenation Study of Nickel Substituted NdCo4B

J-Ph. Soulié 1, N. Penin 2 and K. Yvon 3 1 Ilika Technologies Ltd., Kenneth Dibben House, Chilworth Science Park, Southampton, SO16 7NS, UK

2 Institut de Chimie de la Matière Condensée de Bordeaux – UPR-CNRS 9048, 87 Av. du Dr. Albert Schweitzer, 33608 Pessac, France

3 Laboratory of Crystallography, University of Geneva, 24 quais E. Ansermet, CH-1211 Geneva 4, Switzerland

Email: klaus.yvon@unige.ch In an attempt to observe hydrogen (deuterium) induced atomic ordering of transition (T) metals in the AB5-type derivative structure of NdCo4B, neutron diffraction and hydrogen cycling experiments were performed on a nickel substituted sample of composition NdCo3NiB. While uncycled NdCo3NiB crystallizes with the centrosymmetric CeCo4B-type structure (space group P6/mmm), hydrogenation (deuteration) and cycling of NdCo3NiB at 373 K between 0 and 60 bar hydrogen (deuterium) atmosphere induces a symmetry decrease to non-centrosymmetric space group P6mm. No evidence for cobalt/nickel ordering was found on any of the three T metal sites in the structure. Compared to the structurally related boron free AB5-type compounds deuterium occupies only those interstices that have no boron atom in their coordination sphere. These findings are consistent with the onset of repulsive B-D interactions in the structure as is usually observed in these types of compounds. At 303 K the hydrogen equilibrium plateau pressure of the NdCo3NiB-H system is about 2 bar, and the hydrogen content at 10 bar is about 3.1 H atoms per formula unit.

50

Positron Lifetime Measurements for Monitoring Vacancies and Vacancy Clusters in Hydride Forming Materials.

L. Ravelli1, W. Egger1, G. Dollinger1, R. S. Brusa2, R. Checchetto2 1 Institut für Angewandte Physik, Universität der Bundeswehr, München, Germany 2 Dipartimento di Fisica,

Università degli Studi di Trento, Trento, Italy Email: luca.ravelli@unibw.de

Recently, theoretical investigations have shown that the presence of vacancies in hydride forming materials is of crucial importance for the hydrogenation and dehydrogenation mechanisms. Vacancies, in fact, enhance the mobility of hydrogen and thus the kinetics of the H2 sorption process [1, 2]. Positron Annihilation Lifetime Spectroscopy (PALS) is a very powerful technique capable to detect and characterize non-destructively open volume defects such as vacancies, vacancy clusters, dislocations and small void with high sensitivity in single crystals, powders and nanocrystalline compounds.

s

Pd capped Mg-based film samples (thickness 10 μm) were produced by r.f. magnetron sputtering [3]. The presence of vacancies and the formation of vacancy clusters were studied in the as-prepared sample and in samples submitted to 1, 2, 4 and 8 H2 absorption and desorption cycles. For this task a monoenergetic pulsed positron beam of variable energy is necessary to control the implantation depth of the positrons and to depth- profile by PALS the Mg films. The measurements were performed with the Pulsed Low Energy Positron System (PLEPS) [4] installed at the high intensity positron source NEPOMUC (NEutron-induced POsitron source MUniC) at the research reactor FRM-II. Disappearence of vacancies due to their clustering was observed after the second H2 sorption cycle. References: 1. M. S. Park, A. Janotti and C. G. Van de Walle, Phys. Rev. B 80 (2009) 064102. 2. R. Checchetto, N. Bazzanella, A. Miotello, R. S. Brusa, A. Zecca and P. Mengucci, J. Appl. Phys. 95 (2004) 1989-1995. 3. N. Bazzanella, R. Checchetto and A. Miotello, Appl. Phys. Lett. 85 (2004) 5212-5214. 4. P. Sperr, W. Egger, G. Kögel, G. Dollinger, C. Hugenschmidt, R. Repper, C. Piochacz, Appl. Surf. Science 255 (2008) 35-38.

51

Simulation Study on Structure Variation of Metallic Nanoparticles due to Hydrogenation

H. Ogawa Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

Email: h.ogawa@aist.go.jp Metallic nanoparticle is considered as a potential material for hydrogen storage because its large surface area advantageous to hydrogen absorption and desorption. Storage properties of hydrogen in nanocrystals has been investigated by several authors. Pundt and coworkers showed the structure variation of Pd nanoparticles due to hydrogen loading and its cluster size dependency by X-ray diffraction [1]. The present authors investigated the hydrogen absorption in model metallic nanoparticle by classical MD simulation with assuming the potential parameters as phenomenological variables [2]. In this study, the authors extend the time and particle radius ranges in MD simulation to study the structure variation of nanoparticles due to hydrogenation. The figure shows typical structure changes of b.c.c., hydrogenated nanoparticles observed in the simulation [3]. In the left case, the b.c.c. lattice is vertically elongated hence turns into body-centered-tetragonal (b.c.t.) phase. In the middle and right cases, generation of grain boundaries and variation of particle shapes were observed. Grain boundaries were in parallel (middle) or in complicated three-dimensional arrangement (right) which induced asymmetric particle shapes. Dependency on the particle size was not clearly observed in b.c.c. nanoparticles. Structure variation in f.c.c. and h.c.p. cases were also investigated.

Figure. Examples of structure variation of b.c.c. nanoparticles due to hydrogenation. References 1. M. Suleiman et al., J. Alloy Comp., 356-7, 644 (2003). 2. H. Ogawa et al., Mater. Trans., 49, 1983 (2008) 1983-1986. 3. H. Ogawa et al., Mater. Res. Soc. Symp. Proc., 1216 (2010) W03-02.

52

Vibrational Properties of CeNiSn-Hydrides J.P. Maehlen a, R.G.Delaplane a, R.V. Denys a, A.J. Ramirez-Cuesta b, and V.A. Yartys a

a Institute for Energy Technology, P.O. Box 40, Kjeller NO-2027, Norway b ISIS facility, Rutherford Appleton Laboratory, Chilton, Didcot, OX11 0QX, United Kingdom

Email: jan.petter.maehlen@ife.no The vibrational properties of hexagonal CeNiSnH2 and orthorhombic CeNiSnH have been investigated using inelastic neutron spectroscopy (INS) performed on the TOSCA instrument at the ISIS pulsed neutron and muon source. Initial hydrides were synthesised from a TiNiSi-type equiatomic CeNiSn internetallic compound by a two-step hydrogen absorption process. Although the crystal structures of both hydrides have different symmetries and hydrogen to metal ratios, the chemical environment of hydrogen in these hydrides is similar with H atoms occupying the Ce3Ni tetrahedra (see Figure 1). The crystal structures of both hydrides were characterised with neutron powder diffraction that is reported here for the first time for CeNiSnH(D)2 (data collected for both the hydride and the deuteride with the R2D2 instrument, Studsvik Neutron Research Laboratory, Uppsala University, Sweden). Interatomic Ni-H distances are close to each other; 1.632(6) Å in CeNiSnH2 and 1.626(6) Å in CeNiSnH. Hydrogen-hydrogen separations well exceed 2 Å; 2.76(1)Å (CeNiSnH2) and 2.66(1)Å (CeNiSnH). The vibrational modes of the INS spectra were unambiguously assigned based on the DFT calculations (Figure 2). For CeNiSnH2 two well-defined peaks appear at 690 and 1130 cm-1; these were assigned to the fundamental Ni-H bending and Ni-H stretching modes, respectively. For CeNiSnH two peaks are found at 825 and 960 cm-1 (Ni-H bend) and a third at 1245 cm-1 (Ni-H stretch). The crystallographic data are summarised below. CeNiSnH[D]2: space group P63/mmc (filled ZrBeSi type); a= 4.3927(2) [4.3947(2)]; c=8.5452(7) [8.5329(4)] Å; V=142.79(2) [142.72(1)] Å3. Ce is in 2a (0,0,0); Ni in 2c (1/3,2/3,1/4); Sn in 2d (2/3,1/3,1/4); and H[D] is in 4f (1/3,2/3,0.0591(7)[0.0607(2)]). CeNiSnD [1]: space group Pna21; a = 7.2720(3); b = 8.4951(4); c = 4.4021(2) Å; V = 271.95 Å3. 4 Ce in 4a: 0.010(4) 0.3063(15) 0.211(6); 4 Ni in 4a: 0.7868(19) 0.8999(9) 0.233(7); 4 Sn in 4a: 0.6729(23) 0.5753(15) 0.259(7); 4 D in 4a: 0.4325(22) 0.0757(17) 0.768(7).

References

Figure 1: Stacking of the H-occupied Ce3Ni tetrahedra in CeNiSnH1 and CeNiSnH2.

Figure 2: Experimental and calculated INS spectrafor CeNiSnH2.

1. V.A.Yartys, B.Ouladdiaf, O.Isnard, O.Yu.Khyzhun, K.H.J.Buschow, J.Alloys Comp. 359 (2003) 62.

53

Structural Studies of Hydrogen Storage Materials using Total Scattering and the PDF Method

Y. Nakamuraa, J. Nakamuraa, H. Kimb, T. Proffenb, E. Akibaa

a National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan b Los Alamos National Laboratory, Los Alamos, USA

Email: yumiko.nakamura@aist.go.jp Hydrogen storage materials with a higher capacity working under ambient conditions are highly demanded for future hydrogen energy systems. Fundamental research including structural studies on materials has been conducted for understanding reaction mechanisms between materials and hydrogen. Atomic arrangement in materials is closely related to hydrogenation reaction. This study focuses on local structure obtained from neutron/X-ray total scattering and the Pair Distribution Function (PDF) method 1. This method analyzes not only Bragg peaks originated from the periodic arrangement of atoms but also diffuse scattering caused by disordered arrangement, short-range ordering, local displacement, etc. Results for two kinds of materials are presented. Mg-Co alloys synthesized by mechanical alloying were hydrogenated at room temperature2. The hydrogen uptake was around 3 mass% at maximum. Conventional X-ray diffraction provided extremely broad pattern, suggesting possibility of nano-crystalline or disordered structure. Neutron and X-ray PDFs showed quite different patterns, reflecting that Mg and Co have the opposite contrast for neutron and X-ray. The analysis suggested that the material contains two domains, i.e. Mg-rich and Co-rich domains, and that the only Mg-rich domain absorbs hydrogen. Ti, V based solid solution alloys with a BCC structure have preferable hydrogenation properties under ambient conditions 3. Local disordering besides the average structure in this kind of materials has been studied. PDFs of deuterated V, Ti-V and Ti-V-Mn showed similar patterns, but the decreasing rates with interatomic distance depended on the alloy composition. They were simulated with structural models assuming local displacement or a reduced domain size. This work was supported by “The New Energy and Industrial Technology Development Organization” (NEDO) under “Advanced Fundamental Research on Hydrogen Storage Materials (HYDRO-STAR)”. References 1. T. Egami and S.J.L. Billinge, ‘Underneath the Bragg peaks: structural analysis of

complex materials’ Pergamon, 2003. 2. Y. Zhang, Y. Tsushio, H. Enoki, E. Akiba, J. Alloys and Compounds, 393, (2005) 147-

153. 3. E. Akiba, H. Iba, Intermetallics, 6, (1998) 461-470.

54

Phase Stability in the LiNH2:MgH2 System D. Pottmaier1, F. Dolci2, M. Orlova3, W. Lohstroh4, G. Vaughan3, M. Fichtner4 and M.

Baricco1 1Dipartimento di Chimica IFM and NIS - Università di Torino - Torino, Italy.

2Insttitut for Energy JRC - Petten, Netherlands. 3ID11- European Synchrotron Radiation Facility - Grenoble, France.

4 Karlsruhe Institute of Technology (KIT), Institute of Nanotechnology –Karlsruhe, Germany. Email: daphiny.pottmaier@unito.it

Reactive hydride composites consisting on amides/hydrides systems have been subject of intense investigation for solid hydrogen storage due to their high storage capacity, good cyclability and good thermodynamic properties [1-8]. The system LiNH2-MgH2 is a promising one as changes in stoichiometry [2-6] and ball milling conditions [7,8] result in different reaction mechanisms. Investigating how the system is affected by these changes provides specific insight for tackling an effective hydrogen storage material. In this work, LiNH2-MgH2 in ratio 2:1 and 1:1 and ball milled under different conditions (100 and 600 rpm) were studied by combining ex-situ X-ray diffraction, infrared spectroscopy, thermal programmed desorption and in-situ synchrotron X-ray diffraction. Ex-situ X-ray diffraction patterns of samples ball milled at high speed present peaks signed as nanostructured initial phases (LiNH2, MgH2) and new phases (LiH, Li2NH, Mg3N2). The same is not observed for samples ball milled at low speed. Thermal programmed desorption performed up to 673 K shows, for sample 2:1 ball milled at high speed, a profile with hydrogen release starting as low as 398 K, with suppression of ammonia signal. On the contrary, sample 1:1 ball milled at low speed starts releasing simultaneously both hydrogen and ammonia at 463 K. In-situ synchrotron X-ray diffraction measurements show solid state transformations, such as structural arrangement of nanostructured phases (e.g. LiNH2), formation of intermediate phases (e.g. Mg(NH2)2), allotropic transformation of phases (e.g. α-Li2MgN2H4) and decomposition of single phases (e.g. MgH2). Refinement of these experimental data by the Rietveld method shows evolution of phase fractions, crystallographic parameters and microstructural properties for the 2:1 and 1:1 LiNH2:MgH2 systems. Thermodynamic databases will be used to understand phase stability obtained by experiments as a function of temperature.  References 1. P. Chen, Z. Xiong, J. Luo, J. Lin, K.L. Tan, Nature, 420 (2002) 302-304. 2. W. Luo, J. Alloys and Compounds, 381 (2004) 284-287. 3. W. Lohstroh, M. Fichtner, J. Alloys and Compounds, 446-447 (2007) 332-335. 4. J. Yang, A. Sudik, C. Wolverton, J. Alloys and Compounds 430 (2008) 334-338. 5. Y. Liu, K. Zhong, M. Gao, J. Wang, H. Pan, Q. Wang, Chem. Mater. 20 (2008) 3521-3527. 6. H. Leng, T. Ichikawa, H. Fujii, J. Phys. Chem. B 110 (2006) 12964-12968. 7. R. Shahi, T. P. Yadav, M. A. Shaz, O. N. Srivastava, J. Alloys and Compounds 33 (2008) 6188-6194. 8. C. Liang, Y. Liu, K. Luo, B. Li, M. Gao, H. Pan, Q. Wang, Chem. Eur. J. 16 (2010) 693-702. 9. J. Rijssenbeek, Y. Gao, J. Hanson, Q. Huang, C. Jones, B. Toby, J. Alloys and Compounds, 454 (2008) 233-244. 10. F. Xu, L. X. Sun, P. Chen, Y. N. Qi, J. Zhang, J. N. Zhao, Y. F. Liu, L. Zhang, Z. Cao, D. W. Yang, J. L. Zeng, Y. Du, J. Therm. Anal. Calorim. (2009).

55

In-Situ Neutron Scattering Studies of BCC Ti-Cr-V-Mo Alloy Hydrogen Storage Materials

K. Kamazawa, M. Aoki, T. Noritake, K. Miwa, J. Sugiyama, S. Towata, M. Ishikiriyama1, M. Sommariva2, P. Alexander2, S. Callear2, A.J. Ramirez-Cuesta2, W. Kockelmann2,

M. O. Jones2,3 and W.I.F. David2,3 Toyota Central R&D Labs., Inc. Toyota Motor Corp. 1, STFC, Rutherford Appleton Laboratory, ISIS2,

Oxford Univ3. Email: e1508@mosk.tytlabs.co.jp

Hydrogen storage alloys with a body-centered-cubic (bcc) structure are known to absorb a large amount of hydrogen in their lattice [1]. Particularly, the Ti-Cr-V-Mo alloys recently developed are applicable for a hydrogen storage tank of fuel cell vehicles due to the high dissociation pressure and capacity [2]. Although the initial capacity of hydrogenstorage alloy Ti25Cr50V20Mo5 (2.4 mass%) is considered to be attractive for practical application, the capacity decreases rapidly after hydrogen absorption and desorption [3]. Assuming that the hydrogen responsible for the capacity-fading occupies a certain site in the crystal lattice, the cycle performance of the alloys is expected to be improved by reducing the number density of such site before the initial hydrogen absorption/desorption cycle. We have, therefore, attempted to investigate the hydrogen site(s) and their occupancies as a function of the hydrogen absorption/desorption (a/d) cycle. For such purpose, neutron diffraction (ND) has a great advantage due to its sensitivity for light atoms. Since the large incoherent scattering of H brings a large background signal to a diffraction pattern, ND measurements are usually carried out using deuterated samples. However, there are no evidences that the deuterium (D) occupies the same site(s) to those for the hydrogen in the V-based alloys. In fact, since the pressure-composition (p-c) isotherm for the vanadium metal under H2 atmosphere is very different from that under D2 atmosphere, the H-site(s) is naturally expected to be different from the D-site(s) in the vanadium metal. Hence, we have carried out ND measurements on the hydrogen storage alloy under H2 atmosphere. The pristine (un-cycled/un-hydrogenated) alloy was prepared by an ark melting technique. Then, the alloy was annealed at 1300 ºC for 10 hours. The ND patterns were measured on the General Materials diffractometer (GEM) at ISIS in the U.K. It was found that the ND pattern for the Ti25Cr50V20Mo5 alloy after the initial a/d cycle obtained under H2 atmosphere is different from that obtained under D2, demonstrating that the D-site(s) is different from the H-site(s). Based on the structural analyses, it was determined that the D occupies both at the octahedral and the tetrahedral sites of the body-centered-tetragonal (bct) structure, whereas the H occupies only the octahedral site. We have also carried out an in-situ ND study for the Ti25Cr50V20Mo5 alloy up to 20 MPa H2-pressure at room temperature. Despite the common sense that it is difficult to measure ND patterns for hydrogenarated samples, we successfully observed the change in the H sites and their occupancies with the H2 a/d cycle. References 1. E. Akiba and M.Okada, MRS Bull. 27 (2002) 699. 2. T. Matsunaga, M. Kon, K. Washio, T. Shinozawa, M. Ishikiriyama, Int. J. Hydrogen Energy 34 (2009) 1458. 3. M. Aoki, T. Noritake, M. Matsumoto, K. Miwa, A. Ito, S. Towata, K. Washio, M. Ishikiriyama, The 2009 Spring Meeting of the Japan Inst. Metals.

56

Structure Modification of Nanocrystalline Mg-Nb Films

P. Mengucci, G. Barucca, G. Majni Dipartimento di Fisica e Ingegneria dei Materiali e del Territorio, Università Politecnica delle Marche, Via

Brecce Bianche, I-60131 Ancona, Italy. N. Bazzanella, R. Checchetto, A. Miotello

Dipartimento di Fisica, Università di Trento, Via Sommarive, I-38123 Povo (TN), Italy. Email: p.mengucci@univpm.it

In the present work we study Mg film samples (thickness in the μm range) doped with Nb 5 at.% and submitted to repeated H2 sorption cycles. To avoid surface oxidation and to favour the dissociation of H2 molecules a capping layer of Pd (about 20 nm thick) was deposited on the top surface of the Mg film. After deposition, samples were introduced in a Sievert-type apparatus and submitted to a maximum of 8 repeated H2 absorption/desorption cycles at 623 K. All samples were characterised by X-ray diffraction in Bragg-Brentano geometry (XRD), energy dispersive microanalysis (EDS) and electron microscopy techniques (SEM, TEM). Analyses show that Nb is able to strongly modify the microstructure of Mg film samples. The results can be summarised as follows: − Pd diffuses into Mg upon cycling forming the cubic Mg6Pd compound, its crystalline

state depends on the number of cycles; − only after few cycles the peak of the metallic Nb appears in the XRD spectra and after 8

cycles small particles (∼10 nm) of metallic Nb are always present; − the Mg grains size drops rapidly with the number of cycles; − the strain of the Mg lattice tends to decrease during cycling. Further work is in progress in order to correlate these results to the storage efficiency and the absorption/desorption hydrogen kinetics. References 1. R. Checchetto, N. Bazzanella, A. Miotello, R. S. Brusa, A. Zecca and P. Mengucci, J. Appl. Phys. 95, 1989 (2004) 2. R. Checchetto, R. S. Brusa, N. Bazzanella, G.P. Karwasz, M. Spagolla and A. Miotello, P. Mengucci and A. Di Cristoforo, Thin Solid Films, 469-470, 350 (2004) 3. N. Bazzanella, R. Checchetto, A. Miotello, C. Sada, P. Mazzoldi and P.Mengucci, Appl. Phys. Lett. 89, 014101 (2006)

57

Dependence of the Chemical Composition on the Crystal Structure of Mg2-xRExNi4 (RE: La, Pr, Nd, Sm, Gd, x=0.6, 1.0) Hydride

K. Sakaki1, N. Terashita2, S. Tsunokake2, Y. Nakamura1, E. Akiba1

1. National Institute of Advanced Industrial Science and Technology, Japan 2. Japan Metals & Chemicals Co., Ltd., Japan

kouji.sakaki@aist.go.jp Some of coauthors have developed new hydrogen storage alloys with Mg-containing

Laves phase, especially Mg1-xCaxNi2 with the C15 structure1 and Mg2-xRExNi4 with the C15b structure2. Most of them absorbed hydrogen up to H/M≈0.6 with a pleateau on the P-C isotherms, while MgPrNi4 showed the P-C isotherm with two plateaus and the maximum hydrogen capacity of H/M≈1.12. In this study, we have investigated the dependence of the composition and the rare earth elements on the crystal structure of Mg2-xRExNi4 hydrides using in-situ and ex-situ X-ray diffraction (XRD) and the ab-initio calculation. The crystal structure of Mg1.4Pr0.6Ni4 and MgPrNi4 were the C15b structure (space group:

F-43m) with a=7.012(1) Å and a=7.108(2) Å, respectively. The hydrogenated Mg1.4Pr0.6Ni4H3.2 remained the C15b structure with volume expansion by 13%. MgPrNi4 transformed to orthorhombic MgPrNi4H4 (space group: Pmn21, a= 5.097(1) Å, b= 5.480(1) Å, c= 7.403(2) Å) on the first plateau during absorption. This crystal structure is similar to that of MgNdNi4H~4 reported by Guenee et al3. On the second plateau, the orthorhombic phase transformed to MgPrNi4H7 with the C15b structure which had 25 % larger cell volume than the starting alloy. Mg1.4RE0.6Ni4 (RE=Sm, Gd) and MgRENi4 (RE=La, Nd, Sm, Gd) changed into C15b type

Mg1.4RE0.6Ni4H3.2 and orthorhombic MgRENi4H~4, respectively, in a similar way to Mg1.4Pr0.6Ni4 and MgPrNi4. These results indicate that difference in structure of the hydrides depends on the ratio of Mg and RE, i.e. stoichiometric or Mg-rich compositions. Hydrides with a higher hydrogen content Mg2-xRExNi4H~7 was observed only for

stoichiometric compositions with RE=La, Pr, Nd in the present experimental conditions. These results were consistent with lattice constants and their formation enthalpy of the hydrides obtained from ab-initio calculation. Our ab-initio calculation expected that MgSmNi4H~7 and MgGdNi4H~7 can be synthesized at the higher hydrogen pressure range. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under its “Advanced Fundamental Research Project on Hydrogen Storage Materials” and “Development of high capacity hydrogen absorbing alloy with Laves structure” References 1. N. Terashita, K. Kobayashi, T. Sasai, E. Akiba, J. Alloys and Compounds, 327, (2001), 275-280. 2. N. Terashita, K. Sakaki, Y. Nakamura, S. Tsunokake, E. Akiba, to be presented at MH2010 3. L. Guenee, V. F-Nicolin, K. Yvon, J. Alloys and Compounds, 348, (2003), 129-137.

58

Neutron Diffraction Study of BCC Alloys Containing Ferrovanadium

M. Koudriachova1, , L. Laversenne2, S. Miraglia2, D. Fruchart2, J. Huot3

1 Department of Chemistry, University College London, WC1E 6BT, U.K. 2 CNRS, Institut NEEL, F-38042 Grenoble, France

3 Hydrogen Research Institute, Université du Québec à Tois-Rivières, Trois-Rivières, Québec, Canada Email: jacques.huot@uqtr.ca

Hydrogen storage alloys are considered to be used as hydrogen storage tanks for mobile and stationary applications. Ti-V-based body-centered cubic (BCC) solid solutions have been attracting attention for hydrogen storage applications due to their larger gravimetric storage capacities than the conventional AB5 type alloys and the more suitable operational temperatures than that of the high capacity hydrides, such as MgH2. The hydrogen reaction kinetics of the Ti-V binary alloys is slow and improvements are obtained by adding a third element such as Cr or Mn [1]. Some of the alloys in ternary system exhibit relatively small hysteresis, high hydrogen absorbing capacities at room temperature and fast kinetics of absorption and release of hydrogen, after activation procedures [9]. In a technological point of view, the key challenges for the practical applications of Ti–V-Mn and Ti-V-Cr alloys in hydrogen storage are: (i) the slow activation of these alloys, and (ii) the high cost of pure vanadium. An approach to decrease the cost of Ti–Mn–V and Ti- Cr-V alloys is to replace vanadium by less expensive elements or compounds, but this is a difficult task since vanadium stabilizes the BCC solid solution. In this paper we report a recent in-situ neutron powder diffraction measurements of TiV1.1Mn0.9, Ti(FeV)1.1Mn0.9, TiV0.9Mn1.1, and Ti(FeV)0.9Mn1.1 alloys and results of computer simulations. For the alloy Ti(FeV)1.1Mn0.9 we found a phase transformation at about 70°C under a hydrogen pressure of 20 bar. Crystal structure and hydrogen sorption properties will also be discussed. References 1. A.J. Maeland, G.G. Libowitz, J.F. Lynch, J. Less Common Met. 104 (1984) 361 2. E. Akiba, Curr. Opin. Solid State Mater. Sci. 4 (1999) 267. 3. S.F. Santos and J. Huot, ‘Hydrogen storage in TiCr1.2(FeV)x BCC solid solutions’,

Accepted for publication in Journal of Alloys and Compounds 4. S.F. Santos and J. Huot, ‘Hydrogen storage in Ti-Mn-(FeV) BCC alloys’, Submitted to

Journal of Alloys and Compounds

59

The Use of 3-D Laser Confocal Microscopy to Image Metal - Hydrogen Interactions

A.Walton , Y.Pivak, R.Gremaud, B.Dam

Department of Metallurgy and Materials, University of Birmingham, Birmingham, UK. Chemical Engineering, Faculty of Applied Science, Delft University of Technology, Delft, the Netherlands.

Email: a.walton@bham.ac.uk Metal –Hydrogen interactions are often associated with an expansion of the crystal lattice which can manifest itself in changes of sample morpholgy. These changes are difficult to image using conventional optical or electron microscopy. Samples have to be flat for optical microscopy and become out of focus when height changes occur; whereas electron microscopy is normally performed under vacuum or small partial pressures of gas. In this work an Olympus OLS 3100 laser confocal microscope has been used in conjuntion with an Instec sample stage to produce three dimensional images of hydrogen interactions in-situ. Sputtered Pd thin films, previously used as test samples for hydrogenography [1] , have been hydrided in-situ and imaged during successive absorption / desorption cycles. 3-D maps were produced of the Pd films as they delaminated from the surface of the glass substrates over 15 sorption cycles. It was possible to relate the level of delamination to shifts in the plateau pressure for these samples. Video footage was compiled by stacking hundreds of time elapsed images which demonstrated buckling of the films on hydriding and shrinkage back down to a flat film on dehydriding. Three dimensional images have also been taken of the decrepitation process in NdFeB magnets. Under certain condtions individual grains have been shown to lift out of the surface of the magnets and hydrogen can be observed etching the Nd-rich grain boundaries in the material. There are likely to be many applications for this technique where hydrogen induced micro/macro structural changes occur in materials. References 1. A.Walton, Y.Pivak, R.Gremaud, B.Dam, Acta Materialia, Vol 57, 4 , 1209-1219

60

Diffusion of Deuterium in Zr-2.5Nb Alloy under Neutron Irradiation D. Khatamian

AECL, Chalk River Laboratories, Stn. 55, Chalk River, ON K0J-1J0, Canada khatamiand@aecl.ca

Pressure tubes of cold-worked Zr-2.5Nb (Zr-2.5 wt% Nb) material are used in the core of CANDU® reactors to contain the fuel bundles and the heavy water (D2O) heat transport fluid. If the total hydrogen isotope concentration in the tubes exceeds the terminal solid solubility, the tubes can become susceptible to a crack initiation and propagation process called delayed hydride cracking (DHC). To model deuterium mobility and distribution in pressure tubes as well as to determine DHC velocity, the effect of fast neutron flux on the diffusivity of deuterium must be accounted for. Early studies in Zircaloy-4 and austenitic steel had shown that neutron irradiation can cause a substantial increase in the diffusivity of hydrogen. However, a subsequent study had reported no influence of irradiation on the mobility of tritium in Zircaloy-2. Due to these conflicting results, the present experiments were designed to measure simultaneously the diffusion coefficient of deuterium in Zr-2.5Nb pressure tube material both in and out of neutron flux to determine the magnitude of any irradiation effects. The measurements were carried out at about 260 and 300ºC using the U-2 Loop of NRU reactor at the Chalk River Laboratories. The results showed that deuterium diffusion in Zr-2.5Nb pressure tube material during irradiation at a fast neutron flux of 5x1017 nm-2s-1 is not significantly different from that measured in the absence of neutron flux. This supports the use of deuterium diffusivities determined from out-reactor tests for modeling deuterium mobility in pressure tubes and other reactor core components. ®CANDU–CANada Deuterium Uranium is a registered trademark of Atomic Energy of Canada Ltd.

61

Stabilization of Lattice Defects in HPT-deformed Palladium Hydride

M. Bönisch, M. Krystian, D. Setman, G. Krexner, M. J. Zehetbauer Research Groups Physics of Functional Materials, and Physics of Nanostructured Materials

Faculty of Physics, University of Vienna, Wien, Austria Email: matthias.boenisch@univie.ac.at

Recent investigations on palladium hydride (Pd-H, [1]) showed, for the first time, evidence of formation of vacancy-hydrogen clusters during Severe Plastic Deformation (SPD) effected by High Pressure Torsion (HPT). Vacancy concentrations produced in Pd-H by this method are extraordinarily high, that is on the order of several at% of the host metal. Results furthermore hint at the thermal stabilization of lattice defects by segregation of hydrogen atoms not only for vacancy-type defects but also for dislocations and grain boundaries. The technique of HPT belongs to the family of SPD methods whereby high grade plastic deformation is achieved under hydrostatic pressure at low homologous temperatures. During HPT the sample is put between two anvils and being deformed by pure shear forces resulting from rotation of one anvil against the other. Due to the continuous path of deformation under enhanced hydrostratic pressure, extremely high strains are producible. Experiments were performed on disk-shaped Pd samples with a diameter of 6mm and thickness of 0.8mm loaded with hydrogen in a Sieverts-type apparatus, up to a hydrogen content of [H]/[Pd]~0.78 and then stored in liquid nitrogen. Deformation by means of HPT was carried out both at temperature of liquid nitrogen and frozen CO2, that is 77K and 195K, respectively. Subsequently, Differential Scanning Calorimetry (DSC) as well as thermogravimetric analysis (TGA) were performed in order to follow the evolution of the system with temperature. The vacancy concentration was derived from DSC, TGA, Scanning Electron Microscopy (SEM) investigation as well as from high precision buoyancy measurements. Prompt Gamma Activation Analysis (PGAA) was utilized for precise determination of changes of the hydrogen concentration corresponding to specific features observed in DSC-scans as a function of temperature. In addition microhardness studies were applied to further characterize the system. References 1. Formation of superabundant vacancies in nano-Pd-H generated by high-pressure

torsion, M. Krystian, D. Setman, B. Mingler, G. Krexner, M. J. Zehetbauer, Scripta Mater. 62, (2010) 49-52

62

Hydrogen Dynamics in Icosahedral and Amorphous Zr-based Alloys by Diffusion and Fast Field Cycling Nuclear Magnetic Relaxation Methods.

T. Apih, A. Gradišek and J. Dolinšek

J. Stefan Institute, Ljubljana, Slovenia Email: tomaz.apih@ijs.si

We report on diverse range of broad-band nuclear magnetic resonance (NMR) methods that we applied to study hydrogen dynamics in various metal alloys. The systems studied were Zr69.5Cu12Ni11Al7.5 partially quasicrystalline alloy, icosahedral and amorphous phase of Ti40Zr40Ni20 alloy and Zr50Cu40-xAl10Pdx bulk glassy alloys. The following techniques were used:

• Direct determination of hydrogen diffusion constant D by measuring stimulated-echo decay in a static fringe field of a superconducting magnet. The technique allows for the determination of D down to ~ 10-13 m2/s .

• Measurements of temperature dependence of NMR spin lattice relaxation time T1 allow for the determination of hydrogen jump frequency. Combined with diffusion coefficient data, average jump rate can be estimated.

• Using fast field cycling relaxometry we measured NMR spin-lattice relaxation time T1 as a function of applied magnetic field, typically in the frequency range 5 kHz to 20 MHz. The broad frequency range allows for the determination of hydrogen jumps activation energy distribution, even at fixed temperature.

• For deuterated samples, hydrogen hopping rate and activation energy were estimated both from the dynamic 2H NMR line shape, as well as from the 2H NMR spin-lattice relaxation measurements.

• The lattice expansion upon hydrogen loading was estimated from the change of 27Al NMR line widths.

The combination of the above techniques allowed us to monitor the isotope effects and hydrogen dynamics in metallic alloys as a function of temperature, alloy composition, crystallization and hydrogen loading concentration. References

1. Hydrogen diffusion in partially quasicrystalline Zr69.5Cu12Ni11Al7.5, T. Apih et al., Phys. Rev. B ,68 , (2003), 212202

2. Influence of the hydrogen content on hydrogen diffusion in the Zr69.5Cu12Ni11Al7.5 metallic glass. T.Apih et al, Solid state commun. 134, (2005), 337-341.

3. Hydrogen diffusion in quasicrystalline and amorphous Zr-Cu-Ni-Al. J. Dolinšek et al. Catal. today 120, (2007), 351-357.

4. Deuterium dynamics in the icosahedral and amorphous phases of the Ti40Zr40Ni20 hydrogen-absorbing alloy studied by 2H NMR, A. Gradišek et al, J. Phys.: Condens. Matter 20, (2008), 475209

5. Physical properties of Zr50Cu40-xAl10Pdx bulk glassy alloys, M. Wencka et al, Submitted

63

Atom Probe Analysis of Hydrogen in V-6at%Fe Film and Fe/V-6at%Fe Multi-Layered Film

R. Gemma1, T. Al-Kassab2, R. Kirchheim1, A. Pundt1

1 Institut für Materialphysik, Universität Göttingen, Friedrich-Hund-Platz 1, D-37077 Göttingen, Germany 2 Division of Physical Sci.& Eng., King Abdullah University of Science & Technology (KAUST)

Thuwal 23955-6900, Kingdom of Saudi Arabia Email: rgemma@ump.gwdg.de

Recently, Atom Probe Tomography (APT) has opened up a new quantitative approach

to trace hydrogen in metals [1-3]. Due to its high depth resolution reaching sub-nanometer scale, the atom probe technique can be regarded as one of the strongest tool to analyze local hydrogen distributions in materials. Direct observations of the local chemistry associated with this distribution of hydrogen in alloys and compounds, for instance at defects like dislocations or at grain boundaries would be of particular interest to establish a fundamental understanding of such phenomena like hydrogen embrittlement.

However, it is not so straightforward to detect hydrogen in metals accurately just by utilizing this technique because of diffusion phenomena. Even at cryogenic temperatures as low as 50 K, an interstitially solved hydrogen atom in a metal is highly mobile and has diffusion coefficient of 10-9 cm2 / s (= 32 μm / hour) e.g. in vanadium [4]. To avoid diffusion, use of heavier isotopes like D instead of H is thus strongly recommended for APT, also because D can be ultimately distinguished from residual hydrogen in the analysis chamber. Nevertheless, a special care still must be taken for quantitative analysis of D by considering the influence of analysis temperature on the diffusivity of D.

In this presentation, results of APT analyses on deuterium in V-6at%Fe and Fe/V-6at%Fe multi-layered films will be presented with the focus on correct concentration measurement and correct local distribution determination of D in the initial films. A 1/T dependence of the measured concentration cD on analysis temperature T was found. At 20 K, the concentration of D detected by APT showed good agreement with that expected from the p-c isotherm.

At this low temperature, APT measurements are extremely difficult because of easy sample rupture. Therefore, most D-distribution measurements are taken at 30 K, allowing a certain D-loss at the surface but no D-diffusion. Thus, the local D-distribution in the V-6% Fe film can be regarded as the original one taken at 20 K. Results of local D-distribution and D-concentration inFe/V multi-layered films will be presented and discussed. References

1. A. Pundt, R. Kirchheim, Annu. Rev., Mater. Res. 36 (2006) 555-608. 2. P. Kesten, A. Pundt, G. Schmitz, M. Weisheit, H.U. Krebs, R. Kirchheim, J. Alloys

and Compounds, 330-332 (2002) 225-228. 3. R. Gemma, T. Al-Kassab, R. Kirchheim, A. Pundt, Ultramicroscopy, 109 (2009)

631-636. 4. Zh. Qi, J. Voelkl, R. Laesser, H. Wenzl, J. Phys. F 13, (1983) 2053.

64

Hydrogen Sorption Mechanisms at Various Hydrides Surfaces and Towards Synthetic Fuels

Shunsuke Kato,a Andreas Borgschulte,a Michael Bielmann,a Jean-Claude Crivello,b Arndt Remhof,a Oliver Friedrichs,a Kazutaka Ikeda,c Shin-ichi Orimo,c Andreas Züttela

aLaboratory for Hydrogen & Energy, Empa Materials Science and Technology, Überlandstrasse 129, 8600 Dübendorf, Switzerland.

bICMPE-CMTR, CNRS UMR-7182, 2-8, rue Henri Dunant, 94320 Thiais, France. cInstitute for Materials Research, Tohoku University, Katahira 2-1-1, Sendai 980-8577, Japan.

shunsuke.kato@empa.ch The surface composition and oxidation state of hydrogen storage material is crucial for the hydrogen sorption processes [1, 2]. An overview of hydrogen sorption mechanisms at various hydrides surfaces, i.e. interstitial hydride (LaNi5H6), covalent-like hydride (AlH3), complex metal hydride (Mg2NiH4), and complex hydride (LiBH4), including the composite system (2NaBH4 + MgH2), is given (fig. 1). From the viewpoint of alternative applications of hydrogen storage material, the possibility of efficient methanation process at the hydrides surfaces (fig. 2); CO2 + 4H2 → CH4 + 2H2O (ΔG298 = −110 kJ/mol), called “Sabatier process”, is to be discussed with respect to re-utilization of a metal hydride tank towards synthetic fuels [3, 4].

Fig. 1 Hydrogen desorption mechanisms at various hydrides surfaces/interfaces; (a) AlH3 [1] (b) LiBH4 [2] (c) NaBH4 + MgH2.

Fig. 2 Methanation reaction catalyzed by Mg2NiH4−X during the hydrogen desorption in CO2 atmosphere (1 K/min). References 1. Shunsuke Kato, Michael Bielmann, Kazutaka Ikeda, Shin-ichi Orimo, Andreas

Borgschulte, Andreas Züttel, Appl. Phys. Lett. 96, (2010), 051912. 2. Shunsuke Kato, Michael Bielmann, Andreas Borgschulte, Valentina Zakaznova-Herzog,

Arndt Remhof, Shin-ichi Orimo, Andreas Züttel, submitted to PCCP. 3. Andreas Züttel, Philosophical Magazin, (2010), in press. 4. G. Centi, R. A. van Santen, Catalysis for Renewables, Wiley-VCH Verlag, Weinheim

2007.

65

Irradiation Treatment Effects on Hydrogen Storage Alloy Shun Ohnuki1, Yoshiaki Shinohara1, Fendy Kadec Sutrisna1, Michiaki Utsumi1, Hirohisa

Uchida1 , Yoshihito Matsumura1 and Hiroshi Abe2

Department of Applied Science, Graduate School of Engineering, Tokai University, Japan1

Radiation Effects Group, Quantum Beam Science Directorate, Japan Atomic Energy Agency 2 Email: ncc1701d@keyaki.cc.u-tokai.ac.jp

Hydrogen storage alloys are required to attain high rate of hydrogen absorption for

application to the negative electrode of the Ni-MH batteries. Surface modifications are crucial to improve the reactivity of hydrogen with hydrogen storage alloys. Because, the dissociation of the H2 molecules in the gas phase or the dissociation of the H2O molecules in an electrochemical process is the first step of the overall reaction of hydrogen absorption for hydrogen storage alloys. The ion irradiation treatment improved the hydrogen absorption rate. Improvement of the ion irradiation is caused by inducing defects of vacancies, dislocations, micro-cracks, or interstitial atoms in the surface region of the hydrogen storage alloy [1,2] . However, very few studies have been reported effects of electron beam irradiation for metal hydride. In this work, effects of electron beam irradiation on hydriding characteristics for La-Ni base AB5 type alloys were studied.

The irradiation of electron beam to the LaNi4.6Al0.4 hydrogen storage alloy surface was performed by the dose of 1 x 1017 e-/cm2, at 1 MV and 2 MV of acceleration voltage, in vacuum at 2 Pa and atmospheric pressure in air. Hydrogen absorption measurements were used an electrolytic cell with LaNi4.6Al0.4 cathode apparatus.

Electron beam irradiated LaNi4.6Al0.4 sample was found to induce a higher absorption rate than that of the unirradiated one. The maximum value of the hydrogen absorption rate was obtained in the sample irradiated by electron beam at 2MeV in the vacuum condition. X-ray diffraction (XRD) patterns of the irradiated samples indicate the formation of conductive oxides on sample surface. X-ray Photoelectron spectra of the samples indicate that composition of oxide layer was varied on irradiated conditions. These results suggest that improvement of hydrogen absorption rate for LaNi4.6Al0.4 surface is caused by formation of conductive oxide layer by electron beam irradiation [3]. The electron beam irradiation was found as an effective way to enhance the rate of the initial activation of the hydrogen absorption of La-Ni alloy. References 1. H.Abe, R Morimoto, F.Satoh, Y.Azuma, H.Uchida, J. Alloys Compd, 404-406,(2005), 288. 2. H.Abe, R.Morimoto, F.Satoh, Y.Azuma, H.Uchida, J. Alloys Compd 408-412,(2006), 348. 3. H.H.Uchida, Y.Watanabe, Y.Matsumura, H.Uchida, J. Alloys Compd 231,(1995),679.

66

Cooperative Effects at Formation and Decomposition of Magnesium Hydride in Powders

K.Gerasimova, I.Konstanchuka and J-L Bobetb

aInstitute of Solid State Chemistry and Mechanochemistry SB RAS, Novosibirsk, Russia Email: irina@solid.nsc.ru

bInstitut de Chimie de la Matière Condensée de Bordeaux, Université Bordeaux 1, France Email: bobet@icmcb-bordeaux.cnrs.fr

In recent years, a large number of research works was aimed at a finding a more effective catalyst for magnesium-hydrogen interaction and identification of optimum amount of catalyst in such nanocomposites, required for obtaining a fast kinetics while giving maximal reversible hydrogen storage capacity. A kinetic analysis of experimental data is usually used in these studies to identify a rate-limiting stage. Formation/decomposition of magnesium hydride comprises several steps: transport of hydrogen to the surface, H2 dissociation and chemisorption, surface-bulk migration, H diffusion and nucleation and growth of the product phase (hydride for absorption or metal for desorption). The chemisorption is the slowest rate-determining step for hydrogen absorption by conventional pure magnesium as the recombination of H atoms and desorption is the rate-limiting step for decomposition of MgH2. Catalysts increase the rate of hydrogen adsorption/desorption. If the increase is large enough, another step than those previously mentioned becomes the rate-limiting one. From this moment the further improving of absorption/desorption kinetics is possible only if a way of influencing this limiting step is found. It is obvious therefore, that the kinetic analysis and determination of the rate-limiting step is of practical significance for the kinetic improvements of magnesium-based hydrogen storage materials. Usually, in a typical investigation of the kinetics of reactions of a solid with a gas, the shape of the kinetic curves, together with the dependences of reaction rate on pressure, temperature and geometry (shape and size of solid particles) are used to determine the rate-limiting step. Nevertheless, very often, the kinetic analysis is limited to the fitting of experimental kinetic curves with various formal equations of heterogeneous kinetics, which corresponded to reactions with one or another rate-determining step. All empirical kinetic models, underlying these rate expressions, assume that the particles of a solid reagent have one and the same shape with a narrow distribution of a grain sizes, react independently from each other and that the transformed fraction of each individual particle is approximately equal to the transformed fraction of whole sample (“single particle models”). Such assumption about particles size and shape is hardly realized in a customary research of interaction of magnesium with hydrogen. In this work, it is demonstrated that particles of magnesium or hydride in a powder sample react not independently from each other. The degree of transformation of separate particle can considerably differ from a degree of transformation of the whole sample. To avoid incorrect conclusions about the mechanism of reaction these features should be taken into consideration at the fitting of experimental kinetic curves by the various equations of heterogeneous kinetics.

67

Real-time Observation of Hydrogen Absorption Dynamics for Pd Nanoparticles

D. Matsumura, Y. Okajima, Y. Nishihata and J. Mizuki Japan Atomic Energy Agency, 1-1-1 Koto, Sayo, Hyogo 679-5148, Japan

Email: daiju@spring8.or.jp Palladium is well known to show high performance for the hydrogen storage because of

the small activation barrier for the adsorption and the exothermal reaction for the absorption. Pd metal fine particles show the different interaction with hydrogen from bulk Pd. Although there is a significant phase boundary between low- and high-concentrate phases, the Pd metal fine particles show smooth change between the interstitial and hydride phases.1 In order to understand the size effect of the Pd particles concerning the hydrogen storage process, we have observed the x-ray absorption fine structure (XAFS) spectra with dispersive optics from the viewpoint of the dynamical change of atomic and electronic structures during the reaction between Pd particles and H2 gases.

XAFS spectra were observed at BL14B1 of SPring-8 by dispersive mode.2 Laue configuration with Si(422) reflection plane was adopted for the bend crystal polychromator. The transmitted x rays were observed by CCD camera with Gd2O2S(Tb) phosphor. The local structural transformation of Pd nanoparticles (4 wt%) on Al2O3 during H2 dosing was investigated at room temperature by 50 Hz rate with the real-time-resolved mode. No data accumulation by the repetition of the reaction was operated. We have succeeded to observe the dynamics of Pd nanoparitcles even at the high frame rate of 50 Hz. Figure 1 shows the large expansion of the Pd-Pd interatomic distance from 2.73 to 2.83 Å

under hydrogen atmosphere. The expansion of the Pd particles is completed in 50 ms after the 200 kPa H2 dosing. It was revealed that Pd metal fine particles are directly changed to the hydride phase in a short time. Along with the expansion of the Pd-Pd interatomic distance, the negative shift of the edge position and the decrease of the coordination number (CN) are also recognized. The change of the edge position indicates the charge transfer from hydrogen to palladium and the decrease of the CN implies the reduction of mean particle size. This is the first direct observation of structure, charge, and shape changes of the Pd nanoparticles under H2 gases with the high frame rate of 50 Hz. References 1. M. Yamauchi, R. Ikeda, H. Kitagawa, M. Takata, J. Phys. Chem. C, 112, (2008), 3294. 2. D. Matsumura, Y. Okajima, Y. Nishihata, J. Mizuki, M. Taniguchi, M. Uenishi, H. Tanaka, J. Phys.: Conf. Ser., 190, (2009), 012154.

Fig. 1. Variations of XAFS parameters of Pd-Pd bondings for Pd/Al2O3.

68

Thermodynamic and Kinetic Characterization of H-D Exchange on β-Metals

W. Luo, D. Cowgill Sandia National Laboratory, Livermore CA 94551 USA

A Sieverts’ apparatus coupled with an RGA is an effective method to detect

composition variations during isotopic exchange. This experimental setup provides a tool for the thermodynamic and kinetic characterization of H-D isotope exchange on metals. The equilibrium properties, i.e. the H-D separation factors α and equilibrium constants KHD, are obtained and found to be very close to those in the literature. The exchange rate can be determined from the exchange profiles and a kinetic model is proposed and exchange activation energy can be determined. Both exchange directions, H2+MD and D2+MH, will be discussed. The thermodynamic and kinetic understanding the H-D exchange behavior will provide useful information for hydrogen isotope separation applications.

69

Hydrogenation Kinetics of Aluminum Under High Pressure and High Temperatures

H. Saitoh, A. Machida, Y. Katayama and K. Aoki

Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo, Japan Email: cyto@spring8.or.jp

AlH3 is promising as a hydrogen storage material due to its large gravimetric and

volumetric hydrogen contents (10.1 wt.% and 148 kg/m3, respectively). AlH3 has been synthesized by the desolvation reaction after the chemical reaction between LiAlH4 and AlCl3 in ether. To utilize AlH3 as a practical hydrogen storage material, it is necessary to develop more efficient synthetic route of AlH3. We have realized hydrogenation reaction of aluminum under high pressure and high temerature1, and have been investigating the reaction mechanism. Such fundamental study would provide us with information to help develop new synthetic route of AlH3.

The hydrogenation reaction yield was estimated by recovery experiments at several hydrogenation conditions to clarify its kinetics2. High-pressure experiments were performed using a cubic-anvil-type high-pressure apparatus. A pure aluminum samples were immersed in hydrogen fluid to form its hydride under high pressure and high temperature. After the high-pressure and high-temperature treatment, the samples were recovered at ambient conditions and were analyzed by optical microscope. The hydrogenation reaction yields were roughly estimated from the area ratio of AlH3 to the entire sample that appeared on optical micrograph.

A relationship between the hydrogenation reaction yield and holding time was obtained, which revealed that the reaction decreased with time. This slow hydrogenation kinetics seems to be caused by low diffusivity of hydrogen in AlH3. The reaction yields were measured at several pressure-temperature conditions. In the low temperature region below 550 °C aluminum was not hydrogenated even in the thermodynamically AlH3-stable region. The oxide layer on passivated aluminum prevents the hydrogenation reaction below 550 °C. The latest result of attempt to improve the hydrogenation kinetics will be presented.

This work was supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials". References 1. H. Saitoh, A. Machida, Y. Katayama, K. Aoki, Appl. Phys. Lett. 93, (2008), 151918. 2. H. Saitoh, A. Machida, Y. Katayama, K. Aoki, Appl. Phys. Lett. 94, (2009), 151915.

70

New Insights into the Catalytic Mechanism of H2 Sorption in NaAlH4

C. Rongeat, L. Schultz and O. Gutfleisch IFW Dresden, Institute for Metallic Materials, Dresden, Germany

Email: c.rongeat@ifw-dresden.de Solid state hydrogen storage is one of the safest and more efficient concept for storing hydrogen, in particular for mobile application. Since 1997 and the work of Bogdanovic and Schwickardi,1 most of the research effort has been made towards the complex hydrides. Their initial study shows the reversibility at moderate conditions of hydrogen sorption in NaAlH4 mixed with Ti-based dopants. In the following years, a large number of works has been published on NaAlH4 searching for the most suitable dopants and understanding the catalytic mechanism. Among the tested dopant, TiCl3 has been studied from the beginning and is still considered as one of the most efficient ones.2 Recently, it has been demonstrated3 that ScCl3 and CeCl3 are more efficient than TiCl3. Nevertheless, despite the fact that NaAlH4 is studied for more than 10 years, the catalytic mechanism is still not fully understood. For this work, we performed a systematic study of the H2 sorption properties of NaAlH4 prepared by reactive ball milling4, 5 and mixed with different dopants. The comparison of the performance obtained using these dopants for both absorption and desorption of hydrogen showed different levels of efficiency for the dopants depending on the reaction considered. From these direct observations, a more detailed study was performed on the best dopants, looking in particular to the chemical state of the different compounds by X-ray photoelectron spectroscopy (XPS). The results obtained give new insight into the different steps of the catalytic reaction and a general scheme is proposed. This information was used to further improve the H2 sorption properties of NaAlH4 and should allow further development of hydrogen storage in complex hydrides. References

1. Bogdanovic and Schwickardi, J. Alloys Compd 253-254 (1997) 1. 2. Sandrock et al., J. Alloys Compd 339 (2002) 299 3. Bogdanovic et al., Adv. Mater. 18 (2006) 1198 4. Rongeat et al., Acta Mater. 57 (2009) 5563 5. Rongeat et al., J. Phys. Chem. B 111 (2007) 13301

71

Kinetics of Dehydrogenation of MgH2 and AlH3

I.Gabis, M.Dobrotvorski, E.Evard, A.Voit Physics Department St.Petersburg State University, St.Petersburg, Russia

Email: igor.gabis@gmail.com Magnesium and aluminium hydrides are ion-kovalent ones that determines mechanisms and rates of hydrogen evolution. The detailed study of desorption kinetics of hydrogen from the stoichiometric MgH2 and AlH3 shows that the start of reaction is limited by the formation of nuclei of metal phase. Metallic nuclei or pieces of foreign metal located on the surface of particles of MgH2 and AlH3 serves as facilitated channel of desorption of hydrogen. They can appear after the activation due to transitory heatinng, ball-milling or mechanical deposition. We present the analisis of possible influence of rates of desorption and hydride decomposition on the overall outgassing rate. Magnesium hydride samples were pouders with large distribution of particles by size and shape that partialy masked details of desortion kinetics. In contrast the aluminium hydride had uniform nearly cubic particles with approximately identical size that gave the unique possibility of the correct discrimination of mathematical models of hydrogen evolution. Studies have been performed by means of comparison of mathematical models to experimental results. We checked the adequacy of the models by how well they approximated the experimental data. Mathematical models were developed by taking into account elementary processes of hydrogen transport in metal and hydride phases and their morphology. The approximation provided rate evaluations of the processes considered in the models. The experimental results have been obtained using TDS and barometric method. SEM and metallography were employed to study the morphology of phases and the distribution of particles by size and shape. The interpretation of results has been performed on a base of electronnic structure of materials. The work has been supported by the grant 09-03-00947-a "Theoretical and experimental study of kinetics and mechanisms of hydrogen desorption from metal hydrides" of the Russian Foundation for Basic Research.

72

Halide Stabilized LiBH4: a Room Temperature Lithium Fast-Ion

Conductor H. Maekawa

1, R. Miyazaki

1, H. Takamura

1, S. Orimo

2 and M. Matsuo

2

1Graduate School of Engineering, Tohoku University, Sendai, 980-8579, Japan

2Institute for Materials Research, Tohoku University, 980-8577, Japan

Email: maekawa@material.tohoku.ac.jp

Recently, we have discovered a lithium fast-ion conductivity of LiBH4.1

This was one of the first lithium ion conductors of complex hydride system to be discovered. The conductivity of pure LiBH

4 shows a jump at 115°C, reaching 10

-2 Scm

-1 above 170 °C, showing no obvious polarization

at the lithium metal-LiBH4

interface under a high current density, which is one of the most favorable properties for solid lithium battery applications. However, from an application point of view, room-temperature stabilization of the HT phase is highly desired. We have found that incorporation of lithium halides (LiX), can stabilize the HT phase at low temperature.

2-4 Figure 1

shows the electrical conductivities of the LiBH4-LiX

composites together with those for pure LiI and LiBH4.

All the samples containing LiX showed a substantial decrease in transition temperature (T

tr), with the most

significant decrease being found in LiI-doped samples. The 3LiBH

4·LiI sample showed no apparent transition to

below room temperature. These results suggest that Ttr

can be controlled by a new scheme of chemical modification by LiX. A further progress for the development of fast lithium ionic conductors based on other hydrides as well as the analysis of the nature of the fast-ion conduction of these systems will be presented.

5-7 References 1. M. Matsuo, Y. Nakamori, S.-I. Orimo, H. Maekawa, and H. Takamura, Appl. Phys. Lett., 91, 224103

(2007) 2. H. Maekawa, M. Matsuo, H. Takamura, M. Ando, Y. Noda, T. Karahashi, and S. Orimo J. Am. Chem.

Soc., 131, 894 (2009) 3. M. Matsuo, H. Takamura, H. Maekawa, H.-W. Li, and S. Orimo, Appl. Phys. Lett. 94, 084103 (2009) 4. H. Oguchi, M. Matsuo, J. S. Hummelshøj, T. Vegge, J. K. Nørskov, T. Sato, Y. Miura, H. Takamura, H.

Maekawa and S. Orimo, Appl. Phys. Lett. 94, 141912 (2009) 5. M. Matsuo, A. Remhof, P. Martelli, R. Caputo, M. Ernst, Y. Miura, T. Sato, H. Oguchi, H. Maekawa, H.

Takamura, A. Borgschulte, A. Züttel and S. Orimo, J. Am. Chem. Soc., 131, 16389 (2009) 6. H. Takamura, Y. Kuronuma, H. Maekawa, M. Matsuo, S. Orimo, Solid State Ionics, in press 7. R. Miyazaki, T. Karahashi, N. Kumatani, Y. Noda, M. Ando, H. Takamura, M. Matsuo, S. Orimo and H.

Maekawa, Solid State Ionics, submitted Acknowledgements This work has been supported by CREST, JST under “Novel Measuring and Analytical Technology Contributions to the Elucidation and Application of Materials”, KAKENHI Scientific Research (B), #21360314, and NEDO under “Advanced Fundamental Research Project on Hydrogen Storage Materials".

73

Hydrogen Storage in the Quartenary Mg1-x-yTixAlyHz System as Studied by Hydrogenography

Y. Pivak, H. Schreuders, M. Slaman*, J. Rector*, B. Dam

Materials for Energy Conversion and Storage, Chemical Engineering, Applied Physics Department, Delft University of Technology, The Netherlands

*Condensed Matter Physics, Dept. of Physics and Astronomy, VU University Amsterdam, The Netherlands Email: Y.Pivak@tudelft.nl

MgH2 with a high gravimetric capacity of 7.6 wt% is considered as a promising material for hydrogen storage, although its practical application is limited due to a high thermodynamic stability and a slow (de)/hydrogenation kinetics. To overcome these barriers a lot of work has been done, such as alloying with different dopants (Ni, Ti, Fe), nano-structuring and adding of various catalysts (Nb2O5, La2O3, TiO2). Although the kinetic limitations were thereby solved, the thermodynamic stability of MgH2 (which determines the hydrogen equilibrium pressure) was hardly changed. Here, we focus our attention on the first approach – the alloying process. Instead of pure Mg, we choose a meta-stable Mg1-xTix compound as the starting material. This promising hydrogen storage alloy has a much faster loading/unloading kinetics due to formation of an fcc MgH2-lattice, while no substantial destabilization is observed as compared to pure MgH2. We added a third element, namely aluminum, with the aim to destabilize the Mg1-

xTix while maintaining the fcc crystal structure for a fast kinetics. For the characterization of this ternary Mg1-x-yTixAly system we use our combinatorial thin film technique called Hydrogenography [1]. This method for the search of new metal-hydrogen storage systems [2,3] is based on the optical changes induced in metal films upon hydrogen loading. We deposit Mg-Ti-Al gradient thin films by DC magnetron sputter deposition. The Mg to Ti fraction is chosen in the range from 0.65 to 0.85, since co-sputtered Mg1-xTix films show excellent performance in this compositional range. The chemical composition of the film was determined by Rutherford backscattered spectrometry (RBS). Contrary to Vermeulen et al. [4], who found an additional desorption plateau for Mg0.69Ti0.21Al0.1 close to 1 bar at room temperature, no second plateau was observed for compositions in this range during loading up to 10 bars at 333 K. However, hydrogenography experiments at 333 K reveal a destabilization effect for the Al rich part of the sample. We will present the enthalpy and entropy of hydride formation/decomposition, as calculated from the Van ‘t Hoff analysis for a large number of compositions in the Mg-Ti-Al-H phase diagram, as determined by Hydrogrenography. We will analyze in particular the effect of Al on the structure and stability of the Mg-Ti-H system. References 1. B. Dam, R. Gremaud, C. Broedersz and R. Griessen, Scripta Materialia 56 (2007) 853-858. 2. C.P. Broederz, R. Gremaud, B. Dam, R. Griessen and M. Lovvik, Phys. Rev. B 77 (2008) 024204. 3. R. Gremaud, C. P. Broedersz, D. M. Borsa, A. Borgschulte, P. Mauron, H. Schreuders, J. H. Rector, B. Dam, R. Griessen, Adv. Mater. 19 (2007) 2813. 4. P. Vermeulen, E. F.M.J. van Thiel and P. N.L. Notten, Chem. Eur. J. 13 (2007) 9892.

74

Low Energy Regeneration of Aluminum Hydride

J. Graetz, David Lacina, Yusu Celebi, James Wegrzyn and James Reilly Energy Sciences and Technology Department, Brookhaven National Laboratory, Upton, New York, USA

Email: graetz@bnl.gov Kinetically stabilized hydrides exhibit a low heat of reaction and rapid hydrogen evolution rates at low temperatures making them well suited for mobile PEM fuel cell applications. However, a critical challenge exists to regenerate or recycle these hydrides from the spent fuel and H2 gas in a low cost process. We have proposed a two-step regeneration process, which involves initially forming a stabilized hydride adduct using amines and ethers, followed by adduct separation and hydride recovery. Previously, we demonstrated a low energy process to regenerate LiAlH4 by initially forming LiAlH4-nTHF from catalyzed Al, LiH and THF, followed by desolvation and recovery of pure LiAlH4.1 In this paper we put forward a low energy route to regenerate AlH3 that involves the formation of a stabilized AlH3 adduct, followed by adduct separation and hydride recovery. The first step of AlH3 regeneration involves the low-pressure hydrogenation of catalyzed Al and an amine (NR3) in a liquid medium to form an amine alane (AlH3-NR3).2 We found a number of different tertiary amines were suitable including trimethylamine, triethylenediamine, dimethylethylamine, quinuclidine and hexamine. However, the more stable alane amines that form readily at low pressures tend to decompose at high temperatures where AlH3 is unstable. Therefore, the direct separation and recovery of AlH3 has proven to be difficult. A transamination step is necessary to exchange the amine with one that forms a less stable adduct (e.g., TEA = triethylamine). AlH3-TEA is a liquid at room temperature and can be separated into AlH3 and TEA by heating to 75°C under a nitrogen sweep.3 The full regeneration procedure for AlH3 is shown below: Hydrogenation: Al + NR3 + 3/2H2 → AlH3-NR3 (1) Transamination: AlH3-NR3 + TEA → AlH3-TEA + NR3↑ → AlH3 + TEA↑ (2) Separation: AlH3-TEA → AlH3 + TEA↑ (3) We note that this simple regeneration procedure may be broadly applicable to other kinetically stabilized hydrides (e.g., Mg(AlH4)2).

References 1. J. Graetz, J. Wegrzyn and J. J. Reilly, J. Amer. Chem. Soc. 130, (2008), 17790-17794. 2. J. Graetz, S. Chaudhari, J. Wegrzyn, Y. Celebi, J.R. Johnson, W. Zhou, J.J. Reilly, J. Phys. Chem. C, 111, (2007), 19148-19152. 3. J. H. Murib and D. Horvitz, U.S. patent 3,642,853, (1972).

75

Diborane -the Key to Reversible Hydrogen Storage in Borohydrides

O. Friedrichs1, A. Remhof1, A. Borgschulte1, F. Buchter1, S. I. Orimo2, A. Züttel1 1Empa Materials Science and Technology, Dübendorf, Switzerland. 2Institute for Materials Research, Tohoku

University, Katahira 2-1-1, Sendai, 980-8577, Japan. Email: oliver.friedrichs@empa.ch

Ever since Bogdanovic published his pioneering work on the reversible hydrogen storage in NaAlH4 [1], there was a dream of complex hydrides being the energy carrier of the future [2] replacing the depleting and CO2 emitting fossil fuels. This hope was even more fueled when in 2003 borohydrides were proposed as new hydrogen storage materials [3] with gravimetric hydrogen densities yet exceeding that of gasoline. However, so far no reversible and reliable system could be realized for technical applications. The reason might be that the role of diborane (B2H6) in the formation and decomposition was underestimated so far. In the present work, we show that B2H6 plays a key role for reversible hydrogen storage in borohydrides [4-5]. We identified the crucial role of diborane in the formation and decomposition mechanism of borohydrides and present a model explaining the mass transport during these processes. Based on these insights, we developed a new method for the solvent-free synthesis of borohydrides at room temperature and demonstrated its feasibility with the synthesis of three of the most discussed borohydrides at present: LiBH4, Mg[BH4]2 and Ca[BH4]2 [6-8]. The method will open new ways for the preparation of a wide range of different borohydrides, or even mixed borohydride systems, with tuneable sorption properties [9].

References

1. Bogdanovic, B., Schwickardi, M. J., Alloys Compd. 253, 1-9 (1997). 2. Schlapbach, L., Züttel, A., Nature 414, 353-358 (2001). 3. Züttel, A., Wenger, P., Rentsch, S., Sudan, P., Mauron, Ph., Emmenegger, Ch., J. Power Source 118, 1-7 (2003). 4. Friedrichs, O., Borgschulte, A., Kato, S., Buchter, F., Gremaud, R., Remhof, A., Züttel, A., Chem-Eur. J. 15, 5531-5534 (2009). 5. Friedrichs, O., Remhof, A., Borgschulte, A.., Buchter, F., Orimo, S.I., Züttel, A., submitted (2009). 6. Ramzan, M., Ahuja, R., Vajo, J.J., Skeith, S.L., Mertens, F.J., J. Phys. Chem. B 109, 3719-3722 (2005). 7. Ronnebro, E., Majzoub E.H., J. Phys. Chem. B 111, 12045-12047 (2007) 8 Cerný, R., Filinchuk, Y., Hagemann, H., Yvon, K., Angew. Chem. Int. Edit. 46, 5765-5767 (2007). 9. Nickels, E.A., Jones, M.O., David, W.I.F., Johnson, S.R., Lowton, R.L., Sommariva, M., Edwards, P.P., Angew. Chem. Int. Edit. 47, 2817-2819 (2008).

76

Theoretical Study on Improved Hydrogen Storage Materials H. Mizuseki, N. S. Venkataramanan, R. Sahara, G. Chen, M. Khazaei, and Y. Kawazoe

Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan Doping with alkali metal elements increases the hydrogen storage capacity of many materials. Inspired by these findings, we have explored the hydrogen storage properties of lithium doped Metal Organic Framework (MOF), fullerene, BN fullerene, p-tert-butyl calixarene (LTBC), carbon nanohorn, graphene, and BN sheet. Binding energy of alkali atoms on BN fullerenes were identical to C60. However, the binding on BN fullerene occurs at the bridge site near the tetragonal site. Alkali adsorption can be adsorbed to a maximum of six sites. Each Li atom was found to hold up to three hydrogen molecules. In the case of the MOF materials, Li-doping significantly improves the hydrogen uptake. Each Li atom doped was found to hold three hydrogen molecules firmly due to the charge induced dipole interaction. The most stable position for the Li atom was found to be on the benzene ring, forming a Li-benzene complex and each benzene ring was able to hold two Li atoms [1]. Calculations based on DFT show that Li-functionalized calixarene significantly improves the average binding energy of hydrogen molecules [2]. Moreover, Na-functionalized calixarene molecule was found to hold six hydrogen molecules inside its cavity [3]. Further, the ab initio molecular dynamics simulations show LTBC molecules are stable up to 200 K. Additionally, the pair distribution function calculated for LTBC with four hydrogen molecules inside the cavity shows that the hydrogen molecules are stable inside the cavity until 100K [2]. In the case of carbon nanohorn, Each Li atom on the outer sidewall could bind three hydrogen molecules, while the small room inside the nanohorn limits the adsorbed hydrogen molecules to be eight at maximum. The hydrogen binding energy attracted by Li atoms would not be altered much if both sidewalls are decorated by Li atoms. The total storage capacity could be 5.8 wt.% with 8 and 36 hydrogen molecules respectively adsorbed surrounding the Li atoms on the inner and the outer sidewalls, which has the average binding energy per H2 > 200 meV [4]. In this presentation we will also present the storage capacities and adsorption properties of fullerene[5], graphene[6, 7], and BN sheet[7, 8]. A part of this work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Advanced Fundamental Research Project on Hydrogen Storage Materials”. References 1. N. S. Venkataramanan, et al., Int. J. Mol. Sci. 10, (2009), 1601-1608. 2. N. S. Venkataramanan, et al., J. Phys. Chem. C. 112, (2008), 19676. 3. N. S. Venkataramanan, R. Sahara, H. Mizuseki, and Y. Kawazoe, Comput. Mater. Sci. (2010) in press. 4. G. Chen, Q. Peng, H. Mizuseki, and Y. Kawazoe, Comput. Mater. Sci. (2010) in press. 5. Q. Peng, G. Chen, H. Mizuseki, and Y. Kawazoe, J. Chem. Phys. 131, (2009), 214505. 6. M. Khazaei, M. S. Bahramy, A. Ranjbar, H. Mizuseki, and Y. Kawazoe, Carbon 47, (2009), 3306-3312. 7. M. Khazaei, M. S. Bahramy, N. S. Venkataramanan, H. Mizuseki, and Y. Kawazoe, J. Appl. Phys. 106, (2009), 094303. 8. N. S. Venkataramanan, M. Khazaei, R. Sahara, H. Mizuseki, and Y. Kawazoe, Chem. Phys. 359, (2009), 173-178.

77

Neutron Spectroscopy of Magnesium Dihydride

A.I. Kolesnikov1*, V.E. Antonov2, V.S. Efimchenko2, G. Granroth1, S.N. Klyamkin3, A.V. Levchenko4 and M.K. Sakharov2

1Neutron Scattering Sciences Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6473, USA 2Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow District, Russia

3Moscow State University, Vorob’evy gory, Moscow, 119992 Russia 4Institute of Problems of Chemical Physics RAS, 142432 Chernogolovka, Moscow District, Russia

*Email: kolesnikovai@ornl.gov Under ambient conditions, magnesium dihydride exists in two forms, α-MgH2 (the most stable modification, s.g. P42/mmm) and γ-MgH2 (a less stable modification, s.g. Pbcn). The α-MgH2 phase partly transforms to γ-MgH2 in the course of ball-milling (up to an amount of 25% [1]) and under high pressure and temperature (up to 80% [2]). Due to the high hydrogen content of 7.6 wt.%, magnesium dihydride has been intensively studied for decades as a prospective material for hydrogen storage. So far as inelastic neutron scattering (INS) is concerned, α-MgH2 has been measured by several indirect geometry spectrometers worldwide [3,4], as well as one ball milled sample [5]. However, the results obtained with those spectrometers are strongly contaminated by the large contribution from multiphonon neutron scattering at energies exceeding 100 meV due to the very large momentum transfers. By exposing powder of α-MgH2 to a pressure of 5 GPa and emperature 840 K for 2 hours, we prepared a sample, in which 90% of the α-MgH2 phase as transformed to γ-MgH2. This is the highest degree of the α-to-γ conversion ever achieved. We have measured INS spectra of both the γ-MgH2 sample and starting α-MgH2 powder with the time-of-flight direct geometery spectrometer SEQUOIA [6] at SNS (ORNL, USA) at 5 K with energy transfers from 5 to 400 meV. The obtained spectra have rather large one-phonon neutron scattering contributions as compared to the multiphonon scattering due to the ability of the spectrometer to provide small momentum transfer at large energy transfer. As a result, the measurements gave rather accurate phonon densities of states, g(E), for both γ-MgH2 and α-MgH2. The differences between the g(E) spectra and their agreement with the calculated g(E) for these compounds [5,7] will be discussed in the paper. References 1. J. Huot et al., J. Alloys and Compounds, 293–295, (1999), 495-500. 2. P. Vajeeston et al., Phys. Rev. B, 73, (2006), 224102. 3. J.R. Santisteban et al., Phys. Rev. B, 62, (2000), 37-40. 4. H.G. Schimmel et al., Mater. Sci. Eng. B, 108, (2004), 38-41. 5. H.G. Schimmel et al, J. Alloys and Compounds, 393, (2005), 1–4. 6. G.E. Granroth et al, to be published in J. Phys. Conf. Proc. 7. L. Zhang et al., Phys. Rev. B, 75, (2007), 144109.

78

Improved Dehydrogenation of Ca(BH4)2Comibend with LiNH2

X. B. Yu1, 2 a), Y. H. Guo1, D. L. Sun1, Z. P. Guo2, H. K. Liu2 1 Department of Materials Science, Fudan University, Shanghai 200433, China 2 Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia

Email: yuxuebin@fudan.edu.cn

Recently, metal borohydrides, such as LiBH4, NaBH4, Mg(BH4)2 and Ca(BH4)2, have attracted wide attention due to their high gravimetric and volumetric hydrogen densities. Among them, LiBH4 with the highest theoretical hydrogen capacity of 18.3 wt% is relatively well explored. Compared with LiBH4, the hydrogen storage capacity of Ca(BH4)2 is low (11.6 wt.%). However, based on density functional theory (DFT) calculations, the decomposition enthalpy for Ca(BH4)2 has been estimated to 32 kJ mol-1, if the decomposition products are CaH2 CaB6 and H2 [1]. This enthalpy corresponds to an equilibrium pressure of 1 bar at temperatures below 100 oC, indicating that Ca(BH4)2 have more favorable thermodynamics than LiBH4 and could be considered as a potential low/medium-temperature hydride. Recently, its phase structure [2] and dehydrogenation/rehydrogenation behaviour have been reported [3-5]. It revealed that Ca(BH4)2 eventually decomposes in two steps between 347 and 497 oC with a total weight loss of about 9.0 wt.% and can be partly reversible under 90 bar of hydrogen at 350 oC after doping with TiCl3. Clearly, the decomposition temperature of Ca(BH4)2 is still too high for a practical application and further improvement is required. In this paper, the thermal decomposition properties of Ca(BH4)2/LiNH2 system were investigated. It was found that the mixtures started to release hydrogen at around 250 oC, which is 100 oC lower than the pure Ca(BH4)2.Meanwhile, emission of ammonia at lower temperature was observed. XRD results revealed that, after a shot time ball mining, the Ca(BH4)2/LiNH2 mixtures transferred to unidentified new phases and the decomposed products mainly consist of LiCa4(BN2)3. Further improvement on restraining the ammonia release can be achieved by heating treatment or addition of LiH to the binary system. References 1. K. Miwa, M. Aoki, T. Noritake, N. Ohba, Y. Nakamori, S. Towata, A. Zuttel, S. Orimo,

Phys. Rev. B, 74, (2006), 155122. 2. M. D. Riktor, M. H. Sørby, K. Ch1opek, M. Fichtner and B. C. Hauback, J. Mater.

Chem., 19, (2009), 2754. 3.Y. Filinchuk, E. Ronnebro, D. Chandra, Acta Materialia, 57, (2009), 732. 4. J. H. Kim, S. A. Jin, J. H. Shim, Y.W. Cho, J. Alloys Compd., 461, (2008), L20. 5. J. H. Kim, S. A. Jin, J. H. Shim, Y.W. Cho, Scripta Materialia, 58, (2008), 481

79

Silicon-Based Hydrides for Hydrogen Storage: Relationship Between Hydrogenation Properties and Crystallographic Structures.

J-N. Chotarda, P. Raybaudb, D Sheptyakovc and R. Janota

aLaboratoire de Réactivité et Chimie des Solides, UMR 6007 CNRS, Université de Picardie Jules Verne, Amiens, France

bInstitut Français du Pétrole, Direction Catalyse et Séparation, IFP-Lyon, Solaize, France cLaboratory for Neutron Scattering, ETHZ and PSI, CH-5232, Villigen PSI, Switzerland

Email: jean-noel.chotard@u-picardie.fr In the search of potential new materials for reversible hydrogen storage, the hydrogenation properties of different M-Si alloys (M=alkaline or alkaline-earth metal) have been investigated by both theoretical and experimental approaches. Thanks to density functional theory (DFT) calculations, the hydrogenation enthalpies of M-Si phases have been predicted favorable for reversible hydrogen storage under moderate pressure and temperature conditions. In particular a promising silicon-based hydride with high gravimetric capacities is reported. This hydride has been obtained either by direct solid-gas hydrogenation of the M-Si alloy, or by reactive ball-milling under hydrogen pressure. Its hydrogen absorption-desorption processes have been carefully investigated by complemental experimental techniques such as thermogravimetry, volumetry, DSC calorimetry and mass spectroscopy. We will show that this compound is able to absorb more than 4 wt% of hydrogen at 100°C with very suitable thermodynamic properties. The hydride undergoes a structural transition near room temperature as revealed by DSC. The complete crystallographic structures of the hydrogenated material have been solved on a deuterated sample thanks to neutronic diffraction experiments. We will show that the Si-D distances are very short (~1.46 Å as encountered with silanes) leading to a significant covalent character of the Si-H bonding. The relationship between the hydrogenation properties and the crystallographic structures of the hydride will be discussed and closely correlated with DFT calculations.

80

The Effects of Alkali Metal Borohydrides on the Crystal Structure and Hydrogen Storage Properties of Calcium Borohydride

Scott D. Culligana, Martin Owen Jonesa,b, Peter P. Edwardsa and William I. F. Davida,b

a Inorganic Chemistry Laboratory, University of Oxford, South Parks Road, Oxford, UK, OX1 3QR, b ISIS Facility, Rutherford Appleton Laboratory, Chilton, Didcot, Oxon., UK OX11 0QX

scott.culligan@chem.ox.ac.uk Complex hydrides have attracted a great deal of attention because of their high gravimetric hydrogen capacities and their potential for use in mobile hydrogen storage applications. Calcium borohydride displays a particularly rich variation of crystal structure but is not considered to be of practical use as a hydrogen storage material because of its high desorption temperature. Recent studies of mixed-metal borohydride systems have shown that the decomposition temperature of a borohydride may be tuned by the formation of a ternary borohydride.1,2 Following the observations of Lee et al. 3, we have studied the interaction of alkali metal and calcium borohydride materials as a function of temperature by variable temperature high resolution synchrotron X-ray powder diffraction and solid state 11B NMR. The effect of various group 1 metal borohydrides on the crystal structure of Ca(BH4)2 with increasing temperature has been monitored and the inclusion of Li+ cations into Ca(BH4)2 observed. Pure orthorhombic α-Ca(BH4)2 undergoes a second order ferroelastic transition to the tetragonal α’ phase and transforms to the β phase at ca. 200 °C. Li+ intercalation alters the observed phase transformations for pure Ca(BH4)2 and promotes a transition from the α to β phase at a significantly lower temperature, via the formation of an intermediate γ phase.

Figure 1 – Phase changes of Ca(BH4)2 with increasing temperature References 1. Nickels, E. A.; Jones, M. O.; David, W. I. F.; Johnson, S. R.; Lowton, R. L.; Sommariva, M. and Edwards, P. P. Angew.Chem. Int. Edn Engl. 2008, 47, 2817 2. Černi, R.; Severa, G.; Ravnsbæk, D. B.; Filinchuk, Y.; D’Anna, V.; Hagemann, H.; Haase, D., Jensen, C. M., Jensen, T. R. J. Phys. Chem. C 2010, 114, 1357–1364 3. Lee, J. Y.; Ravnsbæk, D. B.; Lee, Y. S.; Kim, Y.; Cerenius, Y.; Shim, J. H.; Jensen, T. R.; Hur, N. H.; Young Whan Cho, Y. W. J. Phys. Chem. C 2009, 113, 15080–15086

81

Hydrogen Behaviour of New Ternary Alloys with High Magnesium Content S. Couillaud, E. Gaudin, J-L Bobet

CNRS, Université de Bordeaux, ICMCB, 87 Avenue du Docteur Albert Schweitzer, 33608 Pessac Cedex, France

Email: bobet@icmcb-bordeaux.cnrs.fr Magnesium is known as a good material for hydrogen storage. In order to decrease the hydrogen sorption temperature and pressure conditions, binary and ternary Mg alloys are investigated. To complete the study of ternary diagrams RE-TM-Mg (RE = rare earth and TM = transition metal), the high magnesium domain content has been explored. Different RE (Gd, La, Nd and Ce) as well as different transition elements (Ni and Cu) have been investigated and two new compounds have been revealed : La11Cu9Mg81 and Gd13Ni9Mg78. La11Cu9Mg81 crystallizes in the La2Mg17 structure type (S.G. P63/mmc) [1] with the lattice parameters a = 10.1254(2) and c = 10.0751(2) Å. A disordered structure is observed with a random distribution of Cu atoms on some La and Mg positions. For Gd13Ni9Mg78 the determination of the structural parameters is more complex because of the difficulty to obtain a well-crystallized sample. A mixing of amorphous and crystallized part is often observed. As shown in fig 1, this compound can be described as an amorphous matrix with nanocrystallites inside. Improvement of crystallinity is now a challenge to structurally characterize this sample. If the preliminary XRD powder study allows to retain an average cubic structure, further characterization by electron diffraction shows a distorted cell with a long-range period. Both compounds can absorb 4-5 wt% of hydrogen at 300°C and 30bar of H2 but a decomposition into LaH3, MgH2 and MgCu2 for La11Cu9Mg81 and into GdH2, MgH2 and MgNi2H4 for Gd13Ni9Mg78 has been observed. More investigations have been made on La11Cu9Mg81 hydruration. Numerous steps have been identified and some steps seem reversible as already observed for La2Mg17 [2]. Electrochimical measurements have been performed and the preliminary results seem promissing. To finish, hydruration on Gd13Ni9.5Mg77.5 will be studied with attention becausethe nanostructuration of the sample should induce original sorption properties.

Fig. 1 : Dark field image of a Gd13Ni9Mg78 Fig 2 : Kinetics La11Cu9Mg81, 330°C, 30Bars sample References 1. Evdokimenko. V.I, Kripyakevich. P.I, Zeitschrift fuer elektrochemie und Angewandte physikalische chemie, 46 (6), 1940, 357-364 2. D.K. Slattery, Int. J. Hydrogen Energy, Vol 20, No.12, 1995, pp. 971-973

82

Effect of Severe Plastic Deformation on Hydrogen Storage Properties of Magnesium-Based Alloys

J. Huot and J. Lang

Hydrogen Research Institute, Université du Québec à Tois-Rivières, Trois-Rivières, Québec, Canada Email: jacques.huot@uqtr.ca

Because of its high hydrogen storage capacity magnesium hydride could be used in some commercial applications. However, beside its high temperature of operation and slow kinetics, the cost of producing magnesium hydride from magnesium metals is an important problem for commercialization. In this paper, we show that severe plastic deformation (SPD) techniques could be used to enhance activation (first hydrogenation) and hydrogen storage properties of magnesium-based alloys. The SPD technique used was cold rolling and to be as close as possible to industrial processes the rolling was performed in air. The effect of cold rolling on the morphology, crystallite size and hydriding kinetics of magnesium-based alloys was investigated. We found that cold rolling enhance activation properties as well as hydrogen sorption kinetic. These improvements are probably due to nanostructure and smaller particle size of the processed materials. Cold rolling was compared to ball milling techniques and it was found that severe plastic deformation could be as effective as ball milling for enhancement of hydrogen sorption properties.

83

A New Ternary Phase Destabilised Hydrogen Storage System: LiBH4 : MgH2 : LiAlH4

In-situ Neutron Diffraction and Pressure-Composition-Isothermal Techniques

T. E. C. Price, G. S. Walker and D. M. Grant Department of Energy and Sustainability, University Of Nottingham, UK.

Email: tobias.price@nottingham.ac.uk The authors present an investigation into a new ternary phase destabilised hydrogen storage system; LiAlH4 : LiBH4 : MgH2 destabilised through an alloying reaction [1-4]. Development of this system utilises effect of Al addition, dispersed through decomposition of a LiAlH4 component. This ternary phase system provides a reduction in decomposition onset temperature to 250 °C, which is 70 °C lower than for the previously reported binary phase system. Varying system stochiometry yields alloy end products of a composition matching those expected from the ternary phase diagram, the progression of these reactions was investigated through in-situ Neutron Diffraction combined with Pressure-Composition-Isothermal techniques. These unique experiments provided understanding of the sample chemical structure through ramped and isothermal pressure controlled experiments. These investigations allowed the specific phase transitions of each plateau to be resolved, providing insights into the system behaviour. Our experiments were able to pinpoint the formation of both binary and ternary alloys of Li-Al-Mg, with a higher (destabilised) plateau concomitant with formation of a Mg-Al alloy prior to MgH2 decomposition/formation. Cycling experiments show the 0.23LiBH4 : MgH2 : 0.05LiAlH4 system can be fully reversed by heating the decomposition products under 50 bar hydrogen at 400°C with faster kinetics than the 2LiBH4 : MgH2 system. These results demonstrate the effective combination of structural characterisation with pressure based compositional investigation for improved understanding of hydride storage materials.

Figure. PCI PND into LiAlH4 : LiBH4 : MgH2 References 1. Price, T.E.C., et al., International Journal of Hydrogen Energy, 2010. Accepted. 2. Price, T.E.C., et al., Journal of Alloys and Compounds, 2009. 472(1-2): p. 559-564. 3. Walker, G.S., et al., Journal of Power Sources, 2009. 189(2): p. 902-908. 4. Yu, X.B., D.M. Grant, and G.S. Walker, Chemical Communications (Cambridge),

2006(37): p. 3906-8.

84

Na(BH4)1-xClx Prepared by Mechano-Chemical Methods from NaBH4 and Transition Metal Chlorides – Structural and Hydrogen Storage

Properties

B. C. Hauback, N. Aliouane, S. Deledda, J. E. Fonneløp, C. Frommen, H. Grove, K. Lieutenant, I. Llamas-Jansa, S. Sartori, and M. H. Sørby

Institute for Energy Technology (IFE), Physics Department, P.O. Box 40, NO-2027, Kjeller, Norway Email: bjorn.hauback@ife.no

In the search for novel mixed alkaline-transition metal borohydrides mixtures of NaBH4 and selected transition metal (TM) chlorides (TM = Ti, V, Ni, Cu, Y, Rh, and Cd), were prepared by ball milling, including milling in argon, cryomilling and reactive milling. Based on in-house and synchrotron radiation powder X-ray (at SNBL, ESRF) diffraction and powder neutron diffraction data (at JEEP II reactor at IFE) the crystalline products were identified by Rietveld refinements to be Na(BH4)xCl1-x with x covering the whole range from 0.28 to 0.73. All samples possess a cubic NaCl-type structure (space group Fm-3m), with unit cell parameter a between 5.772 and 6.0120 Å, corresponding to the different levels of substitution. Infrared spectroscopy results confirmed and complemented the structural information, in particular related to the amorphous phase(s) present in the samples. In-situ monitoring of the milling processes provided information on the reaction efficiency of the initial mixtures, while Temperature Programmed Desorption (TPD) and Differential Scanning Calorimetry (DSC) experiments were carried out to analyse the effect of the ion substitution on the kinetics and thermodynamics of the samples. Differneces in desorption temperatures are observed, and their origin with respect to thermodynamics and kinetics will be discussed. Financial support from Research Council of Norway is acknowledged.

85

Visualising Hydrogen Absorption/Desorption in a MH Storage Tank Using Neutrons

N. Selvaraja, L. Gondeka, N. Kardjilovb, H. Figiela aDepartment of solid state physics, AGH University of Science and Technology, Krakow, Poland

bBENSC, Helmholtz Zentrum Berlin, Berlin, Germany Email: nivas@agh.edu.pl

The performance of the Metal Hydride(MH) storage tank is influenced by many factors, namely the hydrogen storing capacity of the MH material, the thermal conductivity of the material, packing of hydride particles inside the tankand so on. The experimental evidence of the later is rather weak in the literature. All this factors are just estimated from knowledge of macrosopic conditions such as amount of absorbed hydrogen or its kinetics. It should be very convenient to have any technique which could pour light to the reaction mechanism inside the tank. Neutron imaging technique is very usefull in this aspect, since using neutrons we can visaulize hydrogen very well. Hydrogen absorption/desorption process of the MH storage tank made of aluminium containing LaNi4.7Al0.3 were analyzed using neutron radiography (NR) and Computed Tomography (CT). The insitu NR images of the MH tank were made during the hydrogen absorption/desorption process. In addition we were able to obtain the CT images of the MH tank loaded with hydrogen in different absorption stages. The CT appears to be a new , attractive method of measurement to study the behavior of hydrogen in metallic type absorberes and hydrogen storing systems in the storage tank. In our experiment performed at BENSC institute in Berlin the MH tank filled with LaNi4.7Al0.3 material was exposed to hydrogen pressure 5 and 10 bars at different temperatures. Insitu NR images were taken at specific time intervels it was repeated for desorption as well. MH tank was placed on a rotable table to make CT images, it was done at 5 and 10 bars of hydrogen pressure. Our measurements hint at usefulness of the NR for fast, qualitative, tracking of the hydrogen absorption/desorption profile. In opposite, the CT studies provide as very high quality data, that may be used for quantitative calculations, which are necessary in order to improve the MH tank efficiency. The results of analysis of NR will be presented, together with re-construction of the tomographic images which is a unique attempt in this area.This study provides significant insight into the hydrogen absorption/desorption behaviour of MH storage tank and a first hand information about the influence of temperature and pressure on storage property of the absorbing material in the tank.

86

Effect of Mechanically Induced Modification on TiH2 Thermal Stability

O.S. Morozova1*, T.I. Khomenko1, A.V. Leonov2, E.Z. Kurmaev3, Ch. Borchers4 1Institute of Chemical Physics RAS, 4 Kosygin St, 119991 Moscow, Russia, e-mail: om@polymer.chph.ras.ru

2Moscow State University, Chemical Department, Leninskie Gory, 119899 Moscow, Russia, e-mail: leonov@general.chem.msu.ru

3Institute of Metal Physics, RAS-Ural Division, 18 Kovalevskaya St, 620041 Ekaterinburg, Russia, email: kurmaev@ifmlrs.uran.ru

4Institute of Material Physics, University of Goettingen, 1 Friedrich-Hund-Platz, 37077 Goettingen, Germany, e-mail: chris@ump.gwdg.de

Step-by-step heating in temperature-programmed regime interrupted by a fast sample cooling was used to study effect of ball milling in the absence and in the presence of additives (graphite, amorphous boron) on conceptual stages of commercial TiH2 decomposition. TPD was carried out under flow conditions in the range of 293 - 1000 K. Structure, morphology and changes in the local bond structure of as-milled powders were studied by X-ray diffraction, high resolution transmission electron microscopy and X-ray emission spectroscopy, respectively. The phase transformation sequence of as-milled TiH2 was depicted as a number of consecutive and parallel reactions: (1) tetr. TiH1.9 transition in δTiH2-X and transformation to solid solution (2) δTiH2-X decomposition to αTi(H) accompanied by depletion of αTi(H) in hydrogen. αTi(H) was found to be rather stable: only several wt. % of αTi were detected after heating to ~ 1000 K, contrary to original TiH2, which can be totally decomposed. Both as-milled TiH2/C and TiH2/B powders, which lost 6 – 14 mo% of H2 during mechanical activation, respectively, consisted on highly dispersed cubic phase δTiH2-X. Special feature of their decomposition was low-temperature and fast δTiH2-X → αTi(H) transformation. Enormous high hydrogen content observed in αTi(H) (up to ~ 11 at.%) may be explained by high concentration bulk defects working as traps for H atoms. No phase of αTi was achieved during the TPD. Cubic carbide or boride phases were detected after the heating to 900 K - 1000 K. This work was done with partial support of Russian Science Foundation for Basic Research (Projects No. 10-03-00942-а and 08-02-00148) and the Research Council of the President of the Russian Federation (Grant No. NSH-3572.2010.2).

87

Formation and Decomposition of Lithium-Boron-Nitrogen-Hydrogen Quaternary Compounds

F. E. Pinkerton

Chemical Sciences and Materials Systems Laboratory General Motors Research and Development Center

frederick.e.pinkerton@gm.com The quaternary Li-B-N-H system shows a rich and complex phase behavior along the tie line connecting LiBH4 and LiNH2. The two equilibrium phases with compositions Li4BN3H10 (α-phase, corresponding to 3LiNH2+LiBH4) and Li2BNH6 (β-phase, LiNH2+LiBH4) each contain substantial hydrogen (11.1 and 13.5 wt%, respectively). Curiously, Li4BN3H10 is so stable relative to LiNH2 and LiBH4 that it forms spontaneously from intimately mixed LiNH2 and LiBH4 powders even at room temperature; in situ X-ray diffraction (XRD) confirms complete transformation to the α-phase at slightly elevated temperature (73 °C). Several metastable phases can also be produced by non-equilibrium processing such as ball-milling. Of these the Li3BN2H8 composition (2LiNH2+LiBH4) has been extensively studied because it releases all of its hydrogen when heated above 250 °C, forming ternary Li3BN2. Recently we have observed that ball-milled Li3BN2H8 is unstable even at room temperature and spontaneously transforms over time into a mixture of β-Li2BNH6 and quaternary Li-B-N-H with the α-phase structure, but with a LiNH2-enriched composition intermediate between that of Li3BN2H8 and Li4BN3H10. Recent thermal decomposition studies of Li3BN2H8 and Li4BN3H10 reveal three independent gas release events. The first is a small (~2 wt%) release of NH3 between 50 and 200 °C. The second and third events are H2 and NH3 releases that occur concurrently above 250 °C in uncatalyzed samples. By adding NiCl3 catalyst, however, we can demonstrate that these latter two processes are in fact independent; the Ni nanocatalyst lowers the hydrogen release temperature by more than 100 °C, whereas the NH3 release temperature is unaffected, thereby reducing the amount of NH3 released by more than an order of magnitude. The instability of Li3BN2H8 noted above also suggests alternate routes to hydrogen release. For example, we have obtained similar hydrogen release characteristics by combining the two stable phases α-Li4BN3H10 and LiBH4 in a 1/0.5 ratio. In contrast, Li2BNH6 melts at low temperature (~80 °C) and decomposes via a more NH3-rich mixture with H2. After heating to just above the melting temperature, the melt resolidifies on cooling into α, LiBH4, and β phases. The relationships between stable and metastable phases and their decomposition paths may provide valuable clues to the chemistry of hydrogen storage materials based on LiBH4 and LiNH2.

88

Improving Hydrogen Storage in Magnesium: A First-Principles Study

Süleyman Er,1 Gilles A. de Wijs2 and Geert Brocks1 1Computational Materials Science, Faculty of Science and Technology and MESA+ Research Institute,

University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands 2Electronic Structure of Materials, Institute for Molecules and Materials, Faculty of Science, Radboud

University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands Email: G.H.L.A.Brocks@tnw.utwente.nl

We investigate the hydrogen storage properties of some of the most promising magnesium alloys. In pure form, MgH2 stores 7.6 weight % hydrogen. It would be a very useful hydrogen storage material if the (de)hydrogenation kinetics can be improved and the desorption temperature is markedly lowered. Recently we found from first principles calculations, that hydrides of Mg-transition metal (TM) alloys can adopt a structure that promotes a faster (de)hydrogenation kinetics, as is also observed in experiment [1]. Within the lightweight TMs, the most promising alloying element is titanium. For Mg-Ti hydrides we calculate that a similar structure emerges starting from regularly ordered Mg-Ti alloys, as well as from the random alloys [2]. Alloying Mg with Ti alone, however, is not sufficient to decrease the stability of the hydride phases, which is necessary to reduce the hydrogen desorption temperature. We find that Mg-Ti hydrides are markedly destabilized by adding aluminium or silicon [3]. At the same time, the stability of the metal alloy is increased significantly. Finally, we show that controlling the structure of Mg-Ti-Al(Si) alloys and hydrides by growing them as multilayers, has a beneficial influence on the thermodynamic properties (Fig. 1). Therefore, the Mg-Ti-Al(Si) system becomes a stronger candidate for hydrogen storage.

Figure 1: Perspective views of the layered Mg0.5Ti0.25Al0.25 alloy before (top figure) and after hydrogenation.

References 1. S. Er, D. Tiwari, G. A. de Wijs, G. Brocks, Phys. Rev. B, 79, (2009), 024105. 2. S. Er, M. J. van Setten, G. A. de Wijs, G. Brocks, J. Phys.: Condens. Matter, 22,

(2010), 074208. 3. S. Er, “Hydrogen storage materials: A first-principles study”, Ph. D. Thesis

University of Twente, Enschede (2009). DOI: 10.3990/1.9789036528955

89

Sodium Alanate as a Practical Automotive On-board Solid-state Hydrogen Storage Medium

M.Sulic, M. Cai, S. Kumar General Motors Research and Development Center, Warren, Michigan, USA

E-mail: martin.sulic@gm.com A key goal of the hydrogen economy is realization of on-board vehicular storage. While compressed gas and liquid hydrogen may meet the immediate needs, the utilization of solid-state hydrogen storage is essential. Extensive research has been reported on a variety of metal hydrides; however, investigation into whether solid-state compounds are even suitable materials for long term on-board vehicular hydrogen storage has yet to be explored. Practical studies conducted in concert with fundamental research will help identify the materials that meet the rigors an automobile endures over its lifetime and avoid the ones that do not. The U.S. Department of Energy Hydrogen Storage Engineering Center of Excellence is a consortium of ten partners aimed at designing, building and demonstrating prototype on-board hydrogen storage systems while meeting as many DOE Technical Targets as possible. As a Center of Excellence member, one of our objectives is to investigate metal hydrides as a practical solid-state storage medium. Sodium alanate was chosen as the baseline material due to the extensive research reported over the past decade and its relatively low-temperature and pressure cycling conditions. The work presented will focus on our goal to improve thermal properties, volumetric capacity and mechanical stability and durability without sacrificing hydrogen cycling kinetics and capacities, which are all factors necessary for long-term practical vehicular implementation. Results indicate interesting trends within the material that may be utilized for other metal hydride studies as well as future tank design.

90

Nanoscale Fullerenes and Fullerene Hydrides

V.Somenkov RRC “Kurchatov institute”, Moscow, Russia

E-mail: somenkov@isssph.kiae.ru

Samples of amorphous fullerenes (C60, C70 and C60/C70 mixture) produced by application of mechanoactivation treatment in air and helium were received and their structural stability in relation to temperature and pressure influences were investigated. The results obtained shows that under mechanoactivation of fullerenes two processes occur – first, amorphization (at low milling velocities) with formation of a nanoscale fullerene-like amorphous phase and, second, graphitization (at high milling velocities) with formation of crystalline graphite-like phase (in air) and amorphous graphite-like phase (in inert atmosphere). Annealing of pure amorphous fullerenes C60 and their mixtures with C70 is also accompanied by two processes – first, by return to the crystalline phase at low annealing temperature and second, by polyamorphous transition with formation of a diamond-like amorphous phase at high (> 900 K) annealing temperature. This transition takes place for samples obtained by mechanoactivation both in air and in inert atmosphere.

Behavior of fullerene hydrides at mechanoactivation and following annealing was investigated. It has been shown that formation of nanoscale (amorphous) structures with wide “halos” instead of structure peaks with particle size about few nanometers takes place in fullerene hydrides as well as in pure fullerenes. At a temperature increasing above 800 K a diffraction pattern changes analogous to changes observed for pure fullerenes (a reduction of few first “halos”) are observed.

It has been shown that interaction of hydrogen with amorphous fullerenes under high pressure (P ~ 100-1000 atm) and temperature (T > 700 K) results in formation of a crystal hydride phase containing about 4 % weight of hydrogen (probable composition С2Н).This phase structure determined by X-ray and neutron diffractions appeared graphite like with a ≈ 2аgr, c ≈ сgr (similar to intercalate compounds of alkaline metals). This phase shows ferromagnetic properties; for instance the temperature dependence of magnetic susceptibility is linear increasing and coercive force value is rather high (Hc > 800 Oe). Thus, in contrary to the recently found ferromagnetic phases of high pressure pure and H-containing fullerenes its structure and properties remains stable within, at least, 3 years. With help of neutron activation analysis the presence of Ni in some magnetic samples was revealed, that possibly indicates the doped nature of magnetism.

Supported by RFBR, grant 09-02-00464

91

Combined Effects of Nanoconfinement and Catalysis on the Hydrogen Sorption Properties of LiBH4

P. Ngene, K. P. de Jong and P. E. de Jongh

Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands

Email: p.ngene@uu.nl LiBH4 has attracted much attention as a potential H2 storage material due to its high H2 content. However, the thermodynamics and kinetics of its H2 sorption must be improved before it can be used for automobile applications. Nanoconfinement in porous materials and the use of catalysts are among the promising strategies to enhance the hydrogen sorption properties of LiBH4

[1-4]. In our study, we explored the effect of combining both approaches by confining both Ni nanoparticles and LiBH4 in nanoporous carbon material. Impregnation with an aqueous nickel precursor solution follwed by decomposition and reduction led to 6 nm Ni particles in nanoporous carbon. Subsequently, melt infiltration with LiBH4 was performed at 295 °C under 100 bar H2. Confining LiBH4 in the nanoporous carbon resulted in a significant decrease in the H2 release temperatures compared to the bulk, with most of the H2 relased around 350 °C in Ar flow. Furthermore, the reversibility was improved. The addition of Ni further increased the reversibility, the Ni containing nanocomposites absorbed 10 wt% H2/g LiBH4 in 120 min at 40 bar and 320 °C. Although Ni did not change the dehydrogenation temperature in the first run, surprisingly, it did lowered the desorption temperature in subsequent cycles. XRD indicates metallic Ni nanoparticles disappears upon melt infiltration. However, TEM shows that Ni- containing nanoparticles are still present. EXAFS reveals the formation of nickel boride (NixB) phases after melt infiltration and dehydrogenation. Thus the enhanced hydrogen sorption kinetics results from the formation of nickel boride (NixB) which most likely acts as a catalyst for de/rehydrogenation reactions of LiBH4.

References 1. A. F. Gross, J. J. Vajo, S. L. Van Atta, G. L. Olson Journal of Physical Chemistry C. 2008, 112, 5651-5657. 2. P. Ngene, P. Adelhelm, A. M. Beale, K. P. de Jong, P. E. de Jongh The Journal of Physical Chemistry C. 3. M. S. Wellons, P. A. Berseth, R. Zidan Nanotechnology. 2009, 20. 4. J. Xu, X. B. Yu, Z. Q. Zou, Z. L. Li, Z. Wu, D. L. Akins, H. Yang Chemical Communications. 2008, 5740-5742.

92

Alkali and Alkaline-Earth Metal Dodecahydro-Closo-Dodecaborates: Probing Structural Variations via Neutron Vibrational Spectroscopy

N. Verdal,1 W. Zhou,1,2 V. Stavila,3 J.-H. Her,1,2 M. Yousufuddin,1,2 T. Yildirim,1,4 J. J.

Rush,1,2 and T. J. Udovic1 1NIST Center for Neutron Research, National Institute of Standards & Technology, Gaithersburg, MD, USA

2Department of Materials Science and Engineering, University of Maryland, College Park, MD, USA 3Sandia National Laboratories, 7011 East Avenue, Livermore, CA, USA

4Department of Materials Science and Engineering, University of Pennsylvania, Philadelphia, PA, USA Email: udovic@nist.gov

Alkali (A= Li, Na, K, Rb, and Cs) and alkaline-earth (Ae= Mg, Ca, Sr, and Ba) metal dodecahydro-closo-dodecaborates [A2B12H12 and AeB12H12] are of current interest in hydrogen-storage research as they are possible intermediates during the dehydrogenation of the related borohydrides ABH4 and Ae(BH4)2. To help characterize their crystal chemistry, the hydrogen-weighted phonon densities of states for the series of A2B12H12 and AeB12H12 compounds were measured via neutron vibrational spectroscopy (NVS). Using the known crystal structures, density functional theory (DFT) phonon calculations were able to closely replicate the observed vibrational spectra [1-3]. The spectral details were found to differ considerably with variations in structure, indicating that the internal vibrations of the B12H12

2- icosohedral anions were sensitive to symmetry-dependent interactions with their crystal surroundings. In contrast, these internal vibrations were relatively unchanged among isomorphic A2B12H12 and AeB12H12 compounds possessing different metal cations. These results confirm that the combination of NVS and DFT phonon calculations can be used to help validate postulated local crystal symmetries in these types of materials in instances where the ordering is only short-range, rendering the materials amorphous with respect to diffraction probes. The reorientational dynamics of the B12H12

2- anions were also probed via quasielastic neutron scattering. From preliminary measurements, a mechanism is proposed that best fits the observed elastic incoherent structure factor.

References 1. J.-H. Her, M. Yousufuddin, W. Zhou, S. S. Jalisatgi, J. G. Kulleck, J. A. Zan, S.-J.

Hwang, R. C. Bowman, Jr., and T. J. Udovic, Inorg. Chem. 47, 9757 (2008). 2. J.-H. Her, W. Zhou, V. Stavila, C. M. Brown, and T. J. Udovic, J. Phys. Chem. C 113,

11187 (2009). 3. V. Stavila, J.-H. Her, W. Zhou, S.-J. Hwang, C. Kim, L. A. M. Ottley, and T. J. Udovic,

J. Solid State Chem. (in press 2010).

93

Thermal Conductivity Characterization of Metal Hydrides

A. HarrisA , S. BeattieB and S. McGradyB AC-Therm Technologies Ltd., Fredericton, NB Canada BUniversity of New Brunswick, Fredericton, NB

Canada Email: aharris@ctherm.com

In the development and characterization of metal hydrides for hydrogen absorption, the thermal conductivity of the material is an important material performance property. The thermal conductivity of the solid material is important to know how long it will take to get the pellets to an equilibrium temperature to understand when they will begin releasing hydrogen. Furthermore, it is important to know the thermal conductivity of these pressed powders while engineering a storage device to use the powders commercially. The thermal conductivity of the material changes substantially from a powder to a compressed solid necessitating the direct measurement of both material formats. Test results will be discussed in relation to other performance data on a couple of materials in powder and compressed solid formats including:

• NaAlH4 powder • NaAlH4 compressed pellet • MgH2 powder • MgH2 compressed pellet

The thermal conductivity of each sample material will be measured via the modified transient plane source technique. References 1. Andrei CM, Walmsley JC, Brinks HW, Holmestad R, Srinivasan SS, Jensen CM,

Hauback BC. Electron-microscopy studies of NaAlH4 withTiF3 additive: hydrogen-cycling effects. Applied Physics A 2005; 80: 709-715. DOI 10.1007/s00339-004-3106-z

2. Bogdanovi B, Schwickardi M. Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials. Journal of Alloys and Compounds 1997; 253-254: 1-9

3. Liu X, McGrady GS, Langmi HW, Jensen CM. Facile Cycling of Ti-Doped LiAlH4 for High Performance Hydrogen Storage. Journal of the American Chemical Society 2009; 131(14): 5032-5033

4. Beattie SD, Langmi HW, McGrady GS. In situ thermal desorption of H2 from LiNH2-2LiH monitored by environmental SEM. International Journal of Hydrogen Energy 2009; 34(1): 376-379

5. Chen P, Xiong Z, Luo J, Lin J, Tan KL. Interaction between Lithium Amide and Lithium Hydride. J. Phys. Chem. B 2003; 107(39): 10967-10970

6. Langmi HW, McGrady GS. Ternary nitrides for hydrogen storage: Li-B-N, Li-Al-N and Li-Ga-N systems. Journal of Alloys and Compounds 2008; 466(1-2): 287-292

7. Setthanan U, Werner-Zwaniger U, Chen B, McGrady GS. The Investigation of MgH2 composite with potential for hydrogen storage material. submitted to the Journal of Analytical Chemistry 2009

94

A Reversible Nanoconfined Chemical Reaction

Thomas K. Nielsen,1 Ulrike Bösenberg,2 Rapee Gosalawit,2 Martin Dornheim,2 Yngve Cerenius,3 Flemming Besenbacher,4 Torben R. Jensen.1

1 Center for Energy Materials, iNANO and Dept. of Chem., Aarhus University, DK-8000, Denmark. 2 Institute of Material Research, GKSS, Geesthacht, D-21502 Germany. 3 MAX-lab, Lund University, S-22100 Sweden.

4 iNANO and Dept. of Physics and Astronomy, Aarhus University, DK-8000 Denmark. Here we report on a new concept for hydrogen storage using nano-confined reversible chemical reactions. Nanoparticles of the reactive hydride composites system 2LiBH4 - MgH2 are embedded in nanoporous carbon aerogel scaffolds with pore size Dmax~21 nm.1 Synchrotron radiation powder X-ray diffraction are utilized to study the synthesis of MgH2 from MgBu2 and melt infiltration of LiBH4 into the nanoporous scaffold, see Figure 1A. After melt infiltration the diffraction peaks from LiBH4 appear broader indicating reduction of the crystalline grain size. The grain size was estimated to be ~24 nm using the Scherrer formula. Hydrogen desorption kinetics and stability towards hydrogen release and uptake cycles are studied by the Sieverts’ method, see Figure 2B. Nanoconfinement mediates significantly enhanced hydrogen desorption kinetics and stability compared to bulk samples. The complete nanocomposite system stores 3.9 wt% H2 of which 72% is available after four hydrogen uptake and release cycles.2

Figure 1. (A) In situ SR-PXD data.The sample was heated from RT to 330 °C, kept at a fixed temperature of 330 °C for 25 min and subsequently cooled to RT (heating and cooling rates 5.4 and 20.0 °C/min, p(H2) = 50 bar, λ = 1.072 Å). (B) Hydrogen release kinetics from nano-confined and bulk 2LiBH4-MgH2 illustrated as solid and dashed lines, respectively, using normalized Sieverts’ desorption profiles. References 1. Nielsen, T. K., Manickam, K., Hirscher, M., Besenbacher, F. & Jensen, T. R. ACS Nano 3, 3521-3528 (2009). 2. Nielsen, T. K., Bösenberg, U., Gosalawit, R., Dornheim, M., Cerenius, Y., Besenbacher, F., Jensen, T. R., 2010, Submitted

95

Lithium-Silicon Alloy as Hydrogen Storage Material Takayuki Ichikawa1, Koichi Doi2, Satoshi Hino1, Hiroki Miyaoka1 and Yoshitsugu Kojima1

1Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, 739-8530, Japan 2Department of Quantum Matter, AdSM, Hiroshima University, Higashi-Hiroshima 739-8530, Japan

Email: tichi@hiroshima-u.ac.jp Lithium-silicon alloy has been investigated as a negative electrode material for Li-ion batteries (LIB) because it has quite high lithium packing density in the form of Li22Si5. During electrochemical insertion of Li into Si, stable intermediate phases, i.e., Li12Si7 (Li1.7Si), Li7Si3 (Li2.3Si), Li13Si4 (Li3.3Si), and Li22Si5 (Li4.4Si), have been reported [1]. Li absorbing materials including Li-Si alloy have been studied in details as anode materials for Li-ion batteries (LIB), e.g., LiC6 [2], Li4.4Si [3], Li4.4Sn [4]. The potentials (V vs. Li/Li+) for lithiation of these materials have been reported to a positive value, indicating that Li absorbing alloys should be more stable than Li. Therefore, we expect a decrease of temperature for H2 release on LiH by use of the Li absorbing alloys as dehydrogenated materials instead of Li as follows;

xLiH ↔ xLi + (x/2)H2, xLiH + M ↔ LixM + (x/2)H2.

In this work, the Li-Si alloy was synthesized by mechanical alloying of Li and Si with a 4 : 1 molar ratio. Then, H2 storage properties of Li-Si alloy were investigated. The PC isothermal measurement for this Li-Si alloy revealed that reversible H2 absorption and desorption reactions were accompanied by the phase transformations of the Li-Si alloy, i.e., Li3.3Si + 1.7H2 ↔ Li2.3Si + LiH + 1.2 H2 ↔ Li1.7Si + 1.6LiH + 0.9H2 ↔ Si + 3.3LiH as shown in the figure. Finally, it is clarified that the Li-Si alloy can store 5.4 mass% H2 via these reactions, and the reaction enthalpy was reduced by around 60 kJ·(mol H2)-1 than that of LiH (reaction enthalpy of LiH: 181 kJ·(mol H2)-1).

0 1 2 3 4 510-4

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/ M

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Fig. PC isotherms for the Li-Si-H system at 500 °C.

Acknowledgement This work was partially supported by KAKENHI (21686068) of the Grant-in-Aid for Young Scientists (A) and the project “Advanced Fundamental Research on Hydrogen Storage Materials” of the New Energy and Industrial Technology Development Organization (NEDO). References 1. R.A. Sharma, R.N. Seefurth, J. Electrochem. Soc., 123 (1976) 1763-1768. 2. R. Yazami, K. Zaghib, M. Deschamps, J. Power Sources, 52 (1994) 55-59. 3. S.-J. Lee, J.-K. Lee, S.-H. Chung, H.-Y. Lee, S.-M. Lee, H.-K. Baik, J. Power Sources,

97-98 (2001) 191-193. 4. K. Hirai, T. Ichitsubo, T. Uda, A. Miyazaki, S. Yagi, E. Matsubara, Acta Mater., 56

(2008) 1539-1545.

96

Nanosized Complex Hydrides in Carbon Scaffolds

S. Sartoria, K. D. Knudsena, Z. Zhao-Kargerb, A.Rothb, M. Fichtnerb, B. C. Haubacka

aInstitute for Energy Technology (IFE), P.O. Box 40, Kjeller NO-2027, Norway

bKarlsruhe Institute of Technology (KIT), D-76021 Karlsruhe, Germany Email: sabrinas@ife.no

One of the most promising methods for hydrogen storage for vehicular and stationary applications is as solid material in nanoscaffolds. It has been reported that nano-crystalline metal and metal-hydrogen alloys with particle sizes less than 20 nm possess many properties that differ from those of conventional coarse-grained materials.1-3 In order to develop the most suitable nanoporous compounds the use of small-angle scattering is an invaluable tool. Recently, the successful nano-dispersion of Mg(BH4)2 infiltrated in activated carbon has been demonstrated by using small-angle neutron scattering (SANS).4 Here we present the effect of nano-confining high H-capacity complex metal hydride in carbon nanostructures used to host and “shield” against agglomeration. The composites were prepared by wet infiltration or melt impregnation. SANS performed at the JEEP II reactor at IFE and small angle X-ray scattering (SAXS) performed at ESRF, Grenoble, were used to extract information, in particular about the particle size-range distribution on the nano-scale. The size of the particles for the nanocomposite hydrides has been estimated by SANS measurements to have a significant component in the range < 4 nm. In particular we present the evolution of the particle morphology of magnesium borohydride and sodium alanate, as bulk powders or infiltrated/melted in nanoscaffolds, during in-situ heating from room temperature to the decomposition temperature. Using SAXS, we have observed that during decomposition and release of hydrogen, the bulk powders are reduced significantly in particle size and also their surface undergoes changes. On the contrary, when integrated into a scaffold, the particles were stabilized upon heating. These differences are expected to be an important factor related to the observed change in properties between the bulk and the nanoconfined hydride. Acknowledgments Funding under the EU project NANOHy (‘Novel Nanocomposites for Hydrogen Storage Applications’, contract n. 210092) is gratefully acknowledged. The skilful assistance from the project team at the Beam Line BM26B, ESRF, Grenoble, is also gratefully acknowledged References 1. J. J. Vajo and G. L. Olson, Scr. Mater. 56, 829 (2007). 2. J. J. Vajo, T. T. Salguero, A. F. Gross, S. L. Skeith, and G. L. Olson, J. Alloys Compd. 446-447, 409 (2007). 3. M. Fichtner, Z. Zhao-Karger, J. Hu, A. Roth, and P. Weidler, Nanotechnology 20, 204029 (2009). 4. S. Sartori, K. D. Knudsen, Z. Zhao-Karger, E. Gil Bardaji, M. Fichtner, and B. C. Hauback, Nanotechnology 20, 505702 (2009).

97

Magnesium-Boron-Titanium Hydride System by High Throughput Method

J-Ph. Soulié1, S. Guerin1, D.C.A. Smith1, and B.E. Hayden1,2 1 Ilika Technologies Ltd., Enterprise Road, Southampton SO16 7NS, UK

2 School of Chemistry, University of Southampton, Highfield, Southampton SO17 1BJ, UK Email: jean-philippe.soulie@ilika.com

A major UK Technology Strategy Board research grant entitled "HyStorM - tuning hydrogen storage materials for automotive applications" involves Johnson Matthey, Ilika Technologies Ltd., the University of Oxford and the Science and Technologies Facilities Council. The main project aim is to enable whole ternary materials phase diagrams to be rapidly synthesised and assessed in terms of their hydrogen storage potential. This rapid throughput capability will accelerate the identification and development of compositions of high hydrogen storage promise. A thin film based methodology for the high throughput synthesis (using a unique ultra-high vacuum high throughput physical vapour deposition, HT-PVD) and screening of hydrogen storage materials is used at Ilika Technologies Ltd. [1], [2]. The high throughput methodology allows for the synthesis of libraries of materials, each mixed at the atomic level, the composition of these material within the library varies with position. The Magnesium-Boron-Titanium hydride formulations identified [3] show high hydrogen capacity (> 10 wt.%, see Figure below), reasonable onset temperature (ca. 530 K at 23 Ks-1) and reversibility characteristics under very mild conditions (less than 10 bar H2). All the Mg-B-Ti materials showed no evidence for diborane evolution during dehydrogenation. This material perfectly meets the work package description requirements of the project.

Boron content / at%0 20 40 60 80 100

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References 1. S. Guerin, B.E. Hayden, J. Comb. Chem., 8, (2006), 66. 2. S. Guerin, B.E. Hayden, D.C.A. Smith, J. Comb. Chem., 10, (2008), 37 3. International Patent Application WO 2009/101046

98

Desorption Studies of H2 and D2 Physisorbed on Porous Materials

I.Krkljuš and M.Hirscher Max-Planck Institute for Metals Research, Stuttgart, Germany

Email: krkljus@mf.mpg.de

The nature of interaction of H2 and D2 molecules with porous adsorbents has been investigated by thermal desorption spectroscopy measurements, extended to temperatures of about 20 K. This sensitive experimental technique gives a qualitative idea about the number and kind of adsorption sites, as well as about the quantity of gas stored after an appropriate calibration with Pd hydride. For the first time measurements are performed with D2 which improve the sensitivity by reducing the background disturbance from water.

To exploit further the posibility of ehnacing the interaction potential of conventional carbon-based materials, aimed toward the room temperature application, a special class of activated carbon called Carbon Molecular Sieves (CMS), possesing small micropores are investigated. Three commercially available CMS, Takeda 3A, -4A, -5A, shown distinct differences in the desorption spectra which can be correlated to differences in the pore size distribution. The presence of micropores, with the size comparable to the kinetic diameter of hydrogen molecule, result in a desorption peak centered on 122 K, which is the highest desorption temperature ever measured for physisorbed hydrogen. An overlap of the potential field from the pore walls enhances the strength of carbon-adsorbate interaction inside the small cavities. Furthermore, different MOFs have been investigated from commercially available samples to completely novel materials produced in laboratory scale. Depending on the MOF structure, e.g. unsaturated metal sites, different pore sizes, etc., different adsorption sites have been identified by interruped desorption or stepwise loading. As for the carbon materials, MOFs with smaller pores show a higher desorption temperature and, therefore, tend to possess a higher adsorbent-adsorbate interaction.

Fig. 1. Comparison of hydrogen desorption spectra of MOF-177, Cu-BTC and

Mg-formate correlated to the differences in pore size.

99

Enhanced Hydrogen Sorption Properties of NaAlH4 by Confinement in Nanoporous Carbon

Jinbao Gao, Margriet H. W. Verkuijlen, Philipp Adelhelm, Krijn. de Jong, Petra. de Jongh Inorganic Chemistry and Catalysis, Debye Institute for NanoMaterials Science,

Utrecht University, Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands Email: p.e.dejongh@uu.nl

NaAlH4 is one of most promising metal hydrides for compact on-board storage of hydrogen due to its good thermodynamics with 5.6 wt% H2. However, slow kinetics and reversibility hamper its practical application. A large improvement was obtained when NaAlH4 was doped with titanium, which induced partial reversibility and decomposition at reduced temperatures. Recent studies show that hydrogen sorption properties of NaAlH4 can also be improved by decreasing the crystallite size to the nanometers range using porous carbon as support1. We synthesized nanosized NaAlH4 by melt infiltration of nanoporous carbons and study how H2 sorption properties can be influenced by nanoconfinement of the carbon matrix2, 3. Bulk NaAlH4 releases H2 in three steps (NaAlH4 1/3 Na3AlH6 + 2/3 Al + H2 NaH + Al +3/2 H2 Al + Na + 2 H2) starting from around its melting point (181 ºC), as illustrated by Figure 1. Remarkably, with the presence of non-porous graphite, NaAlH4 starts to desorb around 150 ºC with two clear peaks. Nanoconfined NaAlH4 in porous carbon only shows one decomposition peak and starts to release H2 at around 110 ºC, far below the melting point of bulk NaAlH4. Nanoconfined NaAlH4 also shows partial reversibility under mild conditions. The improvement in (de)hydrogenation of nanoconfined NaAlH4 is not only a kinetic effect, but thermodynamics have also changed , as we show by an extensive studies involving high pressure DSC, solid-state 27Al and 23Na NMR measurements.

Fig.1. Temperature programmed hydrogen desorption of bulk NaAlH4, and nano composites with porous and non-porous carbon References 1. R. D. Stephens et al., Nanotechnology, 20, (2009), 204018. 2. P. Adelhelm et al., Chem. Mater., (2010), DOI: 10.1021/cm902681d. 3. J. Gao et al., J. Phys. Chem. C., (2010), DOI: 10.1021/ jp910511g.

100

The Nature of Hydrogen Adsorption in MOFs

Michael Hirscher, Barbara Streppel, Ivana Krkljuš, Maurice Schlichtenmayer, Kandavel Manickam

Max Planck Institute for Metals Research, Stuttgart, Germany Email: hirscher@mf.mpg.de

Besides high hydrogen storage density, one important prerequisite for automotive application is short refuelling time without evolving a large amount of heat. Owing to the low heat of adsorption involved in physisorption of hydrogen molecules, these requirements are fulfilled by cryo-adsorption systems based on materials, possessing large specific surface areas and high micropore density. The presentation will give an overview on hydrogen adsorption measurements of different MOFs and a comparison to other nanoporous materials. For the maximum hydrogen uptake at high pressure and 77 K an almost linear correlation with the specific surface area is found, whereas, the adsorption at low pressure depends on the pore size or the chemical composition of the materials. Several experimental techniques have been applied to correlate the hydrogen uptake properties to the nanostructure of these novel materials. Examples for extremely high hydrogen uptake or strong adsorbate--adsorbent interaction are given which show that the maximum hydrogen storage capacity as well as the heat of adsorption must be considered to optimize materials for their potential application in storage devices.

Figure: Average isosteric heat of adsorption versus excess hydrogen uptake at 20 bar and 77 K for different MOFs. Acknowledgements Partial funding by the European Commission DG Research (contract SES6-2006-518271/NESSHY) and by the European Hy-Co program financed by the German BMWi is gratefully acknowledged.

101

Reaction Kinetics of a FeTi Alloy with Nano-Structured Surface Layers

H. Uchida1, J. Kobayashi1, M. Hattori1, Y. Miyamoto2 and T.Haraki2

1 Department of Energy Science and Engineering, School of Engineering, 2 Technical Service Coordination

Office, Tokai University, 1117 Kita-Kaname, Hiratsuka, Kanagawa 259-1292 Email: huchida@tokai.ac.jp

The FeTi alloy is a well-known hydrogen storage alloy, however, practical use of the

FeTi has been strongly limited because of its great difficulty in the initial activation of hydrogen absorption. We have reported that the nano-structured FeTi alloys prepared by mechnical alloying (MA) or mechanicl griding (MG) process exhibit very high rates of the inital activation [1]. In that study, we found that MA produces FeTi alloy particles with a nano-structure with a high rate of the initial activation, however, with a much lower hydrogen storage capacity than a standard untreated FeTi alloy. On the other hand, MG produces FeTi alloy particles with single crystal grains covered by nano-structured surface layers. This MG sample exhibits a high initial activation rate, and a similar high hydrogen storage capacity to that of an untreated standard FeTi alloy.

In this study, we investigated the influence of suerface oxidation on the rate of initial activation of hydrogen absorption of the FeTi alloy with a nano-structured surface layers. This study is of great importance in the practical application of the alloy.

We measured the pressure and temperature dependences of the initial hydrogen absorption rate, and found that the rate controlling step of the rate shifts from the dissociation of hydrogen molecules on thin oxide layers to the permeation of hydrogen atoms throgh thick oxide layers as surface oxide layers grows. This kinetic behavior was found similar to that of LaNi5 [2], however, in comparison for LaNi5, the change in the measured kinetic data shows quite different results that surface oxidation strongly increases the activation energy for the hydrogen dissociation, and that the hydrogen molecules can dissociate even on grown oxide layers of the nano-structutred FeTi surface. Discussions are made in terms of kinetoic data and results of surface analyses of the alloy samples. References 1. T.Haraki, K.Oishi, H.Uchida, Y.Miyamoto, M.Abe, T.Kokaji, S.Uchida,

Int. J. Materials Research ( formerly Z.Metallkunde), 99(2008), 507-512. 2. H.Uchida, Int.J.Hydrogen Energy, 24(1999), 861-869.

102

Destabilization of MgH2 with Cd During Hydrogenation of Mg3Cd Alloy

V.M. Skripnyuk and E. Rabkin Departmtnt of Materials Engineering, Technion, Haifa 32000, Israel

We studied the destabilization of MgH2 with Cd. A Mg-25 at.% Cd alloy was synthesized by high energy ball milling (HEBM) technique. The X-rays diffraction pattern of the as-synthesized alloy clearly showed the diffraction peaks associated with the ordered Mg3Cd phase only. The kinetics of hydrogen absorption of the as-synthesized alloy after several hydrogenation cycles is very fast with apparent activation energy, Ea, about 70 kJ/mol H in the temperature range of 120 – 250 oC. The alloy absorbs about 2.5 wt.% of H2 in less than 2 min. The pressure-composition-temperature (PCT) diagrams were measured in the temperature range of 250 - 300 °C. PCT diagrams of the alloy exhibit negligible pressure hysteresis that allowed us to determine the hydride formation enthalpy and entropy from van’t-Hoff plots for different hydrogen contents. The determined from these plots formation enthalpies of MgH2 is 65.5 kJ/mol for the all hydrogen contents. This compares favorably with the value of 75.6 kJ/mol for pure Mg. About one-half of this decrease of the hydride formation enthalpy comes from the enthalpy of mixing of the Mg-Cd solid solution, while the origin of the second half is still controversial. The morphologies of the studied composite at different stages of hydrogenation process were determined in the backscattered electrons mode of the scanning electron microscope (SEM). The as-synthesized composite exhibits a homogeneous microstructure with a single Mg3Cd phase. The energy dispersive X ray spectroscopy (EDS) in SEM confirmed the stoichiometry of the composite: 74.42 at.% Mg and 25.58 аt.% Cd. The composite after full hydrogen absorption/desorption cycle exhibits some inhomogeneity, with a small fraction of whiskers-like Cd-rich phase. The EDS analysis of the whiskers composition confirmed their Cd-rich nature (88.4 at.% Cd). This indicates that Mg3Cd decomposition-recombination during hydrogenation cycling is not completely reversible. This is further confirmed by the corresponding X ray diffraction pattern exhibiting peaks of Cd in addition to the peaks of Mg3Cd. The SEM image of the fully hydrogenated composite confirms that hydrogenation reaction of Mg3Cd proceeds according to Mg3Cd + 3H2 → 3MgH2 + Cd. Cd is presented in hydrogenated composite both in coarse and finely dispersed forms. The corresponding X ray diffraction pattern exhibits the peaks of Mg3Cd and MgCd phases, in addition to the peaks of pure Cd.

103

Hydrogen Sorption in Magnesium Nanoparticles decorated by Transition Metals

E. Callini1, L. Pasquini1, E. Piscopiello2, A. Montone3, T. R. Jensen4, M. Vittori Antisari3, E. Bonetti1

1. Dept. of Physics, University of Bologna, Bologna, Italy. 2. C.R. Brindisi, ENEA, Brindisi, Italy. 3. C.R. Casaccia, ENEA, Rome, Italy.

4. Dept. of Chemistry and iNANO, University of Aarhus, Aarhus, Denmark. Email: elsa.callini@unibo.it

The aim of this work is the investigation of the metal-hydride transformation in magnesium (Mg) nanoparticles (NPs) synthesized by inert-gas condensation (IGC) in esponse to surface functionalization by transition metals (TM) clusters, in detail palladium, nickel and titanium. The TM choice has been made on the basis of their completely different Mg-TM phase diagrams. Mg nanoparticles (Mg_NP) synthesized by IGC are six-fold symmetry single crystals whose average size can be controlled by tuning the inert gas pressure. In this case a helium pressure of 250 Pa yields the formation of NPs whose average size is 450 nm. After the synthesis, the NPs are passivated by slow exposure to oxygen, obtaining a core-shell morphology where a metallic magnesium core is coated by a magnesium oxide shell of about 4 nm thickness. After restoring high vacuum, the transition metal is evaporated in order to decorate the NPs with small clusters (3-4 nm diameter) located on a portion of the magnesium oxide shell (Mg+TM_NP). The material structure was investigated by Transmission Electron Microscopy, also in Scanning and High Resolution mode, Scanning Electron Microscopy (SEM), X-Ray Diffraction (XRD) and real time Synchrotron Radiation Powder X-Ray Diffraction (SRPXD). The sorption kinetics were analysed by a volumetric Sieverts apparatus. Mg_NP exhibit very low reactivity to hydrogen due to reduced probability of hydrogen dissociation/recombination and nucleation at the particle surface [1]. A small TM decoration (2-4 at%) is sufficient to dramatically improve the hydrogen sorption behavior. In fact, previously inert nanoparticles now exhibit metal-hydride transformation with fast kinetics and gravimetric capacity above 5 wt.% [2]. H-sorption kinetics of Mg+TM_NP will be connected to structure and morphology by SEM and XRD analysis on hydrogenated samples. A deeper investigation on the role of intermetallic phases will be reported, thanks to SR-PXD carried out during hydrogen sorption on the Pd-decorated nanoparticles. We clearly show that a Mg6Pd intermetallic phase is formed after the first heating treatment and takes active part in the transformation. A comparison among three different Mg-TM samples will be presented to provide a comprehensive picture of hydrogen sorption in this class of nanostructured storage materials. References 1. L. Pasquini et al., Appl. Phys. Lett. 94, 041918 (2009) 2. E. Callini et al., Appl. Phys. Lett. 94, 221905 (2009)

104

Effect of Different Carbon Allotropies on the Synthesis of Magnesium Hydride by the Reactive Ball Milling in Hydrogen

A.D. Rud and A.M. Lakhnik G.V. Kurdyumov Institute for Metal Physics of NASU, Kiev, Ukraine

Email: rud@imp.kiev.ua It was experimentally found that the ball milling of magnesium with amorphous carbon powder obtained by the electric breakdown of hydrocarbon liquids technology [1] results in the significant improvement of the hydrogen sorption kinetics [2]. The aim of this work is to investigate the effect of different carbon allotropic additives (graphite, ultra dispersive diamonds, multiwalled carbon nanotubes and amorphous carbon) on the structure state and sorption properties of Mg-C nanocomposites synthesized by reactive ball milling (RBM) in hydrogen. It was shown, that addition of all kinds of carbon materials to magnesium leads to reduction in the hydrogenation duration in comparison with undoped magnesium (Fig. 1). The significant decrease of magnesium hydride grain sizes due to formation of carbon coating layer between single particles at RBM has been established. The carbon coating layer prevents particles agglomeration, oxidation of fresh cracked surface and thus activates the surface. It results in simultaneous involving a much greater amount of magnesium into chemical interaction with hydrogen. Among the additives, graphite and amorphous carbon promote more fine powdering of magnesium under ball milling in comparison with other carbon allotropies, and a drastic destruction of crystalline structure of graphite takes place at that because of its low mechanical properties. A hydrogenation rate during ball milling is strongly affected by the initial specific surface area (SSA) of the carbon additives: there is a correlation between initial SSA of graphite powder (Fig. 1, sample 2 – SBET=5 m2/g; sample 5 – SBET=176 m2/g) and specific surface of the synthesized magnesium-carbon nanocomposites as well as hydrogenation process duration.

0 20 40 60 80 1000

1

2

3

4

5

6

7

CH, w

t.%

Time, h

1

2

3

4

5

6

Fig. 1. Hydrogen sorption during the reactive ball milling of magnesium with different carbon allotropic modification: 1 – Mg; 2, 5 – Mg-graphite; 3 – Mg-nanotubes; 4 – Mg- ultra dispersive diamonds; 6 – Mg-amorphous carbon.

References 1. A.D. Rud, A.E. Perekos, V.M. Ogenko, et al. J. Non-Cryst. Solids, 353 (2007), 3650-3654. 2. A.D. Rud, N.I. Kuskova, L.I. Ivaschuk, et al. In «Physics of Extreme States of Matter – 2009», V. Fortov Ed., Chernogolovka: Institute of Problems of Chemical Physics of RAS, 2009, 248-251. 2. A.D. Rud, A.M. Lakhnik, V.G. Ivanchenko, et al. Int. J. Hydrogen Energy, 33 (2008) 1310-1316.

105

Tailoring Thermodynamics in NaAlH4 - Activated Carbon Composites

Wiebke Lohstroh, Arne Roth, Marcus Fehse, Maximilian Fichtner Institute of Nanotechnology, Karlsruhe Institute of Technology, Karlsruhe, Germany

Email: wiebke.lohstroh@kit.edu Hydrogen has the potential to serve as clean and versatile energy carrier, but efficient, reliable and safe storage systems have to be developed for a future hydrogen economy. Besides pressurized gas or liquid hydrogen tanks, solid state storage systems are a viable alternative. However, the materials investigated so far still show too low storage capacity at sufficiently low working temperatures to meet the targets set by the automotive industry. This is not necessarily due to the amount of stored hydrogen but thermodynamic and kinetic reasons restraining the application. Currently, two different pathways are under discussion to alter thermodynamic properties of hydrogen storage materials: (i) the reduction of particle sizes and (ii) the use of reaction based systems. In the former case, the increasing contribution of the surface free energy can lead to altered thermodynamic properties. We will present a study on the hydrogen sorption properties of complex hydrides encapsulated into a nanoporous host material. The hydrogen active material was NaAlH4 (taken without any catalyst) and various types of mesoporous carbons have been used as host material. All carbons were mesoporous with the majority of pore width between 1-4 nm, except for graphite which was used as a non-porous reference material. The influence of the size restriction and encapsulation on the thermodynamic and kinetic properties will be discussed and compared to the ones obtained for powder NaAlH4 (catalysed with CeCl3). Pressure composition isotherms of the composites clearly demonstrate the dramatically changed thermodynamic properties of the compostite materials. First experiments on composites of the binary hydrides LiH and NaH in combination with a mesoporous carbon host indicate hydrogen release at conditions that are more moderate compared to the pure binary hydride.

106

The Combination Importance of Nanostructures and Lightweight Materials for Efficient Hydrogen Storage

Jun Chen, Bo Peng, J. Zhao, Lanlan Li, Fangyi Cheng, Jing Liang, and Zhanliang Tao Institute of New Energy Material Chemistry and Key Laboratory of Advanced Micro/Nanomaterials and Batteries/Cells (Ministry of Education), Nankai University, Tianjin 300071, People’s Republic of China

Email: chenabc@nankai.edu.cn We report that the combination of nanostructures and lightweight materials is meeting the requirement of both nanoscience/nanotechnology and energy storage/conversion. An interpretation of this observation follows. First, one aim of nanosceince and nanotechnology is to obtain functional nanostructures with atoms/molecules; While, one key point of energy study is to produce energy conversion of the reaction atoms/molecules with the maximum efficiency. Thus, the comment point of nano Sci & Tech. and energy is to realize atomic economy. Second, the bottleneck of hydrogen energy development is hydrogen storage with high capacity, near-room temperature operation, controllable absorption/desorption rate, long life, and low cost. Among the present three (high-pressure gas, low-temperature liquid, and solid-state absorption/adsorption) storage methods, solid-state stoage can store hydrogen in solid-state materials through chemisorption or physisorption, being considered as the most promising way of hydrogen storage due to its high energy density and safety. Third, solid-state hydrogen storage involves three subclasses: alloys hydrides, chemical hydrides, and porous solids adsorption. The alloys hydrides (LaNi5H6) become micro and nanoparticles after the absorption/desorption cycles. The chemical hydrides (LiAlH4, NaAlH4, etc) are taking the dehydrogenation/hydrogenation reaction in the atomic level. The porous solid (MOFs, TiS2, etc) adsorption requires the micro/nanoporous channels with high specific surface areas. These three methods illustrate that micro/nanostructures are needed in the hydrogen stroage process. Forth, high-density hydrogen storage materials consist of lightweight hydrides such as alanates, borohydrides, amido hydrides, ammonia borane, magnesium hydride and Mg-based alloy/compound hydrides. However, their corresponding bulk are too stable to be reversible. Therefore, lightweight hydrides are generally combined with nanoclusters or/and nanocatalysts. Our experiments and/or theoretical calculations are carried out for understanding the importance of the combination of nanostructures and lightweight materials for hydrogen storage such as nanostructured Mg/MgH2, NH3BH3, Ni1-xPtx or CoB/CoP catalyzed hydrogen generation from NH3BH3 or NaBH4 solution [1-10]. Finally, the disadvantages of complicated synthsis route, unstability, low density, high surface reaction for nanostructured lightweight hydrides are also discussed. References (*Corresponding author): 1. J. Zhao, J. Shi, X. Zhang, F. Cheng, J. Liang, Z. Tao, J. Chen*, Adv. Mater., 22, (2010), 394-397. 2. B. Peng, J. Chen*, Coord. Chem. Rev., 253, (2009), 2805-2813. 3. B. Peng, J. Liang, Z. Tao, J. Chen*, J. Mater. Chem., 19, (2009), 2877-2883. 4. L. Li, B. Peng, W. Ji, J. Chen*, J. Phys. Chem. C, 113, (2009), 3007-3013. 5. B. Peng, L. Li, W. Ji, F. Cheng, J. Chen*, J. Alloys Compd., 484, (2009), 308-313. 6. H. Ma, W. Ji, J. Zhao, J. Liang, J. Chen*, J. Alloys Compd., 474, (2009), 584-589. 7. X. Yang, F. Cheng, J. Liang, Z. Tao, J. Chen*, Int. J. Hydrogen Energy, 34, (2009), 8785-8791. 8. F. Cheng, J. Liang, J. Zhao, Z. Tao, J. Chen*, Chem. Mater., 20, (2008), 1889-1895. 9. F. Cheng, H. Ma, Y. Li, J. Chen*, Inorg. Chem., 46, (2007), 788-794. 10. W. Li, C. Li, H. Ma, J. Chen*, J. Am. Chem. Soc., 129, (2007), 6710-6711.

107

Binding Energy Estimation of Hydrogen Storage Materials by All-Electron Mixed-Basis Program TOMBO

Ryoji Sahara 1, N. S. Venkataramanan1, Hiroshi Mizuseki 1, Marcel Sluiter 2 Kaoru Ohno 3, and Yoshiyuki Kawazoe 1

1 Institute for Materials Research, Tohoku Univ., university, Sendai 980-8577, Japan 2 Department of Materials Science and Engineering, Delft Univ., Mekelweg 2, 2628, Delft

3 Graduate School of Engineering, Yokohama Natl. Univ., Yokohama 240-8501, Japan E-mail : sahara@imr.edu

To investigate the hydrogen storage capability in Li-functionalized p-tert-butyl calixarene (LTBC), the binding energy of hydrogen to LTBC is estimated. In this study, we use TOhoku Mixed-Basis Orbitals ab initio simulation package TOMBO [1, 2] developed by our research group, which enables us to study based on ”all-electron mixed-basis approach” with smaller number of plane waves. Figure shows calixarene with one hydrogen molecule (left side) and Li-functionalized calixarene with three hydrogen molecules [3]. We found that the Li-functionalized calixarene improves the average binding energy of hydrogen molecules. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials".

References 1. K. Ohno, K. Esfarjani and Y. Kawazoe, Computational Materials Science From ab initio to Monte Carlo Methods, Springer Series in Solid-State Sciences 129 (Springer-Verlag, Berlin, Heidelberg, 1999), pp. 42-46. 2. M. S. Bahramy, M.H.F. Sluiter, and Y. Kawazoe, Phys. Rev. B73 (2007), 045111. 3. N. S. Venkataramanan, R. Sahara. H. Mizuseki, and Y. Kawazoe, J. Phys. Chem. C112 (2008), 19676.

108

Hydrogen in Mg-Ni Thin Films

Pragya Jaina*, Ankur Jaina, Devendra Vyasa, S.A.Khanb, I.P Jaina aCenter for Non-Conventional Energy Resources, University of Rajasthan, Jaipur, India .

bInter-University Accelerator, Aruna Asif Ali Marg, New Delhi 110 067, India Email:pragya.2604@gmail.com

Hydrogen storage materials have attracted world-wide attraction for increasing demands of energy for environmental protection. Among these, Mg is considered as a promising hydrogen storage material due to its high storage capacity (7.6wt %), light weight and low cost. However, thermodynamics indicate that hydrogen desorption from bulk MgH2 only takes place at temperature above 600K, which restricts its use in practical applications, especially as hydrogen storage material in mobile applications and fuel cells which need to operate at moderate temperature and under hydrogen pressure of few bars.

Hydrogen in thin films provides an opportunity to examine a number of unusual properties, which are not present in the bulk systems, as the hydrogen adsorption, absorption and storage is basically a surface phenomena. Recently, various attempts have been undertaken to study Mg based nano composite films, mainly involving alloying Mg with other elements such as MgTi and MgNi or doping with catalysts Nb and Pd. The interest in Mg films also stems from its switchable mirror behavior which could transfer from a high reflecting state to a transparent state during hydrogen absorption. In the present work Mg-Ni and Mg-Mg2Ni thin films, sandwiched between Pd were prepared on Si substrate by vapor deposition technique at 10-6 torr vacuum in a chamber equipped with both electron gun and resistive heating for co and sequential deposition. Structural and morphological characterizations were performed using Grazing Incidence X-ray Diffraction (GI-XRD) and Atomic Force Microscopy (AFM). Hydrogenation of the films was carried out at 200oC under H2 pressure of 5bar in a SS chamber for 2hrs. The chamber was pumped down to 10-5 torr before introducing hydrogen to it. Areal concentration of hydrogen (NH in atoms/cm2) in both as-deposited and hydrogenated films was measured by ERDA using 120MeV Ag9+ beam. The ERDA results indicate increase in hydrogen content in the metallic films from 9*1016atoms/cm2 to 1.4*1018 atoms/cm2upon hydrogen loading. References

1. L.Z. Ouyang, H. Wang, C. Y. Chung, J. H. Ahn, M. Zhu, J. Alloys & Compounds 422 (2006) 58-61.

2. L. Pranevicius, E. Wirth, D. Milcius, M. Lelis, L.L. Pranevicius, A. Kanapickas, Surface & Coating Technology 203 (2009) 998-1003.

109

Economical and Engineering Scalability of Complex Hydrides as New Promising Hydrogen Storage Materials

J. Jepsena, J.M. Bellosta von Colbea, T. Klassenb, M. Dornheima

aInstitute of Materials Research, Materials Technology, GKSS-Forschungszentrum Geesthacht GmbH, Max-Planck-Strasse 1, D-21502 Geesthacht, Schleswig-Holstein, Germany

bInstitute of Materials Technology, Helmut-Schmidt University, Holstenhofweg 85, 22043 Hamburg, Germany

Email: julian.jepsen@gkss.de Novel materials for hydrogen storage like LiBH4 / MgH2 composite and NaAlH4 show rather promising properties [1, 2, 3]. They combine elevated hydrogen storage capacities and relatively fast sorption rates. However, it is not known to what extent they are economically and technically scalable. In the range of 0.1 to 100 kg of hydrogen we investigated in theory the economical scalability of LiBH4 / MgH2 and NaAlH4 storage systems and compare these results with the high pressure and liquid storage systems. The complex hydrides have a costs advantage, which is based primarily on the simplified construction of the tank vessels, due to the improved pressure and temperature conditions during the storage process. The technical scale-up for NaAlH4 was already shown by Eigen et al. [4] and Lozano et al. [5] - for the LiBH4 / MgH2 composite it has not been investigated until now. In this paper we present volumetric titration measurements of 0.25 g, 1.25 g and 5 g powder bed sizes for 8 cycles. For the 5 g powder bed size we measured also the heat distribution inside the sample holder (inner diameter 15.2 mm). We can show that the influence of the powder bed sizes on the kinetic and final capacity seems to be low for absorption and desorption. However, the dependency of the desorption rate on temperature and pressure is strong for all powder bed sizes. In addition we discovered for the heat distribution that the temperature peaks inside the powder bed during the absorption process are very moderate, in comparison to previous results for NaAlH4 [5]. These results provide the basis for future developments of scaled-up complex hydride tank systems. Especially in the case of LiBH4 / MgH2, these will benefit from a simplified heat management. References 1. Bogdanovic B, Schwickardi M. Ti-doped alkali metal aluminium hydrides as potential novel reversible hydrogen storage materials, Journal of Alloys and Compounds 253 (1997) 1-9 2. Barkhordarian G, Klassen T, Dornheim M, Bormann R. Unexpected kinetic effect of MgB2 in reactive hydride composites containing complex borohydrides, Journal of Alloys and Compounds 440 (2007) L18–L21 3. Vajo J J, Skeith S, Mertens F O. Reversible Storage of Hydrogen in Destabilized LiBH4, Journal of Physical Chemistry B 109 (2005) 3719 - 3722 4. Eigen N, Keller C, Dornheim M, Klassen T, Bormann R. Industrial production of light metal hydrides for hydrogen storage, Viewpoint Paper, Scripta Materialia 56 (2007) 847-851. 5. Lozano G A, Eigen N, Keller C, Dornheim M, Bormann R. Effects of heat transfer on the sorption kinetics of complex hydride reacting systems, International Journal of Hydrogen Energy 34 (2009) 1896 – 1903

110

The Rate Limiting Step in the H2 Reaction of Nanostructured Catalysed Magnesium

A. Montone, A. Aurora, D. Mirabile Gattia and M. Vittori Antisari

ENEA, MAT-COMP Research Center of Casaccia, Via Anguillarese, 301 – 00123 Rome, Italy Email: amelia.montone@enea.it

Despite the performances in terms of sorption rate of the Mg-MgH2 system are still far from the DOE’s targets, the study of the reaction Mg + H2 ↔ MgH2 is still object of strong scientific interest because it is reversible and can be significantly speed up by nanostructuring the material through high energy ball milling and by the addition of catalyst. This means that the understanding of the kinetic aspects of the reaction can bring to further improvements, suggesting this kind of material for a possible future technological application. With the view to enlightening the kinetic aspects in the case of a Fe catalysed ball milled magnesium the H2 reaction has been studied at two different temperatures (250°C and 300°C) adjusting the gas pressure in order to keep almost constant the thermodynamic driving force. The resulting samples, as consequence of the different density of nucleation of the growing phase MgH2, show a marked different extension of the Mg-MgH2 interface and a similar extent of particle surface. To elucidate the rate limiting step of the H2 absorption reaction, a key experiment has been carried out where the density of nucleation of the transformed phase has been suitably modified by two steps H2 absorption at the two different temperatures This experiment has allowed, with the support of the most common kinetics models describing the hydrogen absorption curves [1], to distinguish among different hypothesis concerning the reaction rate limiting step of the reaction. It results that the barrier at the external surface of the powder particles represents the limiting step, suggesting the decoration of surface particle with catalyst as the new frontier of material processing to improve the hydrogen sorption rate. The different microstructure due to the different experimental conditions has been observed by metallographic observation following a SEM observation protocol already described [2,3]: the reaction has been stopped at 15% of the transformed volume and the cross sectional samples observed at high resolution low voltage SEM in order to have a snapshot of the early stage of the reaction. References 1. M. Mintz, Y. Zeiri, J. Alloys and Compounds. 216 (1994) 159. 2. M.V. Antisari, A. Montone, A. Aurora, M.R. Mancini, D.Mirabile Gattia, L. Pilloni, Intermetallics 17 (2009) 596. 3. M. Vittori Antisari, A. Aurora, D. Mirabile Gattia, A. Montone, Scripta Materialia 61 (2009), 1064.

111

Mechanochemical Synthesis of Mg2FeH6-Based Nanocomposites and the Effects of Different Additives on its H-Sorption Properties

D. R. Leiva, G. Zepon, J. Huot, A. M. Jorge, T. T. Ishikawa and W. J. Botta

Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, Rodovia Washington Luiz, km 235, CEP 13565-905, São Carlos, SP, Brazil.

E-mail: leiva@ufscar.br Magnesium complex hydrides are interesting phases for the storage of hydrogen in the solid state, mainly due to their high gravimetric and volumetric densities of H2. The major limitations for the practical application of Mg2FeH6 as a hydrogen storing media are the severity of the processing conditions involved in the conventional synthesis method (sintering under H2 atmosphere, [1]) and also the high temperatures needed for H-sorption, which can occur with only partial reversibility. In this work, we have systematically studied the influence of the most important processing parameters for the reactive milling of 2Mg-Fe mixtures under hydrogen. The effects of the form of reactants, type of mill, milling time, hydrogen pressure and ball-to-powder ratio were evaluated in the synthesis of Mg2FeH6. In optimized combinations of the processing parameters, very high proportions of the complex hydride could be obtained, indicating that a good control of the parameters was achieved. Ball milling procedures have been extensively used in MgH2-based systems to reduce the grain and particle sizes to the nanometric scale and to form a fine dispersion of additives. These nanocomposites present fast H-sorption kinetics at around 300°C [2]. However, there are very few studies about the effects of additives in H-sorption properties of Mg2FeH6. In the present work, we have prepared Mg2FeH6-based nanocomposites by RM using different additives as transition metals, transition metals fluorides and graphite. The aim was to obtain more information about the effects of these selected additives (which present comproved beneficial influence on MgH2 properties) on H-sorption and reversibility of Mg2FeH6. Structural analysis was carried out by X-ray diffraction (XRD), transmission and scanning electron microscopy (TEM and SEM). Thermal analysis was performed by differential scanning calorimetry (DSC) coupled to thermogravimetric analysis (TG) and mass spectrometry (MS). H-sorption kinetic measurements were made in a Sievert’s apparatus. The beneficial effects of the different additives is summarized and compared to those obtained for MgH2-based nanocomposites. References

1. J.-J. Didisheim, P. Zolliker, K. Yvon, P. Fisher, J. Schefer, M. Gubelmann, A.F. Williams, Inorg. Chem. 23, (1984), 1953 - 1957.

2. A. R. Yavari, A. LeMoulec, F.R. de Castro, S. Deledda, O. Friedrichs, W.J. Botta, G. Vaughan, T. Klassen, A. Fernandez, Ǻ. Kvick, Scripta Mater. 52, (2005), 719 – 724.

112

Cluster Size Dependence of Hydrogen Desorption from Alkali Metal Hydride and Ammonia

A.Yamane1, F.Shimojo2, K.Hoshino3, T.Ichikawa1,4, Y.Kojima1,4 1Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, Japan.

2Graduate School of Science and Technology, Kumamoto University, Kumamoto, Japan. 3Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima, Japan.

4Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima, Japan. Email: yamane@minerva.ias.hiroshima-u.ac.jp

Hydrogen storage system based on ammonia (NH3) and alkali-metal hydride (MH) is one of the most promising systems to realize on-board hydrogen storage, since ammonia (NH3) easily liquefies at about 1 MPa of pressure and contains 18.1 mass% of hydrogen. This system desorbs H2 as MH+NH3 → MNH2+H2 at room temperature with exothermic reaction, and the reverse reaction MNH2+H2 → MH+NH3 also occurs at relatively low temperatures and pressures1,2. The hydrogen storage capacity of MH-NH3 system is 8.1, 4.9 and 3.5 mass% for M = Li, Na and K, respectively. Recently, we3 have carried out ab initio molecular-dynamics (MD) simulation for LinHn cluster (n = 1, 2) and NH3 molecule at somewhat higher temperature (700 K) up to 15 ps, and shown that the H2 molecule is formed with one H atom from LiH and another H atom from NH3. On the other hand, we also found that clean surface of the crystalline LiH is not likely to react with NH3. The purpose of this paper is to reveal the effect of the cluster size of MnHn on the reactivity of hydrogen desorption. We performed ab initio molecular-dynamics (MD) and structure simulations based on density functional theory (DFT). For searching activation energy (energy barrier), we performed structure optimizations with fixed H-H distance. The systems consist of LinHn cluster or layer and an NH3 molecule, where we regard LinHn cluster as a model of disordered LiH surface. We set n = 1 – 4 for LinHn cluster and n = 32 for (1 0 0) slab and n = 36 for (1 1 0) slab. The MD simulations are carried out at the temperatures of 300, 500, 700 and 1000 K, and up to 100,100 steps (48 ps) with a time step of 0.48 ps. We estimated the activation energy and H-H distance at saddle point of LinHn - NH3 systems, and found that the activation energy and the H-H distance are dependent on the LinHn cluster size. The activation energy of Li4H4-NH3 system (0.9 eV) is similar to that of Li32H32(1 0 0)-NH3 system (1.1 eV), while LinHn clusters with n < 4 show much lower activation energies (0.3 – 0.6 eV). The H-H distance also depends on the cluster size and takes larger value when n < 4. We also performed MD simulations on the system with n = 2, 4. For the MD simulations with n = 4, Hδ- atom in Li4H4 and Hδ+ atoms in NH3 do not approach each other, while the simulations with n = 2 show that Hδ- and Hδ+ approach each other even when they do not make a H2 dimer. Acknowledgment: This work is supported by the Grants of the NEDO project ‘Advanced Fundamental Research on Hydrogen Storage Materials’ in Japan. References 1. Y. Kojima et al., J. Mater. Res, 24 (2009) 2185. 2. H. Yamamoto et al., I. J. Hydrogen Energy, 34 (2009) 9760 3. Yamane et al., J. Mol. Str. (THEOCHEM) 944 (2010) 137.

113

Mechanochemical Synthesis and Characterization of Aluminium Hydride

W.H. Gao, Y.X. Zhang and J. Liu

Institute of New Energy Materials Chemistry, Nankai University, Tianjin 300071, China Email: liujian@nankai.edu.cn

Aluminium hydride (alane) is an attractive material for hydrogen storage due to its high 10.1 wt.% hydrogen capacity. AlH3 is metastable under ambient conditions, and has at least six polymorphs, within which α-AlH3 was found to be most stable. AlH3 was traditionally synthesized by wet chemistry route. Recently, mechanochemical synthesis method was reported to be used to synthesize aluminium hydride[1]. In the present work, alane was synthesized by ball milling different starting materials under hydrogen. The starting materials include LiAlH4, NaAlH4, LiH, NaH, AlCl3 and AlBr3. X-ray diffraction, SEM, TG/DSC were used to characterize the AlH3 mixture. AlH3 obtained by this method was found to be amorphous, as reported before[2]. The separation of AlH3 from by-product such as LiCl is still undergoing. The effects of dopants on synthesis of AlH3 and its hydrogen desorption were also investigated. References 1. M. Paskevicius, D.A. Sheppard, C.E. Buckley, J. of Alloys and Compounds, 487,

(2009), 370–376. 2. Y.J. Luo, S.K. Mao, R.X. Yan, L.B. Kong, L. Kang, Acta Phys. -Chim. Sin., 25(2), 2009,

237-241

114

Can Reduced Size of Metals Induce Hydrogen Absorption: ZrAl2 Case

I. Jacoba, S. Deleddab, M. Bereznitskya, O. Yeheskelc, S.M. Filipekd, D. Mogilyanskie, G. Kimmele, B.C. Haubackb

a. Department of Nuclear Engineering, Ben-Gurion University of the Negev, Beer Sheva 84105, Israel b. Physics Department, Institute for Energy Technology, P.O. Box 40, NO-2027 Kjeller, Norway

c. Nuclear Research Center – Negev, P.O. Box 9001. Beer Sheva 84190, Israel d. Institute of Physical Chemistry, Polish Academy of Sciences, 01-224 Warsaw, Poland

e. Institute for Applied Research, Ben-Gurion University of the Negev, Beer Sheva, 84105, Israel * E-mail: izi@bgu.ac.il.

The hydrogen absorption ability of the non-absorbing Al-rich ZrAl2 compound was examined after reducing its particles-size to the nanometer regime. The hydrogen abstinence of bulk ZrAl2 has been previously related to its excessive elastic shear stiffening [1]. The particle size of ZrAl2 was reduced by attrition milling and cryomilling. The minimal average particle size was estimated from powder X-ray diffraction analysis to be in the 10-20 nm-range. The hydrogen absorption of the milled compounds was measured in different hydrogenation systems at hydrogen pressures between ~6 MPa and ~2 GPa. In all the cases the hydrogen absorption was negligible. In addition, there was a reduction of the hydrogen absorption capacity of nanosized Zr(Al0.5Co0.5)2 as compared to the corresponding bulk compound at the same conditions. We suggest, in view of our and other results, that no significant improvement of the thermodynamics (unlike the kinetics) of the hydrogen absorption can be achieved via the nanoparticle avenue. References 1. I. Jacob, M. Bereznitsky, O. Yeheskel and R. G. Leisure, Applied Physics Letters, 89 (2006) 201909.

115

Sorption Properties of Dispersed MBH4-MgH2 (M=Na, Li) Systems in Nano-Mesoporous Scaffolds

R.Campesi1, C.Milanese2, F.Delogu3, E.Napolitano4, G.Mulas4 1JRC-IE, Petten, Netherlands

2CSGI, Dipartimento di Chimica Fisica "M. Rolla", Università degli Studi di Pavia, Pavia, Italy 3Dipartimento di Ingegneria Chimica e Materiali, Università degli Studi di Cagliari, Cagliari, Italy

4Dipartimento di Chimica, Università degli Studi di Sassari, Sassari, Italy Email: mulas@uniss.it

Wide attention has been addressed in the last years to the study of thermodinamically destabilised hydride mixtures, namely Reactive Hydride Composites, as promising hydrogen storage systems for on board applications. The high gravimetric capacity of such materials is related to the complexity of the systems and their chemical reactivity. Slow kinetics and high desorption temperatures however keep such materials away from requirements for applicative purposes, neither the use of mechanical milling or chemical additives allowed to reach relevant improvements [1,2]. An alternative route could be obtained by reducing the hydride particles to nanometer sizes and improving their dispersion into scaffold materials [3,4].

Along this line, we are investigating the sorptive qualities of MBH4-MgH2 (M=Na, Li) sytstems dispersed, by wet impregnation or melting infiltration, into Si- or C-based nano-mesoporous matrixes. The pore network of the hosting material, controlling the particle size of the active phases, could, at least in principle, make their interaction easier during the hydring-dehydring process. The microstructural characterization of samples have been performed by XRD, neutron diffraction and TEM, while the hydrogen ab/desorption properties have been studied using gravimetric and volumetric apparatuses as well as by TDS and DSC techniques. Microstructural properties have been related to the hydring/dehydring process in order to clarify the effect of the matrix in improving the interaction between the active phases. References 1. J. J. Vajo et al., Scripta Materialia, 56, (2007), 829-834 2. U. Bosenberg et al., Acta Materialia, 55, (2007), 3951-3958 3. A. F Gross et al., J. Phys Chem C, 112, (2008), 5651-5657 4. S. Zheg et al., Chem Mater 20, (2008), 3954-3958

116

Grain Refinement, Solubility Limits, and Low T Hydrogen Storage in TiF3 Catalyzed MgH2

S.Singh,S. Bolhuis, S.W.H. Eijt, F.M. Mulder

Faculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands Email: f.m.mulder@tudelft.nl

In view of its high storage capacity magnesium hydride is a promising hydrogen storage material. However, catalysts are required to enhance the kinetics of the sorption processes, and recently TiF3 was shown to be a very effective catalyst1,2. Here we show that ball milled MgH2 and 5 mol % TiF3 leads to hydrogen absorption from -10 oC onwards. In situ neutron diffraction reveals that during the first stage of rapid hydrogen uptake hydrogen (deuterium) exclusively is adsorbed in the Mg alpha phase up to MgD~0.25. DFT calculations reproduce several of the features observed. Further uptake results in the appearance of the MgD2 beta phase. In addition the crystallites of MgD2 remain remarkably small (~30nm) and they contain abundant vacancies. The vacancies in MgD2-x are not new; they were seen before by us3. However, now it becomes clear that the nanostructured and catalysed material has strongly altered solubility limits on both sides of the solubility gap. Such behaviour has been described before in relation to interface and surface energies in nanoscaled Li insertion materials 3, 4. Further results show that the catalyst forms TiHx and nanoscopic MgF2, the latter having the same structure as MgH2. For this reason MgF2 is proposed to act as seed crystals leading to the observed grain refinement, analogous to some catalysts in NaAlH4 5. The picture then emerges that grain refinement leads to altered nanoscale phase behaviour during loading and unloading of hydrogen [3]. Measurements of the equilibrium pressures as a function of temperature and as a function of overall H content show a strongly H content dependent enthalpy and entropy of formation. At low H content a ΔH as high as -45kJ/mol was determined (compared to -74 kJ/mol in bulk). Furthermore there is a remarkably clear correlation between ΔH and ΔS values. The latter will be related to the H solubility in Mg and the large vacancy density in MgH2-x that influence both configurational entropy and enthalpies of formation. References 1 L. Xie, Y. Liu, Y.T. Wang, J. Zheng, and X.G. Li, Acta Materialia 55, 4585 (2007). 2 S.A. Jin, J.H. Shim, Y.W. Cho, and K.W. Yi, J. Power Sources 172, 859 (2007). 3 H.G. Schimmel, J. Huot, L.C. Chapon, F.D. Tichelaar, and F.M. Mulder, J. Am. Chem.

Soc. 127, 14348 (2005). 4 M. Wagemaker, F.M. Mulder, and A. Van der Ven, Adv. Mater. 21, 2703 (2009). 5 S. Singh, S.W.H. Eijt, J. Huot, W.A. Kockelmann, M. Wagemaker, and F.M. Mulder,

Acta Materialia 55, 5549 (2007).

117

Interaction with Hydrogen of Highly Dispersed Magnesium Eutectic Alloys

P.Fursikov, D.Borisov, and B.Tarasov Institute of Problems of Chemical Physics of RAS, Chernogolovka, Russia

Email: fpv@icp.ac.ru It is known that magnesium based multiphase eutectic alloys, such as Mg-Ni and Mg-La-Ni, may reversibly absorb up to 5–6 mass. % of hydrogen [1]. In order to improve the kinetics of hydrogen sorption and desorption one uses the intensive plastic deformation, in particular equal channel angular pressing (ECAP), of the alloys. This causes the reduction of the grain size of the magnesium constituent of the alloys down to sub-microns and nano-scales, and to increasing of the length of the interphase boundaries [2, 3]. In the case of ternary eutectic magnesium alloy one substitute lanthanum for mischmetal. In the present work we studied the hydrogen sorption properties of the binary eutectic Mg-Ni alloy subjected to preliminary modification by the ECAP under various parameters and perform comparative investigations of Mg-La-Ni vs Mg-Mm-Ni in the process of hydrogen desorption from their hydrides.

Metallographic investigations of the microstructure of the ECAP-ed binary eutectic alloy Mg-Ni and the ternary eutectic Mg-La(Mm)-Ni alloy were performed with the use of light microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy. The obtained data revealed the space distribution of the constituting phases end elements of the ECAP-ed alloy. The ECAP-ed alloy had mainly highly dispersed lamellae microstructure, while variation of parameters of the ECAP procedure (such as temperature pass rate and number) allowing one to increase the dispersion of the alloy. Data of hydrogen sorption by powdered samples of both initial binary eutectic Mg-Ni alloy and the ECAP-ed one obtained with the use of a Sieverts-type experimental setup showed that the ECAP-ed alloy exhibited improved kinetics of interaction with hydrogen as compared to the initial non-modified alloy. The obtained data confirmed that these modified alloys are perspective for elaboration materials with enhanced hydrogen sorption characteristics.

The time resolved in-situ X-ray diffraction analysis performed at various temperatures within the range of 280–350 C showed that at even temperatures the hydride of the ternary eutectic Mg-Mm-Ni alloy desorbed hydrogen at higher rate than the hydride of Mg-La-Ni. In these experimental conditions comparable rates of hydrogen evolution by the hydride of the Mm-alloy were attained when it was heated up to temperatures which were by about 20 degrees lower than those for the hydride of the La-alloy. A more pronounced favorable effect of mischmetal as compared to lanthanum for the hydrogenation of RE-based alloys were reported elsewhere [5], and in our case we explained it by the higher catalytic effect of Mm and some Mm constituents, for instance transition metal iron.

The authors are grateful to the Russian Foundation for Basic Research (Grant No 09-03-01135) for the support. References 1. B.Tarasov, M.Lototskii, V.Yartys, Russ. Chem. Journal, 77, (2007), 694-711. 2. V.Skripnyuk, E.Rabkin, Y.Estrin, R.Lapovok, Acta Materialia, 52, (2004), 405-414. 3. S.Lǿken, JK.Solberg, JP.Mæhlen, et al, J. Alloys and Compounds, 446-447, (2007), 114-

120. 4. B.Tarasov, P.Fursikov, D.Borisov, et al., J. Alloys and Compounds, 446–447, (2007),

183-187. 5. H.Uchida, and T.Kuji, Int. J. Hydrogen Energy, 24, (1999), 871-877.

118

Depth Distributions of D+ Ions Implanted Into Some Pure Metals or D

Atoms Introduced into Diluted Pd-alloys and Measured by RBS (ERDA)

Method A.Yu.Didyk1, R.Wisniewski2, T.Wilczynska2

1Joint Institute for Nuclear Research, Flerov Laboratory of Nuclear Reactions, Joliot-Curi 6, 141980 Dubna, Russia, didyk@jinr.ru

2Institute of Atomic Energy-POLATOM, 05-400 Otwock/Swierk, Poland, roland.wisniewski@gmail.com, teresa.wilczynska@gmail.com

First part of report is devoted to experimental results obtained on the samples of some pure metals (Ni, Cu, Nb, Ti, Zr, V, Pd) and diluted Pd-alloys (Pd-Ag, Pd-Pt, Pd-Ru, Pd-Rh) with different previous treatments were irradiated by deuterium ions with 25 keV energy in fluence interval (1,0÷2,3)×1018 D+/cm2 with the use of ECR ion source beam line of FLNR JINR [1]. The depth distributions of deuterium ions were measured immediately after implantation with the use of elastic recoil detection analysis (ERDA) in Rutherford backscattering spectrometry (RBS). After definite long time the measurements were repeated again. The comparison of obtained results in both series of studies allowed make important conclusions about behavior of deuterium and hydrogen gases in pure metals and diluted Pd alloys. Second part of report is devoted to specially prepared samples with different previous treatments of pure Pd and Pd dilute metal alloys were saturated by deuterium using deuterium high pressure special chamber in Institute of Physical Chemistry of Polish Academy of Science [2]. The depth distributions of deuterium atoms were measured immediately after saturation with the use of elastic recoil detection analysis (ERDA). After definite and sufficient time the measurements were repeated again. The comparison of obtained results in both series of studies allowed make important conclusions about behavior of deuterium and hydrogen gases in such Pd and its diluted alloys.

Reference

1. A.Yu.Didyk, T.Kohanski, V.A.Skuratov et all. Studies of radiation effects in materials on ECR heavy ion source beam line at FLNR. In the book: Materials of XI International Conference “Radiation Physics of Solids”, Sevastopol, Crimea, 2001, pp.340-350.

2. http://malina.inchf.edu.pl/person/filipek.html

119

High Pressure In Situ Diffraction Studies of the Metal-Hydrogen systems V.A. Yartys1,2 *, R.V. Denys1, J.P. Mæhlen1, C. J. Webb3, E. MacA. Gray3, T. Blach3 and

O. Isnard4 (1) Institute for Energy Technology, Kjeller, NORWAY, (2) Norwegian University of Science and Technology,

NORWAY (3) Queensland Micro- and Nanotechnology Centre, Griffith University, Nathan 4111, AUSTRALIA, (4) Institute Néel, CNRS/UJF, 38042 Grenoble, FRANCE

* Email: volodymyr.yartys@ife.no

“Hybrid” H storage, merging together two complementary techniques, yields to improve the overall system efficiency by up to 50 % as compared to either compressed H2 or solid materials for hydrogen storage. The focus of the present contribution is in studies of the metal-hydrogen systems where H storage capacity of the MH can be significantly increased by applying high H2 pressures. Thermodynamically, high equilibrium hydrogen pressures in the metal-H systems are observed when enthalpies of hydrogen absorption/desorption are low, thus decreasing the calorimetric effects of the hydride formation-decomposition processes. This, in turn, assists in achieving high rates of heat exchange during the H loading and removes the bottleneck in making large H stores with low charging time required for the efficient H driven vehicles. Our goal was to investigate the kinetics and mechanism of the phase-structural transformations in the systems with hydrogenation enthalpies close to -20 kJ/mol H2. Two particular systems were in focus, the CeNi5-D2 and the ZrFe2-xAlx (x=0.02; 0.04; 0.20)-D2 ones. In situ NPD were performed at ILL, Grenoble, using a high intensity two-axis powder diffractometer D1B with an 80o PSD. Complementary SR XRD data was collected at a BM01A of Swiss-Norwegian Beam Lines, ESRF, Grenoble. During the in situ NPD studies D2 pressures reached 821 bar D2 for CeNi5-D2 and 999 bar D2 for ZrFe2-xAlx (x=0.02; 0.04; 0.20)-D2. High pressures were generated by use of multistage, heat-based deuterium intensifier. Initial intermetallics crystallise with hexagonal CaCu5 (CeNi5) and cubic Laves-type MgCu2 (ZrFe2-xAlx) structures. In a saturated CeNi5D6.3 deuteride, deuteration resulted in a very significant volume expansion of 30.1 % with rather similar elongation in the basal plane and along [001], Δa/a (10.0 %) and Δc/c (7.5 %). D atoms fill three different types of interstices, including Ce2Ni2 and Ni4 tetrahedra, and Ce2Ni3 half-octahedra. A significant hysteresis was observed between deuterium absorption and desorption which profoundly decreased on a second absorption cycle. In CeNi5D6.3 the unit cell parameters, a= 5.374(2); c= 4.3013(7) Å, are rather close to the values for LaNi5D6+x indicating a Ce valence change on deuteration. For the Al-modified Laves-type C15 ZrFe2-xAlx intermetallics deuteration showed a very fast kinetics of H/D exchange and resulted in an increase of the volumes of the FCC unit cells reaching 23.5 % for ZrFe1.98Al0.02D2.9(1). SR XRD measurements showed that Al substitution for Fe leads to a slight volume expansion. D content, hysteresis of H/D uptake and release, unit cell expansion and stability of the hydrides systematically change with Al content. In spite of the large unit cell expansion, the cubic symmetry does not change upon hydrogenation. D atoms exclusively occupy the Zr2(Fe, Al)2 tetrahedra. Observed interatomic distances, Zr-D = 2.01-2.08; (Fe, Al)-D=1.70-1.75 Å, do not rule out a possibility of occupancy of the Al-substituted sites. Hydrogenation, as it is often observed for the Fe-containing hydrides, slightly yet significantly increases magnetic moments on the Fe atoms [alloy; 1.9 μB at RT] to the corresponding deuteride [2.2 μB at RT]. In situ diffraction studies combining high flux NPD and high resolution SR XRD investigations provide a powerful tool in studies of the solid materials for H storage allowing characterisation of the H storage capacities and kinetics of H exchange in real conditions of the applications in the “hybrid” hydrogen storage systems.

120

IMC Hydrides with High Hydrogen Dissociation Pressure

T.Zotov, R. Sivov, E. Movlaev, V. Verbetsky Chemistry Department Moscow State University, Moscow, Russia

Email: tim.zotov@gmail.com The study of hydrogen absorption properties of the pseudo binary intermetallic compounds based on ZrFe2 and TiCr2 at pressures up to 3000 atm is described in present paper. The hydrogen absorption capacity of IMC ZrFe2 is about 1.7 wt.% and practically all amount of absorbed hydrogen in ZrFe2H3.5 can be desorbed reversibly [1-2]. This is very prospective for practical application of this hydride. The adding of other elements gives possibility to vary the thermodynamics of ZrFe2 hydride. The influence of substitution of A- and B- components on hydrogen sorption properties of ZrFe2 was investigated. Zirconium was partially substituted for titanium and rare earth metals (Y, Gd, Dy) and iron – for various transition metals (Ti, V, Cr, Mn, Co, Ni, Cu, Mo). Also the series of multicomponent alloys Zr1-xTix(Fe1-yBy)2, where B one or several transition metals - Ti, V, Cr, Mn, Ni. It was established that hydrogen desorption pressure of these hydrides varied in wide range. Some of investigated samples can be used for the design of metal hydride compressors with high hydrogen pressure. This group of samples possess peculiar properties like high hydrogen desorption pressures (800 – 2500 atm) and (or) small hysteresis (ln(Pabs/Pdes)<0.1). The hydrogen sorption properties of TiCr2 are unusual compared to other IMC with Laves phases structure. The reaction of this compound with hydrogen at high pressure and low temperature yields formation of CaF2- type FCC hydride. The practical interest for this hydride is due to high hydrogen storage content of 2.5 wt. % [3-5]. The study of alloys Ti(Cr1-xBx)2-a, (B = B, Si, Al, Mn, Ni, Mo; a = 0 – 0.2) and Ti1-xZrx(Cr1-xBx)2-a, (B = Mn, Ni, Mo; a = 0 – 0.2) was performed in present work. The analysis of substitution influence on hydrogen absorption properties is also discussed in this paper. References 1. S.M.Filipek, I.Jacob, V.Paul-Boncour, A.Percheron-Guegan, I.Marchuk, D.Mogilyanski, J.Pielaszek, Polish Journal of Chemistry, 75, (2001), 1921 2. T. Zotov, E. Movlaev, S. Mitrokhin, V. Verbetsky, J. Alloys Comp., 459 (2007), 220-224. 3. J. R. Johnson, J. J. Reilly, F. Reidinger, L. M. Corliss and J. M. Hastings J. Less-Common Met. 88 (1982) 107. 4. S. N. Klyamkin, V.F. Demidov, V.N. Verbetsky, Rus. Vestn. MGU, ser. 2. Himia .34-4 (1993) 412-416. 5. O. Beeria, D. Cohena, Z. Gavraa, M.H. Mintza, J. Alloys Comp., 352 (2003) 111–122.

121

Magnetic and Electronic Properties of FeH Using Synchrotron Radiation Mössbauser Spectroscopy

Naohisa Hirao

Japan Synchrotron Radiation Research Center (Spring-8) hirao@spring8.or.jp

Dr. Hirao has been pursuing consistently the structural and magnetic transitions in FeH up to very high pressures ( ~ 100 GPa ), using high-quality synchrotron radiation beams at Spring-8. In this process, he has developed a novel technique, the synchrotron-radiation Mössbauser spectroscopy, a very effective method for investigating magnetic properties at high pressures. Thus, his work is opening a new era in the study of the Fe-H system.

122

Poster Presentations

123

An Investigation of Liquid Ammonia Electrolysis for Hydrogen Production

B-X.Dong1 and N.Hanada2, T.Ichikawa1, S.Hino1, H. Suzuki2, K.Takai2, Y.Kojima1

1Institute for Advanced Materials Research, Hiroshima University, Higashi Hiroshima, Hiroshima, Japan, 2Department of Mechanical Engineering, Sophia University, Tokyo, Japan

Email: tichi@hiroshima-u.ac.jp

Liquid ammonia (NH3) has a high hydrogen storage capacity of 17.8 mass% and it is easily liquefied by compression under 1.0 MPa at ambient temperature. Liquid ammonia is one of the most compact ways of storing hydrogen. In terms of volume needed to store 1 kg of hydrogen, it is better than almost all competing materials.1 Theoretically, ammonia electrolysis requires 95 % less energy than water electrolysis (1.55 Whg-1H2 versus 33 Whg-1). In addition, NH3 in large quantities has been circulated as agricultural chemicals. Therefore, electrolysis of NH3 to generate hydrogen is expected as the low-cost method for the transportation of hydrogen.

Botte et al.2 have built hydrogen generators using an ammonia alkaline solution electrolytic cell for the production of hydrogen, but their work negates the main advantage of ammonia, which is its high ‘hydrogen density’. In the present study, a liquid ammonia/metal amide electrolytic cell for the production of hydrogen is presented. A series of electrolyte substrate including LiNH2, NaNH2 and KNH2 were tested.

All the electrolysis experiments in this study were performed in a pre-designed platinum foil bi-electrode cell. The 1 M metal amide in liquid ammonia was assembled in an argon-filled glove box. Cyclic voltanmetry and potentialstatic/galvanostatic electrolysis were performed for the electrochemical studies.

In the gas after electrolysis of 1 M metal amide/liquid ammonia solution, hydrogen and nitrogen were successfully detected by gas chromatography. Furthermore, we investigated the efficiency with different electrolyte materials and concentrations. It was found that KNH2 electrolyte facilitates the genration of larger amount of hydrogen than other electrolytes, which may be attributed to the better solubility of it in liquid ammonia. 5M KNH2/liquid ammonia solution generates larger amount of hydrogen than that in 1M KNH2/liquid ammonia. Acknowledgement

This work has been partially supported by NEDO under “Advanced Fundamental Research Project on Hydrogen Storage Materials”. References 1. J. Larminie, A. Dicks, Fuel Cell Systems Explained, Second Edition, John Wiley &

Sons, Chichester, England, 2003. 2. F. Vitse, M. Cooper, G. G. Botte, J. Power Sources, 142, (2005), 18-26.

124

Reactivity of TiH2 with Lithium Ion: New Conversion Mécanism.

1Y. Oumellal, 1W. Zaïdi, 1A. Rougier, 2J. Zhang, 2F. Cuevas, 2M.Latroche, 3J-L Bobet. and 1*L. Aymard

1 : LRCS, UMR CNRS 6007, 100 rue Saint leu Amiens, France 2 : ICMPE, CNRS UMR 7182 2-8 rue Henri Dunant, 94320 Thiais, France. 3 : ICMCB-CNRS UPR 9048, 33608 Pessac France * corresponding author Email: luc.aymard@u-picardie.fr

Recently, the use of metal hydrides (MHx) as negative electrode for Li-

ion technologies has been demonstrated as a promising route for energy storage. Hydrides with high gravimetric/volumetric capacities, suitable voltage (<1V vs. Li+/Li°) and the lowest polarization ever reported for conversion electrodes offer a good opportunity to enhance the efficiency of electrochemical materials.

Starting from the very interesting results obtained for the MgH2 hydride

(reversible capacity of 1480 mAh/g, four times that of conventional Li/C electrodes at an average voltage of 0.5 V vs. Li+/Li°), the conversion reaction theoretically predicted from thermodynamic approach has been experimentally extented to other metallic hydrides: TiH2, NaH, TiNiH, LaNi4.25Mn0.75H5 and Mg2NiH3.7.

The electrochemical discharge reaction results in the formation of a composite containing a metallic compound M embedded in a LiH matrix, which converts back to the hydride MHx on charging. The general mechanism for the reaction is:

MHx + x Li+ + x e- ↔ M + x LiH. Surprisingly, this reaction path is not unique and a new conversion

mecanism is observed for the TiH2 hydride. It involves the formation of TiH2-x fcc solid solution in equilibrium with distorded fcc metastable phases down to approximately x=1. Below this value, the expected conversion process is observed: TiH + Li+ + e- ↔ Ti + LiH. Therefore, the reaction path of TiH2 with lithium ion adresses a new light on the hydride dehydrogenation process. The reversibility of the electrochemical reaction is obtained starting from an intimate composite mixture of 2LiH+Ti prepared by mechano-chemistry from TiH2 and Li powders as : TiH2 + Li → 2LiH + Ti.

Equally promising, the electrochemical reactivity of the titanium hydride with lithium ion is shown as a novel route for the production of nano metals and hydrides usefull for hydrogen storage applications at low temperature. Downsized Ti particles produced by such electrochemical reaction absorb readily hydrogen at 200°C. References 1. Y. Oumellal, A. Rougier, G.A. Nazri, J-M. Tarascon and L. Aymard, Nature materials 7 ( 2008) 916. 2. Y. Oumellal, A. Rougier, J-M. Tarascon and L. Aymard, Journal of Power Sources 192 (2009)698

125

Industrial Production of MgH2 and its Application

H.Uesugi*, T.Sugiyama*, H.Nii*, T.Ito*, and I. Nakatsugawa** *BIOCOKE Lab. Ltd, Japan, **Fuji Kogyo Co. Ltd, Japan

Email: uesugi-h@biocokelab.com Base metal hydrides such as MgH2 and AlH3 possess high H content that can meet the target for FCV application requested by governmental agencies. The advantage as rich in resorce, non-toxic and less expensive are also promising for mass storage of electricity generated by renewable energy. While direct hydrogenation is practically impossble in case of Al, Mg can absorb hydrogen under moderate conditions that is suitable for mass production. However, these base metal hydride cannot desorb hydrogen at the working condition of PEFC. The need of activation process for obtaining fully hydrided MgH2 is another obstacle for utilization. The authors have developed a process for producing MgH2 based on thermodynamic equilibrium technique [1]. The main advantage of this technique is upscaleable to industrial levels keeping high hydrogenation yield. In this paper, the process stability operated at 50kg batch process and the performance of obtained MgH2 compared to commercial reagents are demonstrated. To solve the problem of poor kinetics of MgH2 in hydrogen desorption, hydrolysis process is employed, which can release hydrogen up to 15.2 mass% below 100 deg.C. Several application examples as cartridge-type hydrogen reactors combined with PEFC for portable power generators and personal vehicles are presented. References

1. H. Uesugi, T. Sugiyama, I. Nakatsugawa, and T. Ito, To be presented at 67th Annual World Magnesium Conference, International Magnesium Association, Hong Kong (2010).

126

Hydrogen as Promoter and Inhibitor of Superionicity in Li-N-H Systems

A. Blomqvist1, C. Moysés Araújo1,2, Ralph H. Scheicher1, P. Srepusharawoot1,3, Wen Li4, Ping Chen5 and Rajeev Ahuja1,6

1Condensed Matter Theory Group, Division of Materials Theory, Department of Physics and Astronomy, Box 516, Uppsala University, S-751 20 Uppsala, Sweden

2Department of Theoretical Chemistry, School of Biotechnology, Royal Institute of Technology, S-106 91 Stockholm, Sweden

3Department of Physics, Faculty of Science, Khon Kaen University, 40002, Khon Kaen, Thailand 4Department of Physics, National University of Singapore, 117542, Singapore

5Dalian Institute of Chemical Physics, Dalian 116023, People's Republic of China 6Applied Materials Physics, Department of Materials and Engineering, Royal Institute of Technology

(KTH), S-100 44 Stockholm, Sweden Email: Rajeev.Ahuja@fysik.uu.se

Solid-state systems possessing a high mobility of lithium ions are of tremendous interest for battery and fuel cell applications. As a consequence, the research into new materials with high lithium ion conductivity forms a very active field. Lithium nitride (Li3N) is one such material in which lithium ions are known to be highly mobile. Hydrogenation of this system leads to the formation of lithium imide (Li2NH) and subsequently of lithium amide (LiNH2), a process that has been proposed for its merits in the field of hydrogen storage [1]. In this work, we have employed extensive ab initio molecular dynamics simulations to carry out a comparative study of the Li-diffusion in these three systems. As the main result, we show that the step-wise addition of hydrogen to Li3N can act both as a promoter and inhibitor of the superionic state [2,3], and propose a simple model to explain these surprising findings. Specifically, in Li2NH, we find that the partially positively charged hydrogen atoms of the rotationally disordered NH units enhance the mobility of the Li+ ions, while in contrast to that, the NH2 units in LiNH2 are found to be unable to rotate in the same manner and ultimately cause a hindrance for the Li mobility instead.Furthermore, we show that the creation of cation vacancies has a strong effect on the Li diffusion in Li3N, while the corresponding effects in Li2NH are found to be negligible. Thus, as the hydrogen content is raised, the rate limiting factor for Li diffusion shifts from the creation of vacancies to rotation of NH units. Li-N-H systems have lately received most of the attention due to their role as promising hydrogen storage materials; our results show that the possible technological applications of Li2NH may also be broadenedtowards batteries and fuel cells. References 1. P. Chen, Z. Xiong, J. Luo, J. Lin, and K. L. Tan, Nature 420 (2002), 302. 2. C. Moysés Araújo, A. Blomqvist, Ralph H. Scheicher, P. Chen, and R. Ahuja, Phys. Rev. B 79 (2009), 172101. 3. Andreas Blomqvist, C. Moysés Araújo, Ralph H. Scheicher, Pornjuk Srepusharawoot, Wen Li, Ping Chen, and Rajeev Ahuja, Phys. Rev. B (submitted).

127

Pd-alloy Based thin Films for Hydrogen Sensing and Purification Applications

M. Slaman1, J. van Leeuwen1, L.P.A. Mooij2, R. Westerwaal3, H. Schreuders2, B. Dam2

1 Condensed matter physics, VU University, Amsterdam, the Netherlands, 2 Materials for Energy conversion and storage, ChemE, TUDelft, Delft, the Netherlands 3 Hydrogen and clean fossil fuels, ECN, Petten, the

Netherlands; Email: slaman@few.vu.nl

Thin film based metal-hydride applications such as a quantitative hydrogen sensor or a low-temperature membrane for hydrogen seperation are currently based on Pd. The main reasons for using Pd are its capacity to catalyze hydrogen molecules at lower temperatures as compared to other metals and its high permeance for hydrogen. At room temperature Pd undergoes a sudden transition to PdH0.6 at hydrogen pressures above 20 mbar. This sudden transition causes stress and crack formation in thin films, leading to delamination from the substrate, pinholes, inactivity and an irreproducible response on hydrogen pressure. The transition to the Pd-hydride phase includes also a big hysteresis in the hydrogenation pressure. This makes Pd unsuitable for quantitative hydrogen sensing. Our research is focused on alloying Pd with other metals, such that both the first order phase transition and the hysteresis of the Pd isotherm disappear. By using Hydrogenography1 as a fast scanning tool, we were able to map the the doping behaviour of several metals in Pd. Alloying i.e. with Mo will strongly shift the plateau pressure to higher values which avoids the phase transition to occur at a relativly low pressure. This effect is desired for aplications such as seperation membranes. For hydrogen sensors it is desired to have a larger response upon hydrogen loading. Generally, this implies a higher change in the hydrogen content of the thin film. This effect can be created by using Mg as dopant instead of Mo. Mg doping results in a hydrogenation behaviour characterized by a small hysteresis and a sloped isotherm at room temperature. Such a unique optical response on hydrogen makes it an ideal material for hydrogen sensing.

Fig. 1 The effect of dopants on the isotherm of Pd: (A) dopant is Mo, (B) dopant is Mg.

References 1. R. Gremaud, M. Gonzalez-Silveira, Y. Pivak, S. de Man, M. Slaman, H. Schreuders, B. Dam, R. Griessen, Hydrogenography of PdHx thin films: Influence of H-induced stress relaxation processes, Acta Materialia, Volume 57, Issue 4, Pages 1209-1219

128

Hydrogen Absorption and Desorption Characteristics of High Coercivity NdDyFeCoNbCuB Sintered Magnet: Low Temperature Hydrogen Decrepitation Treatments

J.J. Luo1,2, P. de Rango2,3, D. Fruchart2,3, J.N. Mei1,3, L. Zhou1

1 State Key Laboratory of Solidification Processing, Northwestern Polytechnic University, Xi’an, 710072, P.R. China

2 Groupe IICE, Institut Néel, CNRS, 38042 Grenoble Cedex 9, France 3 Consortium de Recherche pour l’Emergence de Technologies Avancées,

38042 Grenoble Cedex 9, France Hydrogen absorption/adsorption properties of high coercivity NdDyFeCoNbCuB sintered magnets were determined. By differential scanning calorimetry (DSC), hydrogenation kinetics analysis was analysed, using parallel systematic XRD experiments. Hydrogenation of Nd-rich intergranular phase results in a rather broad and large peak at ~ 100 ± 50°C, then the tetragonal main phase (Φ phase) reacts readily close to 195°C. The disproportionation process of the whole magnet initiates at T ~ 500°C, then accelerates in the vicinity of 600°C and finally ends at T ~ 780°C. Furthermore, the first step hydrogenation reaction that monitors the hydrogen diffusion in the bulk via the intergranular Nd-rich phase was seen to operate quite differently depending on the heating rate, or the applied plateau temperature. If hydrogen absorption at 50°C reveals rather slow, it achieves in higher hydrogen uptake than at 150°C, if there it happens much faster. Three modes of hydrogenation process of sintered magnets are discussed in terms of practical operability. Using the optimized Hydrogen Decrepitation/Desorption Annealing route leads demonstrating that the anisotropic NdDyFeCoNbCuB powders obtained by HD/D technique have recovered most of the magnetic performance initially stored in the bulk magnets.

129

Transparent Yttrium Hydride thin Films Prepared by Reactive Sputtering

T. Mongstad1,2, C. Platzer-Björkman1,3, S. Karazhanov1, A. Thøgersen1, A. Holt1, J. P. Maehlen1 and B. C. Hauback1,2

1 Insitute for Energy Technology, Kjeller, Norway 2 University of Oslo, Oslo, Norway

3 Uppsala University, Uppsala, Sweden Email: trygve.mongstad@ife.no

Metal hydrides have been suggested for utilization in semiconductor electronics, specifically for solar cells [1]. We have prepared thin films of yttrium hydrides at high deposition rates by reactive pulsed DC magnetron sputtering. The resulting films are metallic for low partial pressure of hydrogen during the deposition, and black or yellow-transparent for higher H partial pressure. We here show that both metallic and insulating YHx can be prepared in-situ by reactive sputtering. The samples was after preparation kept in air and did not show visible degradation even after several weeks. Our work is motivated by the possibility of using yttrium hydride as a part of an advanced solar cell structure. Yttrium hydride films are observed to go through an optical transition when going from the metallic β-phase (YH2+x) to the transparent, insulating large bandgap semiconductor γ-phase (YH3-δ). Studies suggest that γ-phase yttrium hydride has an indirect band gap of 2.63 eV [2], corresponding to a photon wavelength of 389 nm. Earlier, yttrium hydride was prepared by hydrogenation of yttrium metal in a slow process that could take several days. Capping yttrium films with a thin palladium film shortened the process time dramatically [3]. However, a palladium cap layer is not always desirable, as the layer is light absorbing and palladium is a rare and expensive element, and post hydrogenation introduces strain due to the volume expansion when going from metal to hydride phases. Pulsed laser deposition (PLD) was earlier proposed as a method for in-situ deposition of yttrium hydride, and deposition of metallic yttrium dihydride films has been reported [4]. We have done ex-situ characterization of the electrical, optical and structural properties of our samples. Optical transmission and reflection measurements suggest an indirect band gap of around 2.5 eV for the transparent films. To our knowledge, we are by this the first to report direct in-situ deposition of transparent yttrium hydride films. We acknowledge funding from the Norwegian Research Council through the NANOMAT program. References 1. S. Karazhanov et al., Philosophical Magazine, 88, (2008), 2461 2. A. T. M. van Gogh et al., Physical Review B, 63, (2001), 195105 3. J. N. Huiberts et al., J. Alloys and Compounds, 239, (1996), 158-171 4. B. Dam et al., J. Alloys and Compouds, 356-357, (2003), 526-529

130

Effect of Annealing on Hydrogen Permeability and Microstructure of Melt Spun Amorphous and Crystalline Nb-TiNi Alloys

K. Ishikawa1, Y. Seki2, K. Kita3 and K. Aoki1

1 Dept. of Materials Science and Engineering, Kitami Institute of Technology, Kitami, Hokkaido, Japan 2 Graduate Student of Kitami Institute of Technology, Kitami, Hokkaido, Japan

3 Central Research Institute, Mitsubishi Materials Corporation, Kitamoto, Saitama, Japan Email: ishikazu@mail.kitami-it.ac.jp

Pd and its alloys are used for separation and purification of hydrogen gas. Since Pd is too expensive and scare in resources, alternative metallic membrane is strongly desired. Recently, our research group has found that Nb-TiNi alloys consisting of the bcc-(Nb, Ti) solid solution and the B2-TiNi compound show high hydrogen permeability (Φ) and large resistance to hydrogen embrittlement1. Since hydrogen flux J permeating through the alloy membrane is in proportion to a reciprocal thickness of it, fabrication of thin alloy membrane is quite important for effective hydrogen purification. Thin alloy ribbons can be directly obtained from molten metals using a melt spinning technique, which is employed for preparation of thin Nb-TiNi alloy membrane in the present study. The as-spun Nb20Ti40Ni40 alloy (mol%) shows a single-phase amorphous structure, and its Φ is slightly lower than that of pure Pd at 673 K. In addition, it shows bending ductility and resistance to hydrogen embrittlement. Granular bcc-(Nb, Ti) phase is formed embedded in the B2-TiNi matrix by crystallization. The crystallized alloy also shows large resistance to hydrogen embrittlement, although Φ is slightly reduced. The value of Φ for the crystallized alloy increases with increasing Nb content in the alloy. We can conclude that a melt spinning technique is possible way for production of Nb-TiNi hydrogen permeation alloy membrane. References 1. K. Hashi, K. Ishikawa, T. Matsuda, K. Aoki, J. Alloys Compd., 368 (2004), 215-220.

131

HYDROGEN PENETRATION THROUGH PALLADIUM MEMBRANES FROM THE FLAME OF HYDROCARBON

MATERIALS

G.P. Glazunov Institute of Plasma physics of the National science center “Kharkov institute of physics and technology”

Kharkov 61108, Ukraine, glazunov@ipp.kharkov.ua

The process was investigated of hydrogen permeation through diffusion-catalytic membranes from the flame during combustion of different hydrocarbon materials: alcohol, benzene, gas. The diffusion-catalytic membrane was a palladium pipe of the 0,25 mm thickness, which was hermetically brazed at one end and the another one was connected to vacuum chamber for hydrogen flow measurements or its accumulation. The membrane was placed in a flame and it was heated up to 300-700ºС temperatures (in dependence on a zone in a flameв or on the flame intensity). Note, that the possibility of essential hydrogen flow generation and permeation from the flame of combustion of hydrocarbons is not so evident fact. Really, hydrogen in flame can be consumed, to combine with carbon, etc. The measurement of hydrogen flow through membrane and calculation of a specific flow was carried out with the method of constant pressure, similar as described in the work [1]. With membrane temperature increase the hydrogen pressure p in the vacuum chamber also increases. When the pressure value is steadied on the stationary (highest possible) level, it was measured. Considering this pressure and pumping speed of hydrogen S (1 л/с), it is possible to calculate specific hydrogen flow q through membrane due to equation q = (p-р0)·S/F, where F is the effective area of the membrane surface, (~12 cm2), p0 is the initial pressure in the vacuum chamber. It was shown that at the temperature of 700ºC hydrogen specific flow q from the flame through membrane is about 0,08 Nсм3/c.см2. The total hydrogen flow Q was about 1 Nсм3 Н2/с (0,036 g. Н2/h). For all kinds of hydrocarbons hydrogen flow through membrane was practically the same and it was essentially higher than during the alcohol dehydration in the work [1]. Besides, as carbon combines with oxygen during the combustion process forming CO2, it is not deposited on the membrane surface and, as the result, the degradation of membrane permeation properties is not observed. A purity of hydrogen w2as estimated with help of mass-spectrometer and was better that 99,9999% vol. Note, that when nickel membranes were used instead of palladium, hydrogen flows decreased in one order of value. The analysis was carried out of the physical-chemical processes of hydrogen generation and permeation from a flame of hydrocarbon combustion and the possible variants of their practical applications are discussed.

G.P.Glazunov, E.D.Volkov, D.I.Baron. Study of low hydrogen flows into high-vacuum

systems // Int. J. Hydrogen Energy. 1999. V. 24. P. 829-831.

132

Hydrogen Production by Alkaline Electrolysis: Surface Investigations of Materials for Membranes

V.P. Zakaznova-Herzog and A. Züttel Empa Materials Science and Technology, Dept. Energy, Environment & Mobility, Sec. Hydrogen & Energy,

CH-8600 Dübendorf, Switzerland Email: valentina.herzog@empa.ch Development of the efficient hydrogen production is a high priority task for the growth of the energy sustainable society. The classical and environmentally clean production method of hydrogen is the electrolysis of water; however, it requires high energy costs (Barbaro et al., 2009). High pressure alkaline electrolyser’s are currently the most efficient and the most established type of the electrolysis. One of the main components of an electrolyser is the membrane between cathode and anode separating hydrogen and oxygen gases; it effects strongly energy consumption of an electrolyser and gasses purity. Traditionally used membranes are made from asbestos (chrysotile mineral (Mg3Si2O5(OH)4), which are not only prohibited by recent health regulations, but also require high energy consumption. Therefore, the development of membranes with high ion conductivity and low gas diffusion is required. High ionic conductivity in asbestos membranes is mainly achieved through its excellent wettability (presence of OH group), the effects related to the fibrous structure and the specific porosity. The aforementioned properties most probably with the interplay of surface processes influence the ion conductivity. Inorganic membranes with porous structure can be synthesized from various Mg-silicate minerals (i.g., olivine, Mg2SiO4). Because of their proven high resistance to alkaline high temperature and pressure solutions and low costs, they are perfect candidates to be starting material for an alkaline electrolyser. Thus, the first research direction in the search of new materials is the validation their potential to have high ion conductivity, high wettability and, therefore, the investigation of surface and reaction mechanisms of asbestos and other silicate minerals in aggressive media by means of X-ray Photoelectron Spectroscopy. XPS is one useful technique for probing chemical states at fresh and reacted surfaces, from which insight into surface reaction mechanisms may be gained. In the present study, we collected XPS spectra of pristine and exposed asbestos diaphragm and of pristine and exposed olivine to 25 wt. % KOH solutions at ambient conditions. The survey XPS spectra reveal strong changes in surface composition due to the reaction with KOH. There is a preferential dissolution of siliceous component in asbestos membrane; however, there is no detectable difference between new and used high resolution oxygen spectra (O 1s) obtained from asbestos diaphragm. The changes in oxygen chemical state on the surface of olivine can be clearly detected from high resolution O 1s spectra and show an additional contribution (up to 10%). The position and the line width of the additional oxygen contribution is similar to observed previously OH- species (Zakaznova-Herzog et al., 2008) and is in the same position as the oxygen peaks in asbestos. These data, combined with impedance measurements and tests in the electrolysis cell, will allow the evaluation of new possibilities materials for new diaphragms. References 1. Catalysis for sustainable energy production / ed. by Pierluigi Barbaro et al. (2009) Weinheim: WILEY-VCH. 2. Zakaznova-Herzog V.P., H.W. Nesbitt, G.M. Bancroft and J.S. Tse. (2008) Geochim. Cosmochim. Acta 72 69-86

133

Electrochemical Study of Porous Diaphragms used in Alkaline Electrolysers for Hydrogen Production

`J. Stojadinović1, V. Zakaznova-Herzog1, M. Gorbar1, D. Wiedenmann1,2, U. F. Vogt1,

B. Grobety2, A. Züttel1 1EMPA, Swiss Federal Laboratories for Materials Testing and Research, Dübendorf, Switzerland

2University of Fribourg, Dept. of Geosciences, Switzerland Email: jelena.stojadinovic@empa.ch

Electrolytic hydrogen production regained attention nowadays in the global search

for energy alternatives. The efficiency of alkaline electrolysis is highly influenced by the properties of the diaphragm separating hydrogen and oxygen gases. The diaphragms should provide high ionic conductivity, gas tightness and long term stability in KOH environment. Traditionally used asbestos diaphragms fulfil these requirements thanks to their hydrophilicity, fibrous structure and specific porosity. Nevertheless, asbestos made diaphragms are undesired because of health hazards. Therefore, different porous materials are being developed to replace asbestos. [1] [2]

The aim of this work is to investigate the electrochemical properties of diaphragms made of different porous materials. The effect of pore size distribution and solution intake of the diaphragm on the electrochemical impedance response is of particular interest.

Electrochemical Impedance Spectroscopy (EIS) was used to gain better understanding of the ionic transport in the system diaphragm/electrolyte. Measurements were performed in 25% wt. KOH solution at ambient temperature, by sweeping frequencies from 100 KHz to 10 mHz (Zahner IM6eX potentiostat) at the open circuit potential and under the applied anodic potential. EIS Spectrum Analyser software served for fitting the measured data. [3] Cathode and anode were made of nickel, while asbestos, zirconium dioxide and porous glass served as diaphragms. Zirconium dioxide diaphragms were produced using a pressure of 20 and 50 KPa, which resulted in different pores size distributions. Standard glass diaphragms of three pore sizes (1÷1.6 μm, 10÷16 μm and 100÷160 μm) were used for comparative purposes. The asbestos porous structure was determined by means of scanning electron microscopy and multi-scale tomography.

EIS response is affected by the pore’s size distribution and soaking duration of diaphragms in KOH prior to measurement. The oxidation state of the Ni electrodes, which results from the electrode potential, is significantly affecting the measured data. Equivalent circuits for all investigated diaphragms include similar contributions from the electrolyte resistance and double layer capacitance with additional elements attributed to the effect of porous structure and physico-chemical properties of a material i.e. hydrophilicity.

References 1.Ph. Vermeiren, R. Leysen, H. Beckers, J. P. Moreels, A. Claes, J. Porous Mater. 15 (2008) pp. 259 2.V. Zakaznova-Herzog et al., 4th International Symposium Hydrogen & Energy, Switzerland, 2010, pp. 60 3.A. Bondarenko, G. Ragoisha, EIS Spectrum Analyser, Copyright (2001-2008)

134

Stucture, Morphology and Hydrogen Penetrability of Vacuum Capacitors Pd-Y Formed on Porous Membrane Surface.

Ievlev V. М. 1, Maksimenko А.А.1, Belonogov Е. К. 2, Doncov. А.I. 2, Burkhanov G.С.3,

Roshan N.R.3 1 Voronezh state university,

2 Voronezh state techical university, 3 A.A. Baikov institute of metallurgy and Material Science,

The aim of this work was to etimate the possibility of composite membrane forming

for hydrodgen filtration of stated below structure: microporous foil – solid state Pd-Y vacuum capacitor.

The 6 mkm films was sputtered using magnetron deposition source with Pd - 8%ат.Y target in Ar enviroment (10-1 Pa) on substartes that was heated to 800K. Microporous iton tie foil and iron tie foil covered with TiO2

1 was used as a porous substrate. For comparasion purposes heterostructure SiO2/Si was used as reference substrate. Surface relief and morphology of obtained spicemens was studied with SEM, AFM and TEM.

Initial roughness of SiO2/Si and foils was 5 nm, 1.5 mkm and 0.5 mkm respectively. The roughness of 6 mkm film, condenced on SiO2/Si was 140 nm. The films formed on foils had about 210 nm of surface roughess. Thus, pore covering and rougness decreasing takes place. In the Pd-Yfilm formed on iron tie foil open-ended pores could be found.

The thikness difference of Pd-Y film on SiO2/Si and external layer on single and double-layered (6, 3.5 and 2 mkm respectively) could be connected with atom diffusion of condensate into the foil pores. The covering of pores on TiO2 covered foil occurs earily than on single-layered foil because of pores size, 0.5 and 2 mkm respectively. Therefore pores filling and saturation of foil surface layer with sputtering material occurs on several mkm. The modification of near-surface region took place and porous matrix of substrate have been saturated with sputtering material.

Obtained composites membranes (Pd-Y film/TiO2/iron tie foil with open-ended pores) during hydrodgen passing-through shows unsteadily increasing of H-penetrability

under heating in temeperature region 300-625K and eqals Рн=1,3 1,8·10-33

12 2

mm

sec Pa

cm

cm k

⋅

⋅ ⋅

in 300 and 600K points. This values conforms to Pd-Y foils obtained using milling. Hydrodgen penetrability measuring of Pd-Y films formed on SiO2/Si and separated

from substarte shows that hydrogenation process causes machanical stress and collapsing of films. This work based upon FTP «Science and educational personnel of innovation Russia» on 2009-2013 years (№02.740.11.0126,) and RFFI grant (08-08-00214 а).

1 Obtained in laboratory of L.I. Trusov

135

Influence of Temperature on the Processes of Hydrogen Mass Transfer in Pd-based Membrane Tubular Element

V. Baikov, V. Belitskii, S. Germanovich, N. Kolyago, T. Sidorovich, P. Znovets

Laboratory of Membrane Mass Transfer, A.V. Luikov Heat and Mass Transfer Institute, National Academy of Sciences of Belarus, Minsk, Belarus

Email: kolyago@hmti.ac.by Today the membrane technology for hydrogen separation from synthesis-gas is the most promising. Among the advantages of the membrane method are the ecological purity of the process, reliable operation, compactness, explosion- and fire-safety, flexible characteristics of separation and their smooth regulation, independence of operation, and the mobility of the process [1]. However, not only must one solve a number of technological and instrumental problems for the membrane processes of gas separation to be commercialized, but one must also create calculation methods for these processes. A mathematical model that describes the process of hydrogen separation from synthesis-gas in a tubular element on the basis of Pd-based membrane with account for convective external and intramembrane diffusion resistances, degree of hydrogen dissociation at adsorption on the surface of metal membrane has been developed. The procedure of calculation of the hydrogen permeation rate has been proposed with account for external diffusion convective and intramembrane diffusion resistances, degree of hydrogen dissociation, the physical properties of synthesis-gas, the physicochemical properties of membrane, the technological parameters of the process and the geometry and dimensions of the membrane element. The model has been verified. This mathematical model has proved efficient means of the theoretical calculations for membrane apparatus with palladium membrane The results obtained in the present work have proved the advantages of tubular element when they are applied as membrane elements, which favor the creation of compact and highly efficient apparatuses. In present work the influence of temperature on prosess of hydrogen separation from synthesis-gas is investigated. Temperature is the most important factor that determines the viscosity of gas, diffusion, hydrogen penetrability coefficient, and as a resalt, the hydrogen penetration rate through metal membrane. It has been corroborated that hydrogen penetrability coefficient is described by Arrhenius theory. The researches are carried out for Pd3.18/Ni96.82 membrane, Pd4.75/Ni95.25 membrane, Pd6.66/Ni93.34 membrane. The inconsistency of the temperature effect is observed. It has been established that the temperature rise increases convective external diffusion resistance. This is one of the reasons why degree cleanliness of retentate decreases and retentate requires afterpurification. Alternatively, the inverse effect is observed. Since the hydrogen penetrability coefficient dependences on temperature, the output of hydrogen increases. It should be borne in mind in research that the state of Pd-based membrane depends strongly on its mechanical, chemical, and thermal properties. Research has shown that membrane can be deformed by heat load for a long time. References 1. A. Bazile, F. Galluchchi, A. Yullianelli, Membranes, 34, (2007), 3 – 22.

136

Application of Pd-Based Membranes for Separation of Gas Mixtures in

Pure-Silicon Production Processes

G. Burkhanov1, N. Gorina1, K. Leshchinskaya1, N. Roshan1, D. Slovetskii2, E. Chistov2 1Baikov Institute of Metallurgy and Materials Science, Russian Academy of Sciences, Moscow, Russia

2Topchev Institute of Petrochemical Synthesis, Russian Academy of Sciences Moscow, Russia Email: genburkh@imet.ac.ru

Solar power engineering (photovoltaics) is the promising agile world industry.

Almost 90% of all solar cells produced in the world are based on pure silicon, which also is the principal material for the modern microelectronics. The development of production technology of pure silicon calls for desiging effective methods for the separation of hydrogen from silicon- and hydrocarbon-containing co-products in the silicon industry (waste mixtures). Methods, in which Pd-based separating membranes are used, are the most effective for this purpose. Highly effective membranes must exhibit a set of properties; these are the sufficient strength, low dilatation in hydrogen, high hydrogen permeability and corrosion resistance for components of waste mixtures for silicon productions. In [1], we chose the Pd-6 wt % Ru. In the present study, we prepared vacuum-tight Pd-6 wt % Ru foils and studied their properties, such as strength, dilatation, hydrogen permeability and corrosion resistance at different contents of initial products (silicon tetrachloride, chlorosilane, methyl silane). We determined ranges of operating temperatures and pressures, at which no decomposition of initial products occurs. This allows us to separate hydrogen excess and 8AGYQ-YGKCA-TDCEE-5P34Creturn unreacted reagents to the production process, and, thus, to realized a close resources-economy and wasteless technological process for the production of pure silicon. References 1. G. Burkhanov, N. Korenovskii, N. Klueva, A. Gusev, R. Kornev, Perspectivnye materialy, No. 3, (2007), 62-67.

137

Hydrogen Solubility and Permeability of Nb-W-Mo Alloy Membrane

Y. Awakura1, H. Yukawa1, T. Nambu2, M. Matsumoto3 and M.Morinaga1 1Department of Materials Science and Engineering, School of Engineering, Nagoya University, Japan

2Department of Materials Science and Engineering, Suzuka National College of Technology, Japan 3Department of Mechanical Engineering, Oita National College of Technology, Japan

Email: awakura@silky.numse.nagoya-u.ac.jp Recently, Nb-5mol%W alloy have been designed and developed which possess high hydrogen permeability without showing hydrogen embrittlement when used under appropriate permeation conditions [1]. However, the resistance to hydrogen embrittlement of this alloy is still not enough especially at high hydrogen pressures. For the practical application of Nb-based alloys for hydrogen permeable membrane, it is necessary to improve further the resistance to hydrogen embrittlement at high pressures In this study, the alloying effects of molybdenum into Nb-W alloy on the hydrogen solubility, the resistance to hydrogen embrittlement and the hydrogen permeability are investigated in a fundamental manner. Nb-5mol%W-5mol%Mo alloy is arc melted in a purified argon atmosphere. Pressure-composition-isotherm (PCT) measurements are conducted at 673~773K in order to examine the hydrogen solubility. Hydrogen embrittlement is examined at 773K by using in-situ small punch (SP) test apparatus [2]. In addition, the hydrogen flux, J, through the alloy membranes are measured by the conventional gas permeation method at 773K. It is found that the hydrogen solubility decreases by the addition of molybdenum into Nb-W alloy. As a result, the resistance to hydrogen embrittlement improves at high pressures. The normalized hydrogen flux, J·d, of Nb-5mol%W-5mol%Mo alloy measured at 773K is shown in Fig.1 together with the results for Pd-26mol%Ag alloy. The inlet and outlet hydrogen pressures are denoted in the figure as (inlet/outlet MPa). It is evident that Nb-based alloy possesses more than 5 times higher hydrogen permeability than currently used Pd-based alloy without showing any hydrogen embrittlement. References 1. H.Yukawa, T.Nambu, Y.Matsumoto, N.Watanabe. G.X.Zhang and M.Morinaga, Mater. Trans., 49 (2008) 2202. 2. Y.Matsumoto, H.Yukawa and T.Nambu, Proc. 1st Int’l. Conf. on Small Sample Test Techniques (SSTT), 31 Aug.~2 Sep. 2010, Ostrava, Czech Republic, to be published.

138

Composite Hydrogen Permeable Membranes of TixNiy Alloys M.Ermilova, V.Mordovin, N.Orekhova and G.Tereshchenko A.V.Topchiev Istitute of Petrochemical Synthesis RAS, Moscow, Russia

E-mail: ermilova@ips.ac.ru

The rapid development of hydrogen energy requires the creation of effective plants for separation of hydrogen of high purity (> 99,999 %) from technological gases of chemical and petroleum refining manufactures. Palladium-based alloys have high permeability for hydrogen, sufficient hydrogen resistance at cyclic changes of temperature and high technological flexibility [1]. However, the industrial application of these alloys demands the high capital expenses. Therefore many efforts of researchers are directed on development more economically competitive membranes without palladium. Equiatomic alloy of the titan and nickel has practically absolute selectivity to hydrogen, high thermal and chemical stability, however the hydrogen productivity of the membranes of this alloy inferior considerably to palladium alloy membranes. It was reported the high hydrogen permeability of TiNi3 intermetallics [2], however the method of TiNi3 foil preparation is complex and time-consuming, because of its hardness and fragility.

The present work is devoted to development and investigation of composite membranes from intermetallics of general formula TixNiy. TixNiy composite membranes were prepared by magnetron sputtering of alloy film of 5 microns thickness on a porous stainless steel support from specially prepared target of Ti20Ni80 alloy. The target ingots were made from 99.9% pure Ti and Ni by arc melting in argon. Each alloy button was remelted at least 5 times to ensure the compositional homogeneity. The X-ray analysis of deposit structure has shown to have the following distribution of phases: TiNi3: Ti2Ni: TiNi2: TiNi = 1:1:0.9:1.5. The SEM pictures of composite membrane and its profile show the dense and homogeneous film of TixNiy alloys solid solution, which is confirmed by EMS spectra.

The measurement of hydrogen permeability TixNiy composite membrane in an interval from 330 up to 700 K has shown that its Arrenius pattern has three rectilinear parts. Each of these parts corresponds, apparently, to different hydride phases of TixNiy, the ratio between which being changed with temperature. Really, after processing of membrane by hydrogen at temperatures from 330 up to 700 K phases ratios change on: TiNi3: Ti2Ni: TiNi2: TiNi = 0 : 1 : 1.6 :4.2. The value of permeability coefficient of this composite membrane is higher than the permeability coefficient of foil of equiatomic Ti-Ni alloy, but is lower than that of TiPd (95) alloy. Thus, hydrogen permeability at 700K for TixNiy composite membrane was 1,7.10-5 cm/s bar1/2, that is two decimal order higher than that of TiNi foil, but 5 times lower than hydrogen permeability of Ti(5%)Pd foil. With regard to the high selectivity on hydrogen (FH2 /He >1000 ), the proposed composite membranes are promising for application in devices of hydrogen separation and in catalytic reactors. References 1. Gryaznov V.M., Ermilova M.M., Orekhova N.V., Tereshchenko G.F. “ Reactor with

metal and metal-containing membranes ” Chapter 17 of book “ Structured catalysts and reactors ”, Marcel Dekker, N.Y., 2006, p. 579-614.

2. Linkohr R., Plust H.G. US Pat. 3957534, Diaphragm for the separation of hydrogen from hydrogen-containing gaseous mixtures, 1976.

139

Evaluation of Various Thin Films as a Hydrogen Permeation Barrier

Bojan Zajec, Vincenc Nemanič, Marko Žumer “Jozef Stefan” Institute, Jamova 39, Ljubljana, Slovenia

Email: bojan.zajec@ijs.si Gaseous hydrogen can easily move into and through materials, which causes problems in keeping hydrogen from materials that are sensitive to hydrogen-induced degradation. Currently there are two separate fields where suitable hydrogen barrier is being actively sought: One is a concern regarding hydrogen embrittlement of steel containers for storage of highly pressurized gaseous / liquid hydrogen. The other one comes from future fusion reactors (ITER), where the migration of radioactive tritium in and through the reactor wall would pose a serious threat to public health and to safety of fusion power plants. Our experimental evaluation is based on the all-metal UHV (ultra high vacuum) system that enables measurements of permeation flux as low as 4.1×1010 H2 molec. s-1 cm-2. This low detection limit is achieved with a special membrane holder that has very low hydrogen outgassing at elevated temperatures – due to low permeability most measurements were carried out at 400°C and ~1 bar driving pressure. The substrate for coatings was reduced-activation ferritic-martensitic steel EUROFER that exhibit high hydrogen permeability. We have investigated three different thin-film coatings: Be, TiAlN and Si oxide. Lowest permeation flux of 5×1010 H2 molec. s-1 cm-2 was measured for TiAlN film, while Be film manifested relatively low efficiency. This has been explained by the morphology (pinholes) of the film. Behaviour of the permeation flux versus time and temperature will be discussed and compared to other hydrogen barrier coatings.

140

Induced By Hydrogen Reversible and Unreversible Structural Changes

In Subsurface layers of Palladium and Its Alloys Of Hydrogen

M.Goltsova and G.Zhirov Physics & Metallurgy Department, Donetsk National Technical University, Donetsk, Ukraine

Email: goltsova@fem.dgtu.donetsk.ua There are fulfilled systematic investigations of structural changes in subsurface layers of pure Pd (99,98%) and its alloys. All the samples were in form of wire of 0.5 mm diameter and were preliminary polished. Then longitude metallographic cross sections were researched while hydrogenating under optical microscopy in situ technique. Registered video data were analysed with computer programmes. The following effects are fixed and will be represented and discussed in the report. Reversible stationary swelling. A sample under investigation was put into the working chamber of specially constructed hydrogen vacuum device. The working chamber was vacuumed and the sample was heated up to 350оС. Then the chamber was filled with hydrogen with a the rate 0,1-0,2 МPа/min up to 2,3 МPа. After 30 min exposition in conditions (350оС, 2,3 МPа) the sample was cooled in hydrogen. At cooling rate 3÷5оС/min a local swelling of subsurface layers of palladium was fixed. In isothermal conditions the swelling grew up, reached a maximum and then became less and disappeared. The effect is caused by influence of strong internal stresses generated in subsurface layers of Pd by hydrogen concentration gradients. Internal stresses in this case were not larger than Pd limit of elasticity and relax when hydrogen concentration gradients become smaller. Grain shifts. In this series of experiments pure Pd and PdHx alloys were intensively saturated with hydrogen at T=Const=350оС. There were fulfilled three seria of experiments. In the first series pure palladium undergone an intensive hydrogen saturation with various rate of hydrogenation. In the second one we used various differences of hydrogen pressure (ΔРн2) at the constant hydrogenation rate 1,0 МPа/s. In the third one we used to study intensive hydrogenation of not a pure palladium but α−PdHx .It was found that pure Pd has not change its subsurface layers when saturated with hydrogen intensively. But PdHx alloys have strong and irreversible grains shift even at small preliminary hydrogen contents (PdH0.019 - 0.038). Solitude waves (solitons) on palladium subsurface. At 230оС PdH0,1 alloy was intensively saturated with hydrogen. Firstly grain shifts and then solitude wave-like moving swellings (solitons) in subsurface layers were fixed. Video data demonstrating generation, moving and disappearance of the soliton is on http://donntu.edu.ua/hydrogen-community/soliton.zip. It will be also demonstrated and discussed in the report.

All the experimental results show an extremely important role of internal stresses generated in metal with hydrogen. We believe that soliton generation is a unique mechanism of internal stresses relaxation in Me-H alloys, and we’ll discuss this phenomenon in details in the report.

141

Equal Channel Angular Pressing (ECAP), a Severe Plastic Deformation (SPD) Technique to Promote Fast Hydrogen Absorption in Mg Alloys

G. Girard1, D. Fruchart1, S. Miraglia1, L. Ortega1, A. Prat1, N. Skryabina1,2

1 Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France 2 Department of Physics, Perm State University, 15 Bukireva, Perm, 614990, Russia

daniel.fruchart@grenoble.cnrs.fr Severe Plastic Deformation processes such as the well known Ball Milling (BM), and others like Equal Channel Angular Pressing (ECAP), Cold Rolling (CR), High Pressure Torsion (HPT), etc, reveal valuable tools to modify drastically the mechanical characteristics of alloys, more especially those exhibiting hydrogen absorption properties. Using a temperature controlled ECAP machine, equipped with force and deplacement sensors, very high levels of stresses, texturaturation and fine micro- to nanostructuration was achieved when processing different types of Mg-based alloys. Conventionnal XRD, X-ray texturation analysis, SEM, Vickers’ measurements, DSC experiments were used to analyze the effect os ECAP treatements. Then, several modes of SPD were applied to pure Mg, and two Mg-based alloys (AZ31 and ZK60), such as the number of passes, the mode of pass (so-called route A: anisotropic deformation; so-called route BC: isotropic deformation), the temperature of samples varying from RT to 300°C and for a constant channel angle of 105°. Marked texturation have been readily attained at temperatures as low as 225°C by using the so-called route A. The route BC leads to similar results at higher processing temperatures. Besides the grain refinement as been achieved at the size of 40 to 130 nm, depending on ECAP conditions (number of passes, temperature of ECAP, mode of pass – route A or route BC…). The route A leads to anisotropic distribution of stresses, contrarily to the route BC which delivers a very homogeneous level of stress. In both cases the size of crystallites finalizes to 1250 to 1500 nm. However, it was demonstrated that operating a lower temperature close to the ductile fragile transition of all considered alloys, leads to a similar level of constraints for a reduced number (2 to 3) ECAP passes. So, it is possible to operate much faster provides the ECAP temperature is correctly optimized. Such optimized temperature was determined from systematic micro-mechanics analyses techniques (Vickers). Using DSC analysis of the energy activation at recrystallisation, it is shown that a finest size of crystallite is gained when applying higher ECAP temperatures or better when applying the isotropic deformation route BC instead of the anisotropic route A. From present experiments enabling control of stress level and crystallite size by ECAP, extreme reduction of the size of crystallite appears not critical to promote excellent hydrogenation kinetics provides the temperature of processing leads to effective severe plastic deformation. The shape of the initial hydrogenation traces depend on the type of used ECAP route (A or BC) which evidence (or not) of a nucleation phenomenon. Besides, the maximum hydrogen uptake was found as high at the theoretical one of 7.6w%.

142

Mg-based Multilayers: Thermodynamic Effects at the Nanoscale

A.Baldi, V.Palmisano, L.P.A.Mooij, H.Schreuders, M.Slaman and B.Dam Department of Chemical Engineering, Delft University of Technology, Delft, The Netherlands

Email: A.Baldi@tudelft.nl By studying the hydrogen absorption in Mg-based multilayers, we demonstrate how the thermodynamics of nanosized metal hydrides is influenced by elastic and surface energy effects [1]. Mg films covered with miscible elements, such as Pd and Ni, have equilibrium pressures more than 2 orders of magnitude higher than bulk Mg (see figure below), thanks to the elastic clamping exerted by the cap layer [2]. On the contrary, Mg films sandwiched between immiscible elements have bulk-like quasifree behavior [3]. An elastic model allows us to reproduce the Mg thickness dependence of the equilibrium pressure for elastically constrained films. Surface energy contributions become relevant at very small Mg thicknesses (<10 nm). The clamping and surface energy effects can be exploited to develop advanced optical hydrogen sensors and 3D nanoparticles with optimized storage properties, for use in combination with PEM fuel cells. Loading isotherms (T = 333 K) of Pd-capped Mg films with varying thicknesses. A thinner Mg film feels a stronger elastic clamping and shows a higher equilibrium hydrogen pressure.

Loading isotherms (T = 333 K) of Pd-capped Mg films with varying thicknesses. A thinner

Mg film feels a stronger elastic clamping and shows a higher equilibrium hydrogen pressure.

References 1. A. Baldi, G.K. Pálsson, M. Gonzalez-Silveira, H. Schreuders, M. Slaman, J.H. Rector, G. Krishnan, B.J.Kooi, G.S.Walker, M.W.Fay, B. Hjörvarsson, R.J.Wijngaarden, B. Dam and R. Griessen, submitted (http://arxiv.org/abs/0911.5666) 2. A. Baldi, M. Gonzalez-Silveira, V. Palmisano, B. Dam and R. Griessen, Phys. Rev. Lett. 102, 226102 (2009)A. Baldi et al., Phys. Rev. Lett. 102, 226102 (2009). 3. A. Baldi, V. Palmisano, M. Gonzalez-Silveira, Y. Pivak, M. Slaman, H. Schreuders, B. Dam and R. Griessen, Appl. Phys. Lett. 95, 071903 (2009).

143

Hydrogen Effect on Dislocation Nucleation in Vanadium (100) Single Crystal Examined by Nanoindentation

E. Tal-Gutelmacher, R. Gemma, C.A. Volkert and R.Kirchheim

Institute for Materials Physics, Georg-August University of Goettingen, Goettingen, Germany Email: ervin@ump.gwdg.de

Hydrogen effect on dislocation nucleation in vanadium (V) single crystal with (100) orientation has been examined by means of nanoindentation. This technique coupled with atom-force microscopy offers several advantages for studying hydrogen-deformation interaction in materials [1-3]. In nanoindentation experiments the lateral dimensions of the volume of the deformed material are significantly smaller than the mean dislocation spacing in annealed metals. Consequently, plastic deformation in these ranges occurs via homogeneous formation of new dislocation loops. A sudden excursion, named as ‘pop-in’, occurs in the load-displacement curves at the onset of plasticity, which correlates to homogeneous dislocation nucleation. In this work, the effect of hydrogen on the load-displacement curves, and especially on the unstable elastic-plastic transition indicated by the pop-in behavior, was studied in detail. For hydrogen doped V-samples, charged step-by-step electrochemically to different hydrogen concentrations within the α-phase, pop-ins appeared at lower loads in comparison to annealed hydrogen-free samples. The load at which dislocations are nucleated decreased with the increase of hydrogen concentration and more than single pop-ins were observed in the load-displacement curves of hydrogenated samples. This is clear evidence that the homogenius nucleation of dislocation loops is enhanced in the presence of hydrogen. The interaction between the dissolved hydrogen atoms and the newly formed dislocation loops, resulting in the reduction of their line energy, is evaluated and explained based on the novel thermodynamic defactant concept [4, 5]. References

1. Y. Katz, N. Tymiak, W.W. Gerberich, Eng. Fract. Mech., 68, (2001), 619-646. 2. A. Barnoush, C. Bies, H. Vehoff, J. Mater. Res., 24, (2009), 1105-1113. 3. K.A. Nibur, D.F. Bahr, B.P. Somerday, Acta Mater., 54, (2006), 2677-2684. 4. R. Kirchheim, Int. J. Materials Research, 100, (2009), 483-487. 5. R. Kirchheim, Scripta Mater. 62, (2010), 67-70.

144

Coupling of Manometric and Calorimetric Measurements to Probe Unique Charaterisation of Solid Hydrogen Storage Systems.

Emmanuel Wirth1, Rémi André1, Andre Levchenko2, Karl Gross2, Chiara Milanese3, Pierre

Le Parlouër1

1 : Application Laboratory - SETARAM Instrumentation – 7, rue de l’Oratoire, 69300 Caluire, FRANCE 2 : Hy-Energy LLC/Setaram Inc. – 8340 Central Ave, Newark, CA 94560, U.S.A

3: H2 Lab, C.S.G.I. – Physical Chemistry Department, University of Pavia, Viale Taramelli 16, 27100 Pavia, ITALY.

Email: emmanuel.wirth@setaram.com

In the recent years, the solid hydrogen storage research has experienced a wide development and promising new materials candidates such as complex hydrides, high surface areas materials, and hybrid systems are now focusing a lot of interest. Concerning the fuel cells, a lot of research is carried out to replace the expensive Pd catalyst to foster a large development of the technology.

In parallel, the characterisation for both evaluating the hydrogen sorption properties and understanding of the mechanism of hydrogen-solid interaction requires accurate and reliable tools. Simultaneous analyses of different properties give invaluable information for the material scientist, especially when the repetition of experiments is challenging (small quantity of synthesised material, lack of reversibility, slow kinetics).

The thermodynamic and kinetics of the different candidate storage systems are key parameters for the practical application and among all the knowledge of the enthalpy of formation/dissociation of the hydrides is fundamental. Practically there are two ways to determine this enthalpy. The first one is an indirect method widely used in the literature, i.e. the van’t Hoff technique, where the hydrogenation/dehydrogenation enthalpy is derived from the mid-plateau pressure and the temperature of absorption/desorption isotherms. The second one is a direct method, where the enthalpy is measured via calorimetric technique. The biggest disadvantage of this technique is that it gives a result per mole of solid sample and not per mole of H2. Recently the combination of manometric technique (to quantify the amount of hydrogen absorbed/released) and calorimetry was successful to overcome this issue and the direct measurement of enthalpy of formation per mole of gas was reported [1]. This presentation will give an overview of the state-of-the art possibility of combined manometric – calorimetric analysis and an highlight on the new information that this combination permits to obtain. References 1. C. Milanese et al., IJHE, 35 ( 2010 ) 1285 – 1295.

145

System Analysis of Thermodynamic Characteristics of Complex Alumo- and Binary Hydrides of Alkaline Metals.

U.M.Mirsaidov, B.A.Gafurov, A.B.Badalov

Nuclear and Radiation Safety Agency of the Academy of Sciences of the Republic of Tajikistan.

E-mail: ulmas2005@mail.ru

The results of our work series on study of thermal stability, thermal decomposition property and thermodynamic characteristics of complex tetra-, hexahydridealuminates and binary hydrides. Investigations are carried out by tensimetric methods with membrane zero-manometer, calorimetry dissolution, Roentgen-phase and chemical analyses. Tensimetric investigation is carried out in equilibrium conditions during self-restraint time of figurative point on the curve of steam pressure dependence from barogram temperature during from 200 till 600 hours. It is determined that in 340-770K intervals, the thermal decomposition process of tetrahydroaluminates consist of three stages. The first stage corresponds to tetrahydroaluminates decomposition, second stage – hexahydridealuminates decomposition with lithium, sodium, potassium binary hydrides formation which is differing during the third stage. LiAlH4 decomposition, according to barogram property, is accompanied by formation of solid solutions. The equations of all barogram stages are determined and thermodynamic characteristics of hydride compounds decomposition process are determined. Obtained interconsistency values ofthermodynamic characteristics of hydride compounds by calorimetry and thensimetry methods allowed calculation of similar data for tetra-, hexahydroaluminates and binary hydrides of whole alkaline metals line

146

Separation Factor (H/D)Pd/(H/D)gas for the Pd-D-H System at High Pressure

M.A.Kuzovnikov,V.E.Antonov and M.Tkacz(1) Institute of Solid State Physics, Chernogolovka, Russia

(1) Institute of Physical Chemistry PAS, Warsaw, Poland Email: kuz@issp.ac.ru

If palladium metal is placed in an atmosphere of mixed hydrogen/deuterium gases, the equilibrium H/D ratios established in the metal and gas are different. The separation factor α=(H/D)Pd/(H/D)gas depends on the temperature and pressure and (H/D)gas, but no systematic studies of this dependence has been performed so far. The available estimates show [1] that the separation factor is ~2 for both the diluted solid solutions Pd-D-H with (D+H)/Pd«1 and non-stoichiometric hydrides Pd-D-H with (D+H)/Pd≈0.6, which are formed at low gas pressures. The present work is aimed at studying the separation factors of nearly stoichiometric hydrides with (D+H)/Pd≈1 prepared by exposing Pd powder to an atmosphere of gaseous deuterium/hydrogen mixtures at P=28 kbar and T=300°C. The samples were analyzed for total (H+D)/Pd content by hot extraction and for H/D ratio by mass-spectrometry of the evolved gas. The equilibrium, final concentrations of H and D in the gas mixtures reacted with Pd were calculated based on the material balance in the high-pressure cell.

0.0 0.2 0.4 0.6 0.8 1.00.0

0.2

0.4

0.6

0.8

1.0

α = 1

T = 300oCP = 28kbar

α = 8

α = 12

H/(H

+D),

Pd

H/(H+D), gas

α = 4

present paperref. [2]

PdHxD1-x

The results of these measurements are shown in the figure together with results for the samples used in ref. [2]. The large experimental inaccuracy in the D-rich domain was mostly due to the D↔H exchange inside the mass-spectrometers used. The curves plotted in the figure are calculated for four different values of the separation factor. The values of the separation factor resulting from our experiments significantly exceed those characteristic of the Pd-H-D system at low gas pressures. The effect is yet to be explained.

References 1. E. Wicke and H. Brodowsky, in: Hydrogen in Metals II, G. Alefeld and J. Völkl (eds.), Berlin: Springer (1978), 73-155. 2. V.E. Antonov, A.I. Davydov, V.K. Fedotov, A.S. Ivanov, A.I. Kolesnikov, M.A. Kuzovnikov, Phys.Rev.B, 80, (2009), 134302(1-7).

147

A Computational Study of Thermodynamic Properties of M-H-F Systems for Hydrogen Storage Applications

M.Corno, E. Pinatel, P. Ugliengo and M.Baricco

Dipartimento di Chimica I.F.M. and NIS Centre, University of Torino, Italy Email: marta.corno@unito.it

Ab-initio calculations together with thermodynamic modelling have been applied to M-H-F systems. This work is aimed at characterising thermodynamical properties of solid solutions between light-metal hydrides and fluorides as possible candidates for hydrogen storage applications. The ab-initio periodic CRYSTAL1 code was chosen and different functionals in the DFT framework were used, varying from pure GGA (PBE) to hybrid ones (B3LYP). The complete characterisation of pure and mixed compounds was carried out, from structural to vibrational properties. These computed values were contrasted with experimental data to assess the reliability of the model. A newly implemented algorithm in the CRYSTAL code was used to classify by symmetry all the possible mixed M-H-F configurations, allowing the gain of computational resources.2

Enthalpies of mixing derived from quantum-mechanical calculations were used to fit and integrate data extracted from well-known thermodynamical databases (such as JANAF3) within different models for solid solutions treatment in the CALPHAD scheme.4 Excess energy and full thermodynamic characterisation will demonstrate that this computational approach can be useful to predict the mixing of several compounds, ranging from Al and Mg hydrides to borohydrides (LiBH4, Ca(BH4)2 and others). In this presentation, the methodological aspects and the most relevant results will be discussed in details. This work is part of the European FP7 Project FLYHY “Fluorine Substituted High Capacity Hydrides for Hydrogen Storage at low Working Temperatures”.5 References 1. R. Dovesi, V. R. Saunders, C. Roetti, R. Orlando, C. M. Zicovich-Wilson, F. Pascale, B. Civalleri, K. Doll, N. M. Harrison, I. J.Bush, P. D’Arco, M. Llunell, CRYSTAL2006 User's Manual; www.crystal.unito.it, University of Torino: Torino, 2006. 2. A. Meyer, P. D'Arco, R. Orlando, C. M. Zicovich-Wilson, L. Maschio, R. Dovesi, J. Chem. Phys. (2010), submitted. 3. Chase, M. W., NIST-JANAF Thermochemical Tables. J. Phys. Chem. Ref. Data Monograph 9 4. L. Kaufman, CALPHAD-Computer Coupling of Phase Diagrams and Thermochemistry. Pergamon: Oxford, 1977. 5. www.flyhy.eu

148

In-Situ Diffraction Evidence for Eutectic Formation in the Mg(NH2)2/LiNH2 System

F.Dolci1, M. Baricco2, G. Vaughan3, S. Garroni4, M. Orlova3, D. Pottmaier2, M.Fichtner5,

P.Moretto1, W.Lohstroh5

1European Commission - JRC Institute for Energy, Petten, The Netherlands Email: francesco.dolci@ec.europa.eu

2 Dip. Chimica IFM and NIS, Università di Torino, Torino, Italy 3 ESRF, Grenoble, France

4 Universitat Autonoma de Barcelona, Barcelona, Spain 5 Karlsruhe Institute of Technology, Karlsruhe, Germany

Complex hydrides are of great interest for solid hydrogen storage as evidenced by the large number of experimental and theoretical works on this topic [1]. Recently the idea of mixing different complex hydrides together, or with light metal hydrides, has shown very promising results and opened new possibilities for the design of practical hydrogen storage materials useful for both stationary and automotive applications. Results obtained by following this approach are however different from the ones expected on the basis of a simple thermodynamic modelling of the system. The main difference between the expected simple reaction pathway and the actual one is the occurrence of a multistep hydrogenation/dehydrogenation reaction. The lack of basic knowledge on the de/hydriding processes occurring in the mixture and sometimes for the single components themselves hampers the development of new strategies for circumventing the system limitations and improving the performances of the hydrogen storage material. In this paper, in situ x-ray diffraction results on phase transormations in the two-component mixture formed from magnesium amide and lithium hydride will be presented. Experimental evidence, obtained bt DSC measurements, for the presence of an eutectic composition for the Mg(NH2)2/LiNH2 system will be shown. Results will be discussed on the bases of the phase stability in the Li-Mg-N-H system. References

1. S. I. Orimo, Y. Nakamori, J. R. Eliseo, A. Zuttel and C. M. Jensen, Chem. Rev., 107, (2007), 4111-4132.

149

Thermodynamic Investigations on the Mg-D System by Pressure Composition Isotherm Measurements

F. Leardini, J.R. Ares, J. Bodega, J.F. Fernández, C. Sánchez Dpto. Física de Materiales, Universidad Autónoma de Madrid, 28049, Madrid, Spain

E-mail: fabrice.leardini@uam.es The analysis of H/D isotope effects in metal hydrides provides a better characterization of their physical and chemical properties. Besides, the use of H and D isotopes is being widespread in composite hydride systems since it gives relevant information on the reaction pathways for hydrogen absorption and desorption processes. In this context, it is noticeable the lack of extensive investigations on thermodynamic isotope effects in many archetypical hydrides such as magnesium hydride. Whereas thermodynamics of the Mg-H system have been investigated by means of pressure-composition isotherm (PCI) measurements [1,2], reliable experimental data for the Mg-D system are lacking. Up to now the only reported results concern to middle-plateau pressure values [3]. In this work we present the desorption PCI curves of the Mg-D system obtained at 618, 636 and 656 K in a Sieverts apparatus. The 618 K desorption isotherm of MgH

2 has been also

experimentally determined for comparison purposes. The obtained hydride and deuteride samples have been investigated by x-ray Diffraction, Scanning Electron Microscopy, Thermal Desorption Spectroscopy and Gravimetric measurements. The obtained plateau pressure values of MgD

2 agree with those previously reported,

showing that equilibrium pressures of the deuteride are higher than for the hydride. As concerns the solubility limits of the solid solution and deuteride phases, our results show the importance of taking into account the amount of magnesium oxide in order to obtain good quantitative results. Finally, results on the kinetics of decomposition of magnesium hydride and deuteride samples will be presented and discussed based on Thermal Desorption Spectroscopy studies. Acknowledgements We thank Dr. J.-C. Crivello for his valuable comments and Mr. F. Moreno for technical assistance. Financial support from Spanish MICINN under contract MAT2008-06547-C02-01 is also gratefully acknowledged. References 1. K. Klose and V. Stuke, Int. J. Hydrogen Energy, 20 (1995) 309-316 2. B. Bogdanovic, K. Bohmhammel, B. Christ, A. Raiser, K. Schlichte, R. Vehlen, U. Wolf, J. Alloys Comp. 282 (1999) 84-92 3. J.F. Stampfer, Jr, C.E. Holley, Jr, J.F. Suttle, J. Amer. Chem. Soc. 82 (1960) 3504

150

Lattice Dynamics and Stability of Co and Ni Monohydrides

M.P. Belov1, E.I. Isaev1,2, Yu.Kh. Vekilov1 1Department of Theoretical Physics, Moscow State Institute of Steel and Alloys,

Russia 2Department of Physics, Chemistry and Biophysics (IFM), Linkoping University,

Sweden Email: makspalych@gmail.com

Lattice dynamics of cobalt and nickel monohydrides [1,2] were studied in the pressure range 0-13 GPa by means of first-principles density functional perturbation theory, ultra soft pseudopotentials, and generalized gradient approximation to the exchange-correlation functional. Calculated phonon spectra revealed that NaCl, ZnS, NiAs and DHCP type monohydrides of Co and Ni are dynamically stable. We have also calculated thermodynamic properties such as free energy, entropy, specific heat, the Debye temperature, mean square displacements of atoms in the hydrides. Free energy calculations have shown that NaCl-type structure of CoH and NiH is thermodynamically stable in the pressure range and at temperatures up to 500 K. This is different from results obtained in [3] where the existence of DHCP-type FeH was confirmed from ab initio calculations. References 1. V.E. Antonov, T.E. Antonova, V.K. Fedotov, T. Hansen, A.I. Kolesnikov, A.S. Ivanov, J. Alloys and Compounds, 404–406, (2005), 73–76. 2. V.E. Antonov, J. Alloys and Compounds, 330–332, (2002), 110–116. 3. E.I. Isaev, N.V. Skorodumova, R. Ahuja, Yu.Kh. Vekilov, and B. Johansson, Proceedings of The National Academy of Sciences of the USA (PNAS), 104 (22), (2007), 9168.

151

Phase Diagrams of Hydrogen Clathrate Hydrates: Theoretical Aspects of Hydrogen Storage Application

R. V. Belosludov1, O. S. Subbotin2, H. Mizuseki1, V. R. Belosludov2 and Y. Kawazoe1 1 Institute for Materials Research, Sendai 980-8577, Japan

2 Nikolaev Institute of Inorganic Chemistry, SB RAS, Novosibirsk, 630090, Russia Email: rodion@imr.edu

Interest in hydrogen clathrate hydrates as potential hydrogen storage materials has risen after a report that the clathrate hydrate of cubic structure II (CS-II) can store around 4.96 weight% of hydrogen at 220MPa and 234 K [1]. However, the extreme pressure required to stabilize this material makes it impractical. The formation pressure of hydrogen clathrate can be significantly reduced by adding second “large” guest molecule, such as tetrahydrofuran (THF) [2]. This addition is resulted in filling large cages by THF and hence the reduction in the mass of hydrogen storage. It is well known that there are several types of gas hydrate structures with different cage shapes, and some of these hydrate structures can hypothetically store more hydrogen than the hydrate of structure CS-II. Therefore, for practical application of gas clathrates as hydrogen storage materials, it is important to know the region of stability of these compounds as well as the hydrogen concentration at various pressures and temperatures. In order to accurately estimate the thermodynamic properties of hydrogen hydrates, we developed a method based on the solid solution theory of van der Waals and Platteeuw with some modifications that include multiple occupancies, host relaxation, and the description of the quantum nature of hydrogen behavior in the cavities [3]. Using this approach, the phase diagram (P,T) of the pure hydrogen clathrate of structure CS-II has been constructed in agreement with the recent experimental diagram [4]. It has been also estimated that the pure hydrogen hydrate of CS-I structure can store more hydrogen but this structure is thermodynamically unstable as comparable with both CS-II hydrate and hexagonal ice. The H2-Propane-H2O and the H2-Methane-H2O systems have been investigated with different propane, methane and H2 concentrations. The calculations showed that the formation pressure of hydrogen hydrates was significantly reduced in the presence of propane as in the case of THF [4]. However, in the case of propane there is possibility of increasing the amount of hydrogen stored (around 4 wt% of hydrogen at 270 K) at small concentration of propane in gas phase. In the case of mixture hydrogen-methane hydrate, it was found that the CS-II hydrates can be stabilized at lower pressure than the pure hydrogen CS-II hydrate. The methane can support to stabilization of CS-I hydrate and the thermodynamic region of stability is strongly depends on concentration of methane in gas phase [5]. The possibility of the formation of hydrogen hydrate with other structures has also been discussed. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Advanced Fundamental Research Project on Hydrogen Storage Materials”. References 1. W.L. Mao et al. Science 297 (2002) 2247-2249. 2. L.J. Florusse et al. Science 306 (2004) 469-471. 3. V. R. Belosludov et al. Mater. Trans. 29 (2007) 704-710. 4. R. V. Belolsudov et al. J. Chem. Phys. 131 (2009) 244510. 5. V. R. Belosludov et al. Comp. Mater. Sci. (2010) in press.

152

Combined Optical and Electrical Analysis of Phase Boundaries of Transition Metal Hydride Films

G. K. Pálsson, J. Prinz and B. Hjörvarsson

Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden Email: gunnar.palsson@fysik.uu.se

We present combined electrical resistivity and optical transmission measurements as a means to map out phase diagrams of transition metal hydride films. We demonstrate high sensitivity to phase boundaries, only achievable with the combined approach. Vanadium hydride, with its rich phase diagram is accurately reproduced and effect of finite size and clamping is demonstrated in both thin films and superlattices.

153

Thermodynamics of Stable and Metastable Cu-O-H Compounds P. A. Korzhavyi,1 E. I. Isaev,2,3 and B. Johansson1,4

1 Department of Materials Science and Engineering, Royal Institute of Technology, SE-100 44 Stockholm, Sweden

2 Department of Physics, Chemistry, and Biology (IFM), Linköping University, SE-581 83 Linköping, Sweden

3 Department of Theoretical Physics, National University of Science and Technology “MISIS”, 119049 Moscow, Russia

4 Department of Physics and Materials Science, Division for Materials Theory, Uppsala University, P.O. Box 530, SE-751 21 Uppsala, Sweden

E-mail: pavel@mse.kth.se Density functional perturbation theory [1,2] is applied in order to investigate the structure and physical properties of possible stable and metastable copper(I) compounds with oxygen and hydrogen. Thermodynamic properties are derived from the calculated phonon spectra in the quasi-harmonic approximation. Our calculations reproduce very accurately the experimental heat capacity [3] and the anomalous thermal expansion behavior [4] of copper(I) oxide. Copper(I) hydride, CuH, is found to be a metastable phase exhibiting a semiconducting gap in the electronic spectrum. The calculated structure, enthalpy of formation, and phonon spectra are found to be in good agreementwith existing experimental data [5,6]. The structure of a novel metastable phase, copper(I) hydroxide, is determined. The presence of a semiconducting gap in the electronic spectrum of CuOH implies that chemical bonds in this compound are fully saturated. Copper(I) hydroxide is found to be stable relative to the pure elements in their respective standard states, but unstable with respect to decomposition onto copper(I) oxide and water. Possible implications of the present findings for corrosion science of copper and its alloys are discussed. This work has been supported by the Swedish Nuclear Fuel and Waste Managemen Company (SKB). Computer resources for this study were provided by the National Supercomputer Center (NSC), Linköping, Sweden. References 1. S. Baroni, S. de Gironcoli, A. Dal Corso, and P. Gianozzi, Rev. Mod. Phys. 73, (2001), 515–562. 2. P. Giannozzi, S. Baroni, N. Bonini, et al., J. Phys.: Condens. Matter 21, (2009), art. no. 395502. 3. Chase M.W., NIST-JANAF Thermochemical Tables. Fourth Edition. Part II, Cr-Zr (American Institute of Physics, New York, 1998). 4. W. Schäfer and A. Kirfel, Appl. Phys. A 74 [Suppl.], (2002) S1010–S1012. 5. R. Burtovyy, D. Włosewicz, A. Czopnik, and M. Tkacz, Thermochimica Acta 400, (2003), 121–129 6. V.N. Verbetsky and S.V. Mitrokhin, Solid State Phenomena 73-75, (2000), 503–517.

154

Structure Ti0.9Zr0.1Mn1.2V0.1 and Ti0.9Zr0.1Mn1.3V0.5 and Their Hydrides and Peculiarities of Hydrogen Interaction with Intermetallic Compounds.

S.A. Lushnikov, E.Yu. Anikina, V.A. Somenkov, V.N. Verbetsky Chemistry Department Moscow State University, Moscow, Russia

Email: lushnikov@hydride.chem.msu.ru

In our laboratory we studied the hydrogen interaction with the intermetallic compounds (IMC) AB2 with hexagonal structure C 14 Laves phase by means of calorimetric method using twin-cell differential heat-conducting calorimeter Tia-Calvet type. For this study we picked out IMCs with overall formular (Zr,Ti)MnV with stoichiometric and nonstoiciometric compositions. We took notice that on the plots of the ΔH – X isotherms (ΔH – partial molar enthalpy of hydrogen desorption from hydride phase, X = H/IMC) for such IMCs as ZrMn2, ZrMn2.7 and Ti0.9Zr0.1Mn1.1V0.1 the values of enthalpy on the plateau region decreased with increasing of hydrogen concentration in the metallic matrix and in some cases at certain temperature two regions with constant values of enthalpy could be mark out. However for the Ti0.9Zr0.1Mn1.3V0.5 and Ti0.9Zr0.1Mn1.5V0.8 compounds we found out contrary dependences of ΔH – X that is the values of enthalpy of hydrogen desorption from the hydride phase increased with the rise of X, but the structure of the formed hydride remained the same as initial IMC (MgZn2) only the volume of crystal lattice expanded about 25%. These results brought us to carry out supplementary investigations which could help us to ascertain the reason such hydrogen interaction with IMCs. For this purpose two alloys were prepared Ti0.9Zr0.1Mn1.2V0.1 and Ti0.9Zr0.1Mn1.3V0.5 and their hydrides and deuterides were synthesised. The Ti0.9Zr0.1Mn1.2V0.1 – H system was researched by the calorimetric method and were measured P – X isotherms at temperature range from 62 to 132ºC and hydrogen pressure up to 60 atm. According to X-ray diffraction parttens the samples under study were single-phase and had MgZn2 structure type. Two methods – X-ray and neutron diffraction analysis – were used for determination of position parameters of metallic atoms. This allowed us to determinate the positions of the atoms which have close number (Ti and Mn) invisible for X-ray and V atoms almost invisible for neutrons. The structural data show that there are differences in the distribution of metallic atoms on positions of metallic matrix. These differences correlate with the thermodynamic features of these IMCs- H systems about which we wrote hereinbefore.

155

Calorimetric Study of Hydrogen Interaction with CaSi.

E.D. Devyatkina, E.Yu. Anikina, V.N. Verbetsky. Chemistry Department Moscow State University, Moscow, Russia

Email: anikina@hydride.chem.msu.ru It is known that CaSi reversibly absorbs and desorbs hydrogen [1, 2, 3]. In a number of articles there are thermodynamic data of hydrogen interaction with CaSi, namely, in ref. [1, 2] the authors estimated the enthalpy and entropy of hydride formation calculated using van’t Hoff plot as -62 kJ/mol H2 and -116 J/K·mol H2, respectively. N. Ohba et al. [3] estimated the enthalpy oh hydrogen reaction with CaSi as -42kJ/mol H2 from the calculation based on the crystal structure symmetry determined by the Rietveld refinements of synchrotron X-ray differential data. In this work the hydrogen interaction with CaSi in the first time was studied by means of calorimetric method using the differential heat-conducting calorimeter Tian-Calvet type. Before the beginning of every run measurements the sample of CaSi was hydrogenated at 275ºC and hydrogen pressure 55 atm. The isotherms of desorption ΔH-X and P-X were obtained (P – equilibrium hydrogen pressure, X=H/CaSi, ΔH – the partial molar enthalpy). The values of ΔHdes and ΔSdes in plateau region are ~53 kJ/molH2 and ~95 J/K·molH2, respectively. References 1. J. Alloys and Compounds, 404-406 (2005) 402-404. M. Aoki, N. Ohba, T. Noritake, S. Towata. 2. J. Applied Physics Letters, v.85, No 3 (2004) 387-388. M. Aoki, N. Ohba, T. Noritake, S. Towata 3. J. Physical Review B, 72 075104 (2005). N. Ohba, M. Aoki, T. Noritake, K. Miwa, S. Towata

156

Thermodynamic Aspects of Hydrogen Interaction with Laves Phase Structured Intermetallic Compounds.

E. Yu. Anikina, V.N. Verbetsky. Chemistry Department Moscow State University, Moscow, Russia

Email: anikina@hydride.chem.msu.ru

A number of the IMC – H systems (IMC – intermetallic compound) was studied by two methods: calorimetric and measurement of the P – C isotherms (P – equilibrium hydrogen pressure, C = H/IMC), where IMCs had the Laves phase structure MgZn2 with stoichiometric and nonstoichiometric compositions. The investigation was carried out in the wide temperature range (from 60 to 300ºC) and hydrogen pressure up to 60 atm. The hydrogenation of the IMCs did not result in any changes in these crystal structure and only the expansion of the unit cell occurred (about 20-25%) depending on the composition of the studied samples. The dependence of ΔH on C and P on C as well as ΔS on C (ΔH and ΔS – the partial molar enthalpy and entropy, respectively, of hydrogen reaction with IMC) were obtained. It was established that for the IMC – H systems under investigation the values of ΔH and ΔS changed as a function of the experimental temperature and the hydrogen concentration in the metallic matrix. At the certain temperatures on the plots of ΔH – C could be seen two regions where the enthalpy was constant and on the corresponding them the plots P – C there were flex points. Moreover, the character of the dependence of ΔH – C varied according to the composition of initial IMC. Thus, at small content of V in the IMC (<10 at. %) the values of the enthalpy decreased with an increase of C along the plateau, and at high content of V in the IMC the reversible dependences were observed.

157

Desolvation, Thermal Decomposition and Thermodynamic Properties of Lanthanide Borohydrides of Yttrium Subgroup.

B.A.Gafurov, I.U.Mirsaidov, D.Kh.Nasrulloeva, A.B.Badalov

Nuclear and radiation safety agency under Tajik academy of sciences. E-mail: i.mirsaidov@nrsa.tj

Solvated tristetrohydrofuranates (THF) of lanthanide borohydrides (Ln-Gd, Er, Xb and L4) are obtained by exchange reaction between lanthanides and sodium borohydrides in THF medium. Desolvation processes and thermal decomposition of Ln (BH4)3 · 3 THF are investigated by tensimetric methods with membrane zero-manometer and roentgen-phase analysis. Tensimetric investigations carried out in equilibrium conditions showed that in temperature intervals 300-650 K the curve of steam pressure dependence from temperature (barogram) consist from three stages. The first two stages correspond to desolvation process. The first stage is running at 300-350K with isolation of THF mole and second stage is running at 350-380 K with removal of subsequent two THF moles. The third stage running at 450-630 K, corresponds to decomposition process of lanthanide borohydrides according to the following scheme:

Ln (BH4)3 = 21 LnB6 +

21 LnH2+ 5,5 H2

According to barogram equations thermodynamic characteristics of all stages of desolvation process and decomposition of studied lanthanide borohydride are identified. On their basis and with involvement of referenced data, thermodynamic characteristics of gadolinium, erbium, ytterbium, and lutetium borohydrides are calculated.

158

New Clathrate Phase in the Water-Hydrogen System

V.S. Efimchenko, V.K. Fedotov, M.A. Kuzovnikov, M.K. Sakharov and M. Tkacz1 Institute of Solid State Physics RAS, 142432 Chernogolovka, Moscow District, Russia

1 Institute of Physical Chemistry PAS, Kasprzaka 44/52, 01-224 Warsaw, Poland E-mail: efimchen@issp.ac.ru

In 1993, an investigation of the H2O-H2 system in the pressure interval 7.7–300 kbar

revealed the occurrence of two crystalline hydrogen hydrates, rhombohedral C1 phase stable at pressures up to 25.5 kbar and cubic C2 phase stable at higher pressures [1]. Based on results of Raman studies, the molar ratio H2/H2O of the C1 phase at pressures 7.7–25.5 kbar was estimated as 1/6 that corresponded to 1.8 wt.% H2. Later, one more clathrate hydrate, cubic sII phase was also found to form in the H2O-H2 system at pressures from 1.0–3.6 kbar [2]. Further investigations showed that the unit cell of sII hydrate contained 136 molecules of water and up to 48 molecules of hydrogen (or 3.8 wt. % H2) depending on the temperature and pressure [3,4]. Boundaries of the stability range of this hydrate in composition and pressure and temperature were constructed in ref. [5].

The present work reports on the synthesis of a new trigonal phase C0 in the H2O-H2 system. Using volumetric technique, a 200 mg sample of the new phase was synthesized from the powdered ice at a hydrogen pressure about 5 kbar and temperature –23oC and quenched under pressure to the liquid nitrogen temperature. By hot extraction in vacuum, the sample was found to contain about 1.4 wt.% H2. The phase composition and structure of the water sublattices of phases in the quenched H2O-H2 sample were examined by X-ray diffraction at ambient pressure and a temperature of –193ºC. According to this X-ray study, the quenched sample consisted of the C0 phase and of a minor amount of the low-pressure phase of ice Ih condensed on the sample surface while it was loaded into the X-ray cryostat.

The structure of the C0 phase has no analogue among the structures of ices and clathrates studied earlier. At ambient pressure, the quenched C0 phase has a trigonal structure, space group P31, with the cell parameters a = 6.334 Å and c = 6.203 Å in hexagonal axes. The unit cell contains 8 molecules of H2O. After heating the sample to –110oC, the C0 phase fully transforms to cubic ice Ic without hydrogen.

The discovery of the new hydrogen-rich phase is of interest for planetary science because hydrogen and water are among the basic building materials of many planets and satellites. The C0 hydrate is formed in the pressure and temperature range characteristic of many of these icy bodies and could therefore play a significant role in their evolution. References 1. W. Vos, L. Finger et al. Phys. Rev. Lett., 3150-3153, (1993), 71(19) 2. Yu. Dyadin, E. Larionov, A. Manakov, Zh. Strukt. Khimii, 974-980, (1999), 40(5) {in

Russian} 3. W. Mao, H. Mao et al. Science, 2247-2249, (2002), 297(27) 4. V. Efimchenko, V. Antonov et al. High Pressure Research, 439-443, (2006), 26(4) 5. V. Antonov, V. Efimchenko, M. Tkacz. J. Phys. Chem. B, 779–785, (2009), 113(3)

159

Hydrogen Interaction with Ti-Zr-Hf Alloys in the SHS Mode

D. Mayilyan and S. Dolukhanyan A.B. Nalbandyan Institute of Chemical Physics of Armenian NAS, Yerevan, Armenia

Email: davitmayilyan@gmail.com The current work presents the results of study of combustion processes of Ti-Hf, Zr-Hf, Ti-Zr-Hf alloys in hydrogen in Self-propagating High-temperature Synthesis (SHS) mode. Alloys of different compositions have been synthesized in these systems by “hydride cycle” method, which is developed at the laboratory of technology of SHS processes of IChPh of Armenian NAS [1, 2]. For the first time it was shown, that high-density alloys (Ti-Hf, Zr-Hf, Ti-Zr-Hf) can interact with hydrogen and deuterium in SHS mode without preliminary crushing, and form the hydrogen- (deuterium-) rich hydrides (deuterides): Н(D)/Me = 1.8-2.28. Process of hydrogen interaction with alloys can be presented by the following reactions: ТixHf1-x + H2 ↔ ТixHf1-xHy; ZrxHf1-x + H2 ↔ ZrxHf1-xHy; TixZryHfz + H2 ↔ TixZrYHfzHк. These reactions are reversible – important characteristic for cycling and usage of the hydrides in the quality of hydrogen accumulators. Combustion temperature of an alloy of any composition was between 500-650°C. It was shown, that at interaction of alloy with hydrogen, the developed combustion temperature is rather low in comparison with the temperatures of combustion of metals (Ti, Zr, Hf) [3, 4]. The influence of hydrogen pressure on the process of alloy combustion was investigated. The study proved that the density of compact sample had no influence on the content of hydrogen in the synthesised hydride. With the increase of hydrogen pressure in the interval 1-30 atm, the combustion temperature grew from 450°C to 650°C. It was shown that the crystal structure of the received hydrides depends on the composition of an initial alloy. At some compositions, the interaction of an alloy with hydrogen results in hydrides with cubic structure of fluorite, CaF2; at other compositions the hydrides with tetragonal structure of thorium dihydride, ThH2, are formed. References 1. A. Aleksanjan, D. Mayilyan, S. Dolukhanyan, V. Shekhtman, O. Ter-Galstyan, Int. J. Alternative Energy and Ecology, 9 (65), (2008), 22-26. 2. A. Aleksanyan, S. Dolukhanyan, A. Mantashyan, D. Mayilyan, O. Ter-Galstyan, V. Shekhtman, Carbon Nanomaterials in Clean Energy Hydrogen Systems, NATO Science Series, (2008), 783-794. 3. S. Dolukhanyan, M. Nersesyan, A. Nalbandyan, I. Borovinskaja, A. Merzhjanov, Dokl. AS of USSR. 231 (3), (1976), 675-678. 4. S. Dolukhanyan, H. Hakobyan, A. Aleksanyan, Int. J. of SHS, 1 (4), (1992), 530-535. The current work was implemented in the frame of theme 0567 funded by the Ministry of Education and Science of the Republic of Armenia, and under the financial support of ISTC (grant А-1249).

160

Influence of Hydrogen on Inelasticity-Elasticity Properties of Ti3Al Alloy and SiO2

A.Onanko, O.Lyashenko, G.Prodaivoda, S.Vigva, Y.Onanko Taras Shevchenko Kyiv research national university,

Volodymyrs’ka str.,64, Kyiv, Ukraine, 01601 onanko@univ.kiev.ua

In the present work the results of examinations of the relaxation processes in a crystalline lattice at H, thermal and ultrasonic processing on the temperature spectrum of internal friction (IF) Q-1 and elastic module E (indicatory surface of inlasticity-elasticity state) of Ti3Al alloy are presented.

For measuring of the temperature dependences IF and elastic module E the methods of complete piezoelectric oscillator on frequency were used f ≈ 117 kHz and resonance vibrations on frequency f ≈ 1 kHz during alternative deformation ε ≈ 10-6 in vacuum P ≈ 10-3 Pa.

There was the maximum IF in Ti3Al at TM1 ≈ 400 K with activation energy H1 = 0,77 ± 0,1 eV, time relaxation constant of this maximum IF τ01 ≈ 1,9.10-14 sec, relaxation frequency factor f01 ≈ 5,3.1013 Hz. , probably conditioned by the relaxation mechanism caused by reorientation interstitial atoms of H in dumbbell configurations at the ultrasonic alternative deformation. The maximum IF in Ti3Al at the temperature TM2 ≈ 440 K is discovered with the value of activation energy H2 = 0,85 ± 0,1 eV, time relaxation constant of this maximum IF τ02 ≈ 1,8.10-14 sec, relaxation frequency factor f02 ≈ 5,5.1013 Hz.

Fig.1. Temperature dependence of elasticity module E and internal friction Q-1

(indicatory surface of inelasticity-elasticity state) Ti3Al + H alloy after H during ~ 7200 sec. The maximum IF in Ti3Al at the temperature TM3 ≈ 530 K is discovered with the value of activation energy H3 = 1,0 ± 0,1 eV, time relaxation constant τ03 ≈ 3,1.10-14 sec, relaxation frequency factor f03 ≈ 3,2.1013 Hz.

The relaxation of elastic module E, looked in the same temperature interval testified to the relaxation process, linked with the vacancies V-H complexes under the variable ultrasonic deformation ε.

161

The Effect of Anion Substitution in Metal Borohydrides L.Rude,# Y.Filinchuk,#,* M.Sørby,+ B.Hauback+ and T.R.Jensen#

#iNANO and Department of Chemistry, University of Aarhus, Denmark; *ESRF, BP-220, 38043 Grenoble, France; + Institute for Energy Technology, P. O. Box 40 Kjeller, NO-2027, Norway

Email: line@inano.dk Borohydrides are considered interesting materials for hydrogen storage in mobile applications due to their high theoretical hydrogen content,1 e.g. 18.5 wt% for LiBH4. Unfortunately, most borohydrides are either too stable or unstable for practical hydrogen storage systems. LiBH4 release hydrogen at T > 410 °C (p(H2) = 1 bar) but the system can be modified by anion substitution in order to stabilize the too unstable borohydrides or destabilize the stable compounds.2,3 Anion substitution is a promising and relatively new tool to tailor the properties of hydrogen storage materials. This approach has been investigated both experimentally and theoretically indicating an interesting change of the properties of the substituted compounds.4-6 We have successfully substituted the Cl¯, Br¯ or I¯ for the BH4¯ complex anion in LiBH4. Thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) reveals a stabilization of the hexagonal phase of LiBH4 due to anion substitution and a significant increase in melting point of LiBH4. The melting point for pure LiBH4 is at T = 286 °C and at 378 °C for LiBH4-LiBr (1:1). However, the stabilization of the hexagonal phase has no apparent impact on the hydrogen release temperature, which is determined by Sieverts measurements to be unchanged. We observed recently that a minimum of 50 % of the theoretical hydrogen content in LiBH4-LiX for (X = Cl¯, Br¯, I¯) can be stored reversibly for at least four cycles of hydrogen release and uptake. Interestingly, the rehydrogenation occur at significantly more moderate conditions as compared to pure LiBH4.7 These new anion substituted materials also show interesting structural properties, i.e. the structure of a new Li(BH4/Br) compound is solved.7 Recent studies show that Ca(BH4)2 readily dissolves in CaI2 observed as a solid solution of Ca((BH4)1-xIx)2 with a BH4 content of 70% and stable in a temperature range of RT - 400. At T = 185 °C the substituted material adopt a CaCl2 type structure that turns out to be related to β-Ca(BH4)2. The CaCl2-type Ca((BH4)1-xIx)2 has a similar composition with a BH4 content of ca. 64% and the phase is observed in the temperature range 195 to 350 °C. In a temperature range of 335 to 360 °C a novel tetragonal structure is observed having a lower BH4 content of 38%. The decomposition product, CaHI, is observed at T > 345 °C. Aknowledgements The European Commission (contract NMP-2008-261/FLYHY) and the Danish Natural Science Research Council (DanScatt program) is thanked for financial support. References 1. L. Schlapbach, A. Zuttel, Nature, 414, (2001), 353–358. 2. L. Mosegaard, et al., J. Phys. Chem. C, 112, (2008), 1299-1303. 3. L. M. Arnbjerg, et al., Chem. Mater., 21, (2009), 5772-5782. 4. L. Yin, P. Wang, Z. Fang, H. M. Cheng, Chem. Phys. Lett., 450, (2008), 318-321. 5. H. Maekawa, et al., J. Am. Chem. Soc. 131, (2009), 894-895. 6. H. W. Brinks, A. Fossdal, B. C. Hauback, J. Phys. Chem. C, 112, (2008), 5658-5661. 7. L. Rude, Y. Filinchuk, T.R. Jensen et al, 2010, to be submitted

162

Crystal Structure Analysis of Li3-xMxN (M=Co, Ni) Synthesized by SPS for Hydrogen Storage

J. Zhanga, R. Černýb, B. Villeroya, C. Godarta, D. Chandrac and M. Latrochea

a Chimie Métallurgie des Terres Rares, ICMPE-UMR 7182, CNRS, 2-8 rue Henri Dunant, 94320 Thiais, France

b Laboratory of Crystallography, University of Geneva, 24 quai Ernest-Ansermet, Switzerland c University of Nevada, Reno, USA

Email: junxian@icmpe.cnrs.fr

Lithium nitride has recently emerged as a promising material for hydrogen storage. The theoretical hydrogen storage capacity reaches 11.5 wt% in two steps1,2: Li3N +H2 →Li2NH+LiH ∆H = -116kJ mol-1 H2 (1) Li2NH+H2→LiNH2+LiH ∆H = -66kJ mol-1 H2 (2) Reaction (1) is highly exothermic, and thus requires very high temperature to release hydrogen. This reaction cannot be used for reversible hydrogen storage. Ab initio calculations show that partial substitution of Li by Cu or Ni can reduce the reaction enthalpy between amide and imide3. In this work, we present the synthesis of the ternary system Li3-xMxN (M=Co or Ni) by SPS (Spark Plasma System). The samples are hydrogenated at 255°C by solid gas reaction. Hydrogenated samples have been analysed by high resolution synchrotron X-ray powder diffraction. The data were collected at the Swiss-Norwegian Beamlines (SNBL) at the European Synchrotron Radiation Facility (ESRF) in Grenoble, France, using a high resolution powder diffractometer equipped with the multi-crystal analyser, λ = 0.50195Å. The crystal structure has been analysed by the Rietveld method. The structural models for Co [4] and Ni-substituted [5] Li3N have been confirmed. The influence of the substitution on the crystal structure and hydrogenation properties will be discussed. References 1. P. Chen, Z. Xiong, J. Luo, J. Lin, and K. L. Tan, Journal? 420, (2002), 302-304. 2. P. Chen, Z. Xiong, J. Luo, J. Lin, and K. L. Tan, Journal of physical Chemistry B 107, (2003), 10967-10970. 3. M. Gupta and R. P. Gupta, Journal of Alloys and Compounds 446-447, (2007), 319-322. 4. A. G. Gordon, R. I. Smith, C. Wilson, Z. Stoeva and D. H. Gregory, Chem. Commun., (2004), 2812-2813. 5. D. H. Gregory, P. M. O’Meara, A. G. Gordon, J. P. Hodges, S. Short and J. D. Jorgensen, Chem. Mater. 14, (2002), 2063-2070.

163

Electrochemical Hydrogen Charging of Sigma Phase Investigated by In-Situ Neutron Diffraction.

L. Laversenne, L. Cagnon, P. de Rango, D. Fruchart, S. Miraglia, N. Skryabina#

CNRS- Institut Néel, Grenoble, France #Perm State University, Perm, Russia Laetitia.Laversenne@grenoble.cnrs.fr

Since over 50 years, sigma phase receives particular attention due to both scientific and technological considerations. The sigma phase forms in transition metal elements binary systems and pertains to topologically close-packed phase. The crystal structure is tetragonal with five nonequivalent lattice sites which differ both in coordination number and local symmetry [1]. The atomic distribution on the 5 sites has been reported as nonstatistical [2-4].

From a fundamental point of view, the sigma phase presents relevant physical properties such as low temperature weak magnetism, high specific heat, superconductivity... The deteriorating effect on mechanical properties (embrittlement) of steels resulting from the phase precipitation represents a significant technological issue.

This work aims at a better understanding of the material behavior in hydrogen environments. Two iron based sigma phases of composition Fe53.5Cr46.5 and FeV have been investigated. The hydrogen locations have been determined from powder neutron diffraction measurements performed at ILL (D1A diffractometer) by means of Rietveld analysis (FULLPROF software). Additionally, the hydrogenation mechanism has been investigated in-situ (D20 diffractometer) by performing electrochemical charging.

References 1. G. Bergman, D.P. Shoemaker, Acta Cryst, 20, (1954), 857-865. 2. K.L. Yakel, Acta Cryst, B 39, (1983), 20-28. 3. J. Cieslak, M. Reissner, S. M. Dubiel, J. Wernisch, W. Steiner, J. Alloys and Compounds, 460, (2008), 20-25. 4. J.M. Joubert, Prog. Mater. Sci., 53, (2008), 528-583.

164

The Tetragonal-to-Orthorhombic Phase Transformation in Ammonia Borane and in Its Deuterium Substituted Compounds

O. Palumbo1,2, A. Paolone1,2, P.Rispoli1, R. Cantelli1

T. Autrey3, A. Karkamkar3, M. A. Navarra4 1 Sapienza Università di Roma, Dipartimento di Fisica, Piazzale A. Moro 2, I-00185 Roma, Italy

2 CNR-ISC, U.O.S. Sapienza, P.le A. Moro 2, I-00185 Roma, Italy 3 Pacific Northwest National Laboratory, 908 Battelle Blvd., Richland, WA 99352, USA

4 Sapienza Università di Roma, Dipartimento di Chimica, Piazzale A. Moro 2, I-00185 Roma, Italy Email: oriele.palumbo@roma1.infn.it

Ammonia borane (NH3BH3) is one of the complex hydrides currently studied as a promising hydrogen storage material, due to its high hydrogen content (~19 wt%) and its possible release on heating the solid at temperatures as low as 100°C. The set-up of operative methods to enhance the rates of hydrogen evolution from NH3BH3 requires a good knowledge of the structural properties and intermolecular interactions. The NH3BH3 lattice symmetry is tetragonal at room temperature, with the B-N bond oriented parallel to the c axis, and undergoes a structural transition to an orthorhombic phase at about 225 K [1, 2], with the B-N bonds oppositely tilted with respect to the c axis. At the transition temperature, a rotational order-disorder character has been observed, with a displacive component due to a distortion in the NH3 unit. It has been suggested that the transition is triggered by the slowing down of the NH3 motion, but at present the mechanism driving the phase transformation is not well understood. In the present work,the tetragonal-to- orthorhombic phase transition has been characterized by means of detailed anelastic spectroscopy (AS) and differential scanning calorimetry (DSC) measurements. DSC experiments revealed the presence of the latent heat associated to the transformation, thus confirming its first order nature. The measurement of the dynamic modulus, carried out on quasi-static thermal conditions, allowed us to evaluate of the “real hysteresis”, which is found to be lower than 1 K. Such a small hysteresis and the observed evolution of the complete transformation within a fraction of kelvin suggest a very narrow range of coexistence between the tetragonal and orthorhombic phases. A comparison of the results obtained in ammoniaborane and in its deuterium substituted compounds provided information about the effect of partial and selective deuteration on both the width of the phase transformation and the time constants. In the deuterated samples the enthalpy of the transition is slightly reduced and the transition is shifted toward higher temperatures by ~1.5 K. The measurements of the time constants for the orthorhombic to tetragonal phase transformation indicate that the main effect of the partial deuteration is the slowing down of the kinetics of the phase transition. References 1. A. Paolone, O. Palumbo, P. Rispoli, R. Cantelli, T. Autrey, J. Phys. Chem. C, 113 (2009) 5872-5878. 2. A. Paolone, O. Palumbo, P. Rispoli, R. Cantelli, T. Autrey , A. Karkamkar, J. Phys. Chem. C, 113 (2009) 10319-10321.

165

Novel Metal Borohydrides – Crystal Structures, Thermal Decomposition and Reactivity

D. Ravnsbæk1, Y. Filinchuk2,1, R. Černý3, T. R. Jensen1 1Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark (inadr@inano.dk), 2SNBL at ESRF, 6 rue Jules

Horowitz, 38043 Grenoble Cedex, France,3 Laboratory of Crystallography, University of Geneva, 1211 Geneva, Switzerland.

Complex metal hydrides such as borohydrides are currently of great interest as potential hydrogen storage materials, since they have high gravimetric hydrogen density and show a variety of decomposition temperatures. However, no single material has yet been found, which fulfil all the criteria for mobile hydrogen storage [1,2]. Therefore, there is an urgent need for discovery of novel classes of materials, such as transition metal or mixed metal borohydrides as potential future hydrogen storage materials. We have recently prepared and characterized a range of novel boron-based materials, e.g. mixed metal borohydrides MZn2(BH4)5 (M = Li or Na), NaZn(BH4)3, the first mixed cation-mixed anion borohydride KZn(BH4)Cl2 and a new high temperature polymorph of Y(BH4)3 [3-5]. These compounds exhibit a variety of structural topologies, e.g. NaZn(BH4)3 consists of a single three-dimensional network, containing polymeric anions with the composition [Zn(BH4)3]n n-, whereas the compounds MZn2(BH4)5 (M = Li or Na) are build of two identical interpenetrated three-dimensional frameworks consisting of isolated complex anions, [Zn2(BH4)5]¯. The latter suggests directionality in the bonding, which indicates some degree of covalent bonding. Several other novel materials are currently under structural investigation and will be presented, e.g. Na-Y-BH4. Furthermore, the stability and the thermal decomposition pathways of the prepared materials have been studied in great detail by in situ SR-PXD and thermal analysis. These studies reveal, that the novel materials decompose at relatively low temperatures via several reactions, including compounds obtained as biproduct from the synthesis. This knowlegde may allow for further optimization of the reaction pathways for the hydrogen release and uptake in future hydrogen storage materials and might in combination with structural studies of novel bimetallic borohydrides hold the key to gain further insight of trends within the thermal stability of this class of materials. References 1. L. Schlapbach, A. Züttel, Nature, 414, (2001) 353. 2. S. Orimo, Y. Nakamori, J. R.Eliseo, A. Züttel, C. M. Jensen, Chem. Rev., 107, (2007), 4111–4132. 3. D. Ravnsbæk, Y.Filinchuk, Y. Cerenius, H. J. Jakobsen, F. Besenbacher, J. Skibsted, T. R. Jensen, Angew. Chem., Int. Ed., 48, (2009), 6659-6663. 4. D. B. Ravnsbæk, L. H. Sørensen, Y. Filinchuk, Y. Cerenius, H. J. Jakobsen, F. Besenbacher, J. Skibsted, T. R. Jensen, J. Eur. Inorg. Chem., (2010), DOI: 10.1002/ejic.201000119. 5. D. B. Ravnsbæk, Y. Filinchuk, R. Černý, M. B. Ley, D. Haase, H. J. Jakobsen, J. Skibsted, T. R. Jensen, Inorg. Chem., (2010), DOI: 10.1021/ic902279k.

166

Analysis of Processes in Metal Materials Caused by Presence of Hydrogen with the Help of Methods of Acoustomicroscopy Defectoscopy

А.I.Kustov1., I.А.Migel

Voronezh State Pedagogical University 1 , Voronezh Military Air University akvor@yandex.ru

Metal materials remain the basis of various industries. For giving they required physical and structural parameters it is necessary to have a set of objective and complementary control methods. The methods should provide analysis of dynamics of structure and properties of the investigated materials. Methods of acoustomicroscopy defectoscopy (AMD) allow to get high level of learning efficiency of such processes in metal materials including processes caused by presence of hydrogen.

Our paper deals with the problem of hydrogen influence on metal materials structure first of all steels. AMD-methods [1] allow directly without any additional chemical effect to visualize material microstructure, to determine the size of the grain (dЗ), as average and real. Presence of hydrogen in any form leads to a structural changes that is fixed directly by visualizing. Grain size and form transformation enables to evaluate values of a number of physical parameters. The data are confirmed by the experiments based on V(Z)-curves dependence analysis [2] received for investigated materials.

As a result of the experimental study of a number of model materials and steels (08X18H10T, 06X14H6MD2T, 55XH, etc) with the help of SAM of reflective type (frequency of operation ~0,5 GHz ) were received characteristic acoustomicroscopy images of their microstructure. The image analysis allowed to set layer thickness with changed properties. Application of V(Z)-curve method gave more valuable information about materials. This method provided high reliability of results received by visualization method. Due to diffraction pattern formed in direct and reflected from near-surface layers of patterns of acoustic waves we calculated the value of the characteristic parameter (ΔZN).On the value of this important material parameter we calculated values of velocity υR of surface acoustic waves SAW of Rayleigh type. SAW velocity is sensitive to hydrogen concentration in the material and characteristic structure. Obtained experimental V(Z)-curves allowed to calculate local, integral values υR and elastic modulus and attenuation of SAW. Depth layers with changed properties in materials were discovered. Dependences on depth penetration of hydrogen and the time of the process of its diffusion were obtained. Experiments showed presence of dependence of attenuation AB (ΔV/V%) on hydrogen concentration in the material.

References 1. Kustov А.1., Migel I.А., Sukhodolov В.G. Study of effect of different types of heat mechanical

treatment on structure and properties of steels and alloys // Metallov. 1 termoobrab. metalov, 1998, N4, 128-137.

2. Kustov А.1. Detection of inhomogenetics by acoustomicroscope methods // Fiz. i khim. stekla, 1998, T. 24, N 6, 809-816.

167

Phase Transformation in Ti-V-Cr-H Composition

N.E. Skryabina1, D. Fruchart2, S. Miraglia2, P. de Rango2, M.G. Shelyapina3 1 Department of Physics, Perm State University, 15 Bukireva, Perm, 614990, Russia

E-mail: natskryabina@mail.ru 2 MCMF, Institut Néel, CNRS, avenue des Martyrs, BP 166, 38042 Grenoble cedex 9, France

3 V.A. Fock Institute of Physics, St. Petersburg State University, Ulyanovskaya 1, Petrodvorets, St. Petersburg, 198504, Russia

For many light metal hydrides, it is of interest to improve markedly their absorption/desorption kinetics in order to expect potential applications in terms of reversible hydrogen storage facilities. E.g. for MgH2, many so-called catalyst additives have been demonstrated more or less efficient in accelerating the reactions with hydrogen. The effective additives are various, standing from metal and alloys to metal oxydes, even fluorides, mostly based on early d-transition elements. A few amount (~ 5%) of metals such as Ti, V, Nb [1] etc, were found to enhance markedly the sorption reactions of MgH2 after energetically ball milling the mixture. More recently, bcc based alloys were revealed even more effective than pure vanadium, as for example TiVCr based compounds [2]. Besides, it was shown that hydrogenation/deuteration of most of such bcc-based on early transition metals provokes a bcc→fcc structural transition between two hydrogenation levels. For hydrogen storage applications as additive, a detailled analysis of the a bcc→fcc transition process reveals of interest. The structure phase transformation was investigated in several formula of TiVCr-H systems, when combined or not with specific additives [2]. It was confirmed by neutron diffraction [3] by DSC and NMR analysis that hydrogen evacuates from the compounds via two steps. The first step of dehydrogenation corresponds as well to the destabilization of the crystal lattice via a fcc→bcc transformation. Indeed, the solubility of hydrogen is not the same in fcc and in bcc lattice. However, it is anticipated that hydrogen can accumulate in bcc phase in superequilibrium concentrations. Then, immediatly after the first step dehydrogenation is thermally activated, the second step can occur. It corresponds to the evacuation of almost hydrogen from the bcc phase. A similar process of dehydrogenation we pointed out in Pd-H alloys [4] when before the PdHx → Pd+xH transition a superequilibrium H concentration in Pd was noticed.. Here, it will be discussed in more details the potential impact of a hydrogen-rich phase accompanying a crystal transformation on the capacity to transfer amounts of hydrogen. This work is granted by RFBR-CNRS, contract # 07-08-92168 and developped under the IAEA project #15933. References 1. G. Liang, J. Huot, S. Boily, A. Van Neste, R. Schulze, J. Alloys Comp. 291 (1999) 295. 2. J. Charbonnier, P. de Rango, D. Fruchart, S. Miraglia, S. Rivoirard, N. Skryabina, Int. Patent WO 2007/096527 A1. 3. S.Miraglia, D. Fruchart, N.Skryabina, M. Shelyapina, B. Ouladiaf, E.K. Hlil, P. de Rango, J. Charbonnier, , Hydrogen-induced structural transformation in TiV0.8Cr1.2 studied by in situ neutron diffraction // Journal of Alloys and Compounds 442(2007) 49. 4. N.E. Skryabina, D. Fruchart, S. Miraglia, D.S. dos Santos, Time-Temperature Stability of the Pd-H System // Hydrogen in Matter, American Institute of Physics, CP837, 2006, 118.

168

The Influence of Contamination by Light Elements on the Structural Stability of CoSn Under Compression

A.S. Mikhaylushkin

Department of Physics, Chemistry, and Biology (IFM), Linkoping University, Linkoping, Sweden Email: arkady@ifm.liu.se

The binary CoSn compound has a unique ground state large-void crystal structure, whose stability under pressure has recently been examined. Whereas theoretical results predicted a series of phase transformations, the room-temperature experiments did not observe any structural change. We suggest that the large void of a CoSn-type structure could contain natural impurities such as hydrogen, oxygen, or nitrogen, which can influence the thermodynamic stability of a CoSn system and explain the unusual disagreement between the theoretical and experimental results. Based on first-principles calculations we revealed that the contamination of CoSn by hydrogen and other light elements only results in a subtle change of structural parameters and the equation of state of CoSn, but drastically increases the stability of the CoSn-type phase in comparison with the high-pressure phases predicted earlier. We argue that the hardly-detectable natural impurities of light elements in porous compounds like CoSn are able to change the phase equilibria.

169

Hydrogen Diagnostics of Structural States in Steel 18Cr10NiTi I. Neklyudov, O. Morozov, V. Kulish, V. Zhurba, P. Khaimovich, A. Galitskiy National Science Center “Kharkov Institute of Physics & Technology”, Kharkov, Ukraine

morozov@kipt.kharkov.ua The method of thermal desorption spectroscopy (TDS) is successfully employed for determining temperature ranges of hydrogen desorption from metals. In this case it is important to know the physical nature of the peaks observed in the spectra of hydrogen thermodesorption from metals. With Ti, Pd as examples, the correlation has been established between the peaks in deuterium thermodesorption spectra and the phase transformations in the metal-hydrogen system [1-3]. The results obtained in the studies suggest the conclusion that the TDS technique can be related to the methods enabling the estimation of the structural state of materials. The present paper reports the results from studies (hydrogen diagnostics) of structural states of materials, using 18Cr10NiTi steel as an example, the structure of which has been subjected to various actions such as reactive-element ion (N+, C+, O+) implantation, cold extrusion deformation. The TD spectrum of deuterium implanted into 18Cr10NiTi steel samples that underwent extrusion deformation at ~78 K with the percent reduction δ =16 % (Fig. 1, curve 2), shows at least two peaks of desorption. The presence of these peaks correlates with the information that the phase transformations occurring in the process of deformation proceed by the γ ⇒ ε ⇒ α, scheme, where γ denotes the austenite with the fcc lattice, α is the martensite with the bcc lattice, and ε is the martensite with the hcp lattice, which is the intermediate phase. In this case it appears logical to assume that the high-temperature peak (Tm~520 K) results from the presence of α-martensite in the 18Cr10NiTi steel, while the low-temperature peak is due to ε-martensite (Tm~350 K). Between these peaks there is apparently an unresolved peak with Tm~400 K, resulting from the presence of the residual γ-austenite. An increase in the percent reduction (curve 3) is accompanied by the increase in the α-martensite concentration and the decrease in the ε-martensite with the result that at δ =44% the TD spectrum of deuterium exhibits a single peak with Tm~520 K. Note that the peaks in the spectra are broad, this confirming a high degree of dispersion of the resulting phases.

Fig. 1. Thermodesorption spectra of deuterium implanted into 18Cr10NiTi steel samples that

underwent extrusion deformation at ~78 K with the percent reductions δ =16% (curve 2) and

~44% (curve 3). The exposure dose for all the samples was 5×1016 D/cm2. Curve 1 was taken

from the virgin sample

The present results indicate that the use of thermodesorption spectrometry of hydrogen (hydrogen diagnostics) holds promise for estimating the structural condition of the metal and its changes under various actions. References 1. I.M. Neklyudov, A.N. Morozov, V.G. Kulish, Materialovedenie, No 11, (2005), 45-56, (In Russian). 2. V.F. Rybalko, A.N. Morozov, I.M. Neklyudov and V.G. Kulish, Phys.Lett., 287A, (2001), 175-182..

V.F. Rybalko, A.N. Morozov, I.M.Neklyudov and V.G. Kulish, Phys.Lett., 287A,(2001), 175-1823. I.M. Neklyudov, O.M. Morozov, V.G. Kulish, V.I. Zhurba A.G. Galytsky, E.V. Piatenko, J. Nuclear Materials, 386–388, (2009) 658–660.

170

In Situ Synchrotron Diffraction Study of the La0.5Ce0.5Ni4Co – H2 System A.B.Riabov1,2, R.V. Denys1,2, J.P.Maehlen1, V.A. Yartys1

(1) Institute for Energy Technology, Kjeller, Norway (2) Karpenko Physico-Mechanical Institute NAS Ukraine, Lviv, Ukraine

Email: alexr@ipm.lviv.ua A single phase hexagonal CaCu5-type La0.5Ce0.5Ni4Co intermetallic alloy (a = 4.9437(3); c = 3.9846(2) Å) was prepared by arc melting and studied in as cast condition as H storage material. A significant shrinking of the unit cell takes place on a substitution of ½ of La in LaNi4Co by Ce (Δa/a = -1.74 %; ΔV/V= -3.43 %). H storage properties of the alloys (La,Ce)(Ni,Co)5 were extensively studied earlier (Mintz 1980, Latroche 1995, 1998, Černý 2000, Klyamkin 2005, Mordkovich 2005, Joubert 2005, et. al). These studies revealed a significant effect of both cerium and cobalt on the stability of the hydrides; a decreased (Co) or increased (Ce) H absorption - desorption hystheresis, and a temperature-related one- or two-step hydrogenation process yielding a saturated β-hydride (La,Ce)(Ni,Co)5H~6, directly or via a formation of an intermediate γ -hydride (La,Ce)(Ni,Co)5H3-4. In the present work, we have performed PCT (abs. / des., T = 273, 313, and 353 K) and in situ SR XRD (BM01A at SNBL, ESRF, Grenoble) studies of the samples equilibrated with hydrogen gas at pressures up to 25 bar at temperatures between 263 and 353 K, by using different heating rates, 1, 2 or 4 K/min, during the thermocycling experiments at pressures 9, 14 or 25 bar H2. In situ SR-XRD hydrogen absorption and desorption experiments performed at constant H2 pressures by cooling and heating at constant rates showed the formation of two hexagonal hydrides, a γ-trihydride La0.5Ce0.5Ni4CoH3-4 (ΔV/V = 14.8 %; lattice expansion mainly in basal plane; exist in a narrow temperature interval of ΔT ~ 20 K), and a saturated β-hexahydride La0.5Ce0.5Ni4CoH~6 (ΔV/V = 24.5 %; lattice expansion predominantly along [001]). In addition, an α-H solid solution was experimentally observed (Figure 1). Small H absorption-desorption hysteresis was observed for the α γ β  transformations. The pressure of formation of the β-phase was strongly temperature-dependent: 9 bar @ 288 K, 14 bar @ 296 K, and 25 bar @ 312 K during the H absorption experiments.

Figure 1. In-situ SR-XRD pattern of H absorption by La0.5Ce0.5Ni4Co.

Figure 2. Hydrogen desorption at PH2 = 25 bar at a heating rate of 4K/min.

171

In-Situ X-ray Powder Diffraction Cell for Hydrogen Absorption Studies C. J Webba, E. MacA Graya, T. R. Jensenb,

aQueensland Micro- and Nanotechnology Centre, Griffith University, Nathan 4111, Brisbane, Australia

b CEM, Center for Energy Materials,iNANO, University of Aarhus

Langelandsgade 140, DK-8000 Aarhus C, Denmark e-mail: j.webb@griffith.edu.au

Understanding the processes by which different materials absorb hydrogen is critical to further development of materials and additives to improve hydrogen content, thermodynamics and kinetics. For metallic hydrides it is important to understand the different phases and location of the hydrogen as a function of hydrogen content as well as the role of vacancies and dislocations. For complex hydrides it is important to understand the intermediate reaction products, their stability and conditions under which they form as well as the role of additives, their function and distribution. In order to gather data as a function of hydrogen absorption it is necessary to perform in-situ experiments. X-ray diffraction is an informative analysis technique for crystalline materials which include most of the solid hydrides. In addition, X-ray scattering typically requires a shorter data acquisition time compared to neutron diffraction and is therefore more amenable to kinetic studies of hydrogen absorption and desorption. This paper describes a new sample cell for in-situ synchrotron radiation X-ray powder diffraction specifically designed for hydrogen adsorption studies. The cell is a modification of previously described sample cells for multipurpose use as described in Clausen et al 1991, Chupas et al 2001 and Chupas, et al 2008. The sample is contained in a single crystal sapphire tube, grown such that the longitudinal direction coincides with the crystallographic c-axis. An associated gas handling system and methods of heating the sample to temperatures up to 800⁰C are described. The advantages of a sapphire crystal cell with regard to rapid pressure cycling and excellent thermal conductivity are discussed and pressure calculations are given for specific sizes of capillary. A comparison of two different manufacturers’ sapphire capillaries and results of destruction pressure testing up to 2000bar are also presented. An improved cell design for pressures to ca 1000 bar is described. References Chupas, P. J., Ciraolo, M. F., Hanson, J. C, Grey, C. P., J. Am. Chem. Soc., 2001, 123, 1694-1702. Clausen, B.S., Steffensen, G., Fabius, B., Villadsen, J., Feidenhans'l, R. Topsøe, H., J. Catal., 1991, 132, 524. Chupas, P.J., Chapman, K.W.,Kurtz, C., Hanson, J. C., Lee, P.L., Grey, C. P., J Appl. Cryst., 2008. 822-824.

172

Hydrogenation of Pd-Ni and Pd-Cu Alloys: Effect on the Interatomic Interactions

V.F. Degtyareva

Institute of Solid state Physics Russian Academy of Sciences, Chernogolovka, Russia Email: degtyar@issp.ac.ru

Hydrogen solubility in metals increases under high pressure, resulting in an increase of their atomic volume per metallic atom and changes of some physical properties [1]. Previous experiments with Pd-Ni and Pd-Cu alloys exposed to high hydrogen pressure at elevated temperatures revealed some changes in the interatomic interactions [2,3]. We compare atomic segregations of the metallic constituents in the Pd-Ni-H and Pd-Au systems. Hydrogenation of Pd-Cu results in the formation of an ordered tetragonal phase similar to CuAu-I. Effects of hydrogen solubility in binary metallic systems are also discussed. References 1. V.E. Antonov, J. Alloys and Compounds, 330-332, (2002), 110-116. 2. V.F. Degtyareva, V.E. Antonov, I.T. Belash, and E.G. Ponyatovskii, Phys. Stat. Sol. (a),

66, (1981), 77-86. 3. V.E. Antonov, T.E. Antonova, I.T. Belash, E.G. Ponyatovskii, V.I. Rashupkin, V.G.

Thiessen, Phys. Stat. Sol. (a), 77, (1983), 71-79.

173

The Role of Hydrogen and Vacancies in Structural Transformations of Palladium and Its Alloys

V. Avdyukhina, D. Bazhanov, G. Revkevich Physical Department Moscow State University, Moscow, Russia

Email: vmaphys@gmail.com, dmibaz@sols347.phys.msu.ru A cycle of X-ray experimental works have been carried out to study the structural characteristics of palladium and palladium based alloys (W, Sm, Er, Mo, Ta, Hf, Cu, In, Ru, Y) both after single and cyclic hydrogenation procedures in order to establish the peculiarities of their changes during long-term relaxation process. Experimentally, the existence of an abnormal amount of vacancies was established for all considered alloys during long-term relaxation process, which was found to be on the several orders of magnitude larger than that at equilibrium state. The theoretical first-principles calculations based on density functional theory and pseudopotential method have shown that the presence of hydrogen within crystal lattice relieves the vacancy formation process and leads to the formation of rather stable «hydrogen-vacancy» dimer complexes (H-Vac) with binding energy ~0.2 eV and their further coalescence. The performed calculations have shown also the possibility in the formation of more complex defect structures (H

m-V

n complexes) with multiple trapping of

hydrogen atoms by vacancies in octahedral and tetrahedral occupation sites of the crystal lattice. The dynamical stability of these defect complexes has been studied theoretically via the phonon spectra calculations using the linear response method in density functional perturbation theory. The experimentally observed simultaneous changes of the lattice constant and the magnitude of microstresses in alloy allowed us to specify the composition of defect complexes which occurred after hydrogenation process. The obtained results have shown that the vacancies and hydrogen were trapped by defect complexes, which exist in the investigated alloys before hydrogenation process, and formed the «hydrogen-defect-metal-vacancy» complexes (H-D-M-Vac -complexes). Specific volume of such complexes was found to be less than the matrix one, which led to the compression of the crystal lattice along the normal to the surface after hydrogenation process. Thus it led to a change in magnitude and sign of the elastic stress observed experimentally. Moreover, we observed also in hydrogen charged palladium based alloys during long-term relaxation process the complicated kinetics of structural transformations, which was ascribed by the aperiodic changes in the number of coexisting cubic phases with various magnitudes of stresses (or without them), the volume of each phase and its defect structure. The first-principles calculations allowed us also to make a conclusion that the presence of vacancy complexes in the vicinity of an impurity metal promotes the hydrogen solubility and its interaction with an impurity can be described by Miedema’s «reverse stability» rule similar to the that case of pure bulk material. It has been shown for various positions of hydrogen (octa- and tetra-sites) in bulk, that the presence of a vacancy can lower the metal-hydrogen interaction energy about ~0.01-0.25 eV and leads to the attraction of hydrogen atom by impurity in good agreement with experimental observations. The results of performed experimental and theoretical studies allowed us to suggest a model of non-monotonic structure evolution of hydrogen charged alloys during long-term relaxation process.

174

Synthesis of ZrCr2 Laves Phases by Arc Melting in Ar/H

2 Plasmas

J. Bodega, F. Leardini, J.R. Ares, J.F. Fernández, C. Sánchez Dpto. Física de Materiales, Universidad Autónoma de Madrid, 28049, Madrid, Spain

E-mail: julio.bodega@uam.es AB

2-type intermetallic compounds may crystallise into Laves phases, namely, C14 and C36

hexagonal phases and C15 cubic phase [1,2]. The three Laves phases are retained at RT in the as-cast samples when ZrCr

2 is prepared by arc melting [3]. Single cubic phase samples

can be obtained by annealing treatments of those as-cast samples. On the other hand, much more complicated experimental procedures seem to be required to obtain single hexagonal ones. In this work we investigate different experimental routes to synthesize hexagonal and cubic ZrCr

2 samples directly by arc melting. We analyze the influence of the sample temperature

during arc melting process on the phase abundances. In addition we investigate the effect of plasma composition in the arc melting process under different Ar/H

2 atmospheres.

Structural, morphological and chemical characterizations of the samples have been accomplished by means of Rietveld refinement of x-ray diffraction patterns, Scanning Electron Microscopy and Energy Dispersive x-ray Analysis. Obtained experimental results will be discussed in the light of present knowledge of the system and their relationship to hydride formation will be considered. Acknowledgements We thank Mr. F. Moreno for technical assistance. Financial support from Spanish MICINN under contract MAT2008-06547-C02-01 is also gratefully acknowledged. References 1. Wernick, J. H., in: Intermetallic Compounds: Westbrook, J. H., (Ed.), New York: Wiley, (1967), 197-216. 2. Laves, F., Theory of alloy phases, Metals Park, OH: American Society for Metals, (1956) 124. 3. Alisova, S. P., Budberg, P. B., and Shakhova, K. I., Soviet Physics-Crystallography, 9 (1964) 343.

175

Thermal Decomposition and Reversibility of Ca(BH4)2

M.H. Sørby, M.D. Riktor, I.L. Jansa and B.C. Hauback Physics Department, Insitute for Energy Technology, Kjeller, Norway

Email: magnuss@ife.no Ca(BH4)2 receives considerable attention as a possible hydrogen storage material due to a) its high gravimetric and volumetric hydrogen capacity, b) predicted expected suitable thermodynamics [1] and c) easier reversibility than other investigated borohydrides [2,3]. The chemistry of Ca(BH4)2 is complicated. It crystallizes in at least 4 ploymophs (α, α’, β and γ are well characterized). Earlier in-situ synchrotron powder X-ray diffraction (SR-PXD) work [4], showed formation of small amounts of a new phase suspected to be a fifth modification, tentatively called δ-Ca(BH4)2. Recent efforts have been successful in obtaining a sample with the δ-phase as the only crystalline product. However, the new experiments revial that the formation of the phase is accompanied by gas release. It is thus not a new Ca(BH4)2 modification, but an intermediate decomposition product. Its crystal chemistry and thermal decomposition behaviour are investigated by high-resolution and in-situ SR-PXD, repectively. The thermal decomposition routes of Ca(BH4)2 are highly dependant on the experimental conditions. Decompositon proceeds through mixtures of amorphous and crytalline phases and many intermediate decompostion products are not yet fully characterized. An intermediate decompsition product, CaB2Hx, has been suggested to allow reversibility at mild conditions and without use of catalysts [5]. Further investigations have shown that easy rehydrogenation in some cases is possible also without the presence of the CaB2Hx phase: A mixture of crystalline CaH2 and amporhous decomposition products was rehydrogenated at 100 bar and 305 oC to yield α- and β-Ca(BH4)2 as well as unreacted CaH2 without use of catalyst. The conditions for easy rehydrogenation are discussed. References 1. K. Miwa, M. Aoki, T. Noritake, N. Ohba, Y. Nakamori, S. Towata, A. Zuttel,, S. Orimo, Phys. Rev. B 74, (2006), 155122. 2. E. Rønnebro and E. H. Majzoub, J. Phys. Chem. B 111, (2007), 12045. 3. J.-H. Kim, J.-H. Shim, and Y. W. Cho, Journal of Power Sources 181, (2008), 140. 4. M. D. Riktor, M. H. Sørby, K. Chlopek, M. Fichtner, F. Buchter, A. Zuettel, B. C. Hauback, Journal of Materials Chemistry 17, (2007), 4939. 5. M. D. Riktor, M. H. Sørby, K. Chlopek, M. Fichtner, B. C. Hauback, Journal of Materials Chemistry 19, (2009), 2754.

176

Hydrogen Dissolution in Pd Nanoparticles Effect on Their Structure in Metal-Carbon Nanocomposite

A.A. Nekrasova*, M.N. Efimov, E.L. Dzidziguri*, E.N. Sidorova*, L.M. Zemtsov,

G.P. Karpacheva A.V. Topchiev Institute of petrochemical synthesis RAS

*National University of Science and Technology «MISIS» Email: _nekrasova1987@mail.ru

The goal of this work is investigation Pd nanoparticles structure at hydrogen

dissolution in them in metal-carbon nanocomposites based on IR-pyrolyzed polyacrylonitrile (PAN), which has graphite-like structure, nanodiamonds (ND) and nanoscale Pd particles.

Metal-carbon composites were prepared under the conditions of IR pyrolysis of a precursor based on PAN, ND and PdCl2. X-ray structure analysis showed splitting Pd reflection peaks as synthesis temperature increased. That indicates hydrogen (which released in the dehydrogenation of the main PAN polymer chain) dissolution in metal. The table 1 shows results of calculations of the lattice parameters of Pd nanoparticles and dissolved hydrogen amount. Table 1. The lattice parameters of Pd nanoparticles and mean amount of dissolved hydrogen depend on synthesis temperature.

T, °C d, Å Δ, Å Hydrogen amount, at. %

500 2,2296 0,0249 21,47

600 2,2216 0,0169 14,57

800 2,2176 0,0129 11,12

900 2,2067 0,002 1,72

1100 2,2018 -0,0029 - Δ – the lattice parameter difference between Pd and Pd with dissolved hydrogen, Δ

= dPd - dPd/ND. There are dPd – the lattice parameter of Pd with dissolved hydrogen (Pd/PAN–ND); dPd/ND – the lattice parameter of Pd which was prepared on ND (Pd/ND) under the same conditions. dPd/ND = 2,2047 Å.

The photomicrographs were used to construct particle-size distribution histograms by the method of random secants. Respective of the intensity of IR pyrolysis, metallic particles were distributed over sizes in a narrow interval from 1 to 12 nm.

It was shown hydrogen dissolubility in palladium decreased as pyrolysis temperature increased. That may be caused both decreasing structure faultiness of metal phase and Pd lattice parameter decreasing.

That may be caused decreasing both structure faultiness of metal phase and Pd lattice parameter.

177

Structural Peculiarities of Zr(Hf)4Fe2OxDy Deuterides I.Yu. Zavaliy1, R.V. Denys1, I.V. Koval’chuck1, R. Černý 2

, V. Pecharski3, P. Zavalij4 (1) Physico-Mechanical Institute of NAS of Ukraine, 5 Naukova Str., 79601 Lviv, Ukraine

(2) University of Geneva, Laboratory of Crystallography, 24, quai Ernest-Ansermet, 1211 Geneva 4, Switzerland (3) Ames Laboratory, US Department of Energy, Iowa State University, Ames, IA 50011-3020, USA

(4) Department of Chemistry and Biochemistry, University of Maryland, College Park, MD 20742, USA E-mail: zavaliy@ipm.lviv.ua

The ability to dissolve oxygen or to form new oxygen-stabilized compounds is an interesting peculiarity of intermetallic compounds with the Ti2Ni type structure. The so-called η-phases with this structure display intriguing behaviours during their hydrogenation. For example, the hydrogenation behaviour of the parent Zr2Fe (CuAl2-type) and derivative η-Zr4Fe2Ox compounds is considerably different with respect to their disproportionation. Furthermore, hydrogen storage capacity of Ti-, Zr-, and Hf-based η-phases is a function of oxygen concentration. The Hf2Fe intermetallic compound (Ti2Ni-type) forms the hydride with ~4.8 H/f.u., whose crystal structure and magnetic properties were studied in the past [1]. However, some inconsistencies in the proposed model as well as the successful synthesis of the series of Hf4Fe2Ox (x=0÷0.6) and Zr4Fe2Ox (x=0.25÷0.6) deuterides prompted us to further examine details of their crystal structure. Local disorder of the metal and D atoms was found in the deuterides with low O-content (see Tables 1 and 2). Structural peculiarities and possible reasons for disorder in these compounds will be discussed. Table 1. Atomic parameters of the Hf2FeD4.0(1) deuteride (sp.gr. Fd-3m; a=12.84086(8) Å, comb. refinement: PND (�=1.494 Å), XRD (� =1.5406 Å); Rwp=4.41%, Rp=3.48%, χ2=2.63)

Atom Site Surrounding x/a y/b z/c Uiso×102 (Å2) Occup. Hf1 48f – 0.3201(1) 1/8 1/8 2.90(3) 1.0(–) Hf2 32e – 0.4834(2) x x 3.3(1) 0.5(–) Fe1 32e – 0.3057(2) x x 3.49(8) 0.622(3) Fe2 32e – 0.2664(3) x x 3.49(8) 0.378(3) D(T0) 32e Hf13 0.0680(7) x x 4.2(1) 0.290(8) D2 192i Hf12Hf1Fe1 0.2613(4) 0.1851(5) 0.3653(4) 4.2(1) 0.254(4) D3 96g Hf13Fe1 0.2827(8) x 0.155(1) 4.2(1) 0.179(5) D3(T) 96g Hf13 0.2697(3) x 0.0939(7) 4.2(1) 0.209(5) D4(T) 48f Hf1Hf22 0.486(1) 1/8 1/8 4.2(1) 0.163(6) D8 16c Hf16 0 0 0 4.2(1) 0.27(1)

Table 2. Atomic parameters of the Zr4Fe2O0.25D8.5(3) deuteride (sp.gr.Fd-3m; a=13.06981(5)Å, comb. ref.: PND (λ=1.4875 Å), synchr. XRD (λ=0.8502 Å); Rwp=6.42% Rp=5.72% χ2=1.79)

Atom Site Surrounding x/a y/b z/c Uiso×102 (Å2) Occup. Zr1 48f – 0.31747(8) 1/8 1/8 2.61(2) 1.0(–) Zr2 32e – 0.4834(1) x x 3.51(8) 0.5(–) Fe1 32e – 0.3000(1) x x 2.77(6) 0.698(3) Fe2 32e – 0.2625(3) x x 2.77(6) 0.302(3) O 16c Zr16 0 0 0 2.82(9) 0.251(9) D(T0) 32e Zr13 0.0660(3) x x 2.82(9) 0.51(1) D1 32e Zr13Fe1 0.205(1) x x 2.82(9) 0.19(1) D1(T) 32e Zr13 0.173(1) x x 2.82(9) 0.161(9) D2 192i Zr12Zr2Fe 0.2648(3) 0.1850(5) 0.3685(4) 2.82(9) 0.253(3) D3 96g Zr13Fe1 0.2812(4) x 0.1543(6) 2.82(9) 0.362(6) D3(T) 96g Zr13 0.2656(6) x 0.107(1) 2.82(9) 0.189(6) D4(T) 48f Zr1Zr22 0.476(1) 1/8 1/8 2.82(9) 0.149(6)

Reference: 1. Soubeyroux J.L, Fruchart D., Derdour S. et al. J. Less-Common Met. 129 (1987) 187–195.

178

Hydrogenation of Pseudo-Binary Ho1–xMxFe2 Compounds (M = Zr, Hf; 0 ≤ x ≤ 0.2)

I.V. Koval’chuck1, A.B. Riabov1, O.R. Myakush2, P.S. Myronenko2, B.Ya. Kotur2

1 Karpenko Physico-Mechanical Institute, NAS of Ukraine, Naukova St. 5, 79601 Lviv, Ukraine 2 Ivan Franko National University of Lviv, Kyryla and Mefodia St. 6, 79005 Lviv, Ukraine

E-mail: kovalchuk@ipm.lviv.ua Many of AB2 (A=rare earth element; B=3d-element) binary compounds absorb hydrogen forming amorphous or crystalline hydrides depending on the hydrogenation temperature and hydrogen pressure [1-3]. One can modify hydrogenation properties of AB2 compounds by doping them by a third component either in the rare earth or in the 3d-element sublattice. Earlier we have studied hydrogenation capacity and crystal structure of pseudo-binary alloys HoFe2–xAlx (x = 0.4; 0.8) [4]. Substitution of Fe by Al causes structure transformation of alloys from the C15 (MgCu2) cubic Laves phase into the C14 (MgZn2) hexagonal Laves phase type structure for x = 0.8. The hydrides retain the structure of the basic alloys. The aim of this investigation is to study influence of partial substitution of Ho by other hydride forming elements – Zr or Hf – on the structure and hydrogenation capacity of the HoFe2 alloy. Ternary alloys Ho1-xZrxFe2 and Ho1-xHfxFe2 (0 ≤ x ≤ 0.2) are single phase and adopt the structure of the parent binary compound HoFe2 (C15-type). Partial substitution of Ho (rHo=1.76 Å) by smaller Zr (rZr=1.60 Å) or Hf (rHf=1.59 Å) linearly decreases the lattice parameter of the cubic Laves phase. However, the contraction of the unit cell for Zr-containing pseudobinaries is substantially weaker than that for the Hf-substituted compounds, being 1.8 and 4.5% for Ho0.9M0.1Fe2 (M=Zr, Hf) compounds, respectiely. The alloys were hydrogenated at room temperature under a pressure of 0.12 MPa after preliminary activation in vacuum at 350-400 oC. Substitution of Ho by Hf linearly decreases hydrogenation capacity of alloys from 4.39 H/f.u. for HoFe2 to 3.1 H/f.u. for Ho0.8Hf0.2Fe2. Hydrides remain crystalline and preserve the structure of the parent alloys. Hydrogenation of Zr-containing pseudo-binary compounds is accompanied by volume expansion for appr. 24% for both studied hydrides, whereas for Ho0.9Hf0.1Fe2H3.72 hydride this parameter is somewhat lower, 22%. Hydrogenation ability and structure characteristics of the Ho1-xZrxFe2 alloys and their hydrides are similar to the characteristics of the Ho1-

xHfxFe2 alloys. Specific increment of the unit cell volume per absorbed hydrogen atom for Zr-containing alloys increases linearly from 2.7 Å3 to 3.5 Å3, remaining constant for Hf-substituted material. Results of the crystal structure refinement of the pseudobinary Ho1–xMxFe2 (M=Zr, Hf; 0 ≤ x ≤ 0.2) compounds and their hydrides will be presented and discussed. References 1. X.G. Li, A. Chiba, K, Aoki, T. Matsumoto, Intermetallics, 5 (1997) 387-391. 2. M. Dilixiati, K. Kanda, K. Ishikawa, K. Suzuki, K. Aoki, J. Alloys Compd., 330-332 (2002) 743-746. 3. I.Yu. Zavaliy, R. Černý, V.N. Verbetsky, R.V. Denys, A.B. Riabov, J. Alloys Compd., 358 (2003) 146-151. 4. I. Koval’chuck, O. Myakush, R. Denys, B. Kotur, Visnyk Lviv Univ. Ser. Chem., Issue 48 (2007) 194-197.

179

Lattice Strain Formation in Ti-V-Mn During the First Absorption and Desorption

S. Yamazaki, J. Nakamura, K. Sakaki, Y. Nakamura and E. Akiba

National Institute of Advanced Industrial Science and Technology (AIST) AIST Central 5, 1-1-1 Higashi, Tsukuba, Ibaraki 305-8565, Japan

Email: saishun.yamazaki@aist.go.jp

Ti-V-Mn solid-solution alloy with a BCC structure forms three hydrogenated phases between 0.001 and 5.0 MPa H2 at moderate temperatures [1]. The crystal structure changes from BCC to pseudo-cubic FCC and FCC with increasing the hydrogen content. The metal lattice expands by ~45% totally during hydrogen absorption. In this study, we evaluated lattice strain introduced into each hydride phase of Ti1.0V1.1Mn0.9 during the first absorption and desorption using powder X-ray diffraction (XRD).

An alloy ingot of Ti1.0V1.1Mn0.9 was prepared by arc melting. Hydride samples were prepared by hydrogen absorption and desorption along the P-C isotherms. The measurements were stopped at selected hydrogen contents and then the samples were deactivated with acetone before exposing air. XRD of the prepared samples was measured using a diffractometer, Rigaku, RINT-2500V. Structural parameters were refined using the Rietveld refinement program RIEAN-2000 [2]. Isotropic lattice strain was evaluated from the profile parameters in the Gaussian and Lorentzian components of the pseudo-Voigt function, obtained from the refinement.

The solid solution phase (Ti1.0V1.1Mn0.9H1.2), mono-hydride phase (Ti1.0V1.1Mn0.9H2.8) and di-hydride phase (Ti1.0V1.1Mn0.9H5.4) were obtained during the first absorption. Isotropic lattice strain of the solid solution phase, mono-hydride phase and di-hydride phase was ~0.7 %, ~1.2 % and ~2.3 %, respectively. The hydride phase (Ti1.0V1.1Mn0.9H2.8) obtained in the desorption process contained both the mono-hydride phase and di-hydride phase, although the hydrogen content is the same as the mono-hydride sample obtained in absorption. Lattice strain of the two phases was ~3.2 % and ~2.7 %, respectively. Significant change was not observed in crystallite size during the whole reaction. These results indicate that lattice strain increased with phase transformation during absorption, and it increased more with the following phase transformation during desorption.

This work was supported by the New Energy and Industrial Technology Development Organization (NEDO) under “Advanced Fundamental Research on Hydrogen Storage Materials (HYDRO-STAR)”. References 1. Y. Nakamura, E. Akiba, J. Alloys Compd., 311 (2000) 317 2. F. Izumi, T. Ikeda, Mater. Sci. Forum, 321–324 (2000) 198

180

Pressure-Induced Phase Transformation of LaH3 Studied by Raman and UV-Visible Absorption Spectroscopy

T. Kume,A N. Shimura,A S. Sasaki,A H. Shimizu,A A. Machida,B T. Watanuki,B K. AokiB

and K. TakemuraC A Dept. of Materials Science and Technology, Gifu University, Japan

B Synchrotron Radiation Research Center, JAEA, Japan C National Institute for Material Science, Tsukuba, Japan

Email: kume@gifu-u.ac.jp

For various rare-earth tri-hydrides, the structural phase transitions have been investigated under high pressure[1]. The hexagonal phases of metal tri-hydrides, for example YH3, ScH3 and so on undergo the phase transition to the fcc phases by applying the pressure[1,2]. The transition pressure depends on the ion size of the rare-earth metal, and linearly increases as the ion size decreases. On the other hand, for LaH3 which is in the fcc structure at the ambient condition, there is no report for the structural change up to 25 GPa[3]. In this paper, we present high-pressure Raman and visible absorption studies on LaH3 which is initially in fcc phase. The experiments at high pressures were carried out by a diamond anvil cell (DAC). Figure 1 shows the high pressure Raman spectra of LaH3 surrounded with H2 pressure medium. We observed a distinct change of the Raman spectrum at 22 GPa, at which a strong La peak at 82 cm-1 and H peak at 780 cm-1 appear suddenly. Since the fcc phase of LaH3 possesses only one Raman active mode, the appearance of these new peaks means the phase transition to a structure with lower symmetry than the fcc. Moreover, the spectral feature of this post-fcc phase is quite difference from the hcp phases of YH3 and ScH3[4]. Therefore, the structure of the post-fcc phase is thought not to be in the close packed structure even in the higher density phase. From the optical absorption measurements of LaH3, the optical band gap of about 1.5 eV at ambient condition was found to be still open even at 45 GPa, in contrast to the cases for YH3 where the optical gap is closed in the fcc phase at 25 GPa[4]. References 1. T. Palasyuk and M. Tkacz, Solid State Commun. 141 (2007) 354. 2. A. Machida, et al., Phys. Rev. B 76 (2007) 052101. 3. T. Palasyuk and M. Tkacz, J. Alloys and Comp. 468, (2009) 191. 4. T. Kume, et al., Phys. Rev. B 76 (2007) 024107.

Fig. 1 Raman spectra of LaH3 obtained for various pressures up to 45 GPa. The strong peaks at 1330 cm-1 are from diamond windows.

0 500 1000 1500

LaH3

Inte

nsity

(arb

. uni

ts)

Pressure (GPa)

Wavenumber (cm-1)

0.4

11.2

15.4

31.125.722.119.7

36.4

39.1

42.7

45.4

181

Investigation of Interaction of Ti–Al Alloys with Ammonia

V.Fokin, E.Fokina, and B.Tarasov Institute of Problems of Chemical Physics of the Russian Academy of Sciences, Chernogolovka, Russia

Email: fvn@icp.ac.ru

Earlier by us [1] it has been shown, that at interaction of titanium powder with the size of particles about 100 microns with ammonia under initial pressure of 0.7–0.8 MPa at the temperature 250–300°C in the presence of NH4Cl the high-dispersed dihydride of titanium is formed, containing 0.1–0.15 atoms of nitrogen on a molecule of dihydride, with parameters of a tetragonal lattice a = 0.4468 and c = 0.4391 nm. The powder has a specific surface area of 30–55 m2/g and is steady in an inert atmosphere up to 600°C. Such value of a specific surface area corresponds to the sizes of powder particles of 15–30 nm. In the given work the processes occurring in systems TiAl–NH3, Ti3Al–NH3, Ti10.1Al–NH3 and Ti15.7Al–NH3 in an interval of the temperatures 100–500°C under ammonia pressure of ~1.5 MPa are investigated in the presence of activator NH4Cl. Initial powders of alloys TiAl and Ti3Al with the average size of particles about 100 microns represent single-phase intermetallic compounds, and powders of alloys Ti10.1Al and Ti15.7Al are the solid solutions of 9 and 6 at. % Al in α-Ti. It is established, that at interaction of the such solid solutions, i.e. practically of the titanium with small additives of aluminium, with ammonia the formation of cubic and/or tetragonal modification of titanium dihydride with the size of particles of 35–45 nm are observed only at temperature of 300°C, that can testify to decrease of a rate of titanium hydrogenation at doping by aluminium. The appreciable interaction of TiAl with NH3 begins at temperature of 100°C. At treatment at 150°C the hydride phases of composition TiAlH0.7–1.5 with minor alteration of parameters of a crystal lattice of initial intermetallide are formed. At the temperature 300°C the hydride-nitride of titanium aluminide of composition TiAlH0.6N0.2 was obtained as a powder with the size of particles about 0.3 microns. Intermetallide Ti3Al in an ammonia atmosphere is steadier – the hydride-nitride of titanium aluminide with the size of particles of 0.25–0.15 microns is formed only at temperatures of 450–500°C. Reference 1. V. Fokin, E. Fokina, B. Tarasov, S. Shilkin, Int. J. Hydrogen Energy, 24 (1999), 111-114.

182

Formation of Transition Metal Hydrides at High Pressures O. Degtyareva, C.L. Guillaume, J.E. Proctor, E. Gregoryanz

Centre for Science at Extreme Conditions and School of Physics & Astronomy, The University of Edinburgh, Edinburgh, EH9 3JZ, United Kingdom

Email: o.degtyareva@ed.ac.uk There is a considerable interest in producing metallic, and possibly superconducting, states of hydrogen at multimegabar pressures; the pressures that are thought to be needed for metallization (>400 GPa) are however currently not achievable with static compression techniques. It has been recently suggested that hydrogen-rich compounds such as CH4, SiH4, and GeH4 with hydrogen being “chemically pre-compressed” will require pressures far less than expected for pure hydrogen at equivalent densities to enter metallic states [1,2]. As is the case for pure hydrogen, these compounds are considered to be good candidates for high temperature superconductors in their dense metallic forms. For silane (SiH4), however, there is a disagreement between different theoretical studies with metallization pressure ranging from above 91 GPa [2] to as high as 220-250 GPa [3,4]. Recent experimental study claimed a discovery of metallization and superconductivity of silane at pressures above 50 GPa and reported a hexagonal close-packed (hcp) structure for the metallic phase of silane [5]. On further compression above 110 GPa this phase is found to partially transform to a molecular insulating phase with a positive volume change of �25% which co-existed with the metallic hcp phase up to 190 GPa [5] – an observation that contradicts thermodynamic rules (i.e. Le Chatelier's principle). Subsequent ab initio calculations [4,6] showed that the proposed metallic hcp structure is mechanically unstable suggesting a possible partial dissociation and a phase of a different composition. These discrepancies between various theoretical studies as well as experimental work prompted us to further investigate the crystal structure of silane at high pressures. Using raman and x-ray diffraction techniques we found [7] that silane partially decomposes at high pressures and room temperature into pure Si and hydrogen, where released hydrogen readily reacts with the surrounding metals in the diamond anvil cell chamber forming metal hydrides. We find a formation of Re hydride after decomposition of silane and reaction of hydrogen with the Re gasket. We also identify the recently reported metallic hcp phase of silane [5] as PtH [8], that forms upon the decomposition of silane and reaction of released hydrogen with platinum metal that is present in the sample chamber. Thus, silane is shown to be acting as an internal hydrogen source in the high-pressure synthesis of metal hydrides. References 1. N.W. Ashcroft, Phys. Rev. Lett. 92 (2004), 187002. 2. J. Feng et al., Phys. Rev. Lett. 96 (2006), 017006. 3. C. Pickard and R. Needs, Phys. Rev. Lett. 97 (2006), 045504. 4. M. Martinez-Canales et al., Phys. Rev. Lett. 102 (2009), 087005. 5. M. Eremets et al., Science 319 (2008), 1506. 6. D. Kim et al., PNAS 105 (2008), 16454 7. O. Degtyareva et al., Solid State Commun. 149 (2009) 1583-1586 8. N. Hirao, H. Fujihisa, Y. Ohishi, K. Takemura, T. Kikegawa, International Symposium on Metal-Hydrogen Systems, Reykjavik, Iceland, 2008; See also Acta Cryst. A 64 (2008) C609-C610.

183

Hydrogenation of TiNi Shape Memory Alloy Produced by Mechanical Alloying T. Saito, T. Yokoyama and A. Takasaki

Department of Engineering Science and Mechanics, Shibaura Institute of Technology, Tokyo, Japan Email: m408030@shibaura-it.ac.jp

TiNi shape memory alloy has shape memory effect due to thermo-elastic martensitic transformation between B2 parent and monoclinic martensitic phases. Effect of hydrogen on the martensitic transforamation has been studied by several researchers. However, the conclusion is still contraversial. Mutiple-stage transformation was shown after hydrogenation [1], on the other hand, there was report that martensitic transformation temperature was lowered by cathodic hydrogen charging [2]. Mechanical alloying (MA) and direct current sintering are one of ways to produce powder and bulk alloy by solid state reaction, for which we have previously reported [3, 4]. In this study, influence of hydrogen on martensitic transformation behavior of TiNi shape memory alloy produced by a combination of MA and direct current sintering was investigated. Commercially pure Ti and Ni elemental powders with chemical composition of Ti50Ni50 (at%) were mechanically alloyed in stainless steel vials (45ml) with several stainless steel balls in an argon atmosphere. The powder after MA was compacted and sintered at 973K for 10min under vacuum condition (2Pa) at a pressure of 20MPa. The sintered bulk sample was then annealed in a furnace at 773K for 1 hour under a high vacuum condition (10-3Pa). Gaseous hydrogen charging was conducted at several hydrogen pressures, temperatures and times to control hydrogen concentration in the sample in order to evaluate the relation between hydrogen concentration and their martensitic transformation behaviors. The phases of the samples were determined by X-ray diffraction (XRD) measurement. The martensitic transformation behavior was determined by differential scanning calorimetry (DSC), and the hydrogen desorption property was measured by thermal desorption spectroscopy (TDS). The bulk samples after MA and direct current sintering consisted of TiNi (B2) phase with a small amount of Ti2Ni phase, and showed martensitic transformation (exthothermic) and reverse transformation (endothermic). The TiNi hydride, with TiNi (B2) phase and unknown phase, was observed after hydrogenation. The martensitic and reverse transformations were observed after hydrogenation, however, enthalpy of the martensitic transformaiton was smaller than that of the reverse transforamtion. Eventually, enthalpy of the martensitic transformation turned to be similar to that of the reverse transformation after 1 cycle of the transformations. It is implied that hydrogen-induced martenstic transfroamtion occured during hydrogenation. References 1. T. Ohba, F. Yanagita, M. Mitsuka, T. Hara and K. Kato, Mater. Trans., 43 5, (2002), 798. 2. W. Jihong, Z. Xiaotao, W. Zhiguo, L. Yanzhang, Rare Metals, 24 2, (2005), 190. 3. A. Takasaki, Phys. Stat. Sol. (a), (1998), 183. 4. T. Saito, A. Takasaki, Trans. Mater. Res. Soc. of Japan, 34[3], (2009), 403.

184

Boron - Impurity Trap for Atomic Hydrogen in Nickel Alloys

Zvyagintseva A.V. Voronezh State Technical University, 394026, Moskovsky pr. 14, Voronezh, Russia

tel. (4732) 52-19-39 E-mail: zvygincevaav@mail.ru One of the biggest challenges in creating a promising technology products (electronics, nuclear power engineering, mechanical engineering, space technology, etc.) is to develop coatings to extend the service life of the product. State of the surface determines the operational characteristics of structural elements for various applications. Among the surface-active substances determining role belongs to hydrogen. The aim of this work is to study the influence of boron on the process of hydrogenation coatings based on nickel. The relative content of boron in the alloy Ni-B is 0,5-1%. In terms of the atomic weight ratio of the alloying component increases by about 6-10 atm. %. This means that for every 10-15 Ni atoms as the implementation phase consists of 1 atom of boron. In this case, if there is unevenness in the distribution of the implementation phase (boron), there is instability in the force fields caused by the distortions of atomic structures of the main component with varying degrees of defects. Boron is an impurity substitution of small atomic radius and Ni doping boron observed decrease in the lattice parameter according to the results of electron-graphically research. According to our research increases the boron concentration in the alloy leads to a sharp increase in dissolved hydrogen in the coating, for two reasons: 1) increasing defect structure due to the increase in the number of lattice distortions by increasing the concentration of boron and, consequently, increases the probability of occurrence of structures with high potential; 2) According to electron diffraction studies for samples with high percentage of boron is observed a higher degree of "smearing" of the interference rings, which can be explained by the increase of the amorphous structure of the sample. The interaction with hydrogen atoms of the boron impurity form complexes. The binding energy of such complexes can be determined using the method of internal friction. Doping with boron and the formation of complexes of boron-hydrogen extends resource exploitation Ni coatings. This is due to the fact that the hydrogen atoms are certain times in the complexes (the boron atoms are traps hydrogen atoms). Thus, the hydrogen atoms remain in the coating and does not penetrate into the bulk of the base metal. Creating traps for hydrogen atoms may lead to an increase in the strength characteristics of the coating. In addition, there are structural traps, i.e. defects in the crystal structure. The pilot studies and on the basis of a mathematical model the following conclusions: 1.It was showed, that when extracting hydrogen from the nickel-based alloys with its doping boron atoms by the vacuum extraction of some fraction remains in the coating. A possible reason for this behavior is the presence of impurity and structural traps for hydrogen atoms. As an impurity traps should be considered the boron atoms. 2. Held mathematical modeling of the interaction of hydrogen atoms with impurity and structural traps. Determine the kinetics of capture of hydrogen atoms structural traps. 3. The physical model of the formation of tensile stresses in the vicinity of the boron atoms. Their appearance is due to the displacement of nickel atoms in the vicinity of the impurity boron.

185

Hydrogen Capacity of Structural Defects in the Nickel Coatings Doped with Boron

Zvyagintseva A.V.

Voronezh State Technical University, 394026, Moskovsky pr. 14, Voronezh, Russia tel. (4732) 52-19-39 E-mail: zvygincevaav@mail.ru

Structural defects have an impact on the reversible sorption of hydrogen by metal and hydrogen content per unit volume. The comparative analysis of the hydrogen content of the various structural defects in the electroplated nickel coatings doped with boron. The relative content of boron in the alloy Ni - B is 0,5 - 1%, but in terms of atomic weight ratio of the alloying component increases by about 6 - 10 atm. %. Therefore, as an object of study as a basis chosen system Ni - H. Effect of boron on the kinetics of formation of impurity segregations of atoms of hydrogen for possible structural defects of the alloy, obtained by electrocrystallization not taken into account. It is known that nickel in the interaction with hydrogen, forming hydrides. When electrocrystallization metal forming various structural defects, which alter the kinetics of hydrogen absorption and its content in unit volume. Extreme performance coatings on nickel based on reversible sorption of hydrogen were considered in the light of the stress fields caused by structural defects. The most important among them are dislocations, microcracks tops and wedge disclination. The hydrogen atoms interact with the fields of stress defects listed. This leads to the formation of segregation of hydrogen atoms. The hydrogen content per unit volume of metal increases. Edge dislocations formed during plastic deformation of metals. The density of edge dislocations (total length of dislocation lines per unit volume) increases by several orders of magnitude. The tops of microcracks are stress concentrators during the action of external loads. Wedge disclination were used to simulate the stress fields in the vicinity of some structural imperfections nickel coatings. They belong to the triple junctions of grain boundaries, polygonal finite wall of edge dislocations, twin peaks. In addition, the wedge disclination model the temperature and residual stresses in a hollow cylinder. A special feature of a wedge disclination is a logarithmic dependence on the coordinates of the first invariant of stress tensor. This dependence allows to obtain an exact analytical solution of the diffusion equation in the force field. These relationships indicate the ability of various defects capture hydrogen atoms from the solid solution based on nickel. The results of mathematical modeling showed that the major structural defects for hydrogen atoms are edge dislocations. This is due to their high density compared with other structural imperfections: the vertices of cracks and wedge disclinations. A comparative analysis of the kinetics of formation of hydrogen segregation to the edge dislocation, the top of microcracks and wedge disclinations. The kinetics of the process for the wedge disclination is subject to a linear law. The formation of hydrogen segregation to the top of microcracks and the edge dislocation occurs more slowly. For a stationary process defined by the hydrogen capacity of structural defects. In the vicinity of each of the structural defect is formed by hydrogen equilibrium segregation. They slightly increase the hydrogen content per unit volume of metal compared to binary hydrides. The main contribution comes from dislocations. Thus, structural defects do not alter the limiting possibilities of nickel on reversible sorption of hydrogen.

186

Influence of Hydrogen on Magnetic Arrangement of the Intermetallic Compounds RNi (R=Sm, Tb, Dy).

W. Iwasieczko1, H. Drulis1, S.A. Nikitin2, V.N. Verbetsky3, Yu. L. Yaropolov3.

1Institute of Low Temperature and Structure Research, Wroclaw, Poland 2Faculty of Physics Moscow State University, Moscow, Russia

3Chemistry Department Moscow State University, Moscow, Russia Email: W.Iwasieczko@int.pan.wroc.pl

Magnetic ordering temperatures of the rare earth intermetallic compounds (IMC) vary strongly with hydrogenation. The introduction of hydrogen atoms into the IMC lattice affects the electron structure and exchange interactions. The crystal lattice of R2Fe17 IMC strongly expand after hydrogenation [1]. It results in an exchange interaction and Curie temperature increasing. In some IMC it is possible to expect the essential change of electronic structure due to the filling of the 3d-band by the electrons transferred from the hydrogen atoms. The investigation of such compounds is important to understand of the hydrogenation effects on the magnetic ordering. The purpose of the this work is the investigation of the magnetic ordering in the RNi (R=Sm, Tb, Dy) IMC and their hydrides. The starting RNi IMC were synthesized by arc melting. X-ray powder diffraction measurements were performed to establish phase composition of the samples and the crystal structure of the compounds. SmNi, DyNi and TbNi samples were found to be single phase and possess CrB-, FeB- and TbNi-type structure, respectively. Hydrogenation was performed with the Sieverts-type volumetric apparatus at room temperature and hydrogen pressures up to 1.0MPa. Ternary hydrides SmNiH3.9, DyNiH3.4 and TbNiH3.4 have an orthorhombic CrB-type structure. Weak-field (100Oe) and strong-field (up to 50kOe) magnetization measurements were performed at SQUID-magnetometer. The magnetic properties of TbNi and SmNi strongly depend on the measurement conditions. In the ZFC mode in weak field and at temperature 1.7 K the magnitude of magnetizations is very low but increases rapidly with magnetic field. I(H) curves demonstrate the presence of metamagnetic transitions at 10-15 kOe. Isothermal magnetization saturates at 30kOe with large ferromagnetic moment. The remanent magnetization is almost equal to saturation magnetization. I(T) curve after ZFC demonstrates the strong increase of with heating-up. Derived experimental data indicate antiferromagnetic ordering type at low temperatures. These results are in good agreement with the neutron diffraction results, which indicate the presence of ferro- and antiferromagnetic components in the magnetic structure of TbNi and SmNi. From the magnetic properties of the YNi compound it follows, that Ni has no appreciable magnetic moment. Hydrogenation strongly modifies the magnetic ordering character of SmNi, TbNi and DyNi samples. The difference between ZFC and FC curves disappears, and the magnetization indicates the absence of appreciable ferro- and antiferromagnetic interactions. The hydrogen atoms fill or depopulate the conduction band with electrons, which results in the rapid decrease of the electron density at the Fermi level. Those result in the dumping of ferro - and antiferromagnetic interactions in RNi. References 1. I.S. Tereshina, S.A. Nikitin, V.N. Verbetsky, A.A. Salamova, J. Alloys and Compounds, 336, (2002), 36–40

187

Formation of 2NaBH4/MgH2 System from 2NaH/MgB2 by Hydrogenation.

M. Orlova1, S. Garroni2, D. Pottmaier3, F. Dolci4, G. B.M. Vaughan1, M. Baricco3 and M.D. Baró 2

1 ID11, European Synchrotron Radiation Facility, Grenoble, France 2 Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain

3 Dipartimento di Chimica IFM and NIS,Università di Torino, Torino, Italy 4European Commission, JRC-Institute for Energy, Petten, Netherlands

E-mail: maria.orlova@esrf.fr

Borohydrides with a general formula M(BH4)n (where M stands for an alkali or an alkali earth metal) are considered as prospective hydrogen storage materials due to a high percentage of hydrogen (up to 20 wt%) [1].

An interesting complex hydride for hydrogen storage is sodium tetraborohydride (M = Na). NaBH4 desorbs hydrogen relatively easily [2] but the reversible reaction requires very strong conditions (550 – 700 °C and 30 – 150 bar H2) [3]. It was found that MgB2 can facilitate the reversibility reaction [4]. It is thought that formation of NaBH4 does not occur directly, but follows the formation of NaMgH3. Although the reaction mechanism appears to depend strongly on the conditions of experiment.

In order to find out the optimal conditions for formation of 2NaBH4-MgH2 from 2NaH-MgB2 and to have a better understanding the reaction mechanism, several experiments have been performed. Hydrogen absorption by prior ball-milled compounds (2NaH-MgB2) was studied at isotherm at conditions at several temperatures (400, 425, 450 °C) at 100 bar H2 pressure. Diffraction experiments were performed in-situ using synchrotron radiation.

The results indicate different paths to NaBH4 formation depending on temperature and hydrogen pressure. Experimental results will be presented to discuss the optimal conditions for hydrogen absorption in the indicated system. References 1. L. Schlapbach, A. Zuttel, Nature, 414, (2001), 353-358. 2. D.S. Stasinevich, G.A. Egorenko, Russ J Inorganic Chem, 13(3), (1968), 341-343. 3. A. Zuttel, Naturwissenschaften, 91, (2004), 57-172. 4. J. J. Vajo, S. L. Skeith, F. Mertens, J. Phys. Chem. B, 109, (2005), 3719-3722

188

Modelling of Discrete TDS-Spectrum of Hydrogen Desorption

Yu.Zaika and N.Rodchenkova

Institute of Applied Mathematical Research, Karelian Research Centre, Russian Academy of Sciences, Petrozavodsk, Russia

Email: zaika@krc.karelia.ru, NIRodchenkova@yandex.ru A great concentration of hydrogen in metal leads to hydrogen embrittlement. Common metallurgical concentrations of dissolved hydrogen are in the range of 0.1 to 100 ppm. The authors of paper [1] have developed the hydrogen analyzer (AV-1). The device allows to measure the molecular hydrogen desorption flux from a solid sample by thermodesorption (TDS) method using industrial laboratory facilities. A cylindrical sample is placed into the quartz vacuum extractor. The extractor is placed into the furnace at a given temperature. The heat transfer to the sample is determined by thermal radiation. As the sample is heated, atomic hydrogen diffuses inside the bulk and is desorbed from the surface in a molecular form. The extraction curve (measurements of the mass-spectrometric hydrogen analyzer AV-1) is recorded. The curve is used for further processing (in particular, the kinetic parameters of models are estimated). The dependence of the desorption flux with respect to the temperature at uniform heating (the TDS-spectrum) usually has several peaks. Besides the bulk processes, the surface processes may affect the desorption of hydrogen [2]. In experiments with monotonous heating it is observed that background hydrogen fluxes from the extractor walls and fluxes from the sample can not be distinguished. Thus the temperature extraction curve is doubtful. So it is used a discrete TDS-spectrum: the sample is removed from an analytical part of the device for certain time period after external temperature increases stepwise. The report is devoted to the development of mathematical tools for experimental measurements processing. Boundary-value TDS-problem for cylindrical sample taking into consideration sample heating, diffusion in the bulk, hydrogen capture by the defects of two types, penetration from the bulk to the surface and desorption is presented. The model aimed to analyze the dynamics of low common concentrations of hydrogen (without preliminary saturation in laboratory). The difference scheme (of the alternating directions Peaceman-Rachford method) and computational algorithm are developed. It is known than the first TDS-spectrum peak corresponds to surface hydrogen, the second one corresponds to bulk hydrogen. Numerical modelling allows to choose a region on the extraction curve which corresponds to the initial quantity of the surface hydrogen, to evaluate the value of the activation energies of diffusion and desorption, to estimate the parameters of reversible capture and parameters of hydride phases decomposition. The hydride phase is considered as a trap which decomposes only when critical temperature is reached. More complicated model is presented in [3]. The particles of metal hydride powder have a different forms, decomposition begins with new phase nucleation at the surface defects. Nuclei grow and form a metal skin. But if the amount of particles is huge then it is possible to model the powder as spherical particles of large number of radii with growing uniform metal skin. References 1. A.M. Polyanskiy, V.A. Polyanskiy, D.B. Popov-Diumin, E.A. Kozlov, Int. J. Alternative Energy and Ecology, 6 (38), (2006), 29–31. 2. I.E. Gabis, T.N. Kompaniets, A.A. Kurdyumov, in: A.P. Zakharov (Edt.), Interaction of Hydrogen with Metals, Nauka, Moscow, 1987, pp. 177–206 (in Russian). 3. Yu.V. Zaika, N.I. Rodchenkova, Applied Math. Modelling, 33, (2009), 3776–3791.

189

Nuclear Magnetic Resonance Study of Hydrogen Motion in A15-Type Ti3SbHx

A.V. Soloninin and A.V. Skripov

Institute of Metal Physics, Urals Branch of the Academy of Sciences, Ekaterinburg, Russia Email: alex.soloninin@imp.uran.ru

The Ti3Sb compound belongs to the family of cubic A3B intermetallics with A15-type structure. These intermetallics show a number of interesting physical properties including superconductivity with critical temperatures up to 23 K. Some of the A15-type compounds (mostly those with A = Ti and Nb) can absorb large amounts of hydrogen. The host lattice of these materials retains the A15-type structure after hydrogen absorption. However, little is known about H dynamics in these hydrides. In this work, we report the results of a nuclear magnetic resonance (NMR) study of H jump motion in A15-type Ti3SbHx. We have measured the proton NMR spectra and spin-lattice relaxation rates R1 in the powdered samples of Ti3SbHx (x = 0.78, 1.8 and 2.5) over wide ranges of the temperature (40 – 420 K) and the resonance frequency (14 – 90 MHz). Our measurements have revealed peaks in the temperature dependence of R1. As typical of the R1(T) peaks due to atomic jump motion, both the positions and the amplitudes of these peaks depend on the resonance frequency. Each of the peaks is expected to appear at the temperature at which the H jump rate becomes nearly equal to the resonance frequency [1]. At the frequency of 14 MHz, the R1(T) maximum is observed at 255 K for Ti3SbH0.78 and at 320 K for Ti3SbH1.8. These results indicate that hydrogen mobility decreases with increasing H content. It should be noted that the H jump motion responsible for the observed R1(T) peaks is spatially-restricted (localized). This is supported by the behavior of the width of the 1H NMR spectra: the observed motional narrowing of the spectra is only partial, so that the line width remains to be rather large (~10 kHz) up to 420 K. For Ti3SbH2.5, the main R1(T) peak is not reached in the studied temperature range; however, a new minor R1(T) peak appears near 150 K at the frequency of 14 MHz. This low-temperature peak can be attributed to a very fast localized H motion which is not observed in the compounds with lower H content. The unusual features of H jump processes in Ti3SbHx may be related to the structure of the sublattice of interstitial sites partially occupied by H atoms. According to recent inelastic neutron scattering and neutron diffraction results [2], at high H concentrations most of H atoms in Ti3SbHx are located at the tetrahedral 6d (Ti4) sites, and about 11% of H atoms occupy the tetrahedral 24k (Ti3Sb) sites. The sublattice of the 24k interstices consists of closely-spaced pairs of sites (the corresponding k – k distance is 1.48 Å), and the nearest-neighbor d – k distance is also quite short (1.22 Å). It is natural to assume that such short k – k and d – k distances are responsible for the fast localized H motion in Ti3SbHx. References 1. R.G. Barnes, in: Hydrogen in Metals III (ed. H. Wipf), Springer, Berlin, 1997, p. 93-151. 2. H. Wu, A.V. Skripov, T.J. Udovic, J.J. Rush, S. Derakhshan, H. Kleinke, J. Alloys Compd. (2010), doi: 10.1016/j.jallcom.2009.12.187

190

Structural Phase Transitions and Dynamic Relaxation Processes in Calcium Borohydride

A.Paolone,1,2 O. Palumbo,1,2 P. Rispoli,1 R. Cantelli,1 E. Rönnebro3, D. Chandra4 1 Sapienza Università di Roma, Dipartimento di Fisica, Piazzale A. Moro 2, I-00185 Roma, Italy

2 CNR-ISC, U.O.S. Sapienza, Piazzale A. Moro 2, 00185 Roma 3 Pacific Northwest National Laboratory, 908 Battelle Blvd., Richland, WA 99352, USA

4 University of Nevada, 1664 N Virginia Street, Reno, NV 89557-0136, USA Email: annalisa.paolone@roma1.infn.it

A detailed investigation of Ca(BH4)2 has been conducted by means of anelastic spectroscopy, differential scanning calorimetry, thermogravimetry and mass spectrometry, both on commercially available powders (Sigma-Aldrich) and on samples purified in the author’s Lab [1]. Thermal analysis shows that, between 300 K and about 470 K, all samples exhibit release of THF ranging between 2% and 5%. On further heating, hydrogen is released in two steps centered around 640 and 690 K, as indicated by two well defined peaks in the DSC curves. Concomitantly, anelastic spectroscopy experiments have been carried out for the first time. On heating above room temperature, the dynamic Young modulus, E, shows a huge decrease when the THF release is taking place. At about 370 K the E curve displays a drastic slope variation, which is presumably due to the α to α' phase transformation. On further heating, the modulus curve shows an inversion just above 450 K, which is likely the signature of the onset of the α' to β phase transformation. In the as-prepared samples containing the α phase, the elastic energy loss displays a thermally activated relaxation peak centered around 110 K for a vibration frequency of ~580 Hz. This anelastic process can be fitted by a Debye curve in which both the activation energy and the relaxation time are distributed with a gaussian law. The best fit for the mean activation energy and pre-exponential factor of the relaxation rate gave, respectively, the values of W=0.21 eV and τ0

−1= 1014 s-1, which is typical of atom-complex relaxation. Thermal ageing steps from 320 K to 440 K, which induce evolution of the α to α' transformation, reduce the peak height and introduce a broad peak centered around 200 K. Finally, after a thermal treatment at 600 K, when the sample is completely in the β phase, all peaks disappeared. Possible mechanisms responsible for the observed relaxation processes will be discussed. References 1. Y. Filinchuk, E. Rönnebro, D.Chandra, Acta Materialia 57 (2009) 732–738.

191

PAC Study of Hydrogen Diffusion in Hf7Ni10 Combined with TiV0.8Cr1.2

J.M. Gil1, B.F.O. Costa1, P. de Rango2, D. Fruchart2, S. Miraglia2, N.E. Skryabina2,3

1 Department of Physics, University of Coimbra, P-3004-516 Coimbra, Portugal 2 Institut Néel & CRETA, CNRS, B.P.166, 38042 Crenoble Cedex 9, France

3Department of Physics, Perm State University, 15 Bukireva, Perm, 614990 Russia

PAC stands for Perturbed Angular Correlations, a local probe nuclear technique that measures the Electric Field Gradient and/or the Magnetic Field at a probe nucleus by means of the nuclear hyperfine interaction with the surrounding charge distributions. Those quantities are mostly related to the local atomic arrangement and are influenced by atoms at only a few atomic distances from the probe itself. Their parameters will constitute a signature of each local environment where a probe nucleus is placed [1-3]. Moreover, the study of dynamic effects such as the diffusion of light interstitial atoms is also possible by this technique [4]. A common PAC probe is the isotope 181Ta, produced by the radioactive decay of 181Hf, which has a convenient half-life of 42 days. Any material containing Hf in its structure is susceptible of a PAC study by simply activating the natural isotope 180Hf with slow neutrons on a nuclear reactor. Samples of Hf7Ni10 and of the alloyed material (non-hydrogenated and hydrogenated) were irradiated with slow neutrons. PAC measurements were performed at room temperature (RT) and, for the hydrogenated sample, as a function of temperature in the range from 17 K up to 350 K. Two major components, related to two different local environments, are identified on the PAC spectrum taken at RT on the Hf7Ni10 sample. In the combined alloy, the PAC results show that the local environments of the Hf atoms become more defective, possibly due to the smaller size of the alloyed grains. Upon hydrogenation of the alloyed material, one of the Hf sites shows at low temperature a considerable change in some of the PAC parameters, revealing the proximity of H. The hydrogen atoms are observed to become mobile at a temperature between 125 and 150 K. These results will be interpreted taking into account the Hf sites on the Hf7Ni10 lattice, and the possible location and diffusion path for the hydrogen atoms in the hydride. References 1. G. Schatz, A. Weidinger, Nuclear Condensed Matter Physics, Wiley, Chichester, 1995. 2. J.M. Gil, P.J. Mendes, A. Weidinger, N. Ayres de Campos, Z. Phys. Chem. Neue Folge 163 (1989) 193. 3. L.P. Ferreira, J.M. Gil, P.J. Mendes, N. Ayres de Campos, L. Pontonnier, S. Miraglia, D. Fruchart, A. Baudry, P. Boyer, Hyperfine Inter. 60 (1990) 731. 4. L.P. Ferreira, A. Baudry, P. Boyer, Z. Phys. Chem. Neue Folge 183 (1994) 79.

192

Site Occupation and Diffusion of Hydrogen in V1-xMox-H (0 ≤ x ≤ 0.1) Monohydride Phases Studied by 1H NMR

Kohta Asano, Shigenobu Hayashi, Yumiko Nakamura, Etsuo Akiba National Institute of Advanced Industrial Science and Technology (AIST), Tsukuba, Japan

Email: k.asano@aist.go.jp V metal with a body centered cubic (BCC) structure forms the monohydride phase with a body centered tetragonal (BCT) structure and the dihydride phase with a face centered cubic (FCC) structure by hydrogenation [1]. Hydrogen atoms occupy octahedral (O) sites in the monohydride phase and tetrahedral (T) sites in the dihydride phase, respectively [1]. V based alloys have been developed for on board hydrogen storage [2,3]. Alloying V with some metal elements can change the hydrogenation properties, which possibly relates to changes in hydrogen occupation and diffusion in the hydride phases. In the present work, the effect of Mo addition to V on site occupation and diffusion of hydrogen in the monohydride phase have been investigated using 1H nuclear magnetic resonance (NMR). 1H NMR spectra of V1-xMoxH0.68 (x = 0, 0.03, 0.05, 0.1) monohydrides with a BCT structure were measured at 19.65 and 200.13 MHz in the temperature range of 138 - 420 K. With increase in temperature, motional narrowing of the signal was observed. The full-width at half-maximum (FWHM) of the signal were almost same among the four samples above room temperature but that of V0.9Mo0.1H0.68 became smaller than others below 240 K. The activation energy for the hydrogen diffusion, E, was calculated from the temperature dependence of the spin-lattice relaxation time, T1. The value of E for the O sites was reduced by Mo addition. In V0.9Mo0.1H0.68, hydrogen atoms occupied not only the O sites but also the T sites because two components of T1 were observed. The value of E for the T sites was lower than that for the O sites. It can be concluded that Mo addition affects the site occupation of hydrogen and enhances the diffusion of hydrogen in the monohydride phase of V. This work is supported by The New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Reseach on Hydrogen Storage Materials (Hydro-Star)". References 1. T. Shober, H. Wenzl, in: G: Alefeld, J. Völkl (Eds.), Hydrogen in metals, Vol. II, Springer-Verlag, Berlin, 1978, p. 11. 2. H. Iba, E. Akiba, J. Alloys Compd. 253-254 (1997) 21. 3. E. Akiba, H. Iba, Intermetallics 6 (1998) 461.

193

Rotational and Diffusional Dynamics in Calcium Borohydride from DFT and Quasi Elastic Neutron Scattering

D. Blancharda, M. D. Riktorb, H. S. Jacobsena, J. B. Maronssona, J. Kheresa, D. Sveinbjorssona, E. Gil Bardají c, A. Leonc, M. Fichtnerc and T. Veggea

a Materials Research Division, Risø National Laboratory for Sustainable Energy, DTU, Building 228, P. O. Box 49, DK-4000 Roskilde, Denmark.

b Physics Department, Institute for Energy Technology, P. O. Box 40, No-2027 Kjeller, Norway. c Institute for Nanotechnology, Forschungzentrum Karlsruhe, P. O. Box 3640, D-76021 Karlsruhe, Germany.

E-mail: dibl@risoe.dtu.dk Hydrogen dynamics in crystalline calcium borohydrides can originate from long-range diffusion or localized motions like rotations, librations and vibrations. In this study, the rotational and diffusional dynamics of hydrogen in �-Ca(BH4)2 (P42/m structure) were studied by quasielastic neutron scattering (QENS) combined with Density Functional Theory (DFT) calculations. QENS experiments were performed at SPHERES (FRM II, Garching, Germany), an high resolution neutron backscattering spectrometer, energy resolution: 0.65 �eV, and at MARS (SINQ, PSI, Villigen, Switzerland), an inverted geometry time of flight spectrometer, energy resolution: 15 �eV. The DFT calculations were performed using the Atomic Simulation Environment (ASE) package. The DACAPO plane wave basis set implementation was used to solve the electronic structure problem within the DFT formalism. The Nudged Elastic Band (NEB) method was used to calculate the energy paths of the re-orientational changes (Fig. 1). The calculational supercell was the unit cell (22 atoms) repeated once in each spatial direction and contained 176 atoms. Experimentally, two types of motions were detected: localized re-orientations and longrange diffusion. Between 95 and 280K, two thermally activated rotational motions were observed around the 2-fold (C2) and 3-fold (C3) axis of the BH4 unit (Fig. 2). At the lower temperatures, only the C3-rotation, the energetically easiest to activate, was detected while at higher temperatures a combination of the two rotations, with different characteristic times, was found to occur (Fig. 3). The experimental energy barriers were found comparable, albeit slightly lower, with the ones obtained from DFT (EaC2= 0.14 vs 0.16 eV and EaC3=0.10 vs. 0.12 eV). Long-range diffusion of hydrogen was observed at SPHERES at 224 and 260K (Fig. 3). The effective jump length for the diffusion was identified as the shortest H-H distance between two neighboring BH4 complexes. The energy barrier for the diffusion, obtained from DFT, whereas slightly higher (EaD= 0.3 vs. 0.2 eV) is comparable with the one obtained from the experiments.

Fig. 1: NEB energy paths for C2 Fig. 2: C2, C3-axis. Fig. 3: Arrhenius plots of the characteristic (Ο) and C3 ( ) rotations. of aBH4 complex times for the thermally activated C2 (Ο),

C3 ( ) rotations and long-range diffusion (x).

194

Hydrogen Trapping Properties of Zr-based Intermetallic Compounds in the Presence of Contaminant Gases

J.Prigent1 , M. Latroche1, E. Leoni2 and V.Rohr2

1CMTR-ICMPE, UMR 7182, CNRS, 2-8 rue Henri Dunant, 94320 Thiais, France 2AREVA NC, , 1 rue des Hérons, 78182, Montigny le Bretonneux, France

Email: michel.latroche@icmpe.cnrs.fr Radiolytic production of hydrogen and other flammable gases is a major safety concern in the nuclear energy industry. Safety considerations related to flammability impose that hydrogen concentration is limited to a level below the lower flammability limit (H2 < 4% at room temperature in air). The use of materials presenting a high reactivity to hydrogen gas and capable to getter it would allow to avoid any accumulation of hydrogen. Intermetallic compounds are known to react spontaneously with hydrogen to form metallic hydrides in wide ranges of temperature and pressure. They exhibit very high hydrogen volumetric densities and are ideal materials for the design of hydrogen getters. Such intermetallic compounds able to store irreversibly hydrogen are known as Non Evaporable Getters (NEG) and are used nowadays for ultra-vacuum pumping [1], atmosphere purification [2] or tritium recovery in nuclear applications [3]. For application in the nuclear energy industry, these materials must work in arsh operating conditions. In particular, the required thermodynamic conditions, timescale and the nature and concentration of the gases other than hydrogen in equilibrium with the intermetallic compounds can be very challenging. Since the hydrogenation reaction proceeds through a dissociation step at the metal surface, the presence of inhibiting gas molecules can strongly affect the gettering performances of the material. In the present work, the hydrogen sorption properties of Zr-based intermetallic compounds have been investigated in the presence of different contaminant gases such as carbon monoxide or nitrogen. Reaction rates as a function of partial pressures, gas compositions, surface treatments and activation conditions will be reported. We show that the hydrogen sorption properties of the studied Zr-based intermetallic compounds are affected by the presence of contaminant gases in a way different than expected from litterature. FeZr2 and CoZr compounds are still able to absorb hydrogen when it is diluted by several percents of carbon monoxyde. On the contrary, the hydrogen absorption of these compounds is strongly reduced and even hindered by the presence of nitrogen. References 1. C. Benvenuti, P. Chiggiato, P. Costa Pinto, A. Escudeiro Santana, T. Hedley, A. Mongelluzzo, V. Ruzinov, I. Wevers, Vacuum, 60, 1-2, (2001) 57-65. 2. S. Fukada, K. Tokunaga, M. Nishikawa. Fusion Engineering and Design 36 (1997) 471-478. 3. T. Nagasaki, S. Konishi, H. Katsuta, Y. Naruse, Fusion Technology, 9, (1986) 506-509.

195

Hydrogen Absorption Behavior of Nano-Crystalline Mg Thin Films

H.T. Uchida, R. Kirchheim and A. Pundt Institut für Materialphysik der Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

Email: huchida@ump.gwdg.de

In preparation for the coming hydrogen society, Mg has been identified as one of the highest hydrogen content carrier (7.6wt%). But the slow hydrogen sorption kinetics, caused by the stable hydride MgH2 which blocks hydrogen diffusion („Blocking effect“), is a hindrance for a practical use. In this paper the influence of grain boundaries on hydrogen diffusion in Mg films is studied by adjusting a nano-crystalline micro-structure [1].

Nanocrystalline Mg (nc-Mg) films of different thicknesses (20nm-2100nm) were prepared in an UHV chamber, by means of ion beam sputter deposition at room temperature under Ar atmosphere at the pressure of 2.5x10-4 mbar. nc-Mg films were deposited on Si (100) substrates for P-C-T measurements of hydriding, and on annealed Pd-substrates with thicknesses of less than 0.25mm for hydrogen permeation measurements. All films were covered by a 20 nm thick layer of Pd in order to prevent oxidation. XRD measurements using a Phillips X-Pert diffractometer with a Co-Kα radiation were performed before and after hydrogenation in order to study phase transitions and a change of texture. TEM observations were also performed. Hydrogenation properties were observed by measuring the electromotive force (EMF).

Results of electrochemical hydrogen loading measurements for Pd-capped nc-Mg-films surprisingly show a strong dependency on the loading current density. All potential curves obtained at higher current densities lay above the equilibrium pressure of the Mg-H system at room temperature. We suppose that magnesium hydride even in early nucleation stages already blocks hydrogen diffusion (“Blocking effect”). In case of a small current density (< 10-7 mA/cm2), the plateau region was about 10-6 bar which corresponds to the plateau pressure of H in bulk-Mg at room temperature[2]. Reactions proceed up to 5 wt.% in case of low current density. The solubility limit of hydrogen in α-Mg was 2x10-4 (H/M) which is far larger than literature data of bulk Mg, extrapolated at room temperature [3].

XRD and TEM observation show that Mg grains have columnar morphology. Grain sizes calculated from the FWHM of Mg (0002) peaks were in the range of 35-55 nm. In XRD observation, a strongly oriented peak of β-MgH2 (110) appeared after H loading. A remained Mg(0002) peak confirms that Mg was not completely hydrogenated.

The diffusion coefficient of hydrogen in Mg films at room temperature was determined by hydrogen permeation measurements using Pd/nc-Mg/Pd multilayer films with low-loading current density. The determined diffusion coefficient of H in nanocrystalline Mg (α-phase) at 300K was 3.5x10-10m2s-1 which was larger than the extrapolated value of bulk-Mg at 300K (8.9x10-11m2s-1)[4].

References 1. A. Pundt and R. Kirchheim, Annu. Rev. Mater. Res., 36 (2007), 555-608. 2. F. Ellinger et. al., J. Am. Chem. Soc., 77 (1955), 2647-2648. 3. J. Stampfer et.al., J. Am. Chem. Soc., 82 (1960) 3504-3508. 4. C. Nishimura et. al., J. Alloy. Comp., 293-295 (1999), 329-333.

196

Ab Initio Study of Influence of Pd, Ti, Cr, and Mn Atoms on Dissolution Energy of Hydrogen in BCC Iron

M.S. Rakitin and A.A. Mirzoyev General and Theoretical Physics Department, South Ural State University, Chelyabinsk, Russia

Email: rms85@physics.susu.ac.ru

Dissolution of hydrogen decreases with cooling of steels based on iron. This process induces high pressure inside the material and can cause its failure. It is known that such effect can be avoided by adding of impurities of Pd or Ti during steel production. To understand nature of the phenomenon ab initio calculations have been performed for ferromagnetic bcc iron with hydrogen and several impurities (Pd, Ti, Cr, and Mn), but without structural relaxation. We used DFT-based WIEN2k simulation package with LAPW basis. Recently we studied using this method the adsorption of a hydrogen atom in pure bcc iron. Our results are in good agreement with the results of Jiang and Carter [1]. Namely, we found tetrahedral site of bcc iron to be more stable than octahedral site for hydrogen dissolution in Fe54H supercell and dissolution energy of hydrogen in tetrahedral site was 0.30 eV and 0.19 eV for unrelaxed and relaxed structures respectively with experimental value 0.296 eV [2]. Atoms of Pd, Ti, Cr, or Mn have been inserted in iron lattice as substitutional impurities using parameters from Fe-H system calculations. We varied position of each impurity relative to hydrogen atom in tetrahedral site. Case of hydrogen in octahedral site hasn’t been studied due to instability of the site.

Fig. 1. Dependence of dissolution energy of hydrogen on used impurity

and its distance from hydrogen atom.

Figure 1 displays the results of the calculations. All the impurities trap hydrogen atom in its third coordination sphere. Atoms of Pd and Ti initiate the most effect on hydrogen trapping in bcc iron. Atom of Mn practically doesn’t trap hydrogen atom. Structural relaxation of the Fe-Pd-H and Fe-Ti-H systems is being performed at present. The work is supported by Federal Aim Program (State contract No. 1939 from October 29, 2009) and grant No. 2.1.1/1776. References 1. D. E. Jiang, E. A. Carter, Phys. Rev. В, 70, (2004), 064102. 2. J. P. Hirth, Metall. Trans. A, 11A, (1980), 861.

197

Synthesis of Si Nanoparticles to Improve Reaction Kinetics and Thermodynamic Properties of Magnesium Hydride

Anna-Lisa Chaudhary1, Mark Paskevicius1, Drew Sheppard1 and Craig Buckley1,2 1Hydrogen Storage Research Group, Curtin University of Technology, Australia 2CSIRO National Hydrogen Material Alliance, CSIRO Energy Centre, Australia

Email: anna-lisa.chaudhary@postgrad.curtin.edu.au Alternative energy sources, such as hydrogen, have recently been brought into prominence due to the decline of the world’s crude oil production. Hydrogen production, storage and use as a fuel can potentially create a hydrogen run economy and also reduce greenhouse gas emissions thus improving the global warming problem. Magnesium hydride is an inexpensive material that can reversibly store hydrogen up to 7.6 wt% in a solid state. Despite its promising storage capacity, thermodynamic stability and reaction kinetics are not yet ideal for practical use. Thermodynamic calculations have shown that the addition of silicon (Eq. (1)) into magnesium hydride significantly reduces thermodynamic stability of the system [1] and that MgH2 should begin to dehydrogenate at room temperature at 1 bar of pressure.

2MgH2 + Si → Mg2Si + 2H2 (1) However, attempts to create this system have not been able to achieve these ideal conditions [2, 3]. Experimental work has shown that the addition of Si [3] and Si with other additives [2] can improve the thermodynamics, however, reaction kinetics become the limiting factor of the reaction. Crystallite and particle size both have an influence on the reaction kinetics [1, 4, 5] therefore the focus of this work is to synthesize nanoparticles of Si (< 10 nm) to enhance the diffusion of Si through the MgH2 matrix during dehydrogenation thus improving kinetic rates and thus reducing thermal stability. In-situ neutron diffraction showed that the diffusion of Si atoms into the MgH2 matrix is limited by crystallite size. To overcome this problem and therefore increase reaction kinetics, nanoparticles of Si were synthesized using two different reaction pathways and methods. The first was to use a reducing agent, NaBH4 combined with ultrasonication and the second was to use a mechanochemical ball milling process to initiate a solid – liquid reaction. Characterization of these nanoparticles was undertaken using XRD, SAXS, TEM and DSC. References 1. Bystrzycki, J., M. Polanski, and T. Plocinski, Nano-Engineering Approach to Destabilization of Magnesium Hydride (MgH2) by Solid-State Reaction with Si. Journal of Nanoscience and Nanotechnology, 2009. 9(6): p. 3441-3448. 2. Polanski, M. and J. Bystrzycki, The influence of different additives on the solid-state reaction of magnesium hydride (MgH2) with Si. International Journal of Hydrogen Energy, 2009. 34(18): p. 7692-7699. 3. Vajo, J.J., et al., Altering Hydrogen Storage Properties by Hydride Destabilization through Alloy Formation: LiH and MgH2 Destabilized with Si. The Journal of Physical Chemistry B, 2004. 108(37): p. 13977-13983. 4. Paskevicius, M., D.A. Sheppard, and C.E. Buckley, Characterisation of mechanochemically synthesised alane (AlH3) nanoparticles. Journal of Alloys and Compounds, 2009. 487(1-2): p. 370-376. 5. Sheppard, D.A., M. Paskevicius, and C.E. Buckley, The Mechanochemical synthesis of magnesium hydride nanoparticles. Journal of Alloys and Compounds, 2010. 492(1-2): p. L72-L74.

198

Low Temperatures Hydrogen Evolution from LiAlH4-Based Systems X. L. Zheng, Z. T. Xiong, H. Chen, and P. Chen*

Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China, E-mail:pchen@dicp.ac.cn

LiAlH4 is regarded as a prospective material for hydrogen storage due to the high hydrogen content (10.5wt %), however, the step-wise hydrogen desorption from LiAlH4 in solid phase suffers from high kinetic barrier and has to raise the temperature up to 200 °C,1 which is considerably higher than the PEM fuel cell operation conditions. To solve this kinetic problem, the dehydrogenation is investigated in solvents. Since mass transport in a solid-state reaction is likely to be the main origin of kinetic barrier due to the lattice confinement. That barrier can be alleviated by dissolving reactant(s) in proper solvents.2,3 HMPA (hexamethylphosphoramide) was chosen as a candidate solvent because HMPA is a dipolar aprotic solvent with super ability to form cation-ligand complexes. LiAlH4 was mixing with a small amount of HMPA and its decomposition with temperature and time was monitored by volumetric release.The reaction mechanism was studied using FTIR, XRD and NMR. The LiAlH4-HMPA slurry system shows a remarkable improvement on the hydrogen release kinetics, that is, hydrogen can be evolved at ambient temperature, which is ~100 °C lower than its solid-state thermal decomposition. In total 2 equivalent H2 were found to detach at 90 °C. The basic oxygen in HMPA can coordinate to Li+, Na+ and K+ via strong electrostatic interactions,4 which will likely destabilize [AlH4]- tetrahedron. A step-wise dehydrogenation of [AlH4] occurs, leading to the formation of [AlH3], [AlH2], [AlH] and H2 in LiAlH4-HMPA system. With the introduction of a small amount of HMPA, there is a rapid hydrogen release from LiAlH4-LiNH2 system at temperature as low as 50 °C, which is lower than the operation temperature of PEM fuel cell. 5 equiv. H can be detached from the system, which corresponds to 8.1 wt.%. The presence of LiNH2 leads to the enrichment of [AlH] in the early stages of dehydrogenation. In the latter stages of dehydrogenation, LiNH2 reacts with the [AlH] species and produces H2, Al and Li2NH.5

References 1. A. Andreasen, T. Vegge, A. S. Pedersen, J. Solid State Chemistry, 178, (2005), 3672-

3678. 2. Z. T. Xiong, Y.S. Chua, G. T. Wu, W. L. Xu, P. Chen, W. Shaw, A. Karkamkar, J.

Linehan,T. Smuthwaite, T. Autrey, Chemical Communications, (2008), 5595-5597. 3. X. L. Zheng, Z. T. Xiong, S. Qin, Y. S. Chua, H. Chen, P. Chen. International J.

Hydrogen Energy, 33, (2008), 3346-3350. 4. G. Levin, J. Jagur-Grodzinski, M. Szwarc, J. American Chemical Society, 92, (1970),

2268-2275.

199

The Effect of Surface Preparation on the Depth of Hydride Initiation at Lightly Oxidized Uranium Surfaces

W.J. Siekhaus

Condensed Matter and Materials Division, Physical and Life Sciences Directorate, Lawrence Livermore National Laboratory, Livermore, CA 94550 , USA

Email: Siekhaus1@LLNL.gov Uranium surfaces covered by a thin oxide layer exposed to hydrogen exhibit pitting corrosion after an initiation time depending on oxide thickness, temperature, and hydrogen pressure (Teter 2001). The exact location of the initiation, i.e., whether it occurs first at the interface between the oxide and the metal or below that interface inside the metal itself has been a matter of debate ever since Bingert (Bingert, Hanrahan et al. 2004) showed blisters on the surface of uranium in SEM images, implying that hydride initiation occurs below the uranium surface. A recent a publication (Powell 2009) in which it was shown in SEM images generated after focused ion beam etching through hydride initiation pits, led to the hypothesis that hydriding initiates below the oxide-metal interface at a depth consistent with the thickness of the layer affected by mechanical polishing (Beilby layer, (Beilby 1903)). Mechanical polishing may either remove pre-existing uranium hydride sites which are known to facilitate hydride initiation (Balasubramanian, Siekhaus et al. 2003) or change the mechanical properties such that hydriding is retarded (Condon 1973). To check this hypothesis, uranium surfaces were prepared in three different ways: by low energy (500 eV) ion milling, by mechanical polishing using a 1µm diameter polishing agent, and by abrasion with 300 grit paper. Hydriding was stopped as soon as pits were optically detectable. SEM imaging of hydriding pits sectioned by focused ion beam etching proved that the location of hydride initiation is determined by the method of surface preparation. Auspices This work performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. IM release number: LLNL-ABS-425280 References 1.Teter, D. H., Hanrahan, R., Wetteland, C. (2001). LANL Report LA-13772-MS 2.Bingert, J. F., R. J. Hanrahan, et al., J. Alloys and Compounds, 365(1-2), (2004), 138-148. 3.Powell, G. L., Schulze R.K, Siekhaus, W.J., International Hydrogen Conference, Jackson .Hole (2008), Proceedings, 556-561. 5.Beilby, G. T. Proceedings of the Royal Society of London, 72(481), (1903), 218-225. 6.Balasubramanian, K., W. J. Siekhaus, et al., J. Chemical Physics 119(12), (2003), 5889-5900. 7.Condon, J. B., Larson, E.A. J. Chemical Physics 59(2), (1973),855-865.

200

In Situ Study of Hydrogen Exposure of Microcantilevers Coated with Nanometric Palladium Films

1A. Fabre, 1 O. P. Bramant, 2E. Finot; 3T. Thundat

1CEA, DAM, Valduc, F-21120 Is-sur-Tille, France;

2ICB, Université de Bourgogne, 21000 Dijon, France 3Oak Ridge National Laboratory, USA

An in situ technique has been developed to simultaneously measure the static deflection and the resonance frequency of samples shaped as microcantilevers under reactive atmosphere. Aiming at characterizing the absorption (desorption) of hydrogen at the palladium surface, various film thicknesses (ranging from 10 nm to 40 nm) were deposited using thermal evaporation on silicium substrates (300 μm long, 35 μm large, and 1 μm thick). The initial curvature of the samples was optically characterized and the surface morphology was imaged by AFM. During experiments, the measurement cell contained two palladium-functionnalized cantilevers and one pure silicium reference. Prior to hydrogen exposure, the cell was evacuated and the samples were submitted to a secondary vacuum. The deflection of the cantilevers (mainly related to the film stress) and their resonance frequency (mainly dependent on the mass intake and theYoung modulus of the bilayer) were monitored as a function of time, of hydrogen pressure, of film thickness, and of the number of absorption-desorption cycles. Thereafter, results are discussed in terms of kinetics and of thermodynamics (comparison of film phase diagrams to bulk ones). From an instrumentation point of view, the measurement technique developed in this work demonstrates its suitability for studies that involve other metal-hydrogen systems, and generally speaking, thin film-gas interactions.

201

Surface Energy Effects on the Thermodynamics of Mg/Ti Multilayers L.P.A. Mooij1,2, F.N. Claessen1, Ch. Boelsma2, A. Baldi1,2, H. Schreuders1, B. Dam1

1. Faculty of Applied Sciences, Delft University of Technology, Delft, The Netherlands 2. Faculty of Sciences, VU University, Amsterdam, The Netherlands

E-mail: L.P.A.Mooij@tudelft.nl Surface energy plays an important role in the thermodynamic properties of nanosized materials. Recent theoretical calculations have addressed this issue for both metal hydrides [1,2] and Li-intercalation compounds [3]. In metal-hydrogen systems the influence of surface energy is only significant at length scales of the order of 10 nm or less. Due to this short length scale, actual measurements of surface energy effects have, to our knowledge, not been reported in the literature. Mg/Ti multilayers are an ideal platform for studying the effects of different thicknesses and surroundings of Magnesium on the thermodynamics of hydride formation [4]. The hydrogen loading isotherms of Mg/Ti multilayers are measured optically by means of Hydrogenography [5]. The exceptional sensitivity of this technique allows us to determine the hydrogen equilibrium pressure of Mg layers as t hin as 1.5 nm. As expected from a simple thermodynamic model involving surface energy, a linear dependence of the equilibrium pressure with the inverse thickness of the Mg layers is found. We find clear evidence for a destabilization of MgH2 at layer thicknesses below 10 nm. Our results show how surface energy effects play a significant role in the properties of nanosized metal hydrides. Equilibrium pressures of hydrogenation (T= 333K) of different Mg layers versus 1/tMg, where t is the thickness of the Mg layer. References 1. Berube et al. Int J Energ Res (2007) 31 pp. 637-663 2. Kim et al. Nanotechnology (2009) 20 pp. 204001 3. Wagemaker et al. Adv. Mater. (2009) 21 pp. 2703 4. Baldi et al. Phys Rev Lett (2009) 102 pp. 226102; Appl Phys Lett (2009) 95 pp. 071903 5. Gremaud et al. Adv. Mater. (2007) 19 pp. 2813-2817

202

Theoretical Study of Hydrogen Adsorption and Diffusion in Spillover Process on Microporous Carbon

K. Suzukia, M. Kayanumaa, U. Nagashimaa, H. Nishiharab, T. Kyotanib, and H. Ogawaa

aResearch Institute for Computational Sciences, National Institute of Advanced Industrial Science and Technology, Ibaraki, Japan

bInstitute of Multidisciplinary Research for Advanced Materials, Tohoku University, Sendai, Japan Email: u.nagashima@aist.go.jp

Using density functional theory (DFT) calculation, the hydrogen spillover process occurring on microporous carbon such as zeolite templated carbon (ZTC)1,2 was investigated theoretically. Evaluation of chemisorption energies of a hydrogen atom on four graphene-like fragments with different curvature (Fig. 1) showed that hydrogen atoms adsorb strongly at the edge site and convex surface. We also showed that hydrogen chemisorption at edge sites enhances the adsorption energy at the inner site. Fig. 1 Front and side views of molecular structures of C24H12 (coronene, [6]circlene), C20H10 (corannulene, [5]circlene), C28H10 (pleiadannulene, [7]circlene), and C36H12 (triacenaphthotriphenylene). To reveal the mechanism of hydrogen diffusion on a carbon surface in the spillover process, transition states of two types were examined: hydrogen moving along the C–C bond keeping a weak C–H bond, and hydrogen dissociation from the carbon surface. The results suggest that the latter path is more likely to occur than the former path in flat surface and the situation might be modified by introducing curvature. These results suggest that efficiency of hydrogen spillover on carbon-based hydrogen storage materials will be enhanced by controlling the structure of the carbon surfaces.

This work was conducted as a collaborative effort between the New Energy and Industrial Technology Development Organization (NEDO) projects "Advanced Fundamental Research on Hydrogen Storage Materials (Hydro-Star)" and “Development of Technologies for Hydrogen Production, Delivery and Storage Systems”. References 1. H. Nishihara, P.-X. Hou, L.-X. Li, M. Ito, M. Uchiyama, T. Kaburagi, A. Ikura, J. Katamura, T. Kawarada, K. Mizuuchi, T. Kyotani, J. Phys. Chem. C, 113, (2009), 3189-3196. 2. H. Nishihara, Q.-H. Yang, P.-X. Hou, M. Unno, S. Yamauchi, R. Saito, J.I. Paredes, A. Martínez-Alonso, J.M.D. Tascón, Y. Sato, M. Terauchi, T. Kyotani, Carbon, 47, (2009), 1220-1230.

203

Adsorption States of Hydrogen on Surfaces of Thin Tb and Eu Films in the Process of TbHx (0<x<3) and EuHy (0<y<2.2) Formation

R.Nowakowski, M.Knor, E.Nowicka, R.Duś

Institute of Physical Chemistry, Polish Academy of Sciences, Kasprzaka 44/52, 01-224 Warszawa, Poland Email: robas@ichf.edu.pl

Work function changes ΔΦ caused by H2 interaction with thin Tb and Eu films deposited on glass under UHV conditions were correlated with hydrogen uptake and with measured in situ some bulk properties like electrical resistance R and optical transmittance spectrum T(λ). Thin films were obtained by the complete evaporation of Tb(Eu) stripes of known mass from a tungsten heater. Thus the amount of metal atoms Me within the thin films was known (for Eu additionally confirmed by chemical analysis). H2 was introduced in the successive calibrated doses into the reactor of known volume measuring pressure. Hence hydrogen uptake and atomic ratio (H/Me) could be determined at every step of the reaction of the hydrides formation and all determined surface and bulk properties could be expressed as (H/Me) functions. The experiments were carried out under isothermal conditions at 78 and 298K. It was observed for both metals that at 298K at low hydrogen uptake (H/Me< 0.1) every successive H2 dose resulted in rapid decrease of work function, which corresponds to creation of the positively polarized adspecies referred to as β+. This state of the adsorbate is not stable on the surface, but quickly incorporate into the bulk. Such process is observed as the positive (ΔΦ) transients. Increase of hydrogen uptake leads to inversion of polarization of hydrogen adspecies created by successive H2 doses. Rapid increase of work function is now observed due to hydrogen adsorption from successive doses. This corresponds to formation of the negatively polarized hydrogen adspecies referred to as β−. These species are not stable on the surface either, but slowly incorporate into the bulk leading to the negative ΔΦ transients. Large amount of hydrogen was consumed with this ΔΦ(Η/Μe) feature, until appropriate concentration limit in the hydrides was reached. Approaching atomic concentration H/Tb ~ 2.85 ΔΦ transients disappear. This corresponds to remaining mainly on the surface of the β− adspacies created by successive H2 doses. Isothermal evacuation resulted in desorption of some negatively polarized adspecies. Resistance of thin TbHx (x~3) films in our experiments did not exceed 1kΩ, however transition of thin metallic Eu film into thin EuHy (y~2) film increased resistance up to 10 kΩ. This precluded possibility of ΔΦ determination by means of capacitor method applied in this work when H/Eu ratio approaches 2. At 78K very small uptake of hydrogen around H/Me~0.1 can be reached within thin Tb and Eu films. Surface ordered low temperature phase (α*) with positively polarized hydrogen adspecies are formed. These phases strongly inhibit penetration of hydrogen into the bulk. They are stable up to 100K for terbium and 160K for europium. Increasing temperature above these values resulted in additional large absorption of hydrogen. Dipole moment μ0 as small as 6x10-3 D was determined for hydrogen adsorbate on the terbium hydride phase α*. This suggests the presence of the symetrical H-Tb-H species on the surface at 78K.

204

Thermal Degradation Analysis of Deuterium Ion Implanted Hydrogen Storage Materials (TiFe and V25Cr40Ti35) Using Synchrotron Radiation

Photoelectron Spectroscopy. M. Tode, J. R. Harries, Y. Teraoka and A. Yoshigoe

Synchrotron Radiation Research Center, Japan Atomic Energy Agency, Hyogo, Japan Email: tode.mayumi@jaea.go.jp

In hydrogen storage materials the storage and release of hydrogen takes place through the surface. Thus the thermal stability properties of the native oxide surface can have an affect on these processes. In order to study the relationships between the thermal desorption of hydrogen and the surface properties, we have used high-resolution synchrotron radiation X-ray photoelectron spectroscopy to study the thermal degeneration processes of the surface layers. The experiments were performed at the JAEA soft X-ray beamline BL23SU at SPring-8, using the “SUREAC2000” surface reaction analysis apparatus. XPS spectra were recorded for room temperature TiFe and V25Cr40Ti35 following flash heating to 373-1073 K. For each material spectra were recorded for two samples covered with native oxide layers, one of which was also implanted with deuterium ions. 2.5 keV ions were implanted to a dose of 9.5×1014 cm-2 using a separate apparatus, after which the sample was transferred in atmosphere to the SUREAC2000 apparatus. Figure 1 shows the Ti-2p peak (a) and Fe-2p peak (b) of TiFe. At room temperature (300 K), the Ti-Oxide peak and the Fe-Oxide peak were observed. The Ti-2p peak remained unchanged upon annealing to temperatures of up to 523 K. The magnitude of the Ti-bulk component increased above 573 K, and that of the Ti-oxide component decreased above 773 K. The Fe-2p peak remained unchanged upon annealing to temperatures up to 473 K. The magnitude of the Fe-bulk component increased above 473 K, and that of the Fe-oxide component decreased above 573 K. There was about a 200 degrees difference in the temperatures at which the Ti-oxide and the Fe-oxide peaks began to disappear. In the deuterium-implanted TiFe sample, the temperature at which the oxide components disappeared was lowered by 200-250 degrees. In VCrTi, however, the thermal stability of the natural oxide layer was increased by the deuterium implantation.

Acknowledgements This work is supported by the New Energy and Industrial Technology Development Organization (NEDO) under "Advanced Fundamental Research Project on Hydrogen Storage Materials (HYDRO�STAR)".

Fig. 1. Ti-2p and Fe-2p synchrotron radiation photoelectron spectra for TiFe

205

The Influence of the Cathode Surface on the Deuterium IECF

Y. Taniuchi1, K. Taira, M. Utsumi2 and Y. Matsumura2 Faculty of Engineering, Tokai University, Kanagawa, Japan

Graduate School of Science and Technology, Tokai University, Kanagawa, Japan Email: weaklepton@tokai-u.jp

An Inertial Electro-static Confinement Fusion (IECF) device is one of the candidates

among the neutron sources, and it is possible to produce the neutrons by a compact device of simple configuration. The IECF is a concept for electrostatically confining high-energy fuel ions in a spherical potential well. It consists of two spherical grid electrodes, radii are different and centers are same. An inner sphere grid is a cathode and outer sphere grid is an anode. In a low current glow discharge, generated ions oscillate inside of the spherical anode and interacts gas molecules or cathode. Neutrons are produced by the fusion interaction that mainly interacts oscillated ion and gas molecule (beam-beam), oscillated ion and absorbed deuterons inside the cathode (beam-cathode), first neutral molecule and gas molecule (neutral-background). One of the methods to increase the Neutron Production Rate (NPR) is to use hydrogen absorption metals for grid cathode. However, it has been reported that the effect of the hydrogen absorption metals was a little in increasing the NPR in hot cathode glow discharge. This is because the cathode was rapidly heated by ion bombardment. In the high-power IECF device, the cathode temperature goes up to over 1000 K so that deuterium atoms were desorbed. In spite of that, the use of Ti grid cathode enhances the NPR in our measurements. This is because the little electrons released at the Ti cathode by the ion impact (γ effect). If there is little γ effect of the cathode surface, ion density increases near the cathode. The present work is intended to clarify the efficacy of little γ effect of the cathode surface. In these experiments, the NPR was measured in low-power glow discharge condition. In other words, the present work is to pilot the future possibilities of the use of little γ effect of cathode materials. References 1. P.T. Fransworth, “Space Charge Device for Producing Nuclear Reactions” Canadian Patent, 654, 306, 1962 2. R. L. Hirsh, “Inertial-Electrostatic Confinement Ionized Fusion Gases” J. of Appl. Phys, 38, 4522, 1967

206

Formation of AlH3 in Hydrogen-Aluminum System: A Density Functional Study

Phung Thi Viet Bac, Hiroshi Ogawa

Nanosystem Research Institute, AIST, 1-1 Umezono,Tsukuba, Ibaraki, 305-8568, Japan Email: vietbac@wriron1.s.kanazawa-u.ac.jp

Chemisorption of hydrogen on aluminum surfaces and the formation of AlH3 have been studied by using first-principles density functional calculations within the generalized-gradient approximation (GGA). The geometry structures, energetics, electronic structure of AlH3 were investigated in detail. We focus on the adsorption of hydrogen on aluminum (111) and (100) surfaces with calculated binding energies of Al-H bonds. The interaction of aluminum surface and crystals of AlH3 were investigated to understand the not-fully hydrogenated aluminum surface observed by the experimental measurements of H. Saitoh et.al. References

1. June W. Turley, H. W. Rinn - Inorganic Chemistry, 8, (1969), 18-22. 2. H. Saitoh, A. Machida, Y. Katayama, K. Aoki, Applied Physics Letters, 93, (2008),

151918. 3. P. Vajeeston, P. Ravindran, H. Fjellvag, Chem. Mater. 20, (2008), 5997-6002. 4. C. Wolveton, V. Ozolins, M. Asta, Phys. Rev B 69, (2004), 144109.

207

In-Situ TEM Observation of Hydrogenation / Dehydrogenation Reaction with Environmental Cell

T.Wakasugi, H.Hirasawa, E.Morita, H.Yao, A.Ono, S.Isobe, Y.Wang, N.Hashimoto, S.Ohnuki

Graduate school of Engineering, Hokkaido university, N-13, W-8, Sapporo, 060-8278, Japan E-mail : takenobuwakasugi@gmail.com

We have studied on microscopic reaction mechanism of hydrogen storage materials such as MgH2, MH-NH3 (M=Li, Na), NH3BH3, and NaAlH4 by means of transmission electron microscope (TEM) with environmental cell (EC), by which we can controll temperature and gas atmosphere. Figure.1 shows one of the results obtained by in-situ TEM ( 200kV ) observation with EC controlling 10kPa NH3 gas flow at room temperature. LiH react with NH3 gas to generate LiNH2 and H2 gas at room temperature [1]. LiH + NH3 → LiNH2 + H2 With the reaction progress, the production of LiNH2 and volume expansion are confirmed from diffraction pattern and bright field image, respectively. Moreover, EC is being developed for high voltage electron microscope (HVEM: 1250kV). By using HVEM, it is expected thet high resolusion images are obtained to discuss the reaction mechanism of hydrogen storage materials in detail. Figure.2 shows the scene of setting up EC for HVEM.

Figure 1. In-situ TEM micrographs (LiH kept under 10kPaNH3 for 0, 10, 30, 60min )

Figure 2. Setting up HVEM-EC ( L ) Pipe arrangement to goniometer ( R ) Pipe connection to environmental cell References 1. Y. Kojima, et al. Journal of Materials Research, 24, 2185 (2009).

208

Microstructure and Hydrogen Storage Properties of Magnesium Hydride with Zirconium and Niobium Fluoride Additives After Cycling Loading

I. E. Malka*, T. Czujko, J. Bystrzycki

Faculty of Advanced Technology and Chemistry, Military University of Technology, 2 Kaliskiego St, 00-908 Warsaw, Poland

*E-mail: imalka@wat.edu.pl Magnesium hydride has been intensively studied for the last two decades as a hydrogen storage material. Unfortunately, high desorption temperature of the magnesium hydride (∼ 300 °C) hampers its usage in practical applications. However, it has been shown that ball milling of MgH2 with some transition metal halides can decrease the decomposition temperature of MgH2 [1,2]. Recently, we have shown that among different metal halides, the ZrF4 and NbF5 additives showed the most significant influence on the desorption temperature and the kinetics of MgH2 [3]. In this work we present new results on the effect of the ZrF4 and NbF5 additives on the microstructure and hydrogen storage properties of MgH2 after cycling loading. There is a lack of information about the microstructure and hydrogen storage properties of MgH2 with both halides after cycling hydriding and dehydriding. Commercial MgH2 powder was mixed with 7 wt. % of metal halide powder and subsequently ball milled in an inert atmosphere in a planetary ball mill. The phase structure, morphology and chemical composition were investigated by XRD, SEM and EDS techniques. The morphology and microstructure of the powders after cyclic loading were investigated with a high-resolution field emission scanning electron microscope by using the BSE and STEM detectors and an energy dispersive X-ray spectrometer. The thin samples for microstructural observations were cut out of the largest particles by using the focused ion beam technique. The hydrogen sorption properties and pressure composition isotherms were evaluated by using a volumetric Sievert’s apparatus. Our results clearly show that there is a considerable catalytic and thermodynamic effect of the ZrF4 and NbF5 additives on the hydrogen desorption temperature of MgH2 and both absorption and desorption kinetics. The obtained nanocomposite exhibits a good reversibility evaluated by the pressure composition isotherm measurements at 300-350ºC range. However, the degradation of nanostructure and hydrogen storage capacity after prolonged cycling is observed. The degradation has been attributed to the grain growth and non-homogenous distribution of halide particles in the Mg/MgH2 matrix observed after long-time cycling loading. References 1. S-A. Jin, J-P. Ahn, J-H. Shim, Y.W Cho, K-W Yi, J. Power Sources., 172, (2007), 859-862. 2. Y. Luo, P. Wang, L-P. Ma, H-M. Cheng, . J. Alloys Compd. 453, (2008), 138-142. 3. I.E. Malka, T. Czujko, J. Bystrzycki, Int. J. Hydrogen Energy, 35, (2010), 1706-1712.

209

The Activation of Hydrogen by Fractal d-Metal Nanoparticles L.Fomina, S. Vazhenin, O. Maslova

Chemistry Department Altai State University, Barnaul, Russia Email: flvbaan@mail.ru

As the catalyst of oxidation of hydrogen on the anode of a fuel element traditionally use platinum metals. Replacement of metals of family of platinum on more accessible, but not less effective catalysts is economically and technically important stage of development of the industry of fuel elements. In present work we take under consideration some foundations of new approach to the treatment of this problem on the basis of application of principles of nanotechnology.

The essence of the offered treatment consists in multifunctional use of submicronic system of a porous of the anode as reactors of synthesis and carriers of nanocomposite d-metal-carbon catalysts accelerating chemical reactions of oxidation of hydrogen on the interface of an electrode with electrolyte at the expense of bi-radical forms of molecules of hydrogen Н↑-Н↓ [1]. These bi-radical molecules are activated by d-transition metal atoms of fractal clusters super-adsorbed on a carbon nanogel surface of the catalyst. The research of processes of formation of nickel catalyst as nanodendritic coverings on a carbon nanogel surface of the catalyst was realized by means of computer simulations. Processes of arising, growing and reconstruction of nickel fractal nanodendrites was investigated, calculation of its physicochemical properties was also given. In witness of denoted feature it is shown in the work that typical dendrite structure is appreciably intact after optimization in the case of resonance contact bonding whereas the compact spheroid structures are obtained in the case of metallic nature of bonding. However it seems to be doubtful that metallic bonding can exist in dendrite-like systems by reason of its sponginess in contrast to bulk metal materials. So it must be noted a great importance of variations in electronic structure of quantum-sized nanoparticles for the specifying of structural evolution course in such systems. The results of quantum-statistical thermodynamic calculation for the local active centres Ni2 and Ni2H2 cyclic complex confined inside of space 100×100×100 nm at standard temperature are submitted. Translational qt, rotational qr, anharmonic vibrational qv

anh, harmonic vibrational qv

h and electronic qe contributions to statistical sum Q are reported together with thermodynamic functions such as Helmholtz energy F, internal energy U and entropy S. As it is shown vibration statistical sums for Ni2 and Ni2H2 in the case of anharmonic vibrations are rather higher in comparison with harmonic approximation and hence the ground state population is some lower as expected according to crowding of levels. Approximate closeness of the compared results indicates satisfactory accuracy of the used computational quantum-statistical model. References 1. S. Beznosyuk, B. Zhanabaev, D. Sokolskii, V. Litkin, Dokl. Akad. Nauk. USSR, 266, (1982), 380-383.

210

Kinetics of Ytterbium Hydride Decomposition

W. Iwasieczko and H. Drulis Polish Academy of Sciences, Trzebiatowski Institute of Low Temperature and Structure Research Wroclaw

Poland Email: H.Drulis@int.pan.wroc.pl

Most of the investigations in the area of hydride decomposition are theoretical. Different models are suggested considering different processes as limitative [1, 2]. In the most experimental work [3] a method to evaluate hydride formation/ decomposition parameters are based on the barometric approach. The aim of this paper is to examine the ytterbium hydride decomposition as well as to evaluate the rate constants of elementary processes which influence hydrogenation / dehydrogenation of this system. Ytterbium was chosen because it forms a complex phase equilibria with hydrogen [4]. It has been found that, apart from the orthorhombic hydride YbH2 under appropriate conditions of pressure and temperature the absorption of hydrogen by ytterbium metal resulted in the formation of the f.c.c hydride referred to as the β phase with the composition about YbH2.55. It decomposes at elevated temperatures of 200-300 oC yields another f.c.c modification called β’ with a larger lattice constant compare to those in β phase. It follows from our data that the ytterbium hydrides are more similar to the light rare earth hydrides than to the heavy lanthanide hydrides. The dehydriding kinetics in Yb-H system were determined in the two-phase (α + β) and (β +β’) regions under isothermal, isochoric and variable pressure conditions. A rate equation was derived by taking into account the reversible nature of the hydriding and dehydriding reactions dn/dt = k (P/Pc)a { 1 – (Pf/P)a (n/nf)b } Decomposition reactions were observed to proceed differently in both regions of hydrogen equilibria. The isothermal reaction kinetics rate constants k have been estimated for a given hydrogen content within the plateau pressure at several temperatures. It has been found that the rate constant k determined for (β + β’) phase equilibria is not keep constant under isothermal condition what suggests that there is the phase change from the (β + β’) region to the β’ region. Activation energies and prexponantial factors for the rates of ytterbium hydride decomposition and hydrogen desorption have been evaluted and the sugestions for the rate-controlling steps will be given. References 1. F. J.Castro, G. Meyer, J. Alloys Comp., 330-332, (2002), 59 2. F. Schweppe, M. Martin, F. Fromm, J. Alloys Comp., 261, (1997), 554 3. M. Ron, J. Alloys Comp., 283, (1999), 178 4. H. Drulis, Monika Drulis , W. Iwasieczko and N.M. Suleymanov, J. Less Comm. Metals, 141, (1988), 201-206

211

Chemical Surface Modification for the Improvement of the Hydrogenation Kinetics and Poisoning Resistance of TiFe and MmNi5

M.Williams1, M.V.Lototsky1, M.W.Davids1, V.Linkov1,V.A.Yartys2,3 and J.K.Solberg3 1South African Institute for Advanced Materials Chemistry, University of the Western Cape,

Bellville, South Africa Email: 2438658@uwc.ac.za

2Department of Energy Systems, Institute for Energy Technology, Kjeller, Norway Email: volodymyr.yartys@ife.no

3Norwegian University of Science and Technology, Trondheim, NO-7491, Norway Email: jan.solberg@material.ntnu.no

This experimental study summarises the developments of new surface engineering approaches, which were tailored to address the issues of difficult activation, poor resistance to gaseous impurities, and slow hydrogenation kinetics of the H storage alloys. They are based on electroless plating of the Pd-based catalytic layers on the surface of MmNi5- and TiFe-based alloys. We found that the modification of MmNi5-based alloy results in the formation of discontinuous Pd-based films on the surface of the substrate; the films consist of nanoscale (50–150 nm) particles. The Pd deposition, in combination with fluorination of the intermetallic substrate and surface functionalisation with aminosilanes, significantly improves the hydrogenation kinetics of the intermetallic alloy even at low H2 pressures and room temperature (Figure 1). TiFe was synthesised by sintering of the Ti and Fe powders and by the arc-melting. Sintered samples revealed three phases: TiFe (major), Ti4Fe2O, and Ti3O. Hydrogen absorption showed that the sintered material was almost fully activated after the first vacuum heating (400 oC) when compared to the arc-melted sample requiring several activation cyles. Especially active in interaction with hydrogen were sintered samples covered by Pd electroless deposition. The effect of improving activation performances by surface deposition of Pd was shown to be very pronounced for the TiFe-based materials whose hydrogen sorption properties are greatly suppressed by trace amounts of the admixtures of active gases, including oxygen and water vapour. This work is supported by South Africa – Norway Research Cooperation Programme (Project 180344) and ESKOM Holdings Ltd.

Figure 1. Dynamics of hydrogen absorption (P=5 bar, T=20 oC) by the powder of unmodified (1) and surface-modified (2–4) AB5 alloy pre-exposed to air for 2 weeks, without activation by vacuum heating: 2 – Pd deposition using conventional

Figure 2. Dynamics of hydrogen absorption (P=30 bar, T=20 oC) by the powder of the unmodified (1) and surface-modified by Pd electroless deposition (2) TiFe material

prepared by arc-melting (a) and sintering (b), and activated by vacuum heating to 400 oC for 1 hour deposition after fluorination and surface Prefunctionalisation with γ-APTES pre-functionalisation with γ-APTES; 4 – Pd electroless plating; 3 –Pd deposition after surface

Sodium Alanate Thin Films Grown In-Situ by Reactive Sputtering

M. Filippi1,4, J. H. Rector1, R. Gremaud3, M. J. Van Setten2 and B. Dam4 1Department of Physics and Astronomy, Condensed Matter Physics, Vrije Universiteit, De Boelelaan

1081,1081 HV Amsterdam, The Netherlands2 2 Institut für Nanotechnologie, Forschungszentrum Karlsruhe P.O. box 3640 D-76021 Karlsruhe, Germany 3 Empa, Swiss Federal Laboratories for Materials Testing and Research, Hydrogen & Energy Laboratory,

Überlandstrasse 129, CH-8600 Dübendorf, Switzerland 4 Delft University of Technology, DelftChemTech, MECS, Julianaweg 136, 2628 BL Delft, The Netherlands

Here we report for the first time the synthesis and characterization of a complex hydride (sodium alanate) thin film. Thin films are a model system to explore new metal hydride storage options, using combinatorial methods such as hydrogenography. These methods allow a fast and efficient exploration of the thermodynamic properties, having a speed of analysis that is out of reach for bulk chemical methods. We co-sputter Na-Al thin films in a hydrogen reactive atmosphere. Atomic hydrogen is provided by a hydrogen atomic source which splits molecular hydrogen at a hot W filament. We characterize the films with a combination of optical transmission (in the UV-visible range) and infrared transmission both in the as deposited state and after high temperature annealing. Only when we apply the atomic hydrogen source, we find optical signatures (in the IR and UV regions) of the formation of NaAlH4, which in turn decomposes into NaH and Al after desorption. After desorption we observe a macroscopic Al segregation (in clusters bigger than 1000 nm), which probably hinders the reverse reaction under moderate conditions (no reloading is observed in 10 bar of hydrogen pressure at several temperatures between T=300 K and T=550 K). Generally, (de-)hydrogenation studies are carried out on bulk samples prepared through a complex chemical route, while the dopant is added during ball milling. Here we study the kinetics and thermodynamics of metal hydrides using a thin film approach. The Ti containing dopants are believed to have a two-fold effect on the properties of the alanates namely a catalytic and grain refining effect. Despite the large efforts, the correlation among catalytic role, structure and location of the Ti for (de-)hydriding catalysis is not yet clear We study the role of titanium doping in the desorption properties of the NaAlH4 films, using various artificial heterostructures where the dopant and the alanate are mixed at the nanoscale in a controlled way. The optical characterization of thin films can thus be used to explore the reaction kinetics and phase segregation phenomena in light-weight metal hydrides. References 1. M. Filippi, J. H. Rector, R. Gremaud, M. Van Setten, B. Dam Applied Physics Letters, 95, (2009), 121904.

212

Hydrogen Absorption by α-Scandium at High Temperature

G. Mazzolai Telematic University e-Campus, Via Isimbardi 10, 22060 Novedrate (Co), Italy.

e-mail: giovanni.mazzolai@uniecampus.it

The rate of isothermal H absorption was investigated over a wide range of temperature (790-1280 K) and pressure (10-150 mbar). It was found that the absorbed quantities of H were in line with expectations from p-c-T data in the literature [1] only for temperatures higher than 1000 K. For temperatures lower than 900 K these quantities were markedly smaller than expected. The obtained absorption curves could be fitted to an Avrami-Erofeev type of relationship:

)exp(1 mktf −−= where f is the fraction of the reacted gas quantity and k= Aexp(-W/kT) is the reaction rate constant.

The reaction was first order and the rate constant k exhibited an Arrhenius type of temperature dependence with an activation energy for α-ScHx of 2.14±0.2 eV. The factor controlling the absorption rate turned out not to be H diffusion in the bulk of the α-ScHx solid solution. As a matter of fact, the values of the diffusion coefficient of H for the α phase calculated from absorption data were several orders of magnitude smaller than expected from the extrapolation of lower temperature anelastic [2] and spin-lattice [3] relaxation data. The factor governing absorption rates appears to be the reaction at the external surface. References 1. F. D. Manchester and J. M. Pitre J. Phase Eq. 18, (1997), 194-199. 2. P. Vajda, J. N. Daou, P. Moser and P. Remy J. Phys.: Condensed Matter 2, (1990), 3885-3890. 3. R.G. Barnes, M. Jerosch-Herold, J. Shinar, F. Borsa, D.R. Torgeson and D. T. Peterson, A. J. Lucas, G. A. Styles and E.F-W. Seymour, Phys. Rev. B 35 (1987) 890-893.

213

Hydrogen Generation by Hydrolysis of Mg17Al12 Hydride-Salt Mixtures

Xiao Yan ,Chen Yungui and Wu Chaoling College of Materials Science and Engineering, Sichuan University, Chengdu, China

Email:ygchen60@yahoo.com.cn

Pure Mg or Al and their hydrides can be hydrolyzed for hydrogen generation. In comparison with the pure Al or Mg, Mg17Al12 is a brittle intermetallic compound, which can be easily pulverized and hydrogenated. The hydrogen generation by hydrolysis of Mg17Al12 alloy hydride-salt (NaCl, KCl, MgCl2) mixtures was investigated in this paper. The result showed that the hydrolysis reaction of Mg17Al12 alloy hydride without the addition of salt was rapidly interrupted because of the formation of a passive layer on the Mg17Al12 alloy hydride .The addition of hydrochloric acid can dissolve the passive layer, but it is detrimental to the equipment users. The ball-milling process of Mg17Al12 alloy hydride together with NaCl, KCl or MgCl2 can effectively improve the hydrogen generation of Mg17Al12 alloy hydride hydrolysis. The best result in this experiment is present in Fig.1. For the mixture of the mole ratio 1:1 of MgCl2 to Mg17Al12 alloy hydride which was milled for 1h before hydrolysis, 1363 ml hydrogen per gram Mg17Al12 alloy hydride at 70℃ was generated after 60 min of hydrolysis reaction and the yield reached 90%. The improvement mainly comes from the following three factors:(1)Due to their friability, the salt additive can increase both the specific surface area and vavious defects in Mg17Al12 alloy hydride. (2)The salts are embedded into the Mg17Al12 alloy hydride particles, producing salt gates to make water penetrate deeply inside the Mg17Al12 alloy hydride and react with innermost atoms[1]. (3)The driving force related to the exothermic dissolution of the salt additive is also a key factor to promote the Mg17Al12 alloy hydride hydrolysis.

Fig.1. Hydrolyzed hydrogen generation of the mixture with the mole ratio 1:1 of MgCl2 to

Mg17Al12 alloy hydride milled for 1h. References 1. Babak Alinejad, Korosh Mahmoodi, Int J Hydrogen Energy, 34, (2009), 7934-7938.

214

Dehydrogenation Properties of Catalyzed LiBH4-MgH2 Composite Probed by In-Situ Synchrotron X Ray Diffraction

J. Andrieux a, L. Laversenne b, R. Chiriac c, C. Goutaudier c and V. Honkimaki a

a European Synchrotron Radiation Facilities (ESRF), 38042 Grenoble, France b CNRS- Institut Néel, Grenoble, France

c Université de Lyon, CNRS-UMR 5615 LMI, Lyon, France.

Email: jerome.andrieux@esrf.fr In the field of Solid Hydrogen Storage solutions, complex hydride-binary hydride composites, and especially LiBH4-MgH2 system, stand as promising compounds with high hydrogen storage capacity (8-10 wt% [1]). Destabilisation of LiBH4 by MgH2 lead to a decrease of the dehydrogenation temperature from ~500 °C [2] to ~225 °C [1]. Thus, during the dehydrogenation step, several pathways have been identified [1,3,5-7]. In this case, the hydrogen backpressure is a key parameter [1,3]. Thus, kinetics is still a crucial limiting factor to the development of these composites as SHS solutions. This point gives rise to intensive researches mainly oriented on transition metal salts [1,4-8]. This study is focused on these two main issues and lies in the identification of the dehydrogenation properties of Ti-V-Cr catalyzed LiBH4-MgH2 composite. Investigations have been carried out coupling in-situ synchrotron X ray diffraction and mass spectroscopy during heat treatment of the composites. After a presentation of the high pressure - high temperature capillary system develloped on ID15 for the study of SHS solutions, recent results obtained on catalyzed LiBH4-MgH2 composites will be presented. Both the influence of the LiBH4:MgH2 ratio and the quantity of catalyst on the dehydrogenation pathways and on the kinetics will be presented. The stability of the catalyst over these experimental conditions will also be discussed. References 1. J.J. Vajo, S.L. Skeith, F. Mertens, J. Phys. Chem. B, 109, (2005), 3719-3722. 2. A. Zuttel, P. Wenger, S. Rentsch, P. Sudan, Ph. Mauron, Ch. Emmenegger, J. Power Sources, 118, (2003), 1-7. 3. G.S. Walker, D.M. Grant, T.C. Price, X. Yu, V. Legrand, J. Power Sources, 194, (2009), 1128-1134. 4 J. Graetz, S. Chaudhuri, T.T. Salguero, J.J. Vajo, M.S. Meyer, F.E. Pinkerton, Nanotechnology, 20, (2009), 204007-204015. 5. U. Bösenberg, S. Doppiu, L. Mosegaard, G. Barkhordarian, N. Eigen, A. Borgschulte, T.R. Jensen, Y. Cerenius, O. Gutfleisch, T. Klassen, M. Dornheim, R. Bormann, Acta Materialia, 55, (2007), 3951-3958. 6. T.C. Price, D.M. Grant, I. Telepeni, X. Yu, G.S. Walker, J. Alloys Compd, 472, (2009), 559-564. 7. F.E. Pinkerton, M.S. Meyer, G.P. Meisner, M.P. Balogh, J.J. Vajo, J Phys. Chem. C Letters, 111, (2007), 12881-12885. 8. J.J. Vajo, T.T. Salguero, A.F. Gross, S.L. Skeith, G.L. Olson, J. Alloys Compd, 446-447, (2007), 409-414.

215

Atomization Energy Approach to the Quantitative Evaluation of Catalytic Activities of Metal Oxides during Dehydrogenation of MgH2

H.Hirate1, M.Morinaga1, H.Yukawa1 and H.Nakai2

1. Department of Materials Science and Engineering, Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8603, Japan

2. Department of Chemistry, School of Science and Engineering, Waseda University, Okubo, Shinjuku-ku, Tokyo 169-8555, Japan

Email: morinaga@numse.nagoya-u.ac.jp The hydrogen desorption reaction of magnesium hydride (MgH2), , is accelerated by mixing catalytic metal oxides (e.g., Nb2O5). This catalytic activity of metal oxides, MxOy, is theoretically estimated in a quantitative way using atomization energy concept. Following the energy density analysis [1], the total energy of a system is partitioned into the atomic energy densities in the oxide.The atomization energies, ΔEM for metal ion and ΔEO for oxide ion in various metal oxides are then evaluated by substracting the respective atomic energy densities from the energy of isolated neutral atom, M or O. As shown in Fig.1, the measured hydrogen desorption rate increases monotonously with increasing values of metal oxides [2]. The value is the energy of the oxide ions in a chemical formula unit of MxOy.This correlation implies that the oxide ions in MxOy interact mainly with hydrogen atoms in MgH2. Thus, the value is a measure of the magnitude of the O-H interaction operating between MxOy and MgH2, and hence it is a good parameter to show the catalytic activities of each metal oxide. 22HMgMgH+→OyEΔ× OyEΔ× OyEΔ×

A series of experiments is performed to prove this theoretical prediction. The O-H vibration on the Nb2O5-catalyzed MgH2 is investigated experimentally using FT-IR spectroscopy. The broad absorption band due to the O-H stretching mode is clearly observed in the range of 2800 to

Fig.1 yvs. desorption rate of MgH2 with l id l OEΔ× 3600 cm-1 in the FT-IR spectra of the specimens when hydrogen desorption reaction is in progress [3]. The absorbance of the band decreases monotonously with decreasing content of hydrogen in the specimen during the course of dehydrogenation of MgH2. This experimental result is a direct evidence for the existence of the O-H interaction in the hydrogen desorption process. The atomization energy approach is also useful for the quantitative evaluation of the catalytic effect of metal chlorides (e.g., TiCl3) on the decomposition reaction of NaAlH4, expressed as, . 23263314HAlAlHNaNaAlH++→ References 1. H. Nakai, Chem. Phys. Lett., 363, (2002), 73-79. 2. H. Hirate, Y. Saito, I. Nakaya, H. Sawai, Y. Shinzato, H. Yukawa, M. Morinaga, T. Baba and H. Nakai, International Journal of Quantum Chemistry, 109, (2009), 2793-2800. 3. H. Hirate, H. Sawai, H. Yukawa and M. Morinaga, International Journal of Quantum Chemistry, in press, DOI 10.1002/qua.22544.

216

Tailoring MgH2 with Ternary Oxides of Mg-Nb System Towards Fast Hydrogen Sorption Kinetics

M.W. Rahmana, S. Livraghia, F. Dolcia,b, M. Bariccoa, S. Enzoc and E. Giamelloa aDipartimento di Chimica IFM, NIS Centre of Excellence, Università di Torino,

Via Pietro Giuria 9, 10125, Turin, Italy bEuropean Commission – JRC Institute for Energy, Clean Energy Unit,

Westerduinweg 3, NL-1755 ZG Petten, The Netherlands

cDipartimento di Chimica, Università di Sassari, I-07100, Sassari, Italy Email: rmd.wasikur@unito.it

Magnesium hydride (MgH2) has been considered as one of the most promising hydrogen storage materials because it possesses a high nominal H2 storage capacity (7.6 wt%)1. However, the reaction kinetics of hydrogen absorption and desorption is too slow in the moderate conditions2. Milling MgH2 with additives, in particular whit Nb2O5 improves kinetics of the system by the formation of ternary Mg-Nb-O phases during the hydrogen sorption cycles3,4,5. In this work, H2 sorption kinetics of MgH2 promoted by ball-milling with 1 mol% MgNb2O6, Mg4Nb2O9 and Mg3Nb6O11 have been investigated. Each pure ternary oxide was prepared by solid state reactions6 and mechanical milling was performed using a SPEX 800 Mixer-Mill. This was equipped with a hardened steel vial and balls (ball-to-powder mass ratio was 7:1). MgH2 was milled with the oxides for 12 h at a rotational speed of 875 rpm under a high purity Ar atmosphere. Hydrogen storage properties of the milled samples were examined using an automatic Sievert-type apparatus (USA Advanced Materials) at 653 K with a hydrogen pressure of 2 MPa for absorption and 0.1 MPa for desorption. Commercial MgH2, milled MgH2 and a MgH2-Nb2O5 milled mixture were adopted as a reference materials. MgH2 milled with all the ternary phases listed before shows kinetics faster than that milling the bare Nb2O5, the best kinetics performer reported so far7. MgNb2O6 and Mg3Nb6O11 phases show fastest absorption and desorption kinetics respectively. In the case of MgNb2O6 the system absorbs about 80% of its maximum capacity (5.40 wt%) in 15 mins whereas, MgH2-Mg3Nb6O11 mixture takes only 3 mins for complete desorption.

The absorbed amount in the presence of Mg-Nb-O phases is lower than the maximum stoichiometric capacity. The reduction of H2 storage capacity of the milled samples has been reported and may be ascribed to the presence of non-permeable MgO layer on the MgH2 grains4. References

1. L. Schlapbach, A. Zuttel, Nature, 414, (2001), 353-358. 2. B. Bogdavonic, K. Bohmhammel, B. Christ, A. Reiser et al. J. Alloys and Compounds,

282, (1999), 84-92. 3. O. Friedrich, F. Aguey-Zinsou, J.R. Ares Fernandez et al. J. Acta Mater. 54, (2006), 105-

110. 4. O. Friedrich, J.C. Sanchez-Lopez, C. Lopez-Cartez et al. J. Phys. Chem. B. 110, (2006),

7845-7850. 5. F. Dolci, M. Di Chio, M. Baricco, E. Giamello, Mater. Res. Bull. 44, (2009), 194-197. 6. S. Pagola, R.E. Carbonio, J. Solid State Chem. 134, (1997), 76-84. 7. G. Barkhordarian, T. Klassen, R. Borman, Scripta Mat. 49, (2003), 213-217.

217

Catalysts in Ca(BH4)2

I. Llamas-Jansa and B. C. Hauback Physics Department, Institute for Energy Technology,

P.O. Box 40, NO-2027 Kjeller, Norway Email: isabel.llamas@ife.no

Systematic studies on the addition of catalysts to the three most common modifications of Ca(BH4)2 (α, β, and γ) have been carried out using the ball milling technique. The initial mixtures contained an specific Ca(BH4)2 polymorph together with different amounts of TiCl3 or TiF3, ranging from 1.6 to 10 mol%. The resulting powders were characterized by powder X-ray diffraction (PXD) and their desorption behavior studied by means of differential scanning calorimetry (DSC) and temperature programmed desorption (TPD) in dynamical vacuum. Preliminary results indicate a decrease of the desorption temperature compared to pure Ca(BH4)2, both in terms of increased milling time and catalyst content. No additional phases were obtained after the addition of the catalyst, although the possible formation of intermediate compounds during decomposition, such as those observed in doped LiBH4 [1], might explain the observed catalytic effects. The effect of the borohydrides structural modification on the final behavior of the samples is still under investigation. The authors acknowledge the contribution of Max Fichtner’s group at Karlsruhe Institute of Technology (KIT). Financial support from Research Council of Norway and European Commission FP6 and FP7 programs are also acknowledged. References [1] M. Au, A. R. Jurgensen, W. A. Spencer, D. L. Anton, F. E. Pinkerton, S.-J. Hwang, C. Kim, and R. C. Bowman, Jr., Journal of Physical Chemistry C 112, 18661 (2008)

218

Compositional Effect on the Kinetics of LiH-Mg(NH2)2 Reaction Yongming Wanga, Takenobu Wakasugia, Takayuki Ichikawab, Naoyuki Hashimotoa,

Somei Ohnukia, Yoshitsugu Kojimab a Graduate School of Engineering, Hokkaido University, N13-W8, Kita-ku, Sappro, 060-8628, Japan b Materials Science Center, N-BARD, Hiroshima University, 1-3-1 Kagamiyama, Higashi-Hiroshima

739-8526, Japan Email: wang@eng.hokudai.ac.jp

The mixture of LiH and Mg(NH2)2 has been being researched as a promising hydrogen storage material in recent years [1]. The reaction 2LiH + Mg(NH2)2 = Li2Mg(NH)2+2H2

contributes to forming the main hydrogen desorption peak at the low temperature side in non-isothermal measurement [2]. In present study, it was found that this peak temperature could be affected by the molar ratio of LiH to Mg(NH2)2 (Fig.1), as shown in Fig. 2, the larger value of the molar ratio, the lower peak temperature. Based on the observations of transmission electron microscope, we quantitatively interpreted this phenomenon, and then demonstrated that a new method utilizing the phenomenon can be used to determine the activation energy of the heterogeneous solid-state reactions being similar to the dehydrogenation reaction in this work.

References 1. P. Chen, Z. Xiong, G. Wu, Y. Liu, J. Hu, W. Luo, Scr. Mater., 56, (2007), 817-822. 2. M. Aoki, T. Noritake, Y. Nakamori, S. Towata, S. Orimo, J. Alloys and Compounds, 446-447, (2007), 328-331.

219

Hydride Decomposition Characterization by Means of “Morphological Trajectory” Method. Application to AlH3.

E.Evard and A.Voyt

Physics Department of Saint-Petersburg State University, Saint-Petersburg, Russia Email: evard@yandex.ru

Study of kinetics of hydride decomposition requires formulation of adequate physical

model of process and further mathematical processing to obtain estimations of kinetic parameters. There are two most used and diametrically opposite methods for hydride decomposition description: 1) Avrami-Erofeev approach characterized by few integral parameters, and 2) detail description of every possible reaction for idealized geometry. The first approach often doesn’t allow unambiguous identification of limiting stage, the second one leads to system of multiparametric equations which can’t be solved in general case.

We propose some intermediate variant of kinetics analysis operating integral morphological parameters as well as kinetic parameters of possible limitating reactions (nucleation, desorption and reaction at interphase). Morphology of new phase growth is described in terms of specific values of new phase volume (VMe), outer surface occupied by new phase (SMe_out), interphase (SMe_int) and theirs interrelations (“morphological trajectores”).

For establishing interrelation of these values a number of computer modeling experiments was performed for different sets of particle shape, constant and shifting rates of nucleation and growth. As a result of modeling we obtained simple analytic formulas SMe_out=f(VMe), SMe_int=g(VMe) which depend on few parameters and satisfactorily describe all cases under consideration. On the basis of this functions simple models were developed for the cases of limitation by desorption at outer surface of new phase, by reaction at interphase and for the case of concurrence of these two reactions. There are no restrictions in the models on shape of particles and on shape of growing nuclei of new phase. Inverse problem solution (fitting of experimental data on the bases of developed models) allows estimating kinetic and morphological parameters. Obtained “morphological trajectory” allow to suppose shape and quantity of new phase nuclei.

This approach was applied for study of AlH3 under conditions of isothermal decomposition (353 – 423 K) and TDS (heat rates 0.01 – 0.2 К/s; decomposition temperatures 390 – 470 K). Analysis was facilitated in this case by very narrow size and shape distribution of material. Data processing showed that limiting stage is the reaction at interphase with activation energy 104 kJ/mole. It was found that transformation morphology depends on experiment conditions: the higher reaction temperature, the smaller quantity of new phase nuclei have time to appear. In TDS-experiments high temperature is reached quickly so it is typical for them 1-2 nuclei formation that is confirmed by SEM study of AlH3 samples dehydrided to different transformation degree.

Acknowledgements. The study have been supported by the grant 09-03-00947-а of the Russian Foundation for Basic Research. SEM study data presented in this work were obtained using the equipment of Interdisciplinary Resource Center for Nanotechnology of St. Petersburg State University, Russia

220

Coadsorption of H and CO on Gd(0001)

M. Getzlaff Institute of Applied Physics and Nanotechnology, University of Düsseldorf, Düsseldorf, Germany

Email: getzlaff@uni-duesseldorf.de Rare earth metals are of great scientific and technological interest due to their unusual electronic and magnetic properties which arise from their highly localized 4f electrons. Detailed knowledge about the electronic structure of the surface is therefore essential to understand the mechanisms being responsible for surface magnetic order. Adsorbates can significantly influence the corresponding electronic behavior of the underlying substrate and are additionally of great importance in technological processes, e.g., heterogeneous catalysis. We report on the electronic structure of hydrogen and carbon monoxide on Gd(0001) and the development of the adsorption processes studied by means of photoelectron spectroscopy in combination with scanning tunneling microscopy. This knowledge is used in order to obtain a deeper insight into the behavior of catalytic processes. For this purpose the Gd surface was exposed to small amounts of hydrogen with a subsequent dosage of carbon monoxide. The adsorption process of a hydrogen covered Gd film being exposed to carbon monoxide consists of five steps. At the beginning the whole amount of adsorbed hydrogen atoms is removed from the surface (see Figure). In the intermediate regime, carbon and oxygen is adsorbed at or near the surface. The last step demonstrates the oxidation to Gd2O3 acting as a catalyst for the transformation of CO to CO2 which creates stable carbonate species at the surface. This formation also occurs for the adsorption of oxygen and carbon monoxide. The visualization of the adsorption process during specific steps is obtained by STM.

Figure: Photoemission spectra taken with hν = 16.85 eV for a smooth Gd film being pre-exposed to 1 L hydrogen as a function of CO dosage. With increasing offer the hydrogen-induced peak at 4 eV binding energy disappears, whereas around 2 eV a broad structure shows increasing intensity

221

Thermocycling and Isothermal Studies of Kinetics of Yttrium Hydrides Transformation YH3↔YH2.

A.Voyt, E.Evard, V.Vinogradskaya, I.Gabis.

Physics Department of Saint-Petersburg State University, Saint-Petersburg, Russia Email: voytalexey@mail.ru

Yttrium trihydride formation and decomposition (YH3↔YH2) kinetics was studied by

two experimental methods: • Thermocycling in closed volume at different initial pressures; • Step pressure change at isothermal conditions.

Kinetics of transitions YH3↔YH2 were studied at pressures 1-100 Torr and temperatures 80-350OC. The heat rates used at thermocycling were 0.002-0.2 K/s. Samples after cycling become a powder with particles size 2-25 micron.

Pic.1. Cycling at pressures 5.0-5.5 Torr; Heatrates are from 0.01 to 0.2 K/s.

Pic.2. Step-like pressure change at 140OC Pressures are 2.0, 4.0, 4.5 and 5.0 Torr.

50 100 150 200 250 300

2,2

2,4

2,6

2,8

3,0

x, Y

Hx

T,OC0 50 100 150 200

2,0

2,2

2,4

2,6

2,8

3,0

YHx

Time, s

Thermocycling experimental results depend on heatrate value at x=(2.2-3.0) but there is

no dependence on heatrate at x=(2.0-2.2). This can be explained as a greater influence of interphase boundary movement in comparison with adsorption-desorption of hydrogen on particles surface. Isothermal experiments with step-like change of hydrogen pressure show the linear dependence of transition kinetics on pressure at initial stages of transformation:

( *~ PPdtdx

− ) where P* depends on temperature. Van’t Hoff relations of temperature and

equilibrium pressure of transformation YH3↔YH2 were measured. Enthalpy of formation is H(YH2→YH3)=70 kJ/mole; enthalpy of decomposition is H(YH3→YH2)=91 kJ/mole. Acknowledgements

The study was supported by the grant 09-03-00947-а of the Russian Foundation for Basic Research.

SEM study data were obtained using the equipment of Interdisciplinary Resource Center for Nanotechnology of St. Petersburg State University, Russia.

222

Improved Hydrogen Storage Performance of the LiNH2-MgH2-LiBH4 System by Addition of MCo (M=Ti, Zr) Hydride

Zhinian Li, Xugang Zhang, Fang Lv, Hualing Li, Jing Mi, Shumao Wang, Xiaopeng Liu,

Lijun Jiang General Research Institute for Nonferrous Metals, Beijing 100088, China

1 Corresponding author: Tel.: +86 01 82241238 E-mail address: lzngrinm@163.com

Significant improvements in the hydrogen absorption/desorption properties of the 2LiNH2-1.1MgH2-0.1LiBH4 composite have been achieved by adding 3wt% MCo (M=Ti, Zr) hydride. The 3wt%ZrCoH3-doped composite can absorb 5.3wt% hydrogen under 7.0MPa hydrogen pressure in 10 minutes and desorb 3.75wt% hydrogen to 0.1MPa H2 in 60 minutes at 150℃, compared with 2.75wt% and 1.67wt% hydrogen under the same hydrogenation/dehydrogenation (H/D) conditions without the ZrCoH3 addition, respectively. TPD measurements showed that the dehydrogenation temperature of the ZrCo hydride-doped sample decreased about 10℃ comparing to that of the pristine sample. It is deduced that both the homogeneously distribution of MCo (M=Ti, Zr) hydride particles on the matrix observed by SEM and EDS maps and the destabilized N-H bonds detected by IR spectrum are the main reasons for improving the H/D kinetics of the 2LiNH2-1.1MgH2-0.1LiBH4 system. Keywords: Hydrogen storage materials; Li-Mg-N-H; LiBH4; ZrCoH3; TiCoH

223

Effect of Ti31Cr15.5V45Fe8.5Ce0.5 on Desorption Kinetics Property of NaAlH4 Doped by Ce Hydride

Jing Mi, Xiaopeng Liu Fang Lv, Lijun Jiang, Zhinian Li, Zhuo Huang, Shumao Wang Energy Material and Technology Research Institute,

General Research Institute for Non-ferrous Metals, Beijing China, 100088 Email: topmijing@yahoo.com.cn

Effect of Ti31Cr15.5V45Fe8.5Ce0.5(identified as BCC in this paper for easy depiction )on desorption kinetics property of NaAlH4 doped by Ce hydride has been studied by X-ray diffraction, scanning electron microscopy, 3-dimensional diffusion model simulation and desorption kinetics measurement. The results indicated that with the addition of BCC, the hydrogen desorption capacity of first desorption step of NaAlH4 increases from 1.89wt% to 2.30wt% and the first step desorption time decreases from 40min to 20min. According to the calculation of P-B ratio and 3-dimensional diffusion simulation, the product of first desorption step of NaAlH4 forms a porous product layer, the first desorption step is diffusion-controlled and the rate-controlled step is H2 diffusion through this product layer. The BCC alloy added in NaAlH4 is as hydrogen diffusion channel and increases the rate of hydrogen diffusion in the product layer, and then improves the desoprtion kinetics property of NaAlH4. Key words: hydrogen storage materials; Ti-V based BCC alloys; Sodium alanate

224

5f Magnetism in UTGe Hydrides

A. Adamska1,2, L. Havela1, J. Pospíšil1, N.-T.H. Kim-Ngan3 1 Department of Condensed Matter Physics, Charles University, Prague, The Czech Republic

Email: anna@mag.mff.cuni.cz 2 Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Kraków,

Poland 3 Institute of Physics, Pedagogical University, Kraków, Poland

Intermetallic compounds of 5f elements, including uranium, are especially sensitive to hydrogen absorption. In the case of purely band systems the most important parameter determining the magnetic properties is the interatomic distances between e.g. uranium atoms. However, most of uranium intermetallics are characterized by a 5f-ligand hybridisation, then the strength of hybridisation becomes a crucial parameter. Hydrogen intrusion can easily modify the hybridised band by withdrawing electronic states due to bonding with the atoms which contribute to the band. Hydrogenation of UTSi compounds, where T = Co, Pd, Ni [1,2] and UTGe compounds, where T = Fe, Co, Rh [3] led to a notable lattice expansion and an increase of respective magnetic ordering temperatures. Our results on the hydrides of the compounds with UTGe stoichiometry (T = Rh, Pd, Ir and Ni) obtained at the highest hydrogen pressure (pH2 ≈ 160 bar) complete the study. In the case of new α-hydride of URhGe (TiNiSi type of structure) with hydroden concentracion of 0.3 H/f.u. and the volume expansion of 1.3 %, TC was shifted from 9 K for URhGe [4] up to 17 K for the hydride. Hydrogenation of UPdGe and UIrGe did not change the TiNiSi type of sturcture (space group Pnma), it leads only to the volume expansion of 0.5 % and 0.7 %, respectively. For UPdGe, two phase transitions were reported, the ferromagnetic one at TC ≈ 30 K and the antiferromagnetic one at TN ≈ 50 K [4]. Hydrogen absorption in UPdGe does not change TN, but it leads to a decrease of TC to 26 K. In the case of UIrGe, the antiferromagnetic ground state (TN ≈ 16 K) [4] was transformed into ferromagnetic one for UIrGeH0.1. Such a transition was revealed by a well-pronounced but broad peak of ac susceptibility with maximum around 30 K. The onset of ferromagnetism can be assumed around 40 K, but the system looks magnetically inhomogeneous. Upon hydrogenation of UNiGe at the highest pH2 pressure, the crystal symmetry increases, and UNiGeH1.2 crystallizes in the ZrBeSi type of structure (space group P63/mmc), the unit cell volume expands by 7.6 %. The pure UNiGe exhibits two antiferromagnetic phase transitions, one below below TN ≈ 42-44 K [4] and the second one just below 50 K [5], whereas UNiGeH1.2 is a ferromagnet with TC below 100 K. Other intermediate hydrides of UNiGe (UNiGeH1.0 and UNiGeH0.3), obtained at a much lower hydrogen pressure of 2 bar and less exhibit two phase transitions, the antiferromagnetic one with TN below 35-38 K and most probably a ferrimagnetic phase below 7-10 K. References 1. K. Miliyanchuk et al., J. Alloys Comp. 383, (2004), 103-107. 2. A. V. Kolomiets et al., Phys. Rev. B 66, (2002), 144423. 3. A. M. Adamska at al., Magnetism in hydrogenated UTGe compounds, IOP Conf. Proc 2010, in press. 4. R. Troc, V.H. Tran, J. Magn. Magn. Mater. 73, (1988), 389-397. 5. A. Purwanto at al., Phys. Rev. B 53, (1996), 759-765.

225

Electrical Properties of FeHx under High-Pressures and Low-Temperatures

T. Matsuoka1, N. Hirao1, Y. Ohishi1, K. Shimizu2, A. Machida3, K. Aoki3 1Japan Synchrotron Radiation Research Institute (JASRI/SPring-8), Sayo, Hyogo, Japan

2KYOKUGEN, Center for Quantum Science and Technology under Extreme Conditions, Osaka University, Toyonaka, Osaka, Japan

3Japan Atomic Energy Agency (JAEA), Sayo, Hyogo, Japan Email: tmatsuoka@spring8.or.jp

Study of metal hydride at various pressure and temperature conditions is fundamental interest, since both are thermo-dynamical parameters tuning effectively and significantly the structural and electronic properties of materials. In particular the high-pressure study contribute essentially to deep understanding of the interactions between hydrogen and metal atoms in MH-systems through contraction of the host metal lattice. The physical properties of iron (Fe) have been investigated for a wide range of pressure and temperature, and the structural transformation from the bcc to hcp lattice with ferromagnetic-nonmagnetic transition was observed at pressures around 13 GPa at ambient temperature [1]. Surprisingly, superconductivity appears near the bcc-hcp phase boundary at temperatures reaching to 2.5 K at around 22 GPa[2,3]. Hydride of iron (FeHx) is an attractive M-H system for studying electronic and magnetic property under high pressure. FeHx is formed at 3.5 GPa at ambient temperature accompanied with bcc-dhcp structural transition. Ferro-magnetic dhcp-FeHx was found to lose gradually the magnetism with increasing pressure to about 32 GPa[4]. To study the electronic state and search for the superconductivity in compressed FeHx, we have investigated the electrical property of FeHx under high-H2 pressure by the simultaneous measurement of electrical resistance and synchrotron X-ray diffraction up to 25 GPa and down to 8.5 K. A tiny chip of Fe-foil and fluid H2 were loaded into a sample chamber of a diamond anvil cell with electrodes welded in advance for electrical resistance measurement. The electrical resistance showed a small but sharp jump up at 3.5 GPa with the transformation from bcc-Fe to dhcp-FeHx. FeHx was found to be metallic up to 25 GPa and no signal for superconducting transition was observed at temperatures down to 9 K. Below 25 K, the electrical resistance vs. temperature curves up to 16.5 GPa approximately follow Fermi-liquid law ρ = ρ0+AT2, where ρ0 is residual resistivity and A is coefficient. However, the temperature dependence deviates clearly from AT2 law at 25 GPa. The change in resistance vs. temperature slope is likely related to the magnetic transition observed at the corresponding pressures in the previous work[4]. References 1. D. Bancroft, E. L. Peterson, and S. Minshall, J. Appl. Phys. 27, (1956) 291. 2. K. Shimizu, T. Kimura, S. Furomoto, K. Takeda, K. Kontani, Y. Onuki and K. Amaya,

Nature 412, (2001) 316. 3. D. Jaccard, A.T. Holmes, G. Behr, Y. Inada, Y. Onuki, Phys. Lett. A299, (2002) 282. 4. N. Hirao, T.Mitsui, Y. Ohishi, M. Seto, K. Aoki, K. Takemura, T. Kikegawa, Special

Issue of the Review of High Pressure Science and Technology, 19, (2009) 232.

226

In-Situ Optical Microscopy Study of the Absorption and Desorption of H2

by Mg-Pd-Ni Thin Films J. F. Fernandez

1, D. Azofeifa

2, J. R. Ares

1, F. Leardini

1, F. Vasquez

2, J. Bodega

1, N. Clark

2

and C. Sánchez1.

1 Dpto. Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Madrid, Spain

2Centro de Investigación en Ciencias e Ingeniería de Materiales and Escuela de Física, Universidad deCosta

Rica, 2060 San José, Costa Rica Email: carlos.sanchez@uam.es

The reaction of Mg with H2

to form MgH2

is coupled to a metal-insulator transformation that results in pronounced changes in the optical properties of the material [1,2]. In the optical region, it changes from a highly reflective state to a transparent one. Optical methods coupled to H

2 absorption/desorption may give valuable information on the several stages of the reaction

process such us metal activation and kinetics of the reaction. Thin films of Mg-Pd-Ni with an atomic composition close to Mg

6(Pd

0.5Ni

0.5) were prepared by

ion beam sputtering and characterised by Glancing angle X-ray diffraction, Profilometry, Atomic force microscopy and Scanning electron microscopy. Reaction of H

2 with the films was

carried out in a Sieverts type reactor as well as in a microscope stage able to work up to 300ºC and 1 bar of H

2 pressure. The last system allows taking micrographs of the film during H

2 absorption/desorption. Fig.1 shows images taken in transmission mode at several temperatures during heating (20ºC/min) of a partially transparent hydrided film in an Ar atmosphere. Around 300ºC, black nucleus start to form, growing quickly to cover the analysed surface in a short time. The black nucleus correspond to metallic (highly reflectance) phases formed during the H

2-desorption process.

In this communication we will report about the characterisation of the films and their behaviour toward H

2-absorption/desorption. Comparison with the same material prepared in bulk [3] will

be presented.

227

Acknowledgements. We thank the Spanish Minister of Education and Science and Minister of Foreign Affairs for financial support under contracts Nº. MAT2008-06547-C02-01and A/017362/08. We thank to Dr. P. Adeva (CENIM, CSIC) for kind help on preparation of the mother alloy. References 1. J.N. Huiberts, R. Griessen, J.H. Rector, R.J. Wijngaarden, J.P. Dekker, D.G. de Groot, and N.J. KoemaNature 380, 231 (1996). 2. TJ Richardson, JL Slack, RD Armitage, R. Kostecki, B. Farangis, MD Rubin. Applied Physics Letters, 78(20), 3047-3049 (2001) 3. J.F. Fernández, J.R. Ares, F. Cuevas, J. Bodega, F. Leardini, C. Sánchez, Intermetallics 18, 233–241 (2010).

The Effect of Hydrogenation on Magnetic Ordering in Y2Fe17-xMnx Compounds

W.Iwasieczko1, H.Drulis1, S.Nikitin2, N.Pankratov2, I.Tereshina3, G.Politova3,K.Skokov4

and A.Karpenkov4 1 Institute of Low Temperature and Structure Research, Wroclaw, Poland

2Physical Department, Lomonosov Moscow State University, Moscow, Russia 3Baikov Institute of Metallurgy and Material Science RAS, Moscow, Russia

4Physical-Technical Department, Tver State University, Tver, Russia Email: nikitin@phys.msu.ru

Intermetallic compounds based on rare-earth (R) and 3d-transition metals form a large family of the magnetic materials. Due to the coexistence of both the 3d and rare earth magnetic subsystems the unical properties (high spontaneous magnetization and magneto-crystalline anisotropy) can appear at temperatures higher than room temperature. Along with the practical and fundamental importance, many aspects of magnetism of the R2Fe17 compounds have attracted much attention of investigators. The aim of this work is to study of the effect of hydrogenation on the magnetic properties of the R2Fe17 compounds, in which Mn atoms partially substitute the Fe atoms. In order to get the deeper understanding of the 3d - sublattice magnetism, as R atom we used Y that is a nonmagnetic analog of REMs. Samples of Y2Fe17-xMnx (0 ≤ х ≤ 8) were prepared by induction melting of the high purity metals with subsequent annealing of the ingots at 900oC for 3 days. The hydride syntheses were carried out in a high-pressure reactor chamber. Before hydrogenation the samples were activated for 4 hours in vacuum at 670 K. The Y2Fe17-xMnxHy (0 ≤ y ≤ 4.4) hydrides have been obtained. X-ray powder diffraction was employed to determine the lattice parameters. The magnetization measurements were carried out using a SQUID magnetometer in the temperature range of 1.7 – 420 K and in magnetic fields up to 50 kOe. It has been found that the hydrogenation of Y2Fe17-xMnx causes an increase of the unit cell volume. Hydrogen has no important influence on the spontaneous (MS) magnetization for Y2Fe17-xMnx compounds when x < 2 whereas there is essential increasing (more than 10%) of MS for hydrides with х ≥ 2. The temperature dependence of the magnetization at low magnetic fields (H = 100Oe) have shown that the hydrogenation of Y2Fe17-xMnx (0 ≤ x ≤ 6) alloys rises the Curie temperature. We suggest that this is due to the increasing of Fe-Fe distances and the exchange interaction between the ordered Fe atoms (in the region of TC the Mn-sublattice does not participate in magnetic ordering). Mn-sublattice in Y2Fe17-xMnx (0 ≤ x ≤ 6) alloys orders only at low temperatures below the characteristic temperature TMn where the magnetization starts to decrease rapidly. The TMn increases with Mn concentration increasing in Y2Fe17-xMnx alloys but it decreases rapidly after hydrogenation. For example, in the Y2Fe14Mn3 TMn = 125 K and TC = 257 K. Contrary to this in the Y2Fe14Mn3H4 hydride phase the TMn diminishes up to 30 K whereas TC increases to 355 K. The Y2Fe17-xMnx (x = 7 and 8) samples are antiferromagnetics with TN ≈ 150 K however, the introduction of 3 hydrogen atoms to Y2Fe10Mn7 unit cell leads to partial suppressing antiferromagnetic ordering and induces the ferromagnetic state. Our investigation showed that the hydrogenation raises the exchange interactions within the Fe-sublattice and diminishes similar interactions in Mn-sublattice. 00

228

Effect of Hydrogen Atoms Introduction on Magnetic Domain Structure and Magnetocaloric Effect of R2Fe17 Intermetallic Compounds

A.Arefev1, Yu.Koshkidko1, K. Skokov1, Yu. Pastushenkov1,

S. Nikitin2, T. Ivanova2, A. Salamova2 1Tver State University, Tver, Russia

2Moscow State University, Moscow, Russia Email: Arefev_Arthur@mail.ru

Hydrides are formed by the introduction of hydrogen atoms in the crystal lattice. As a result of hydrogenation the symmetry of the structure of compounds remains unchanged [3], with the observed expansion of the crystal lattice, and in consequence there are changes of magnetic properties such as magnetization, magnetocrystalline anisotropy, the Curie temperature, etc. [1-3]. The change of these parameters can significantly affect the magnitude of the magnetocaloric effect (MCE) and the magnetic domain structure of the sample. The aim of this work is the study of the effect of the introduction of hydrogen atoms on the MCE of R2Fe17 and R2Fe17Hx compounds. The results of measurements of the MCE, as well as the results of observations of magnetic domain structure of R2Fe17 intermetallic compounds and their hydrides R2Fe17Hx are shown. The arising interest in R2Fe17 compounds is caused by their unique magnetic properties [4] and widened practical application. Also, they are often used to clarify the theoretical concepts, which are used to describe the magnetic ordering [5]. Tb2Fe17 and Y2Fe17 single crystals were chosen as the samples for investigations. The alloys were obtained by the high-frequency induction melting in the high purity argon atmosphere. The samples were hydrogenated at the Department of High Pressure of Chemical Faculty of Moscow State University at the laboratory of Verbetskii. The measurements of the MCE were carried out by the direct method. The magnetic domain structure investigations were performed by optical and atomic force microscopy. As a result of the work it was revealed that hydrogenation led to the change in the magnetic domain structure character and MCE values. The observed domain structure changes are caused by magnetocrystalline anisotropy changes [2]. The MCE magnitude changes due to the magnetization value [1]. The work is supported by RFBR grant # 09-02-01274 References 1. Tereshina I.S. et al. Journal of Alloys and Compounds,2003, 350, 264-270 2. Nikitin S. A. et al. Journal of Alloys and Compounds,1999, 195, 464-469 3. О. Isnard et al. Journal of Magnetism and Magnetic Materials,1994, 137, 151 - 156 4. K. P. Belov. Rare-Earth Magnetic Materials and Their Applications [in Russian],

(Nauka, M.), 1980, 240 . 5. S.A. Nikitin. Magnetic Properties of Rare Earth Metals and Alloys, Moscow State

University Publishers, 1989, Moscow, [in Russian],248 .

229

The Effect of Hydrogenation on the Electrical Resistivity of Disordered Alloys

M.Ornat and A.Paja Faculty of Physics and Applied Computer Science, AGH University of Science and Technology, Krakуw,

Poland Email: paja@agh.edu.pl

Theoretical investigations of the influence of hydrogen contents on the electrical resistivity of amorphous metallic alloys have been carried out. We have made use of our method of calculations of the electrical resistivity of disordered systems based on the ground of Morgan-Howson-Saub and Evans models. Our method is fully quantum, includes multiple scattering effects and uses the scattering matrix operators for describing the electron-ion interactions. The model gives good agreement with experiment for many binary systems and should work for ternary systems as well thus we performed calculations with hydrogen as one of the components of a ternary alloy. The results of some exemplary calculations show that the resistivity increases with hydrogen concentration. We are considering hypothetical systems, which may not be stable in practice, but we propose a model that could give some predictions for experimental works. Μ

230

Electric Field Gradients in Be, Mg, and Al Hydrides V.P.Tarasov1 and D.E.Izotov2

Institute of General and Inorganic Chemistry RAS, Moscow, Russia1

Chemistry Department, University of the Pacific, Stockton, CA, USA 2

Email: tarasov@igic.ras.ru Binary hydrides of light metals-BeH2, MgH2, and AlH3 have three-dimensional polymeric structures, in which chemical bonding is through bridging hydrogen atom. The coordination polyhedron for the metal atom is a slightly distorded octahedron for Mg and Al hydrides and a tetrahedron for Be hydride. The metal-hydrogen bond in these hydrides is characterised by electron density transfer from metal to hydrogen. The specific features of the charge distribution at the atoms in these hydrides manifest themselves in the values of the electric field gradients (EFG) at the hydrogen and metal positions. Here, we report the results of measuring of the quadrupole coupling constans (χQ) and tensor EFG asymmetry parameters (η) at deuterium and metal sites in amorphous BeD2, crystalline α-MgD2, and crystalline α-AlD3 by 2H, 9Be, 25Mg, and 27Al NMR (7.04T, 14.1T). The results of ab initio Hartree-Fock calculations of the EFG tensors at hydrogen and metal sites for some (BenHm), (MgnHm), and (AlnHm) clusters are also presented [1]. Table. Experimental values of χQ and η, and EFG at deuterium and metals positions. Compounds χQ in kHz and asymmetry

parameters η Deuterium Metals

Electric field gradients in atomic units* Deuterium Metals

BeD2 (amorphous)

D(1) 150±2 Be(1) 0 η = 0,18(4) D(2) 65±2 Be(2) 0 η=0,25(4)

D(1) 0,223 Be(1) 0 D(2) 0,097 Be(2) 0

MgD2 (crystalline) 73± 5 2900±50 η=0,58(4) η=0,1

0,109 0,06

AlD3 (crystalline) 89±2 264±2 η=0,08(3) η=0

0,134 0,007

*1au (2H) = 672 kHz,1au (9Be)=12,43 MHz; 1au(25Mg)=46,85 MHz; 1au(27Al)=35,06MHz Calculations were performed with the GAMESS program package. The 6-311G** basis set with polarization functions on metal and hydrogen atoms was used. It follows from calculations that (i) the magnitude of the EFG at the hydrogen sites is more than an order of magnidude larger than at metal sites, (ii) the sign, amplitude, and η of the EFG at hydrogen depend on the M-H-M angle, (iii) for (BeH2)n, EFG are positiveat both sites hydrogen positions, (iv) for (MgH2)k, the EFGs at magnesium and hydrogen sites are negative, (v) for (AlH3)m, the EFG at aluminium site is negative, and the hydrogen site is positive The work was supported by RFBR (project # 10-03-00055) References 1. V.P.Tarasov, Yu.B.Muravlev, D.E.Izotov. Doklady Physical Chemistry RAS, 404,(2005), 190-194

231

Quantitative Predictions of Superconductivity in Metal Hydrides Duck Young Kima,b, Ralph H. Scheicherb and Rajeev Ahujab,c

a Theory of Condensed Matter Group, Cavendish Laboratory, University of Cambridge, UK b Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Sweden

c Applied Material Physics, Department of Materials Science and Engineering, Royal Institute of Technology (KTH), Stockholm, Sweden

Email: dyk26@cam.ac.uk All the elements grouped in the first column of the periodic table readily enter a metallic state upon condensation with themselves into a solid; with one prominent exception of course: hydrogen. This deviating behaviour is thought to be due to the relatively strong binding of the single electron in a hydrogen atom. But, when brought sufficiently close together under an applied pressure, hydrogen too is expected to eventually transform into a metal, and more, be superconducting, perhaps even up to very high temperatures. Unfortunately, the estimated pressure required to reach that metallic state of hydrogen is enormously large; a formidable obstacle for experimental tests of this prediction. Metal hydrides, in the form of tetra-hydrides (e.g., SiH4, GeH4, SnH4) or tri-hydrides (e.g., AlH3, ScH3, YH3, LaH3) represent an opportunity to conduct ”proxy-studies” of metallic hydrogen and associated high-temperature superconductivity at pressure levels which can be reached by contemporary experimental techniques. That is so, because chemical pre-compression in these metal hydrides helps to lower the pressure threshold at which an insulator-metal transition occurs. Besides a strong fundamental interest in the physics of such transitions and associated superconductivity, there is also the aspect of possible applications of metallic phases for hydrogen storage materials [1], if such high-pressure structures can indeed be stabilized under ambient conditions [2]. In this presentation, we will provide an overview of some of our most recent research on metal hydrides. For example, we identified [3] from ab initio, out of a pool of plausible candidates, a crystal structure possessing all the required characteristics of an experimentally observed metallic phase of SiH4. We showed that the cubic metallic phase of YH3 is dynamically stabilized at high pressure [4], and subsequently applied a state-of-the-art technique (which has been demonstrated [5] to be highly accurate in quantitatively predicting the critical temperature of superconductivity) to calculate a Tc of 40 K at a record low pressure of 17.7 GPa for cubic YH3 [6]. As the pressure rises, superconductivity disappears, only to re-emerge again at a higher pressure, albeit due to a different mechanism. Intriguingly, despite a number of similarities in the evolution of Tc with pressure [7], this second phase of superconductivity is absent in ScH3 and LaH3, and we propose a possible explanation for this surprising behaviour. References 1. R. H. Scheicher, D. Y. Kim, S. Lebиgue, B. Arnaud, M. Alouani, and R. Ahuja, Appl. Phys. Lett. 92, 201903 (2008). 2. D. Y. Kim, R. H. Scheicher, and R. Ahuja, Phys. Rev. B 78, 100102(R) (2008). 3. D. Y. Kim, R. H. Scheicher, S. Lebиgue, J. Prasongkit, B. Arnaud, M. Alouani, and R. Ahuja, Proc. Natl. Acad. Sci. U.S.A. 105, 16454-16459 (2008). 4. J. S. de Almeida, D. Y. Kim, C. Ortiz, M. Klintenberg, and R. Ahuja, Appl. Phys. Lett. 94, 251913 (2009). 5. D. Y. Kim and R. Ahuja, Appl. Phys. Lett. 96, 022510 (2010). 6. D. Y. Kim, R. H. Scheicher, and R. Ahuja, Phys. Rev. Lett. 103, 077002 (2009). 7. D. Y. Kim, R. H. Scheicher, H.-k. Mao, T. W. Kang, and R. Ahuja, Proc. Natl. Acad. Sci. U.S.A. 107, 2793-2796 (2010).m

232

The Effect of Hydrogenation on Hysteresis Properties of the Rapidly Quenched Nd-Ho-Fe-Co-B Alloys

I.Tereshina1, N.Kudrevatykh2, E.Tereshina3, G.Burkhanov1, O.Chistyakov1, A.Salamova4

and V.Verbetsky4 1Baikov Institute of Metallurgy and Material Science RAS, Moscow, Russia

2Ural State University, Ekaterinburg, Russia 3Institute of Physics, Academy of Science, Prague, Czech Republic 4Chemistry Department Moscow State University, Moscow, Russia

Email: teresh@imet.ac.ru The study of the rapidly quenched (RQ) (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 alloy draws much attention from both the fundamental and application viewpoints owing to the possibility to attain the high-coercivity state (jHc > 20 kOe at Т = 300 К) upon the certain quenching rate and as a result of formation of the nano-sized grains of the main 2-14-1 phase. (The Nd-Ho-Fe-Co-B compound is also known to have the spin-reorientation transition of the easy-axis – cone of easy axes type as the temperature decreases.) The spontaneous hydrogen absorption (from the air) and subsequent change of magnetic properties may occur for such intermetallics. The aim of the present work was to investigate the influence of the controlled hydrogen content on hysteresis properties of the parent (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2 in a wide temperature and magnetic field ranges. The parent material obtained as a result of the spinning process had a form of the ribbon fragments with a length of about 10 mm, 2-5 mm wide, and 0.03 mm thick. The interaction with hydrogen was studied under the pressure of up to 13 atm. In order to initiate the reaction, the sample was heated up to 250оC. No incubation period was required to start the hydrogenation process, and the reaction ended up with the (Nd0.55Ho0.45)2.7(Fe0.8Co0.2)14B1.2H2.5 hydride formation. The analysis of diffraction patters allowed the conclusion that no segregation release of Fe occurred at that temperature, and only the hydride phase was obtained. Moreover, it was shown that a small amount of amorphous (soft magnetic, SM) phase was formed in the studied compounds together with the main (hard magnetic, HM) phase. The comparative investigation of magnetic properties of the RQ and the hydride samples was performed at the 4.2 – 300 K temperature range. Hydrogenation was found to cause the increase of magnetization. In both the RQ compound and its hydride, a presence of the SM and HM phases was manifested in the characteristic for such a structural state magnetic hysteresis loops measued at T = 4.2 K. However, in order to observe the full hysteresis loop for the parent Nd-Ho-Fe-Co-B and the hydride alloys, the application of the fields of 100 kOe and 50 kOe, respectively, was required. One could explain the decrease of coercivity of the hard-magnetic phase in the hydrogen-charged material by the decrease of the magnetocrystalline energy (anisotropy field decrease) of the 2-14-1 phase as a result of the hydrogen atoms penetration. This fact was also confirmed from our study of the Y-Fe-Co-B hydrides. The work is supported by RFBR, pr. N 10-03-00848.

233

Structure and Magnetic Properties of RNi (R=Gd, Tb, Dy, Sm) and R6M1.67Si3 (R=Gd, Tb, M=Ni, Co) Hydrides.

Yu.L. Yaropolov1, A.S. Andreenko2, S.A. Nikitin2, S.S. Agafonov3, V.P. Glazkov3, V.A. Somenkov3, V.N. Verbetsky1

1Chemistry Department Moscow State University, Moscow, Russia 2Faculty of Physics Moscow State University, Moscow, Russia

3 RSC “Kurchatovsky Institute, Moscow, Russia Email: yaropolov@inbox.ru

It is well known that the intermetallic compounds of the rare earth elements present interesting magnetic properties due to their large magnetic moments. They attracted considerable attention owing to their potential for various applications. Recently, there has been a great interest in the development of magnetocaloric materials, which are applied in magnetic refrigeration. The interest to IMC of rare earth metals has increased after the observation of a giant MCE in Gd5Si2Ge2 [1]. The magnetic properties of the intermetallic compounds depend on the exchange interactions between atoms, which are related to the interatomic distances and electron structure of the compound. It is known that hydrogenation results in essential changes in the crystal and electron structure of intermetallic compounds. Therefore the hydrogenation influence on the structure and magnetic properties of rare earth metals IMC represents considerable interest. Thus, the basic purpose of the given work was the investigation of hydrogenation effects on the structure and magnetic properties of the RNi (R=Gd, Tb, Dy, Sm) and R6M1.67Si3 (R=Gd, Tb, M=Ni, Co) intermetallic compounds. Neutron diffraction measurements were performed on deuterated samples in order to refine the structure of hydrides. Measurements were performed at neutron diffractometer with λ=1.668Å. Magnetization measurements were carried out at vibration magnetometer in temperature range 78-300K. RNi and R6M1.67Si3 compound easily interact with hydrogen at room temperature and hydrogen pressure up to 1 MPa. Ternary hydrides of the RNi compounds possess orthorhombic CrB-type structure (S.G.Cmcm). The hydrogenation results in substantial expansion of the crystal lattice. The hydrogen atoms occupy three types of interstices: tetrahedral 8(f), trigonal bipyramid 4(c) and octahedral 4(b). The hydrides of R6M1.67Si3 compounds retain the hexagonal structure of the starting IMC (S.G. P63/m). The hydrogenation causes the anisotropic lattice deformation: the a parameters increase by 6-6.5% and the c parameter decrease by 4.5-5%. The transition temperatures of the hydrogenated samples appeared to be lower than 78K. The calculated dependences of reciprocal magnetic susceptibilities were linear in the range 78-300K and followed the Curie-Weiss law. That allowed to estimate the values of paramagnetic Curie temperature and effective magnetic moments. The formation of the hydrides is accompanied with a weakening of the ferromagnetic interactions and significant decreasing of the paramagnetic Curie temperatures. The 3d-bands of nickel or cobalt atoms in the intermetallic compounds are filled, because the effective magnetic moments of the IMC are almost equal to the moments of the free rare earth ions. In other words, nickel and cobalt atoms are nonmagnetic in these compounds and the magnetism is provided by rare earth metal atoms. Therefore we suppose that the weakening of the ferromagnetic interactions with hydrides formation is connected with the filling of conductive band by the electrons from hydrogen atoms and the increase of the interatomic distances, related to the lattice expansion at hydrogenation. References 1. V.K. Pecharsky, K.A. Gschneidner, Physical Review Letters, 78, (1997), 4494–4497.

234

Mössbauer Study of Changes of Phase Composition of NaAlH4 Based Complex Hydrides

P. Roupcová1,2 and O. Schneweiss1

Institute of Physics of Materials, Academy of Sciences of CR, Brno, Czech Republic. Institute of Material Science and Engineering, Faculty of Mechanical Engineering, Brno University of

Technology, Brno, Czech Republic. Email: roupcova@ipm.cz

The hydrogenation and dehydrogenation of complex hydride belong to the hot topics of hydrogen storage research. In this paper we present results of study of AlNaH4 alloyed with Fe chloride. We have investigated influence of time of milling and an effect of ambient atmosphere on properties of this material. The complex hydride sample was prepared by dry milling of mixture of pure AlNaH4 and 2 mol % FeCl2.H2O powders in the protective Ar atmosphere and in air. The XRD and Mössbauer spectroscopy were applied for characterisation of the structure of the as-prepared (before milling) powder, and after 0.5; 1 and 2.5 hours of milling. Subsequently, changes during contact with ambient atmosphere were investigated. The aim of this study was high temperature Mössbauer measurement at the temperature of decompostition of material during recharging cycles. The precious phase analysis of doped phase should help us to understand the role of added phases [1]. XRD measurement taken in Ar does not indicate any changes in phase composition. The XRD taken on the sample after milling in air shows formation of sodium carbonate Na2CO3 and amorphisation of remaining phases in dependence on time. None change in phase composition due to milling in Ar were observed in MS spectra. It is contain two components: doublet with isomer shift δ=1.15 mm/s and quadrupole splitting ΔEQ=2.32 mm/s – can be ascribed to FeCl2 and the second component – doublet with δ=0.31 mm/s and ΔEQ=0.99 mm/s – represents of FeOCl. The phase composition in the sample milled in air changed already after the first step of milling for 0.5 hr and remain constant after the longer milling times. The doublets have following parameters: δ=0.17 mm/s and ΔEQ=0.55 mm/s and δ=0.5 mm/s and ΔEQ=0.63 mm/s. These values are close to Fe(III) and Fe(III-II) in iron oxides and they probably represent paramagnetic iron bearing oxides spread in the matrix. The disappearing of the doublets of iron chloride and iron oxychloride can be explained by their further oxidation during milling and/or by a chemical reaction with sodium alanate. High temperature Mössbauer measurement in reduction atmosphere shows decreasing of valence of iron. References 1. B. Bogdanovic, R. A. Brand, A. Marjanovic et al., J. Alloys and Compounds, 302, (2000) 36–58.

235

Synthesis and Characterization of Metal Aluminum Amides

T. Ono, K. Shimoda, M. Tsubota, S. Hino, K. Kojima, T. Ichikawa, Y. Kojima Institute for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan

E-mail: kshimoda@hiroshima-u.ac.jp It is well known that the composite of LiH and LiNH2 reversibly released 6.3 mass% H2 at around 200 °C [1]. This mechanism is understood as the NH3-mediated reaction pathway, leading to the improved thermodynamics [2]. Recently, Janot et al. reported that the composite of LiH and LiAl(NH2)4 released 5.2 – 5.6 mass% H2 at 130 °C [3]. LiAl(NH2)4 are attractive because it indirectly stores hydrogen in the form of amide [NH2]− and is more labile than LiNH2. Thermal decomosition properties of LiAl(NH2)4 have been shown to release a large amount of NH3 gas below 140 °C. In the present study, we successfully synthesized a series of M[Al(NH2)4]x (M = Li, Na, K, Mg, and Ca; x = 1 and 2), where Mg[Al(NH2)4]2, and Ca[Al(NH2)4]2 have no structural reports to the best of our knowledge. Structural characterization has been done by using synchrotron radiation X-ray diffraction (SR-XRD), infrared (IR), and nuclear magnetic resonance (NMR) spectroscopies. Thermogravimetry coupled with mass spectroscopy (TG-MS) was also carried out for understanding the thermal gas desorption property. The starting materials, LiH (99.4 %) and Al (99.9 %) for M = Li, NaAlH4 (90 %) for M = Na, K (99.95 %) and Al for M = K, Mg (99.9 %) and Al for M = Mg, and CaH2 (99.99 %) and Al for M = Ca, respectively, were put together into a Cr-steel milling vessel with the ratio of M : Al = 1 : 1 or 1 : 2. Gaseous NH3 was introduced into the vessel at –79 °C, and NH3 was immediately condensed into liquid. Samples were prepared by ball milling under liquid NH3 for <10 hours at room temperature. The SR-XRD profiles suggested that KAl(NH2)4, Mg[Al(NH2)4]2, and Ca[Al(NH2)4]2 have novel structures. The crystal structures of LiAl(NH2)4 and NaAl(NH2)4 were identical to those previously reported [4,5]. Both the IR and 27Al MAS/3QMAS NMR suggested that they all have an anion complex unit [Al(NH2)4]– as a basic structural unit, indicating the successful synthesis of the metal aluminum amides. The TG-MS curves showed a large amount of NH3 desorption below 140 °C, and the NH3 desorption peak temperature Tdes decreased with the increasing atomic number. The 27Al isotropic chemical shift was correlated with Tdes, which suggest that the weaker Al-N bond involves the lower NH3 desorption temperature. The present study gives useful information that the thermal stability of the anion complex [Al(NH2)4]– can be controlled by the cation M, and thus could provide a new insight for hydrogen storage application when the MH-M’[Al(NH2)4]x composite materials are prepared. This work was partially supported by the NEDO project “Advanced Fundamental Research Project on Hydrogen Storage Materials”. References 1. P. Chen, Z. Xiong, J. Luo, J. Lin, K. L. Tan, Nature, 420, (2002), 302-304. 2. T. Ichikawa, N. Hanada, S. Isobe, H. Leng, H. Fujii, J. Phys. Chem. B, 108, (2004),

7887-7892. 3. R. Janot, J. Eymery, J. Tarascon, J. Phys. Chem. C, 111, (2007), 2335-2340. 4. J. Rouxel, R. Brec, C.R. Acad. Sci. Paris C, 262, (1966), 1071-1073. 5. R. Brec, J. Rouxel, C.R. Acad. Sci. Paris C, 264, (1967), 512-515.

236

Li4NH and Li1.5NH1.5 as intermediary compounds during hydrogenation of Li3N

J.-C. Crivelloa*, M. Guptab, R. Černýc, M. Latrochea, D. Chandrad

aICMPE-UMR7182, CNRS, 2-8 rue H. Dunant, 94320 Thiais, France bTPCHO, Université Paris Sud, 91405 Orsay, France

cLaboratory of Crystallography, University of Geneva, Switzerland dUniversity of Nevada, Reno, USA

*Email: crivello@icmpe.cnrs.fr It has been suggested recently that the Li3N hydrogenation pathways [1] might be more complex than suggested by Eqs. (1-2), since the formation of new compounds Li4NH and Li1.5NH1.5 has been detected experimentally [2-3]. Li3N + H2 ↔ Li2NH + LiH (1) Li2NH + H2 ↔ LiNH2 + LiH (2) In this work, we investigated the possible formation of Li4NH and Li1.5NH1.5 using electronic structure calculations based on the density functional theory (DFT). From our DFT results, we find that the formation of Li4NH is possible through the reaction involving Li3N and LiH with an enthalpy of reaction much less negative than for the direct formation of Li2NH. Li4NH reacts with H2 exothermically with an enthalpy of reaction less negative than for the direct process (1). This corresponds to the following two steps: 2 Li3N + H2 ↔ Li4NH + Li2NH (3) Li4NH + H2 ↔ Li2NH + 2 LiH (4) The direct formation of Li4NH by hydrogenation of Li3N through the release of ammonia is however not possible. We also find that the formation of the intermediate phase Li2-xNH1+x for x=0.5 between imide (x=0) and amide (x=1) is possible. We show that Li1.5NH1.5 formation mechanism may be the decomposition of (2) into the two following (5) and (6) reactions: 2 Li2NH + H2 ↔ 2 Li1.5NH1.5 + LiH (5) 2 Li1.5NH1.5 + H2 ↔ 2 LiNH2 + LiH (6) In agreement with the crystal structure refinements [3], Li1.5NH1.5 is found to be stable in a cubic Li-vacant type compound. After full relaxations of several structural models, the Li1.5NH1.5 compound presents a coexistence of ordered [NH]2- and [NH2]- anions in equal proportion. This feature confers to Li1.5NH1.5 (x=0.5) the transition state between the [NH]2- disordered compound Li2NH (x=0), and the [NH2]- ordered compound LiNH2 (x=1). These results are discussed in terms of an analysis of the electronic structures of all of these compounds, and a comparison of heats of reaction for several pathways [4]. References 1. P. Chen, Z. Xiong, J. Luo, J. Lin and K. Tan., Nature, 420 (2002) 302. 2. E. Weidner, D. Bull, I. Shabalin, S. Keens, M. Telling and D. Ross, Chem. Phys. Lett. 444 (2007) 76. 3. D. Chandra, R. Černý, D. Phanon and N. Penin, In preparation (2009). 4. J.-C. Crivello, M. Gupta, R. Černý, M. Latroche and D. Chandra, Phys. Rev B, accepted, in production (2010).

237

Synthesis, Structure and Dehydrogenation of Alkali-Earth Metal Amidoborane Derivative

Y. S. Chua, G. T. Wu, Z. T. Xiong, J. P. Guo, M. X. Jian, P. Chen

Dalian Institute of Chemical Physics, Dalian, China 116023; Department of Chemistry, National University of Singapore, Singapore 117542.

Email: pchen@dicp.ac.cn Compounds or complexes with high hydrogen content are potential hydrogen storage materials. Ammonia borane (AB) has been extensively investigated recently, owing to its high hydrogen capacity (19.6 wt%) and moderate dehydrogenation temperature, which promise for the application as a hydrogen storage material. However, its onboard application is subjeted to improvement in dehydrogenation kinetics and rehydrogenation. In order to improve the dehydrogenation performance, considerable efforts have been given to the chemical modification of AB. Recent researches show show that reacting alkali metal or alkali earth metal hydride (LiH, NaH, or CaH2) with AB possess improved dehdyrogenation properties compare to pristine AB. Lithium amidoborane (LiAB), sodium amidoborane (NaAB) and calcium amidoborane (CaAB), are capable of releaseing ca. 10.9 wt%, 7.5 wt% and 8wt% of H2 at moderate temperatures, respectively. In this presentation, we are going to report a new alkali-earth metal (i.e. Ca) amidoborane derivative. The structure and thermal decomposition of this material have been investigated by XRD, TPD, DSC and volumetric release. References 1. Z. T. Xiong, C. K. Yong, G. T. Wu, P. Chen, W. Shaw, A. Karkamkar, T. Autrey, M.

O. Jones, S. R. Johnson, P. P. Edwards, W. I. F. David, Nat. Mater., 2008, 7, 138. 2. H. V. K. Diyabalanage, R. P. Shrestha, T. A. Semelsberger, B. L. Scott, M. E. Bowden,

B. L. Davis, A. K. Burrell, Angew. Chem. Int. Ed. 2007, 46, 8995. 3. Y. S. Chua, G. T. Wu, Z. T. Xiong, T. He, P. Chen, Chem. Mater. 2009, 21, 4899. 4. S. R. Johnson, W. I. F. David, D. M. Royse, M. Sommariva, C. Y. Tang, F. P. A.

Fabbiani, M. O. Jones, P. P. Edwards, Chem. Asian J. 2009, 4. 849. 5. G. Soloveichik, J. H. Her, P. W. Stephens, Y. Gao, J. Rijssenbeek, M. Andrus, J. C.

Zhao, Inorg. Chem. 2008. 47. 4290.

238

Possible Fluiorine Substitution for H Atoms in Li[BH4] and LiH During Hydrogen Absorption/Desorption

1I.Saldan, 1J.Bellosta von Colbe, 1K.Suarez, 1R.Gosalawit, 1C.Pistidda, 1U.Bösenberg, 2M.Schulze, 2T.Klassen, 3T.Jensen, 4Y.Cerenius, 1K.Taube, 1M.Dornheim

1 Institute of Materials Research, Materials Technology, GKSS-Forschungszentrum Geesthacht GmbH, 1 Max-Planck Str., D-21502 Geesthacht, Germany

2 Institut für Werkstofftechnik, Schweißfachingenieur Helmut-Schmidt-Universität, 85 Holstenhofweg, D-22043 Hamburg, Germany

3 Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Århus, 140 Langelandsgade Str.,DK-8000 C Århus, Denmark

4 MAX-lab, Lund University, 1 Ole Römers väg, S-22100 Lund, Sweden Email: Ivan.Saldan@gkss.de

Because of its high gravimetric hydrogen density lithium borohydride is considered as potential reversible hydrogen storage material. This complex light metal hydride can desorb theoretically up to ~ 13.8 wt.% H2 by the following reaction:

LiBH4 → LiH + B + 3/2 H2 (1)

The experimental value of enthalpy for this reaction is ~ 69 kJ/mol H2, therefore the temperature for hydrogen release at 1 bar H2 pressure is close to ~ 400 ºC [1]. The mixtures LiBH4 with light metals hydrides called as “reactive hydride composites” (RHCs) show lowered reaction enthalpies with about the same gravimetric hydrogen density. For example, reaction:

2 LiH + MgB2 + 4 H2 ↔ 2 LiBH4 + MgH2 (2)

has a total reaction enthalpy of approximately 46 kJ/mol H2 [2]. However, for most practical applications a reaction enthalpy about 30 kJ/mol H2 or even less is desired. In recent work [3] the decomposition reaction of LiBH4 with F anion doping was investigated by first-principles calculations, where was showed formation of Li8B8H32–xFx and Li8H8–xFx (x≤4) and a favourable thermodynamics (34.9 kJ/mol H2 at x=3; 27 kJ/mol H2 at x=4). In this experimental work we tried to synthesise LiBH4 with F anion doping and understand the mechanism for H→F substitution. Hydrogen titration (2-3 cycles) for mixture of LiF and MgB2 with different molar ratios (4:1 and 1:1, respectively) as well mixture of LiF, LiH with MgB2 in molar ratio 1:1:1 has been presented. References 1 A. Züttel, P. Wenger, S. Rentsch, P. Sudan, Ph. Mauron, Ch.Emmenegger, J. Power Sources 118, (2003) 1. 2 U. Bösenberg, S. Doppiu, L. Mosegaard, G. Barkhordarian, N. Eigen, A. Borgschulte, T. Jensen, Y. Cerenius, O. Gutfleisch, T. Klassen, M. Dornheim, R. Borman, Acta Materialia 55, (2007) 3951-3958. 3 L. Ying, P. Wang, Zh. Fang, H. Cheng, Chemical Physics Letters 450, (2008) 318-321.

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Decomposition Reaction and Reversibility of LiBH4Mg(BH4)2 Studied by In-Situ Diffraction and Thermal Analysis Techniques Bo Richter,1 Young-Su Lee,2 Young Whan Cho,2 and T. R. Jensen1

1 Center for Materials Crystallography, iNANO and Department of Chemistry, University of Aarhus, Langelandsgade 140, DK-8000 Aarhus C, Denmark. 2 Materials Science and Technology Research Division,

Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea Renewable energy in the form of solar, wind or wave energy is an alternative inexhaustible resource, but its utilisation is hampered by its fluctuation in time and non-uniform geographical distribution. The solution is a safe, cheap and efficient energy carrier. Hydrogen is a world-wide target receiving increasing political and scientific interest. Unfortunately, safe, efficient and economic viable storage of hydrogen allowing it to be the successor of gasoline is still lacking. Extensive efforts have been made to develop solid state hydrogen storage systems, i.e. a variety of metal hydrides have been investigated as possible hydrogen carriers. Unfortunately, no material which has the combination of a high gravimetric hydrogen density, adequate hydrogen-dissociation energetic, reliability, and low cost required for commercial vehicular application has yet been found [1]. The goal of our research is to develop new families of hydrogen storage materials that fulfil the above requirements. LiBH4 is one of the promising candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen capacity. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its use in real applications. In order to overcome this barrier and to adjust the thermal stability, the composite system xLiBH4 + (1-x)Ca(BH4)2 was investigated. Interestingly, this composite undergoes a eutectic melting at ca. 200 °C in a wide composition range and the eutectic composition is in the range 0.6 < x < 0.8. The decomposition temperature for the composite is lower than for the two pure substances LiBH4 and Ca(BH4)2, e.g. composite x ≈ 0.4 release about 10 wt% of hydrogen at T < 400 °C and, importantly, reveal partial reversibility noticed for the first time for a mixed borohydride composite [2]. This has prompted us to investigate other systems, e.g. LiBH4-Mg(BH4)2, using in situ synchrotron X-ray diffraction, differential scanning calorimetry, thermogravimetric analysis and mass spectrometry. Hydrogen is released at significantly lower temperatures as compared to the decomposition temperatures of the individual substances. Secondly, apparently the mechanism for the decomposition is significantly altered for the composite system, which may hold a key to further tailor the decomposition properties of eutectic melting composites. References 1. S. Orimo, Y. Nakamori, J. R. Eliseo, A. Züttel and C. M. Jensen, Chem. Rev. 107, (2007), 4111-4132, 2007. [2] J. Y. Lee, D. Ravnsbæk, Y.-S. Lee, Y. Kim, Y. Cerenius, J.-H. Shim, T. R. Jensen, N. H. Hur, and Y. W. Cho, J. Phys. Chem. C, 113, (2009), 15080–15086.

240

Direct Synthesis of Hydrogen Storage Alloys from Their Oxides

S. Tan, K. Aydınol, I. Karakaya and T. Öztürk Dept. of Metallurgical & Materials Engineering, Middle East Technical University, 06531, Ankara Turkey

Email: ozturk@metu.edu.tr

Hydrogen storage alloys may be synthesized in a variety of ways. It starts almost always with pure elements, and the alloys are produced by melting the elements under protective atmosphere. Powder processing of elemental powder mixtures, i.e. the so-called mechanical alloying, is also quite common. All of these processes are quite complex and time consuming -and added to the high cost of the elements themselves- make hydrogen storage alloys prohibitively expensive. It is therefore desirable to find alternative methods of material synthesis which would be less complicated, more direct and as a result less costly. The present work explores such an alternative in which hydrogen storage alloys are synthesized directly from their oxides. The method originally developed for extraction of pure Ti from titanium oxide[1] was adapted in the current work for the well known hydrogen storage compositions; Mg2Ni and FeTi. The method simply involves mixing of oxides in the right proportions and deoxidizing the mixtures in the solid state. This is achieved via electrolysis in which the oxide mixture is made cathode and oxygen from it is stripped, carried through the electrolyte (typically CaCl2) and finally discharged from the anode (graphite). Following this route, FeTi had been succesfully synthesized from the mixture of Fe2O3 and TiO2 [2]. In the current work, oxide compacts with different porosities were deoxidized (at 900°C by 3.2 V) so as to determine optimum porosity for the improved efficiency of the deoxidation process. In the case of MgO-NiO mixtures , the approach was not as succesful. The mixtures rich in NiO could be electrolysed successfully yielding pure Ni as well as the intermetallic MgNi2, but the mixtures rich in MgO e.g. MgO:NiO=2:1 were difficult to electrolyse. This has been attributed to low conductivity of the powder compact where MgO is the matrix phase. Work is curently in progress to identify conditions which would remedy this sistuation and enable successful synthesis of the intermetallic compound Mg2Ni.

1- G.Z .Chen, D.J.Fray and T W Farthing, Nature, 407 (2000) 361. 2- S. Tan, T. Örs, K. Aydınol, T. Öztürk and I. Karakaya “Synthesis of FeTi from

mixed oxide precursors”, Journal of Alloys and Compounds 475(2009) 368 3- Serdar Tan, Kadri Aydınol, Tayfur Öztürk and İshak Karakaya “Direct synthesis of

Mg-Ni compounds from their oxides”, Journal of Alloys and Compounds, in press.

241

Stabilization of Metastable d-Metal Ternary Magnesium Hydrides at High Temperature and Under Some GPa H2 Pressure

G. Girard1, D. Fruchart1, S. Miraglia1, M. Shelyapina1,2, 1 Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France

2 Department of Physics, St Peterburg State University, Petrodvorets, St. Petersburg, 198504, Russia daniel.fruchart@grenoble.cnrs.fr

HP trials using a CONAC 28 high pressure geometry were performed in order to synthesize members of the Mg7TiHx type series starting from a mixture of MgH2 and Ti0.7V0.3H1.9. The main result of XRD analysis leads to evidence a structural transition from β-MgH2 to γ-MgH2. However, a careful examination of the data suggests that a minor fraction of the expected ternary phase was present. In order to characterize better the sample, we have used a bulk penetrating beam to perform powder neutron diffraction experiment. In fact, tiny evidence of presence of a significant fraction of the desired Mg7TiHx type phase was recorded. Experiments using a mixture of MgH2 and microcrystalline Ti0.6V0.4H1.9 lead to similar results, even when applying up to ~7 GPa pressure. Then it was foreseen to replace the current precursor (hydrogen provider) anthracene by a mixture of NaBH4 and Ca(OH)2, such type of combination being no more concluding. However, working with a different metal hydride precursor TaHx successively for appropriated ratio TaHx/MgH2 components, we succeed to synthesize new hydrides under application of a lower pressure (5 GPa). The formula of the main ternary is approximately Mg9TaH~18, but on the corresponding XRD pattern, evidence for another combination Mg~3TaHx can be pointed out. Interestingly, the structure of the new Mg9TaH~18, hydride was partly resolved on the basis of the orthorhombic Pmma space group with cell parameter a = 4,532 Ǻ, b = 5,517 Ǻ, c = 4,474 Ǻ. Also band structure calculations were undertaken on the basis of the .Mg7TiHx type series and related formula combining other metal elements. The main result is the different stability of the two type of hydrogen atoms occupying either pure 4-Mg tetrahedra or mixte tretrahedra such as 1-Ti,3-Mg tetrahedra. Results will be discussed on the basis of the nature of the substiting elements.

242

Structural Analysis of novel Mg-based Hydrides Prepared by Gigapascal Hydrogen Pressure Method

N.Takeichi, X.Yang, K.Shida, H.Tanaka, N.Kuriyama and T.Sakai

Research Institute for Ubiquitous Energy Devices, AIST, Ikeda, Japan Email: n.takeichi@aist.go.jp

Magnesium is one of the promising elements for hydrogen storage media because of the

high hydrogen capacity, 7.6 mass%, as MgH2. However, the high thermodynamic stability of MgH2 causes difficulty in dehydrogenation at ambient temperature. Therefore, various Mg-based alloys and compounds have ever been investigated in order to improve the reaction kinetics through metallurgical methods such as elemental substitution, mechanical alloying and laminate composites.

Ultrahigh-pressure (UHP) technique using multi-anvils would be one of the useful methods to synthesize novel hydrides. Our group have reported that Mg-TM (TM: transition metal) hydrides with face-centered cubic (fcc) structure, prepared with a cubic anvil press, show reversible and rapid absorption and desorption of hydrogen at 523 K. In this study, we have succeeded to synthesize a series of novel Mg-Zr-A hydrides (A=Na, Li) by the UHP technique. In addition, we investigated hydrogen storage properties and crystal structure of the hydrides.

Initial mixture pellet, 6MgH2+ZrH2+xAH (A=Na, Li; x=0~1), was sealed in an NaCl capsule together with hydrogen source. The capsule was inserted into an octahedral pyrophyllite cell. Then, the assembly was compressed up to 8 GPa by using a high-pressure generating and held at 873 K for 1 hour under 8 GPa. Hydrogen storage properties were examined by a differential scanning calorimeter and pressure-composition isotherms measurements. The crystal structures were analyzed based on XRD data obtained at the beam-line BL19B2 in SPring-8. The wavelengths were calibrated to λ = 0.070067(1) nm by use of CeO2 as a standard. The structure was refined by use of the Rietveld program RIETAN-2000.

In case of the ternary Mg-Zr hyderide, the Mg-Zr hydride with a simple fcc structure, lattice constant a = 0.48588(2) nm, was formed. Rietveld refinements of XRD profile indicated that Mg and Zr atoms disorderly occupy at 4a (0,0,0) using space group Fm-3m. In the Mg-Zr-Li system, the quaternary hydrides were formed and these kept the same crystal structure, simple fcc structure, up to x = 1.0. Mg, Zr and Li atoms are sharing the 4a site because of their similar ion radius. While in the Mg-Zr-Na system, the quaternary hydrides were formed and these kept simple fcc structure, up to x = 0.3. With addition of 0.7 or 1.0NaH, Ca7Ge type super lattice phase was formed instead of simple FCC type. Mg6ZrNax hydride can be described by the atomic positions: Mg and Zr at 24d (0, 0.25, 0.25), Na at 4a (0,0,0), Zr and Na at 4b (0.5, 0.5, 0.5) using space group Fm-3m (no.225).

Mg-Zr hydrides and Mg-Zr-A hydrides (A=Na, Li) can reversibly absorb and desorb a large amount of hydrogen, ~ 4wt.%, at 523~573 K. Formation of quaternary hydrides can reduce the hydrogen releasing temperature compared with the Mg-Zr-H ternary hydride. We will discuss that the reason for the improvement of the hydrogen storgae properties and reaction kinetics at low temperature, the relationship between crystal structure and those properties.

This work was financially supported by the New Energy and Industrial Technology Development Organization (NEDO)

243

244

High-Pressure Synthesis of Novel Hydrides in Pd-X Systems (X = Ba, Y, La)

M. Kawakami, T. Kuriiwa, A. Kamegawa and M. Okada Department of Materials Science, Graduate School of Engineering, Tohoku University

Email: kawakami@ceram.material.tohoku.ac.jp A few superconducting hydride systems are known to such as PdHx [1] and NaPd3H2

[2]. On the other hands, among numbers of syntheses of novel hydrides, high-pressure synthesis method is an effective technique to explore novel hydrides. In this study, exploration for novel Pd-based hydrides was focused on by using high-pressure synthesis, and the occurrence of superconductivity of novel hydride may be expected. The purpose of this study is to explore novel hydrides in Pd-X systems, where X = Ba, Y and La, by high-pressure synthesis and to investigate their crystal structures, thermal stabilities and magnetic properties. Figure 1 shows XRD pattern of Pd-25 mol%BaH2 prepared at 1100 � for 8 h under 5 GPa with hydrogen source using X-ray of λ = 0.07 nm. A cubic-type structure and unidentified phases were observed. This cubic-type structure phase was found to exhibit a crystal structure (space group Fd3-m, No. 227) with lattice parameters of a = 0. 7727(2) nm. Figure 2 shows XRD pattern of Pd-25 mol%YH3 prepared at 1100 � for 8 h under 5 GPa with hydrogen source using X-ray of λ = 0.075 nm. A hexagonal-type structure and unidentified phases were observed. This hexagonal-type structure phase was found to exhibit a crystal structure (space group P63/mc, No. 186) with lattice parameters of a = 0. 2892(1) nm, c = 0. 4783(1) nm.

Figure 1 XRD patterns of Pd-25 mol%BaH2 prepared at 1100 �

Figure 2 XRD patterns of Pd-25 mol%YH3 prepared at 1100 �

for 8 h under 5 GPa with hydrogen source using X-ray of

for 8 h under 5 GPa with hydrogen source using X-ray

λ = 0.07 nm. of λ = 0.075 nm. References 1. T. Skośkiewicz, A. W. Szafrański, W. Bujnowski, and B. Baranowski, Journal of Physics C: Solid State Physics, 11 (1973) K 123-126 . 2. K. Kadir, P. Lundqvist, D. Noréus, and Ö. Rapp, Solid State Communications, 85 (1993) 891-893 .

Formation of Alloys in Ti-V System in Hydride Cycle and Synthesis of Their Hydrides in Self-Propagating High-Temperature Synthesis Regime

Aleksanyan AG1*, Dolukhanyan SK1, Shekhtman VSh2, Huot J3, Mnatsakanyan NL1

1A.B. Nalbandyan Institute of Chemical Physics of Armenian NAS, 5/2 P.Sevak Str., Yerevan 0014, Republic of Armenia, E-mail: a.g.aleks_yan@mail.ru, seda@ichph.sci.am

2 Institute of Solid State Physics, RAS, Chernogolovka, Moscow District, 142432 3 Institut de recherche sur l’hydrogène, Université du Québec à Trois-Rivières

E-mail: jacques_huot@uqtr.ca

An original and powerful way to synthesize the alloys of transition metals and their hydrides has been developed at the Laboratory of High-temperature Synthesis of the B. Nalbandyan Institute of Chemical Physics of Armenian NAS [1]. This method could be used for a variety of metal systems. For example, it could be used to synthesize BCC alloys of the Ti-V system. Because of their particular crystal structure, these alloys show good hydrogen sorption-desorption characteristics that could make them suitable as materials for hydrogen storage application as well as catalysts for synthesis of other hardly hydrogenated metals and alloys (for example, as magnesium and magnesium-based alloys) [2]. In the present work, we investigated the synthesis of titanium and vanadium based alloys of BCC structure using “hydride cycle” method, through interaction of TiН2 with VНх. These hydrides are synthesized by using the self-propagating high-temperature synthesis (SHS) technique [3]. The mechanism of formation of compact alloys in Ti-V system from the powders of hydrides TiН2 and VНх by their compaction and further dehydrogenation was investigated. We investigated also the interaction of these alloys with hydrogen in combustion regime (SHS) resulting in formation of their hydrides. The thermal stability, heats of formation and decomposition of synthesized alloys and their hydrides was studied by DTA and PDSC. The work is performed at financial support of their IAEA Research Contract No: 15720, ISTC (Grant A-1249), and Ministry of Education and Science of Armenia (theme 0567). References

1 Aleksanyan A.G., Dolukhanyan S.K., Mantashyan A.A., Mayilyan D.G., Ter-Galstyan O.P., Shekhtman V.Sh. New technique for producing the alloys based on transition metals. Carbon Nanomaterials in Clean Energy Hydrogen Systems. NATO Science Series. 2008: 783-794.

2 M.V. Lototsky, V.A. Yartys, I.Yu. Zavaliy. Vanadium-based BCC alloys: phase-structural characteristics and hydrogen sorption properties. Journal of Alloys and Compounds 404-406(2005), 421-426.

3. S.K. Dolukhanyan, SHS of Binary and Complex Hydrides, in Self-Propagating High-Temperature Synthesis of Materials, Borisov, A. A., De Luca, L, and Merzhanov, A., Eds., translated by Scheck Yu. B., New York: Taylor and Francis, 2002, pp. 219—237

4. Dolukhanyan S.K, Aleksanyan A.G., Ter-Galstyan O.P., Shekhtman V.Sh, Sakharov M.K. and Abrosimova G.E. Specifics of the formation of alloys and their hydrides in the Ti-Zr-H system. Russian Journal of Physical Chemistry B, 2007, 2, (6) 563–569.

245

Synthesis of New Hydrides in Li-Nb and Li-Ta Systems

A.Kamegawa, R.Kataoka, T.Kuriiwa and M.Okada Department of Materials Science, Graduate School of Engineering, Tohoku University, Sendai, Japan

Email: kamegawa@material.tohoku.ac.jp As is well known, alkaline metals such as Li posses high compressibility (vs. pressure) of atomic radii. This means that atomic ratio between lithium and components would change under the pressure of GPa-order. As a result, novel compounds might be synthesized. Moreover, melting point of lithium hydride is theoretically estimated to increase about 200 K under 5 GPa. This allows solid-state reaction at higher temperature under the pressure of GPa order than that of ambient pressure. In this study, new Li-Nb and Li-Ta hydrides were investigated. In the Li-TM systems (TM=Nb, Ta), no hydride has been reported. Exploration of new Li-TM hydride by using high-pressure method has never been conducted up to now. It seems to be possible to obtain new Li-TM hydrides by high-pressure method due to the merits as mentioned above. Nb and Ta form hydride and stabilities of their hydride are lower than that of lithium hydride. Therefore, novel Li-TM hydride is expected to be lower stabilities than that of lithium hydride. The purpose of this study is to explore a new hydride of the Li-Nb, Ta systems by using the anvil-type apparatus and to investigate the crystal structure, thermal stability and hydrogen content of the newly found hydrides. Phase present and the thermal stability of hydrides in the Li-Nb, Li-Ta systems synthesized by using highpressure up to 5 Pa were studied. For the Li-Nb system, new hydrides were synthesized under the pressure of 5 GPa at 973 K for 8 h, and structurally characterized by X-ray powder diffractions as primitive hexagonal structure (space group P6/mmm, No. 191) with a= 0.56250(5) nm, c= 0.57416(4) nm. For the Li-Ta system, the novel hydride was obtained under 5 GPa at 973 K for 8 h. the hydride has a C-face centered monoclinic structure with a= 0.7918(5) nm, b= 0.8012(4) nm, c= 1.030(7) nm, �= 111.27 (6)°. These novel hydrides obtained in Li-Nb and Li- Ta systems were thermally stable up to 510 K and 573 K, respectively.

Fig.1 XRD pattern of LiH-20 mol%NbH prepared at 973 K for 8 h under 5GPa

with hydrogen source and the simulated pattern.

246

Infrared Thermography Screening of Hydrogen Sorbing Mg-based Thin Film Libraries

R. Domènech-Ferrer, G. Garcia and J. Rodríguez-Viejo

Group of Nanomaterials and Microsystems, Universitat Autònoma de Barcelona, Bellaterra, Spain Email: gemma@gnam.uab.es

High-throughput screening techniques provide a unique solution to study in a short period of time the properties of large amounts of metal hydrides. This paper presents results on the combinatorial synthesis and hydrogen storage characterisation of magnesium-based thin films libraries. Compositional spread libraries were obtained by co-sputtering Mg and Ti pure metals, as well as Mg, Fe and Cu, on silicon substrates. Infrared imaging was used to characterise the surface emissivity of the libraries, as changes in the electronic surface behaviour from metal to semi-conducting states can be related to dehydrogenated and hydrogenate phases, respectively. IR Thermography during constant heating rate or isothermal experiments permitted the determination of hydrogen absorption and desorption temperatures for each location, i.e each composition of the library, and for a given hydrogen partial pressure. Preliminary results concerning the kinetic influence of added elements on the Mg properties are discussed and compared with literature data determined using other techniques.

247

Alkali Metal Based Molecular Hydrogen Storage Systems: A DFT Study

Süleyman Er,1 Gilles A. de Wijs2 and Geert Brocks1 1Computational Materials Science, Faculty of Science and Technology and MESA+ Research Institute,

University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands 2Electronic Structure of Materials, Institute for Molecules and Materials, Faculty of Science, Radboud

University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands Email: s.er@utwente.nl

The hydrogen storage properties of a number of promising molecular systems and nanomaterials are investigated by first-principles calculations. We consider polylithiated carbon and oxygen molecules and study their interactions with hydrogen molecules. For polylithiated molecules it is found that the Li atoms connected to a central C or O atom, bear substantial positive charges. Hydrogen molecules are then clustered around these Li atoms via electrostatic interactions. According to our calculations such molecules can attach hydrogen up to ~40 wt % with average hydrogen binding energies between 0.1 and 0.2 eV/H2. To prevent clustering of polylithiated molecules, we attach them to (doped)graphene (Fig. 1). The now immobilized molecules have a similar interaction with hydrogen molecules as free molecules. Naturally, the hydrogen weight percentages are then reduced to 5-8 wt % due to the additional weight of the graphitic templates [1].

Figure 1: Polylithiated carbon (CLi4) molecules immobilized on the Be (left) and B doped graphene. Hydrogen molecules gather around the Li atoms.

As an alternative storage system, we consider the boron sheets that have recently been proposed as novel structures [2]. Direct interaction of molecular hydrogen with the naked boron sheet is weak (0.05 eV/H2), similar to the interaction with graphene (0.03 eV/H2). We find that dispersion of alkali metal (AM = Li, Na, and K) atoms onto the boron sheet markedly increases both hydrogen binding energies and storage capacities. The unique structure of the boron sheet presents a template for creating a stable lattice of strongly bonded metal atoms with a large nearest neighbor distance. The strong interaction between the boron sheet and the AM atoms results in a partial transfer of the AM valence electrons to the boron sheet. In particular, Li is found to be a promising doping element for the purpose of hydrogen storage (Fig. 2). Electrostatic interactions between the Li atoms and the hydrogen molecules then lead to an average binding energy of 0.2 eV/H2, and up to a maximum of 10 wt % hydrogen [2].

Figure 2: Side and perspective views of the Boron-Li system in its fully hydrogenated state. Up to three hydrogen molecules surround each Li metal on the boron surface.

References

1. S. Er, G. A. de Wijs, G. Brocks, J. Phys. Chem. C, 113, (2009), 8997-9002. S. Er, G. A. de Wijs, G. Brocks, J. Phys. Chem. C, 113, (2009), 18962-18967.

248

Fast and Slow Dehydrogenation of Catalyzed Ball Milled Lithium Alanate (LiAlH4)

R.A. Varin and L. Zbroniec Department of Mechanical and Mechatronics Engineering, University of Waterloo, Waterloo, Canada N2L

3G1 Email: ravarin@uwaterloo.ca

In the future Hydrogen Economy a viable solid state hydrogen storage system is needed for efficient supply of pure hydrogen to fuel cells in automotive and a variety of non-automotive applications like electronic consumer goods. For a Proton Exchange Membrane (PEM) fuel cell a viable hydrogen system requires operating temperature range of 60-100°C and a practical hydrogen capacity exceeding at least 6 wt.% for automotive [1]. One of the most interesting hydrides for solid state hydrogen storage is a complex hydride LiAlH4 (lithium alanate) since it can liberate a purity-uncorrected quantity of 7.9 wt.%H2 below 250°C [1]. Some metal chlorides such as TiCl3, ZrCl4, VCl3, NiCl2 and ZnCl2 were added to LiAlH4 as catalysts which enhanced quite dramatically the kinetics of desorption and in effect lowered the effective desorption temperature of LiAlH4 [1]. However, the addition of nanometric metallic catalyst to LiAlH4 has not been investigated so extensively. In the present work we report the results of comprehensive studies on the effect of 5 wt.% catalytic additives of both nanometric nickel (n-Ni) produced by Vale Inco and MnCl2 to LiAlH4. The effect of n-Ni addition was to a very limited extent investigated by Kojima et al. [2]. They found that a n-Ni doped LiAlH4 decomposed during milling. The effect of MnCl2 on the behavior of LiAlH4 has never been investigated. In the present work the nanocomposites were processed by controlled ball milling for 15 min in the magneto-mill Uni-Ball-Mill 5 and subsequently investigated by Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD) and volumetric hydrogen desorption in a Sieverts’ - type apparatus. No decomposition during milling is observed for LiAlH4+5wt.% n-Ni but some reaction of LiAlH4 with MnCl2 is observed for LiAlH4+5wt.% MnCl2. A doping with n-Ni combined with high energy ball milling under impact mode completely eliminates melting of LiAlH4 in a DSC test. In contrast, LiAlH4 doped with MnCl2 still exhibits a weak DSC peak due to melting. Ball milled LiAlH4+5wt.% n-Ni desorbs fast within 140-250°C the quantity of 7.4 to 7.8 wt.%H2 within 10,000 to 600 s, respectively. In contrast, ball milled LiAlH4+5 wt.%MnCl2 desorbs relatively fast within 140-250°C the quantity of 6.7 to 7.2 wt.%H2 within 19,000 to 600 s, respectively. Both nanocomposites after 15 min of high energy ball milling desorb hydrogen slowly at room temperature and 40°C. LiAlH4+5wt.% n-Ni desorbs at room temperature and 40°C about 3.4 wt.%H2 within 25 days and 4.6 wt.%H2 within 20 days with the corresponding slow desorption rate of ∼0.136 and 0.230 wt.%H2/day, respectively. LiAlH4+5wt.% MnCl2 desorbs at room temperature and 40°C about 3.0 wt.%H2 and 4.4 wt.%H2 within 35 days with the corresponding slow desorption rate of ∼0.086 and 0.126 wt.%H2/day, respectively. The obtained results are discussed in view of the microstructural evolution observed by XRD. References 1. R.A. Varin RA., T. Czujko, Z.S. Wronski, Nanomaterials for Solid State Hydrogen Storage, New York, NY: Springer Science+Business Media, 2009. 2. Y. Kojima, Y. Kawai, M. Masumoto, T. Haga, J. Alloys and Compounds, 462, (2008), 275-278.

249

Synergetic Effect of C (Graphite) and Nb2O5 on the H2 Sorption Properties of the Mg - MgH2 System.

C. Milanese, A. Girella, G. Bruni, V. Berbenni, A. Marini H2 Lab., CSGI & Physical Chemistry Department, University of Pavia, Pavia, Italy

e-mail: chiara.milanese@unipv.it

In the frame of “Nanostore”, an Italian joint project focused on the preparation and the characterization of innovative Mg-based nanomaterials for hydrogen storage, many solutions were explored in order to improve the sluggish kinetics of the Mg/MgH2 sorption reactions and to lower the working temperature of this same system [1-3]. In particular, several different transition metals and their oxides and many non-metallic materials were added to Mg in different ratios to test their efficacy as catalyzing/destabilizing agents. The composites were prepared by ball milling in Ar for different times and deeply characterized by manometric and calorimetric measurements and by coupling the two techniques, in order to obtain meaningful kinetics and thermodynamic data. The sorption activation behaviour, the effective sorption performance and the cycling ability of the different mixtures were investigated with the aim to choose the best performing solution in view of practical applications. Among the new materials developed during the project, the Mg 97.5 mol % - Nb2O5 0.5 % - graphitic C 2.1 % composite is one of the most promising: it shows both a very good activation behaviour and interesting sorption performance after only 1 h of milling. Neither the mechanical processing nor the high temperature/high pressure treatments lead to reactions among the three components of the mixtures and Mg is the only hydrogen active phase. Four cycles at 350 °C and 35 bar/1 bar charging/discharging pressure are enough for the full activation of the composite, while ten cycles are needed for a pure Mg sample milled in the same conditions. At 320 °C the ternary mixture reversibly exchanges up to 6.8 wt % H2, and it charges/discharges 6.0 wt % H2 in 0.5 min/1.7 min respectively (20 times/4.5 times more quickly than pure Mg). The TPD measurements performed at 1 bar H2 show that the composite starts desorbing hydrogen at 290 °C, a temperature 40 °C lower than the value recorded for pure MgH2. The dehydrogenation enthalpy, obtained by coupled calorimetric – manometric measurements, is +71 ± 1 kJ/mol H2, to be compared with +75 ± 1 kJ/mol H2 for pure MgH2. The activation energy for the absorption process, obtained by fitting the kinetic profiles recorded at different temperatures by the Avrami-Erofeev equation, is 11 kJ/mol, 3.6 times lower than for the pure Mg sample (40 kJ/mol). The desorption activation energy is 103 kJ/mol, i.e. a half of the value for pure MgH2. All these data point out to both a catalytic (very good) effect and a destabilizing (more limited) effect played by the simultaneous presence of C and Nb2O5 towards the Mg/MgH2 system. References

1. C. Milanese, A. Girella, G. Bruni, P. Cofrancesco, V. Berbenni, A. Marini, M. Villa, P. Matteazzi, Journal of Alloys and Compounds, 465, (2008), 396–405.

2. C. Milanese, A. Girella, G. Bruni, P. Cofrancesco, V. Berbenni, A. Marini, M. Villa, P. Matteazzi, International Journal of Hydrogen Energy, 33 [17], (2008), 4593–4606.

3. C. Milanese, A. Girella, S. Garroni, G. Bruni, V. Berbenni, P. Matteazzi, A. Marini, International Journal of Hydrogen Energy, 35 [3], (2010), 1285-1295.

250

Solid-state Catalytic Dehydrogenation of Ammonia Borane for Hydrogen Storage

Teng He, Zhitao Xiong, Guotao Wu, Hailiang Chu, Chengzhang Wu, Tao Zhang and Ping Chen

Dalian Institute of Chemical Physics, Chinese Academy of Sciences, 457# Zhongshan Road, Dalian, China, 116023

Email: pchen@dicp.ac.cn Ammonia Borane (AB in short) has been considered as one of the most promising hydrogen storage materails due to its abnormal high hydrogen content (19.6 wt %).[1] But, the relatively high kinetic barrier during dehydrogenation of AB renders its application. Other drawbacks of AB include the emission of poisoning side products (NH3 and borazine) and severe material foaming in the dehydrogenation. Previously studies on the modification of AB focused either on catalyzing AB in solution[2] or on spreading AB on supports[3]. However, the those approaches inevitably bring additional weight (solvents and supports etc.) to the system, and thus, considerably reduce the overall hydrogen content. In this study, we introduced 2.0 mol % Co- and Ni-based catalysts into AB in solid state by using co-precipitation method[4] to catalyze the dehydrogenation of AB. The experiment results show that the catalysts are 2-5 nm in size. About 1 equiv. hydrogen can be released from doped-AB at a temperature as low as 59 °C in 28 hours. In addition, the dehydrogenation doesn’t bring any detectable borazine, NH3 and sample foaming. References 1. G. Wolf, J. Baumann, F. Baitalow, F. P. Hoffmann, Thermochimica. Acta. 343,

(2000), 19-25. 2. M. C. Denney, V. Pons, T. J. Hebden, D. M. Heinekey, K. I. Goldberg, Journal of

American Chemistry Society. 128, (2006), 12048-12049. 3. A. Gutowska, L. Li, Y. Shin, C. M. Wang, X. S. Li, J. C. Linehan, R. S. Smith, B. D.

Kay, B. Schmid, W. Shaw, Maciej Gutowski, T. Autrey, Angewandte Chemie International Edition. 44, (2005),3578-3581.

4. T. He, Z. Xiong, G. Wu, H. Chu, C. Wu, T. Zhang, P. Chen, Chemistry Materials. 21, (2009), 2315-2318.

251

Mathematical Model of Metal-hydride Hydrogen Tank with Quick Sorption

I.Chernov, and I.Gabis

Inst. Appl. Math. Res., Karelian Res. Centre, RAS, Petrozavodsk, Russia V.A.Fock's Inst. of Physics, St-Petersburg, Russia

Email: IAChernov@yandex.ru Developing a method of storing hydrogen on-board a car is very important [1]. A possibility is using metal-hydrogen systems. It seems safer compared to high-pressure tanks. A serious problem is to dissipate much heat while loading the tank by hydrogen. For metal with rather low heat of hydriding 21 kJ per mole sorbing 2 kg of hydrogen releases 21 MJ of heat. Interesting effects appear due to gas redistribution between more and less cooled domains of the tank after the initial inflow of gas, when concentration of the sorbed hydrogen is in the binary phase area. They are especially noticeable in case of very high rates of hydrogen sorption and desorption, so that metal-hydride system is constantly in equilibrium with the surrounding hydrogen gas. In order to maintain equilibrium, cooled parts of hydride sorb more hydrogen releasing heat but reducing the pressure; those areas that are far from the cooled surfaces release hydrogen partially restoring the pressure. When the pressure becomes low enough, the inverse redistribution takes place. If some hydride becomes saturated up to the sinle-phase area, it keeps the equilibrium (with respect to pressure and temperature) concentration cooling down and serving as a cooler for other parts of hydride. For modelling the tank we chose the Laves phase hydride (Ti0.9Zr0.1)1.1CrMn. P-C-T diagrams for this alloy are in [2]. It has rather high rates of sorption-desorption. We present a rather general cell mathematical model of the tank. The domain occupied by hydride is divided to elementary cells interacting with each other via their faces (simple version of the finitie element method). Different shapes of tanks with different configuration of cooler systems and cooling laws can be simulated by the model. The equations are derived from the conservation laws. The model is the system of ordinary differential equations for concentrations in the cells and the pressure. It can be efficiently calculated on parallel computers. In the report we show the results of numerical simulation focusing on the concentration redistribution effect. The work has been financially supported by the grant 09-03-00947-а “Theoretical and experimental study of kinetics and mechanisms of hydrogen desorption from metal hydrides” of the Russian Foundation for Basic Research. References 1. S. Satyapal et al, Catalysis Today, 120, (2007), 246-256. 2. M. Kandavela et al, Int. J. Hydrogen Energy, 33, (2008), 3754-3761.

252

Structures and Electrochemical Characteristics of As-Cast and Annealed La0.75Mg0.25Ni3.3Co0.2Six�x= 0-0.2�Electrode Alloys

Hui-ping Rena, Bao-wei Lia, Yang-huan Zhang a,b*, Yi-ming Lia, Shi-hai Guob, Xin-lin Wangb

a School of Material, Inner Mongolia University of Science and Technology, Baotou 014010, China bDepartment of Functional Material Research, Central Iron and Steel Research Institute, Beijing 100081,

China Email: zyh59@yahoo.com.cn

La-Mg-Ni-system A2B7-type alloys were considered to be most promising candidates used as negative anode electrode in Ni-MH batteries owing to their higher discharge capacities (360-410 mAh/g) and low production costs. However, their electrochemical cycling stability needs to be further intensified for practical application. In order to improve the electrochemical performance of the La-Mg-Ni system A2B7-type electrode alloys, element Si was added in the alloy and the La0.75Mg0.25Ni3.3Co0.2Six(x=0, 0.05, 0.1, 0.15, 0.2) electrode alloys were prepared by casting and annealing technologies. The microstructures and electrochemical characteristics of the as-cast and annealed alloys were investigated in detail. The results obtained by XRD, SEM show that the alloys have a multiphase structure which consists of two main phases (La, Mg)Ni3 and LaNi5 as well as a residual phase LaNi2. The addition of Si and the annealing treatment lead to the emergence of NiSi and MgNi2 phases. The results of the electrochemical measurement indicate that the addition of Si markedly enhances the cycle stability of the alloy, but it also causes a visible decline of the discharge capacity and high rate dischargeability (HRD) of the alloy. When Si content rises from 0 to 0.2, the cycle life prolongs from 69 to 239 cycles, and the discharge capacity falls from 386 to 342 mAh/g for the as-cast alloys. And for the as-annealed (950 �) alloys�the cycle life prolongs from 233 to 324 cycles, and the discharge capacity drops from 405 to 354 mAh/g. The annealing treatment significantly ameliorates the electrochemical performances of the alloys, involving the cycle stability and the discharge capacity, whereas it results in a slight decrease in the high rate dischargeability (HRD) of the alloy. Electrochemical impedance spectroscopy (EIS), linear polarization, anodic polarization and potential-step measurements show that the exchange current density I0, the limiting current density IL and the hydrogen diffusion coefficient D always decrease with rising Si content. Key words: A2B7-type electrode alloy; Si addition; Annealing, Structures; Electrochemical characteristics References 1. Pan H G, Yue Y J, Gao M X, Wu X F, Chen N, Lei Y Q, Wang Q D, Journal Alloys

and Compounds, 397, (2005), 269–275. 2. Zhang X B, Sun D Z, Yin W Y, Chai Y J, Zhao M S, Electrochimica Acta, 50, (2005),

2911–2918 3. Zhang Y H, Ren H P, Li B W, Guo S H, Wang Q C, Wang X L, International Journal of

Hydrogen Energy, 34, (2009), 6335–6342.

253

Hydrogen Storage Properties of Ca(BH4)2-LiNH2 System Hailiang Chu, Zhitao Xiong, Guotao Wu, Jianping Guo, Xueli Zheng, Teng He,

Chengzhang Wu, Ping Chen* Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian 116023, China

Email: pchen@dicp.ac.cn; chu5063@dicp.ac.cn Metal borohydrides M(BH4)n with high hydrogen densities have been attracting onsiderable interests as potential candidates for hydrogen storage recently [1–3]. Calcium borohydride, Ca(BH4)2, having a theoretical hydrogen capacity of 11.4 wt% and a favourable thermodynamics in dehydriding reaction Ca(BH4)2 → 2/3 CaH2 + 1/3 CaB6 + 10/3 H2 (32 kJ/mol H2, theoretically estimated [4]), shows certain promise to be a hydrogen storage material. However, its high dehydrogenation temperature and limited reversibility has been a hurdle for its practical applications. Our previous investigations on the interaction of amides (such as LiNH2, Mg(NH2)2 and Ca(NH2)2) and hydrides (such as LiH, MgH2 and CaH2 etc.) showed that the main driving force for the interaction is the potential for the combination of H�+ in amide and H�- in hydride to form molecular hydrogen [5]. In addition, the electrostatic attraction between N in amide and metal cation in hydride contributes to the interaction. Driven by those two attractions hydrogen desorption from amide-hydride system can even occur at ambient temperature. In an effort to adjust the thermal stability of Ca(BH4)2 for hydrogne storage, we make a composite system Ca(BH4)2-LiNH2 based on the aforementioned reaction mechanism between H�+

and H�-. Interaction of Ca(BH4)2 and LiNH2 leads to decreased dehydrogenation temperatures and increased hydrogen desorption capacity with comparison to pristine Ca(BH4)2. About 9 wt% of hydrogen can be detached at a temperature of ca. 290 �C from Ca(BH4)2-4 LiNH2 composite system according to the reaction: Ca(BH4)2 + 4 LiNH2 → 1/4 LiCa4(BN2)3 + 5/4 Li3BN2 + 8 H2. Moreover, hydrogen storage properties of Ca(BH4)2-LiNH2 with the presence of CoCl2 as an additive is systematically investigated. An addition of 5 wt% CoCl2 to the Ca(BH4)2-4LiNH2 system greatly reduces the hydrogen desorption temperature. Compared with the other catalysts including Co, Co+B, CoB alloy and [2LiBH4-CoCl2] (representing the products from the following reaction: 2 LiBH4 + CoCl2 → Co + B + 2 LiCl + 4 H2), CoCl2-based catalyst shows superior performance in the following aspects, i.e., lower desorption temperature and faster desorption rate. More than 7 wt% of hydrogen can be released from CoCl2-doped Ca(BH4)2-4LiNH2 sample at a temperature as low as 178 °C, making the system a potential candidate for hydrogen storage. The effectively catalytic species is determined to be active cobalt particles formed in-situ during ball milling process, which are finely dispersed in the sample. Therefore, exceptionally high catalytic performance can be achieved. References 1. L. Schlapbach, A. Züttel, Nature, 414, (2001), 353–358. 2. S. Orimo, Y. Nakamori, J.R. Eliseo, A. Züttel, C.M. Jensen, Chem. Rev., 107, (2007), 4111–4132. 3. J. Yang, S. Hirano, Adv. Mater., 21, (2009), 3023–3028. 4. K. Miwa, M. Aoki, T. Noritake, N. Ohba, Y. Nakamori, S. Towata, A. Züttel, S. Orimo, Phys. Rev. B, 74, (2006), 155122. 5. Z. T. Xiong, J. J. Hu, G. T. Wu, P. Chen, W.F. Luo, K. Gross, J. Wang, J. Alloys

Compd., 398, (2005), 235–239.

254

The Structure and Electrochemical Properties of New La15Fe77B8-type Hydrogen Storage Alloy

Huizhong Yan1, 2,, Fanqing Kong1, 2, Wei Xiong1, 2, Baoquan Li1, 2, Jin Li1, 2, Li

Wang1, 2 1. Baotou Research Institute of Rare Earths, Baotou 014030, China; 2. National Engineering Research

Center of RE Metallurgy & Functional Materials, Baotou 014030, China E-mail: yanhzh@rknerc.com (H. Z. Yan)

The new La-Fe-B system hydrogen storage alloys with excellent properties and low cost were investigated. The La15Fe77B8-type hydrogen storage alloy (La15Fe12Ni64Mn7B2) was prepared by rapid quenching method. The structural and electrochemical properties of the quenched and annealed alloys were systematically studied. The XRD and EPMA results showed that the La15Fe12Ni64Mn7B2 alloy was composed of the LaNi5, the La3Ni13B2, and the (Fe, Ni) phases. The electrochemical testing showed that the high-rate dischargeability (HRD) and low-temperature (233K) discharge properties of the La15Fe12Ni64Mn7B2 alloy electrodes were superior to that of the LaNi5-type hydrogen storage alloy. The electrochemical properties of the La15Fe12Ni64Mn7B2 alloy were improved after annealing. Key words: Hydrogen storage materials; La-Fe-B system hydrogen storage alloy; High rate dischargeability; Low temperature dischargeability; Electrochemical properties; Ni-MH battery

255

HyStorM – Tuning Promising Hydrogen Storage Materials for Automotive Applications

A. H. Pohl1, S. K. Callear1, M. O. Jones1,2, W. I. F. David1,2, S. R. Johnson2, P. P.

Edwards2, G. Purdy3, B. E. Hayden3, J.-Ph. Soulié3, S. Guerin3, S. Ellis4, M. Stevens4, C. Nuttall4, and A. Amieiro4.

1STFC Rutherford Appleton Laboratory, ISIS Facility, Harwell Science & Innovation Campus, Chilton, Oxon, OX11 0QX, UK. 2Inorganic Chemistry Laboratory, University of Oxford, South Parks Road,

Oxford OX1 3QR, U.K. 3Ilika Technologies Ltd., Enterprise Road, Southampton SO16 7NS, UK. 4Johnson Matthey Plc., Technology Centre, Blounts Court, Sonning Common, Reading RG4 9NH, UK.

Email: alexander.pohl@stfc.ac.uk HyStorM is a major hydrogen-storage project funded by the UK Technology Strategy Board and involves Johnson Matthey, Ilika Technologies Ltd., Oxford University and the Science and Technologies Facilities Council. We aim to synthesise ternary and quaternary metal borohydrides using high throughput methodologies and assess them in terms of their hydrogen storage potential. At Ilika Technologies, the primary screening consists of state-of-the-art physical vapour deposition of combinatorial thin-film hydride materials that are collated into libraries on microfabricated hot-plates and screened for hydrogen storage performance. The best material compositions are forwarded to Oxford University, Johnson Matthey and STFC, who undertake synthesis and secondary screening of potential candidates. Material characterisation is performed at the European Synchrotron Radiation Facility in Grenoble and at the Diamond Light Source, UK. In addition, neutron scattering studies at the Rutherford Appleton Laboratory enable us to evaluate the structure, kinetics and dynamics of the most promising candidate systems, in-operando, while they absorb and desorb hydrogen. The principal materials that we have studied to date have been mixed metal borohydrides and we have been studying combinatorial modifications that include Ca(BH4)2. This material has a relatively high hydrogen storage capacity of 9.6 wt.% H2 which is released between 350°C and 450°C. It is also attractive as a potential hydrogen storage material as it has shown indications of reversibilty1. However, Ca(BH4)2 is thermodynamically too stable to be of practical use for hydrogen storage in automotive applications. By doping Ca(BH4)2 with manganese, zinc or titanium2 borohydride, we aim to tailor the thermodynamic properties of the resulting mixed borohydride. Here we report the synthesis, structural characterisation and dehydrogenation behaviour of M1-xCax(BH4)2 (M = Mn, Zn, Ti; 0 ≤ x ≤ 0.2). References 1. E. Ronnebro and E. H. Majzoub, J. Phys. Chem. B 2007, 111, 12045. 2. Z. Z. Fang, L. P. Ma and X. D. Kang et. al, Appl. Phys. Lett. 2009, 94, 044104.

256

Influence of the Presence of Ti33V33Fe33 Precipitates on the Hydrogenation Properties of Ti-V-Fe BCC Compounds

A. Guéguen, J.M. Joubert and M. Latroche

Institut de Chimie des Matériaux Paris Est, Thiais, France Email: gueguen@glvt-cnrs.fr

One attractive metal for hydrogen storage is vanadium because of its low mass. Vanadium has a body cubic centered (bcc) structure and can absorb reversibly up to 2.2 wt %. However it is an expensive element and thermal treatments are needed to activate the metal. Alloying vanadium with other elements such as titanium or iron helps lowering the cost of such compounds and also allows a fine tuning of the hydrogenation properties of the system. Ti and V are known to form bcc solid solutions at temperatures above 882°C [1]. Using the data collected by Tsin-Khua and Kornilov [2,3], Raghavan [4] and Cornish and Watson [5] proposed an isothermal section of the ternary phase diagram at 1000 °C. However the diagram does not agree with some results from Challet [6] about the solubility limit of Fe in Ti-V rich bcc solid solutions. A recent detailed study of the Fe-Ti-V system was performed by Massicot et al. to determine the solubility limit of Fe in the Ti-V system [7]. They reported a solubility minimum of ~ 15 at. % for any Ti/V ratio. Challet [6] and Massicot [8] measured as well the hydrogenation properties of several bcc compounds. All exhibit very fast kinetics. The equilibrium pressures of Ti0.305V0.555Fe0.14 being quite low (8.10-3 MPa at 25 °C) [5], compounds with compositions slightly above the solubility limit of the bcc domain are considered to improve these values. Micropobe analysis on different samples indicate the presence of Ti33V33Fe33 type precipitates with C14 structure embedded in the bcc matrix. In order to understand the effect of such second phase on the hydrogenation properties of the bcc phase, compounds with different contents of C14 phase were synthesized. The isothermal section of the ternary phase diagram at 1000°C determined by Massicot was used to determine the exact composition of the alloys, the composition of the matrix being fixed. The structural analysis and hydrogenation properties of these materials will be discussed and compared. References

1. J.L. Muray, Bulletin of Alloy Phase Diagrams, 2, (1981), 48-55. 2. B. Tsin Khua, I.I. kornilov, Russ. J. Inorg. Chem., 5, (1960), 434-436. 3. B. Tsin Khua, I.I. kornilov, Russ. J. Inorg. Chem., 6, (1961), 694-696. 4. V. Raghavan, Phase Diagram of Ternary iron alloys, vol 1, (1987), 73-84. 5. S. Challet, M. Latroche, F. Heurtaux, , J. Alloys and Compounds, 439, (2007),

294-301. 6. L. Cornish, A. Watson, Ternary Alloy System, subvolume D, vol. 11, (2009), 668-

684. 7. B. Massicot, J.M. Joubert, M. Latroche, Int J. Materials Research, (2010), in press. 8. B. Massicot, J.M. Joubert, M. Latroche, manuscript in preparation.

257

Significant Improvement of Hydrogen Desorption in Destabilized Lithium Borohydride

X. B. Yu1, 2 a), Z. P. Guo2, H. K. Liu2

1 Institute for Superconducting and Electronic Materials, University of Wollongong, NSW 2522, Australia 2 Department of Materials Science, Fudan University, Shanghai 200433, China

Email: yuxuebin@fudan.edu.cn

For utilization of hydrogen as one of the clean fuels of the future, it is necessary to develop high-performance hydrogen storage materials. Lithium borohydride, LiBH4, is presently one of the most promising solid-state hydrogen storage materials due to its high hydrogen storage capacity of 18.3 wt %. However, the main evolution of gas starts at 380 oC and only releases half the hydrogen below 600 oC.1 In this paper, the hydrogen storage properties of LiBH4/LaNi3.55Co0.75Mn0.4Al0.3 mixtures with various ratios were investigated. It was found that LiBH4 could react with LaNi3.55Co0.75Mn0.4Al0.3 to form La-Ni-B compounds resulting hydrogen release at low temperature. For the 12h milled LiBH4/ LaNi3.55Co0.75Mn0.4Al0.3 sample, the onset hydrogen desorption started at 160 oC and the majority of hydrogen was released below 350 oC (Fig. 1). Attempt at directly rehydrogenating a dehydrogenated LiBH4/ LaNi3.55Co0.75Mn0.4Al0.3 at 400 oC and 100 bar H2 was failed, suggesting that, to reverse this system, higher conditions are required.

100 200 300 400 500 600

12 h milled

6 h milled

P1 P2

P2

P1

Inte

nsity

(a .u

.)

Temperature (oC)

1 h milled

Fig.1 The MS results for the evolution of hydrogen from LiBH4/LaNi3.55Co0.75Mn0.4Al0.3 sample

with different ball milling time. References 1. A. Züttel, P. Wenger, S. Rentsch, P. Sudan, Ph. Mauron and Ch. Emmenegger, J. Power Sources, 118, (2003), 1.

258

Catalytic Effect of Li5TiN3 on Hydrogen Desorption Properties in the Mechanically Ball Milled Li-N-H System

Y.-L. Teng, T. Ichikawa, S. Hino, Y. Kojima Institute for Advanced Materials Research, Hiroshima University

Email: ylteng@hiroshima-u.ac.jp The Li-N-H system has been paid much attention for one of the model systems of hydrogen storage materials. Our group has reported that some catalysts, especially TiCl3, were effective for improving hydrogen storage properties on this system.1, 2 In addition, Tsumuraya et al. performed the theoretical analysis of X-ray absorption spectroscopy (XAS) spectra of Ti compounds in the Li-N-H system, and found that XAS spectra of some Li-Ti-N compounds such as Li5TiN3 and Li7Ti(NH)4 were quite similar to measured ones of catalytically-active Ti compounds.3 In the present study, we investigated catalytic effect of Li5TiN3 additive on hydrogen desorption properties for the Li-N-H system. The ball-milled mixture of Li3N (Sigma-Aldrich) and TiN (RARE METALLIC Co.,LTD., 99%) was heated at 900 °C under N2 atmosphere, which is 0.2 MPa at the room temperature. LiNH2 and LiH powders with 1:1 molar ratio and 1 mol% additive were ball milled under 1 MPa H2 atmosphere for 2, 20, and 80 hours. After homogenizing the mixed powders, the composites were examined by thermal desorption mass spectroscopy combined with thermogravimetry. The Li5TiN3 single phase was successfully synthesized. It was found that the Li5TiN3 catalyst can absorb large amount of ammonia forming the Li5TiN3(NH3)x compound. We investigated the catalytic effect of Li5TiN3 and Li5TiN3(NH3)x additives on hydrogen desorption properties in the mechanically ball milled Li-N-H system. The composite of LiH and LiNH2 with 1 mol% Li5TiN3 or Li5TiN3(NH3)x that was ball milled for 80 hours at 370 rpm under 1 MPa hydrogen atmosphere shows good thermal desorption properties, for which hydrogen desorption peak becomes sharp and the ammonia emission is largely suppressed. This indicates that Li5TiN3 and Li5TiN3(NH3)x are catalytically effective in the Li-N-H system. This work has been partially supported by NEDO under “Advanced Fundamental Research Project on Hydrogen Storage Materials”. References 1. T. Ichikawa, S. Isobe, N. Hanada, H. Fuji, J. Alloys Compd. 365, (2004), 271-276. 2. S. Isobe, T. Ichikawa, N. Hanada, H. Leng, M. Fichtner, O. Fuhr, H. Fuji, J. Alloys Compd. 404-406, (2005), 439-442.

3. T. Tsumuraya, T. Shishidou, T. Oguchi, Phys. Rev. B 77, (2008), 235114.

259

Crystalline and Electronic Structure of La-Ni-Mn-Al-Fe-B Alloy Investigated by XRD and XPS

C. Wana, X. Jua, Y. Wanga and H. Yanb, c

a Department of Physics, University of Science and technology Beijing, Beijing, China b Baotou Research Institute of Rare Earth, Baotou, China

c Ruike National Engineering Research Center of RE Metallurgy & Functional Materials, Baotou, China Email: jux@ustb.edu.cn

Energy crisis and environmental pollution are urging many countries to deveplop new clean energies. Metal hydrides are a safe alternative for hydrogen storage. Many AB5 internetallic compounds, a metal hydride with hexagonal CaCu5 type structure, can react reversibly with hydrogen at moderate pressure and temperature and exhibit excellent hydrogen storage properties [1]. The intermetallic compound LaNi5 is of great importance for hydrogen storage applications, such as negative electrode materials, hydrogen purification and recovery devixes, etc [2-4]. Partial substitution by M (M=Al, Co, Sn, Ga, Ge) for Ni in the LaNi5 improves some of the practical properties of these hydrogen storage compounds [5]. In this article, the hydrogen storage alloy was prepared form pure La-Ni-Mn-Al-Fe-B in stoichiometric ratio by arc melting under argon atomsphere. The crystal structure, activation performance, hydrogen storage properties and electronic structure were investigated systemically. The unit-cell dimensions of LaNiMn phase are determined by Rietveld refinements of the synchrotron radiation XRD data. The results indicates that the unit cells of LaNiMn continuously increase during annealing and activation. The atomic concentration and chemical shift on the surface of this alloy are studied by X-ray photoelectron spectroscopy. The hydrogenation greatly changes the atomic ratio between Ni and La. The hydrogen induced chemical shift of the La 3d and Ni 2p core levels can be determined with the highest accuracy by the energy difference ΔEB (Ni 2p1/2-La 2d5/2). References 1. S.L. Li, P. Wang, W. Chen, G. Luo, D.M. Chen, K. Yang, J. Alloys and Compounds, 867-871, (2009), 485. 2. J.J.G. Willems, K.H.J. Buschow, J. Less-Common Met. 13-30 (1987) 129. 3. A. Anani, A. Visintin, K. Petrov, S. Srinivasan, J.J. Reilly, J.R. Johnson, J. Power Sources 261-275 (1994) 47. 4. E.D. Snijder, G.F. Versteeg, W.P.M. van Swaaij, Chem. Eng. Sci. 2429-2441 (1993) 48. 5. D. Chen, G.X. Li, D.L. Zhang, T. Gao, Acta Metall. Sin.(Engl. Lett.), 157-162, (2008), 21.

260

Reorientational Motion in Mg(BH4)2: a Nuclear Magnetic Resonance Study

O.A. Babanova1, A.V. Soloninin1, A.V. Skripov1, Y. Filinchuk2, and H. Hagemann3

1 Institute of Metal Physics, Urals Branch of the Academy of Sciences, Ekaterinburg, Russia 2 Swiss-Norwegian Beam Lines at ESRF, Grenoble, France

3 Département de Chimie Physique, University of Geneva, Geneva, Switzerland Email: babanova@imp.uran.ru

Light metal borohydrides are considered as promising materials for hydrogen storage due to their exceptional volumetric and gravimetric hydrogen densities. The magnesium borohydride Mg(BH4)2 has a hydrogen capacity of 14.8 wt.%. In this work, we report the results of the first nuclear magnetic resonance study of atomic jump motion in Mg(BH4)2. Our 1H and 11B spin-lattice relaxation measurements for α-Mg(BH4)2 have revealed a coexistence of at least two frequency scales of reorientational motion of the BH4 groups. Such a coexistence manifests itself as two well-separated peaks in the temperature dependence of the measured proton spin-lattice relaxation rate R1. As typical of the R1(T) peaks due to atomic jump motion, both the positions and the amplitudes of these peaks depend on the resonance frequency. Each of the peaks is expected to appear at the temperature at which the rate of the corresponding jump process becomes nearly equal to the resonance frequency. At the frequency of 14 MHz, the maxima of R1(T) are observed at 165 K and 270 K. The low-temperature peak corresponds to the faster reorientational process, and its estimated activation energy is 0.10 eV. The high-temperature peak is associated with the slower reorientational process, and the corresponding activation energy is about 0.31 eV. Rough estimates of the jump rates τi

-1 for the two processes at T = 300 K yield τ1

-1 ≈ 2×109 s-1 (for the faster process) and τ2-1 ≈ 3×108 s-1 (for the slower process).

Thus, the proton spin-lattice relaxation results suggest that α-Mg(BH4)2 contains BH4 groups with strongly differing reorientation rates. The results of the 11B spin-lattice relaxation measurements are consistent with this picture. The coexistence of at least two frequency scales of the reorientational motion may be related to structural features of the magnesium borohydride. In fact, the structure of α-Mg(BH4)2 is found to be unusually complex [1,2]; it has six inequivalent positions of the BH4 groups. While their local environments are similar (two Mg atoms coordinate the BH4 tetrahedra), the corresponding Mg-B-Mg angles vary in the range 148º - 177º [2]. It is reasonable to assume that the difference in the activation energies of BH4 reorientations originates from the anisotropy of their local environments. References 1. R. Černý, Y. Filinchuk, H. Hagemann, K. Yvon, Angew. Chem. Int. Ed., 46 (2007)

5765-5767. 2. Y. Filinchuk, R. Černý, H. Hagemann, Chem. Mater., 21 (2009) 925-933.

261

HfNi and Hf2Ni Intermetallics - Comparation of Hydrogen Absorption Ability

D.Lj.Stojić1, B.Đ.Cekić2, K.D.Ćirić2, V.J. Koteski2

1Department of physical chemistry, 2Department of Nuclear and Plasma Physics, P.O.Box 522, Vinča Institute of Nuclear Sciences, Belgrade, Serbia

e-mail: estojicd@vinca.rs

The hydrogen absorption abilities of HfNi and Hf2Ni, obtained by experimental and theoretical investigations [1,2,3], were compared. The kinetics of hydrogen absorption in these compounds were investigated in different temperature ranges, up to temperature of 823K, and under the constant hydrogen pressure of 1 bar. Similarly to many other intermetallics, multiple hydriding/dehydriding procedures accelerate hydriding, but diminish the hydriding capacities of both investigated compounds. The maximal hydriding capacities, H/Mmax, were 2.2 obtained at 373K for HfNi and 1,15 obtained at 748K for Hf2Ni. The obtained kinetic parameters of hydrogen absorption reactions indicated improved properties of HfNi in comparison to Hf2Ni. According to the absorption abilities obtained, HfNi is better hydrogen storage material than Hf2Ni. In order to explain the observed differences, changes in crystal structures and morphology of the investigated intermetallics and corresponding hydrides (XRD and SEM measurements) as well as their structural, electronic and bonding properties calculated using the full-potential linearized augmented plane waves method (FP-LAPW), were utilized. References 1. D.Lj. Stojić, S.V. Kumrić, J.N. Belošević-Čavor, J.S. Radaković, B. Dj. Cekić, S.V. Mentus, Hydridic, thermodynamic and kinetic properties of Hf2Ni intermetallic phase, Int. J. Hydrogen Energy, 34 (2009) 3764-3770. 2. K.D.Ćirić, V.J.Koteski, D.Lj.Stojić, J.S.Radaković, V.N.Ivanovski; Int. J. Hydrogen Energy, doi:10.1016/j.ijhydene.2010.01.127 3. D.Lj.Stojić et al., unpublished results

262

Hydrogen Absorption in HfNi Intermetallic Phase – Experimental and Theoretical Investigation

K.D.Ćirić1, B.Đ.Cekić1, D.Lj.Stojić2, V.J.Koteski1

1Department of Nuclear and Plasma Physics, 2Department of phzsical chemistry, P.O.Box 522, Vinča Institute of Nuclear Sciences, Belgrade, Serbia

e-mail: kciric@vinca.rs

The kinetic of hydrogen absorption under isothermal condition in HfNi intermetallic phase have been investigated at five different temperatures in temperature range 323-673K at the constant pressure of 1bar, and kinetic parameters: rate constant and activation energy were determined. Two step hydriding process has been observed with maximal hydrogen absorption at temperature 373K with hydrogen atom to f.u. ratio H/M=2.2. In order to examine cyclic behavior and the catalytic effect of surface modification using PdCl2, compound was further investigated at the temperature of maximal absorption. The palladization caused improvement of kinetic parameters. We performed XRD and SEM measurements in order to examine the changes in crystal structure and morphology caused by multiple hydriding/dehydriding cycles for unmodified and palladized samples. Thermodynamic parameters of hydriding were calculated using the full-potential linearized augmented plane waves (FP-LAPW) code based on the density functional theory (DFT). Within the DFT we have also investigated structural, electronic and bonding properties of HfNi, HfNiH and HfNiH3 [1]. References 1. K.D.Ćirić, V.J.Koteski, D.Lj.Stojić, J.S.Radaković, V.N.Ivanovski; Int. J. Hydrogen Energy, doi:10.1016/j.ijhydene.2010.01.127

263

High Resolution Raman and Neutron Study of Mg(BH4)2 in a Wide Temperature Range

A.Giannasi1, D.Colognesi1, L.Ulivi1, M.Zoppi1, A.J.Ramirez-Cuesta2, E.G.Bardaji3,

M.Fichtner3, E.Roehm3 1Consiglio Nazionale delle Ricerche, Istituto dei Sistemi Complessi, Via Madonna del piano 10, Sesto

Fiorentino (FI), Italy 2Rutherford Appleton Laboratory, ISIS Facility, Chilton, Didcot, OX11 0QX, United Kingdom

3Karlsruhe Institute of Technology, Institute of Nanotechnology, Hermann-von-Helmholtz-Platz 1, 76347 Eggenstein-Leopoldshafen, Germany

Email: alessandra.giannasi@fi.isc.cnr.it We have measured the low temperature Raman spectra of Mg(BH4)2 in the mixed (α plus β) phase, and the Raman and neutron spectra of the same compound in the pure β phase. X-ray diffraction investigation and Raman spectroscopy results revealed that the pristine material is almost in the pure α phase, being the β phase just a small contamination. The low temperature measurements exhibit a significant band narrowing, revealing a complex structure in both the internal (particularly the BH stretching) and the external vibrational modes. The recent ab initio calculations on the α phase by Dai et al. [1] have provided a set of vibrational frequencies that qualitatively agree with our findings in the mixed phase. The low temperature spectra evidence the splitting of the BH vibrational mode, mainly in the α phase. Such an effect is related to the degeneracy lifting of the BH vibrational modes caused by the site splitting effect. Moreover, we observe that the low temperature Raman spectrum shows sixteen different excitation modes, mainly related to the α phase, in the lattice phonon region. Raman spectroscopy has been also used to follow the α to β phase transition and to investigate the β phase at low temperature. In the latter, both the external and the internal vibrational modes of the [BH4]- anion are considerably modified if compared to the mixed phase. The number of external modes turns out to be substantially reduced, while the BH vibrational band results less structured and smoother than the one observed in the mixed phase. The neutron spectroscopy experiment, performed at low temperature, points out mainly the proton dynamics and basically agrees with the Raman results. In addition, it reveals the presence of an extra band which is interpreted as due to the [BH4]- librations. References 1. B. Dai, D. S. Sholl, J. K. Johnson, J. Phys. Chem C, 112 (2008), 4391-4395

264

Synchrotron EXAFS and XRD Studies La-Ni-Mn Alloy During Hydrogen Absorption-Desorption Cycling

Chubin Wana, Xin Jua, Yuting Wanga and Huizhong Yanb, c

a Department of Physics, University of Science and technology Beijing, Beijing, China b Baotou Research Institute of Rare Earth, Baotou, China

c Ruike National Engineering Research Center of RE Metallurgy & Functional Materials, Baotou, China Email: jux@ustb.edu.cn

The intermetallic compound LaNi5 and its partially substituted alloys have been intensively studied in recent years due to their promising properties as hydrogen storage materials, such as fast and reversible sorption and a plateau pressure of a few bars at room temperature, enven if in the full hydride the hydrogen capacity remains below the 2 wt.% [1-2]. The reasons for the degradation in cycling capacity of the alloy have been discussed. La-Ni-Mn alloy were prepared by high-frequency induction melting followed by annealing in Ar atmosphere at 1373K. The evolution of local and crystal structure of the La-Ni-Mn hydrogen storage alloys during hydrogen absorption/desorption cycling using extended X-ray absorption fine structure (EXAFS) and X-ray diffraction (XRD). The completely desorpted alloy were investigated after different cycles. Average coordination numbers and average interatomic distances between first neighbors were found form EXAFS spectra. The XRD results indicate that the lattice parameters of major LaNiMn phases calculated by Rietveld method are gradually reduced with increasing the numbers of cycle. The reasons for the degradation in cycling capacity of the alloy have been discussed. The first one is the reduction of the V-based cell mass during cycling, which can’t hold more hydrogen atoms. The decrease of the cycling capacity also can be attributable to the bond lengths of La-Ni and La-Mn in this alloy during cycling. References 1. O. Palumbo, C. Castellano, A. Paolone, F. Cordero, R. Cantelli, Y. Nakamura, E. Akiba, J. Alloys and Compounds, 33-36, (2007), 433. 2. L. Schlapbach, A. Zuttel, Nature 353-358,(2001) 353.

265

Improvement of the Kinetics of H2 Absorption of the MgH2+2LiNH2 System

Weifang Luo, Vitalie Stavila and Lennie Klebanoff

Sandia National Laboratory, Livermore CA 94551 A reversible hydrogen storage material with a high H capacity is highly desirable for vehicular applications. Currently the metal amide-hydride combination is one of the most promising systems for the delivery of the highest reversible hydrogen capacity at acceptable pressures and temperatures. For these reasons, the (MgH2+2LiNH2) system has received significant attention; however, its H2 absorption rate is unsatisfactory. It has been reported that the pristine material, (MgH2+2LiNH2), is converted to (Mg(NH2)2 +2LiH) after the initial dehydrogenation/re-hydrogenation cycle. Here we will report results concerning the absorption rate improvement and efforts to understand the initial structural change and the effect of sample pre-treatment on the initial desorption process.

266

TiCl3 Additions to Mg(BH4)2: from Kinetic to Thermodynamic Effects

Hai-Wen Li1, Yigang Yan1, Kazutoshi Miwa2, Shin-ichi Towata2 and Shin-ichi Orimo1

1Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan, 2Toyota Central R&D Labs., Inc., Nagakute, Aichi 480-1192, Japan

Email: lihw@imr.tohoku.ac.jp

Development of advanced hydrogen storage materials is regarded as one of the critical issues for fuel cell applications [1]. Magnesium borohydride Mg(BH4)2, which has a high hydrogen density of 14.9 mass %, has been attracting considerable interest as a promising hydrogen storage material [2-10]. The dehydrogenation reaction of Mg(BH4)2 occurred substantially above a certain temperature, e.g., 535 K, regardless of the partial pressure of hydrogen [8]. Hydrogen was found to be released via the following multistep decomposition reaction, accompanied by the formation of an intermediate compound MgB 2H12 [9], the formation of which was confirmed by NMR measurement [10, 12]. 1

Mg(BH4)2 → 1/6MgB12H12 + 5/6MgH2 + 13/6H2 → MgH2 + 2B + 3H2 → Mg + 2B + 4H2 (1)

Furthermore, our recent work on the improvement of dehydrogenation property of Mg(BH4)2 indicated that the initial dehydrogenation temperature was significantly decreased by approximately 170 K when a small amount of TiCl3 was added. That is, the initial dehydrogenation temperature was drastically reduced to approximately 360 K [2].

In this study, we are interested in systematically investigating the dehydrogenation property of the Mg(BH4)2 + xTiCl3 system as a function of the added TiCl3 contents from viewpoints of kinetics and thermodynamics. Furthermore, an insight into the improvement effects of TiCl3 on the dehydrogenation property of Mg(BH4)2 will be discussed, aiming at the further development of more effective additives for hydrogen storage applications. This study was partially supported by NEDO, “Development for Hydrogen Production, Transportation and Storage System” Project. References

2. S. Orimo et al., Chem. Rev. 107, (2007), 4111,. 3. H.-W. Li et al., Scripta Mater. 57, (2007), 679. 4. J. H. Her et al., Acta Cryst. B 63, (2007), 561. 5. K. Chłopek et al., J. Mater. Chem. 17, (2007), 3496. 6. R. Ćerný et al., Angew. Chem. Int. Ed. 46, (2007), 1. 7. M. D. Riktor et al., J. Mater. Chem. 17, (2007), 4939. 8. T. Matsunaga et al., Renew. Energy 33, (2008), 193. 9. Y. Yan et al., Mater. Trans. 49, (2008), 2751. 10. H.-W. Li et al., Acta Mater. 56, (2008), 1342. 11. S. J. Hwang et al., J. Phys. Chem. C 112, (2008), 3164. 12. V. Ozolins et al., Phys. Rev. Lett. 100, (2008) 135501. 13. G. L. Soloveichik et al., Int. J. Hydrogen Energy 34, (2009) 916.

267

Hydrogen Storage Properties of Y(BH4)3

Y. Yan1, H.-W. Li1, T. Sato2, K. Miwa3, S. Towata3, S. Orimo1 1Institute for Materials Research (IMR), Tohoku University, Sendai 980-8577, Japan

2WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan 3Toyota Central R&D Labs, Inc., Nagakute, Aichi 480-1192, Japan

Email: yg-yan@imr.tohoku.ac.jp

Metal borohydrides M(BH4)n have been attracting significant interest as one of the potential candidates for hydrogen storage materials because of their high gravimetric hydrogen densities [1]. So far, the studies on M(BH4)n are mainly focused on alkali and alkali-earth metal borohydrides, e.g. LiBH4 [2], Mg(BH4)2 [3-7] and Ca(BH4)2 [8, 9]. In this study, a transition metal borohydride Y(BH4)3 was synthesized and its dehydriding and rehydriding properties were investigated.

Y(BH4)3 was prepared by liquid-phase synthesis according to the metathesis reaction of YCl3 and LiBH4 [10]. Its crystal structure has been determined to be a primitive cubic lattice with a = 10.852(1) Å [11]. The dehydriding and rehydriding properties of Y(BH4)3 were studied by thermogravimetry and differential thermal analysis. The samples after dehydriding and rehydriding were characterized by X-ray diffraction and Raman spectroscopy. The dehydriding reaction of Y(BH4)3 starts at appropriately 460 K, and a total of 7.8 wt % of hydrogen is released up to 773 K. The decomposition of Y(BH4)3 is found to proceed via multistep dehydriding reactions accompanied with the formation of an intermediate phase, similar to that of Mg(BH4)2 [7]. Furthermore, Y(BH4)3 is proved to be partially rehydrided. This study was partially supported by NEDO and JSPS. References 1. S. Orimo et al., Chem. Rev. 107, (2007), 4111. 2. A. Züttel et al., J. Power Sources 118, (2003), 1. 3. H.-W. Li et al., Scripta Mater. 57, (2007), 679. 4. R. Černý et al., Angew. Chem. 119, (2007), 5765. 5. J. H. Her et al., Acta Cryst. 63, (2007), 561. 6. K. Chłopek et al., J. Mater. Chem. 17, (2007), 3496. 7. H.-W. Li et al., Acta Mater. 56, (2008), 1342. 8. K. Miwa et al., Phys. Rev. B 74, (2006), 155122. 9. Y. Kim et al., J. Phys. Chem. C 113, (2009), 5865. 10. Y. Yan et al., Int. J. Hydrogen Energy 34, (2009), 5732. 11. T. Sato et al., Phys. Rev. B 77, (2008), 104114.

268

Crystal Structure, Polymorphism, and Thermal Properties of Yttrium Borohydride Y(BH4)3

Christoph Frommen, Nadir Aliouane, Stefano Deledda, Jon Erling Fonneløp,

Hilde Grove, Klaus Lieutenant, Isabel Llamas-Jansa, Sabrina Sartori, Magnus H. Sørby, and Bjørn C. Hauback

Institute for Energy Technology, Physics Department, P.O. Box 40, NO-2027 Kjeller, Norway Metal borohydrides M(BH4)n have attracted significant interest as potential solid state hydrogen storage materials due to their high gravimetric hydrogen densities. The alkali- and alkali-earth borohyrides (e.g. LiBH4, Mg(BH4)2, and Ca(BH4)2) have been intensively studied, including their dehydriding/rehydriding behaviours, structural analysis, additive effects etc. As compared to alkali and alkali-earth borohydrides, transition metal borohydrides have been reported to have smaller formation enthalpies and lower stabilities. In this respect, Y(BH4)3 is a relatively stable transition metal borohydride with a high gravimetric hydrogen density of 9.1 wt%, and we present a comprehensive struc-tural and thermal study of this potential candidate for hydrogen storage applications. Y(BH4)3 was synthesized by cryo-milling mixtures of LiBH4 and YCl3 and characterized by powder X-ray and neutron diffraction (PXD, PND), differential scanning calorimetry (DSC), and temperature programmed desorption (TPD). The crystal structure was refined in the space group Pa-3 (no.205) with lattice constant a = 10.8522(7) Å from 11B and D (2H) substituted samples using PND. This is the first structural investigation by PND of a doubly labeled transition metal borohydride, and it has led to more pecise information regarding bond-lenghts, geometries, atomic arrangements etc. than previously known. The structure was found to contain Y3+ cations in a highly distorted octahedral environment formed by six [BD4]- complex anions. Heat treatment under 10 MPa of deuterium at 475 K led to a phase transformation from the primitive cubic room-temperature phase to a face-centered cubic high-temperature phase with space group Fm-3c (no.226) and lattice constant a = 11.0086(1) Å. This high-temperature phase shows an ideal and undistorted octahedral coordination around the central Y3+ cation. In-situ synchrotron radiation powder X-ray diffraction experiments (SR-PXD) show the presence of an intermediate phase during the thermal decomposition of Y(BH4)3 with presumably orthorhombic symmetry, and lattice constants a = 12.170(14) Å, b = 7.670(5) Å, and c = 7.478 (6) Å, in a narrow temperature region between 473 and 520 K. References 1. C. Frommen, N. Aliouane, S. Deledda, J.E. Fonneløp, H. Grove, K. Lieutenant,

I. Llamas-Jansa, S. Sartori, M.H. Sørby, B.C. Hauback, Journal of Alloys and Compounds, doi:10.1016/j.jallcom.2010.02.180

2. T. Sato, K. Miwa, Y. Nakamori, K. Ohoyama, H.W. Li, T. Noritake, M. Aoki, S.I. Towata, S.I. Orimo, Phys. Rev. B. 77 (2008) 104114.

3. Y.G. Yan, H.W. Li, T. Sato, N. Umeda, K. Miwa, S. Towata, S. Orimo, Int. J. Hydrog. Energ. 34 (2009) 5732-5736.

4. T. Jaron, W. Grochala, Dalton Transactions. 39(1) (2010) 160-166.

269

Specific Heat Capacity of LiNH2

B. Paik, M. Tsubota, T. Ichikawa and Y. Kojima IAMR, Hiroshima University, Higashi Hiroshima, Japan

Email: tichi@hiroshima-u.ac.jp

LiNH2 –LiH is considered as a model system one of the most promising hydrogen storage material among the light metal amides since a few important advantages with this system, viz., reversibility of reaction, high storage capacity etc, have been established [1,2]. In order to build up a practical on-board hydrogen storage medium by Li-amide we need to study its thermal properties; as the Hydrogen hydrogen charging/discharging in this system is believed to follow a sorption mechanism triggered by the thermal activation. In the present work we report the study of the thermal properties of tetragonal lithium amide single crystal (tetragonal I-4 phase [3]) by observing the variation of the specific heat capacity (Cp) within a temperature range 400 mK-300 K. The single crystal of LiNH2 was prepared by melting LiNH2 powder. The specific heat capacity was measured by using a commercial Physical Properties Measurement System (PPMS, Quantum Design) based on the relaxation method. From the low temperature specific heat capacity we plot Cp/T vs. T2 and estimated γ=0.013 mJ/K2.mole and β=0.038 mJ/K4.mole where γ and β have their usual meaning in the Debye equation Cp=γT+βT3 (ref Kittle?) . A very low γ value suggests indicates that the ionic LiNH2 crystal does not have significant electronic contribution in the specific heat capacity. As a consequence we may conclude that there is almost no free electrons to carry the thermal energy in the form of kinetic energy in LiNH2 crystal. A low free electron density, as calculated in between the space of Li and NH2 ions in LiNH2 [4], may explain our observation. From the phonon contribution of specific heat (β), we directly estimated Debye temperature (θD) to be 588 K. This is relatively high value in comparison to the most of the metalsionic alkaline halides with Debye temperature typically below room 400 K (except LiF and LiF with Debye tempratures around 470 K and 700 K, respectivelytemperature) [4]. In addition to the collective mode of vibration, characterised by the θD, an independent mode of vibration has also been observed from the Cp/ T3 vs. T graph leading to an Einstein Temperature (θE ) to be 138 K. We propose that the origin of this Einstein oscillation may be the rattling motion of Li ion in a square-type potential well. The independent vibration of the Li ion in the LiNH2 may be able to explain the low mobility of Li ion in this amide [5]. Partial financial support from NEDO HydroStar, Japan is acknowledged for the present study. References 1. P. Chen, Z. T. Xiong, J. Z. Luo, J. Y. Lin, K. L. Tan, Nature, 420, (2002), 302-304. 2. W.I.F. David, M. O. Jones, D. H. Gregory, C. M. Jewell, S. R. Johnson, A. Walton, P. P. Edwards, J.Americal Chemical Society, 129, (2007), 1594-1601. 3. M.H. Sørby, Y. Nakamura, H. W. Brinks, T. Ichikawa, S. Hino, H. Fujii, B. C. Hauback, J.Alloys and Compounds, 428, (2007), 297-301. 4. A. V. Sharko, A. A. Botaki, Debye temperature variations in alkaline-halide single crystals as a function of their chemical compositions, Russian Physical Society, 14, (1971), 765-770K. Miwa, N. Ohba, S-I. Towata, Y. Nakamori, S-I. Orimo, Physical Review B, 71, (2005), 195109.

270

Hydrogen Migration and Its Influence on Micropore Formation in Cast Mg Alloys

Y.H. Cho and A.K. Dahle

National Hydrogen Materials Alliance (NHMA), Materials Engineering, The University of Queensland, Brisbane, Qld 4072, Australia

Email: y.cho@uq.edu.au The catalytic effect of intermetallics in cast Mg alloyed with Ni, Cu and Al is investigated. The hydrogen desorption rates of the alloys are quantitatively analysed by fitting to the relevant kinetic equations in order to determine the rate-limiting step for the overall kinetics. Despite very similar eutectic networks of Mg-Mg2Ni, Mg-Mg2Cu and Mg-Mg17Al12 in the alloys, the structure and characteristics of the intermetallics plays a role in catalyzing desorption kinetics. In binary Mg-Ni, Mg2Ni that has a high solubility of hydrogen in its interstices and is present as a metastable hydride, Mg2NiH0.3, upon dehydrogenation and facilitates the nucleation of dehydrided Mg. Moreover eutectic Mg-Mg2Ni with an interlamellar spacing of a few hundred nanometres provides a large interface area where hydrogen atoms can preferentially diffuse rapidly. Therefore, the desorption kinetics of Mg-Ni alloys are more likely to be controlled by the diffusion of hydrogen through the thickening Mg/MgH2 interface. On the other hand, the dehydrogenation behaviour of both Mg-Cu and Mg-Al alloys is rather governed by the nucleation of dehydrided Mg as well as its two dimensional growth. This indicates that the catalytic effect of Mg2Cu and Mg17Al12 in nucleating Mg from MgH2 is less effective than that of Mg2Ni. It is suggested that the nature of the intermetallic compunds reactivity with hydrogen as well as the structure and morphology controls the hydrogen migration in cast Mg alloys. Micropore formation and its role and influence on the hydrogen migration behaviour, with particular emphasis on the micropore nucleation and its distribution in each system is further discussed.

271

Investigation of Low Temperature Fast Reacting Metalhydrides and Modeling of Metalhydride Reactor

Cheklina A.I., Fateev G.A.*, Germanovich A.P., Silenkov M.A.

A.V. Luikov Heat and Mass Transfer Institute National Academy of Sciences of Belarus 15 P.Brovka str., Minsk 220072 Belarus

Reaction and equilibrium of low temperature fast reacting hydrides of intermetallic alloys kind of AB5 and AB2 on base of lanthanum and zirconium in hydrogen atmosphere are investigated. Equilibrium properties are presented in analytical forms using Van-Hoff and de Bur equations validated for many phases systems. It is shown that for La alloys family of La1-XCeXNi5-YAlY (AB5) variation of their content from (X = 0, Y = 1), to (X = 1, Y = 0) increases equilibrium pressure up to 3-4 orders of magnitude, while for Zr0,9Ti0,1Cr1-

YFe1+Y (AB2) alloys family increases it up to one order at Y varying from 0 to 0.4. Analytical expression derived on base of heat transfer complicated by phase transition Stefan’s problem and describing charging-discharging dynamics of metal hydride reactor at given pressure is presented. The solution is confirmed by experimental results of hydrogen reactor study at heat carrier temperatures varying in range of 20 – 90 °C and pressures in range of 5 – 20 atm. Modeling of pair metal hydride reactors, realizing heat conversion cycle, is fulfilled, using the mathematical solution. Optimization of heat energy output at the given thermal resources of the source and sink of heat and the required temperature of recovered heat source is demonstrated through the choice of the proper metal hydride pair inside of the investigated range of intermetallic alloy compositions.

272

A Thermodynamic and Kinetic Study of the Reaction of H2 with Pseudo-

binary Mg6(Pd

xNi

1-x) at the Ni Solubility Limit.

J. F. Fernandez1, F. Cuevas

2, M. Ponthieu

1, J. R. Ares

1, F. Leardini

1, J. Bodega

1, M.

Latroche2 and C. Sánchez

1.

1 Dpto. Física de Materiales, Facultad de Ciencias, Universidad Autónoma de Madrid, 28049, Madrid, Spain

2CMTR/ICMPE/CNRS UMR 7182 , 2-8 rue Henri Dunant, 94320 Thiais Cedex, France

Email: josefrancisco.fernandez@uam.es Pseudo-binary Mg

6(Pd

xNi

1-x) intermetallic compounds are interesting materials for

hydrogen storage due to their high hydrogen uptake (> 4 wt%) [1-3]. These compounds have the same crystal structure that the binary Mg

6Pd compound. The solubility limit at

673 K attains 9 at.% Ni, i.e. more than four times the value previously reported. Theoretical calculations support a large extension of the binary Mg

6Pd phase into a ternary

region at 300 K. Vibrational and configurational entropic effects are responsible for such temperature stability of the pseudo-binaries. Previous results show that reaction of H

2 with the pseudo-binary Mg

6Pd

0.5Ni

0.5 compound

leads to its disproportionation into MgH2, Mg

2NiH

4 and Mg

5Pd

2 products. The enthalpy

and entropy changes for the hydrogenation reaction are, -63.3 kJ/molH2

and -114.4 J/K molH

2, respectively. Both values are larger than those of pure MgH

2, resulting in a small

destabilisation of the compound compared to MgH2.

In this communication we will present new results about the hydrogenation properties of the pseudo-binary at the Ni solubility limit. The samples have been prepared by induction melting. Thermodynamic properties of the hydride formation and decomposition have been obtained from PCT curves and High H

2-pressure DSC. The kinetics of the

decomposition process has been studied by in-situ optical microscopy and thermal desorption spectroscopy. Results about the disproportionation process will be presented. Acknowledgements. The authors thank the Spanish Minister of Education and Science, MEC, for financial support under contract Nº. MAT2008-06547-C02-01. We thank to Dr. P. Adeva (National Centre for Metallurgical Research, CENIM, CSIC) for kind help on preparation of the mother alloy. References 1. F. Cuevas, J.F. Fernández, J.R. Ares, F. Leardini, M. Latroche, J. Solid State Chem. 182, 2890–2896 (2009). 2. J.F. Fernández, J.R. Ares, F. Cuevas, J. Bodega, F. Leardini, C. Sánchez, Intermetallics 18, 233–241 (2010). 3. J.F. Fernández, F. Cuevas, F. Leardini, J. Bodega, J. R. Ares, G. Garces, P. Pérez, C. Sánchez, J. Alloys Comp., doi:10.1016/j.jallcom.2009.10.090.

200 μm

273

High-Pressure DSC Study of the Hydrogen Sorption Behaviour of MgH2 and MgH2/Graphite Processed by Reactive Mechanical Alloying

G. Urretavizcaya, V. Fuster and F.J. Castro

Centro Atómico Bariloche (CNEA, CONICET) and Instituto Balseiro (UNCuyo), S. C. de Bariloche, Río Negro, Argentina

Email: urreta@cab.cnea.gov.ar The study of the hydrogen absorption and desorption properties of Mg and Mg/graphite materials by high-pressure DSC is reported. The materials were sinthesized by reactive mechanical alloying magnesium and graphite under hydrogen atmosphere [1]. Kinetics of MgH2 with graphite is better than the absorption and desorption rates of MgH2 synthesized without additive. Additionally, the catalytic effect of graphite is more effective when the additive is uniformly distributed in the bulk, i.e., when graphite is incorporated from the beginning of the hydride synthesis by RMA. The high temperatures required during HPDSC runs favours sintering of magnesium and hence, a slight capacity decrease with cycling can be partially attributed to this effect. Additionally, some protection against oxidation is observed in graphite-containing samples. This protection is more effective when graphite is mainly located on the surface of the particles. References 1. V. Fuster, G. Urretavizcaya, F.J. Castro, J. Alloys Compd. 481 (2009) 673-680.

274

Hydrogen Sorption Properties of MgH2/10 wt.% Graphite

V. Fuster, F.J. Castro and G. Urretavizcaya Centro Atómico Bariloche (CNEA, CONICET) and Instituto Balseiro (UNCuyo),

S. C. de Bariloche, Río Negro, Argentina Email: fcastro@cab.cnea.gov.ar

Hydrogen storage in magnesium based systems is largely studied due to the high hydrogen capacity and low cost of this metal. Nevertheless, the drawbacks related to the slow sorption kinetics and high thermodynamic stability of the hydride still give rise to many efforts in order to overcome these issues. Among others, one possibility to improve the hydrogen sorption properties of Mg is the addition of graphite. In this paper, MgH2/10 wt.% graphite prepared by reactive mechanical alloying under H2 atmosphere [1] is studied. The evolution of the desorption behaviour of samples extracted at different milling times, i.e. with different hydrogen content, is analyzed by DSC. The microstructure is studied by optical and electronic microscopy. The sorption properties for different amounts of hydride in the sample are studied by high pressure calorimetry (HPDSC) and conventional isothermal volumetric measurements. The relationship between the hydrogen desorption rate and the hydrogen content in the sample is associated with the reaction mechanism. References 1. V. Fuster, G. Urretavizcaya, F.J. Castro, J. Alloys Compd. 481 (2009) 673-680.

275

Mechanical Properties of Palladium Hydride Using In Situ Tensile Tests and Isotopic Effect

M. Segard, S. Thiébaut, A. Fabre CEA, Valduc, 21120 Is sur Tille, France

F. Montheillet - Ecole des Mines, CNRS UMR 5146, 42000 Saint-Etienne, France Palladium and its alloys are used in tritium facilities for their interesting storage properties but the reliability of such systems requires the understanding of the aging processes. The major factor comes from the radioactive decay of tritium that produces nanometric bubbles of 3He within the lattice. In order to predict such a phenomenon and its consequences on the tritide matrix, a mechanical model of bubble growth has been developed within the frame of continuum mechanics [1]. It provides information about the bubbles size, their internal pressure, and the material swelling, all as a function of time. This model gives consistent results, but some input parameters are still arbitrarily adjusted, like mechanical properties of palladium tritide. Aiming at measuring the mechanical properties of metal-gas systems, a tensile test machine was developed to perform in situ tests under gaseous environment. The first experiments consisted in measurements of palladium hydride and deuteride mechanical properties, respectively under hydrogen and deuterium pressure of 5 bar, thereby ensuring that material is in β phase. Samples were wires 3 cm long and 0.5 mm in diameter. They were annealed and activated prior to hydrogen loading and testing. Strain rates varied in the range 10-6 – 10-2 s-1. No dependence on strain rate was highlighted in the tests: if any, it was smaller than the uncertainty of the measurements. Tensile test experiments on palladium hydride and deuteride produced drastically different results from those obtained with annealed pure palladium. Ductility was found to drop by 95% whereas a significant increase of yield strength and of ultimate tensile strength was measured. A significant isotopic effect was noticed between palladium hydride and deuteride. Mechanical behaviours of these two compounds are quite correctly fitted with the exponential Voce law:

( ) ( )αεσσσσ −−−= ∞∞ expe where σe is the yield strength and σ∞ the stress reached when strain tends to infinity. An extrapolation of these results to palladium tritide is proposed, assuming that the isotopic effect arises from different strain-hardening occurring during the hydride and deuteride formation. References 1. F. Montheillet, D. Delaplanche, A. Fabre, E. Munier, S. Thiébaut – Mat. Sci. Eng. A, No.494, 407–415 (2008).

276

Hydrogen Absorption and Desorption of Storage Tanks Based on Sodium Alanate Material: Simulations and Experimental Work

G. A. Lozanoa,*, Ch. Na Ranongb, J. M. Bellosta von Colbea, R. Bormanna, J. Hapkeb, G.

Fiegb, M. Dornheima a Institute of Materials Research, Materials Technology, GKSS-Forschungszentrum Geesthacht GmbH,

Geesthacht, Germany b Institute of Process and Plant Engineering, Hamburg University of Technology, Hamburg, Germany

*Corresponding author, Email: gustavo.lozano@gkss.de Metal hydride storage tanks require active material in kg scale for practical applications, while basic research and first developments of metal hydride reacting systems are performed with amounts of hydride material in the range of mg only. There are considerable differences with respect to the absorption and desorption behaviour between small and large beds of hydride material [1]. In order to exploit the properties of metal hydrides in suitable hydrogen storage systems, a detailed understanding of their performance in larger powder beds is essential. During hydrogen sorption not only a chemical reaction takes place, but also coupled hydrogen transport and heat transfer. As it is experimentally and theoretically shown in this work, in practical systems heat transfer is very likely the most decisive sorption limiting sub-process in practical systems. Transient and spatial temperature and concentration profiles are developed during the hydrogen storage processes. Advanced tools are necessary for the evaluation and prediction of the sorption behaviour of metal hydride reactors. This work presents the development and results of numerical simulations and experimental measurements of sodium alanate tanks. The final objective was to obtain a reliable and flexible numerical simulation tool, enabling design, optimization and construction of suitable high density hydrogen storage systems based on sodium alanate. Empirical kinetic models were developed for both hydrogen absorption and desorption of sodium alanate material. They are based on kinetic data obtained by volumetric titration measurements comprising a broad range of practical operating conditions (absorption from 10 bar to 110 bar and from 100 °C to 180 °C, desorption from 0 bar to 35 bar and from 100 °C to 190 °C). A hydrogen tank station was designed, constructed and successfully put into operation. Sorption behaviour and temperature profiles at different positions of the tanks were measured under a variety of measurement conditions, demonstrating the scalability of the material preparation and the hydrogen storage in the material. The experiments are the basis for the validation of the numerical simulations. In a final step, the hydrogen sorption of sodium alanate based tanks was numerically simulated on the basis of three sub-processes: hydrogen transport, intrinsic kinetics and heat transfer. The developed and validated numerical simulation tool and the approach implemented in this work for sodium alanate tanks proved to be suitable and can be extended to other reacting material systems and other reactor configurations for hydrogen storage. References 1. Lozano GA, Eigen N, Keller C, Dornheim M, Bormann R. Effects of heat transfer on the sorption kinetics of complex hydride reacting systems. Int. J. Hydrogen Energy 2009;34:1896-1903.

277

278

New Ternary Mg Alloys with a Large Cubic Cell for Solid Hydrogen Storage

S. Couillauda, S. Linsingerb, E. Gaudina, B. Chevaliera, W. Hermesb, M. Eulb

R. Pöttgenb, J-L. Bobeta a CNRS, Université de Bordeaux, ICMCB, 87 Avenue du Docteur Albert Schweitzer, 33608 Pessac Cedex,

France b Institut für Anorganische und Analytische Chemie and NRW Graduate School of Chemistry, Universität

Münster, Corrensstrasse 30, D-48149 Münster, Germany Email: couillaud@icmcb-bordeaux.cnrs.fr

Since many years, magnesium is considered as a good material for hydrogen storage. In order to decrease the hydrogen sorption temperature and pressure conditions, binary and ternary Mg alloys are investigated. In this way, new compounds with RE4TMMg1-xAlx stoichiometry (RE = rare earth,TM = transition metal) have been highlighted. The solid solution (i.e. partial replacement of magnesium by aluminium) can be interesting to modulate the thermodynamic properties of hydrogen sorption.All these compounds crystallize with a cubic structure (space group F-43m) [1] with lattice parameter between 13.52 and 13.73 Å (figure 1). The existence of a solid solution RE4NiMg1-xAlx was confirmed by a linear evolution between the lattice parameter and the Al content. A maximum solubility of x > 0.9 for Gd4NiMg1-xAlx and x < 0.5 for Y4NiMg1- xAlx was found. Hydrogen sorption have been tested for each compound and a good weight capacity has been obtained at room temperature with 10 bars of H2 (figure 2 : Y4NiMg absorbed 2.5 %wt in 50 min) but no desorption could be observed. Moreover, a important oxidation effect has been revealed. The passivation at room temperature, induces a kinectic modification and a decrease of the weight capacity. The hydride stability can be explained by a high hydride formation enthalpy (i.e -346 kJ/molH2) measured by DSC under H2 . Mg replacement by Al, do not allow to obtain a reversible sorption and both the kinetic and the weight capacity decrease with Al content increase.

Figure 2 : Y4NiMg kinetic, 10 bars, 20°C Figure 1: RE4NiMg structure

References 1. Tuncel. S, Rodewald. U.Ch, Chevalier. B, Pöttgen. R; Zeitschrift fur Naturforschung -

Section B Journal of Chemical Sciences 62 (5) (2007), 642-646

Prediction of a New Compound in the Li-Mg-N-H Hydrogen Storage System

Feng Zhang, Yan Wang, and M. Y. Chou School of Physics, 837 State Street, Georgia Institute of Technology, Atlanta, GA 30332

Email: meiyin.chou@physics.gatech.edu

It has been experimentally shown that the hydrogen storage system LiH Mg NH

Li Mg NH H has improved thermodynamics compared with LiH LiNHLi NH H .

1-3 Part of the reason is that the replacement of Li+ with Mg2+ in Li2NH creates vacancies in the cation sites to sterically and electrostatically guide the orientation of the N-H bonds, resulting in a more stable mixed imide Li2Mg(NH)2 than pure Li2NH. However, in Li2Mg(NH)2 there are more vacancies than necessary to accommodate all the N-H bonds. Here, we report through first-principles calculations a new compound Li6Mg(NH)4 that has just enough vacancies to orient the N-H bonds. Li6Mg(NH)4 is stable with respect to phase separation into combinations of Li2NH, Li2Mg(NH)2 and a recently proposed structure for Li4Mg(NH)3

4 at 0K. The reaction LiH Mg NH

LiNH Li Mg NH H can be completed via two steps and releases 6.0 wt% H, at still significantly lower temperatures than that for the cycling between LiNH2 and Li2NH. Since further reduction of the Mg content will not provide sufficient vacant cation sites, Li6Mg(NH)4 also represents the lower limit of the Mg concentration, and thus the upper limit for H wt% of hydrogen storage systems involving stable Li2(x-1)Mg(NH)x. References 1. P. Chen, Z. Xiong, J. Luo, J. Lin, K. L. Tan, Nature, 420, (2002), 302-304. 2. W. Luo, J. Alloys and Compounds, 381, (2004), 284-287. 3. H. Y. Leng, T. Ichikawa, S. Hino, N. Hanada, S. Isobe, H. Fujii, J. Phys. Chem. B, 108, (2004), 8753-8765. 4. K. J. Michel, A. R. Akbarzadeh, V. Ozolins, J. Phys. Chem. C, 113, (2009), 14551-14558.

279

Theoretical Study of the AlH3 Vacancy in the α and γ Phases of NaAlH4 Feng Zhang, Yan Wang, and M. Y. Chou

School of Physics, 837 State Street, Georgia Institute of Technology, Atlanta, GA 30332 Email: meiyin.chou@physics.gatech.edu

It has been suggested that the diffusion of AlH3 vacancies plays an essential role in the decomposition of NaAlH4, a prototypical material for hydrogen storage. 1 Here, we study from first-principles the electronic and vibrational properties of the AlH3 vacancy in two phases of NaAlH4: the conventional α phase and the newly-reported γ phase2. When an AlH3 unit is removed from an AlH4

- anion, the remaining H readily recombines with another neighboring AlH4

- anion to form an AlH52- unit that is slightly deformed from the

D3h symmetry for the α phase; while for the γ phase, the remaining H atom is likely to be trapped near the original location of the AlH4

- anion that is removed and needs an activation energy of 0.07 eV to diffuse to a neighboring AlH4

- anion and form an AlH52-

unit. The formation energy for the AlH3 vacancy is comparable for α and γ phases. Possible diffusion paths of the AlH3 vacancy in bulk NaAlH4 are also identified for both phases. Two gaps exist in the phonon spectrum of pure NaAlH4, separating the Al-H stretching, Al-H bending, and the librational modes. The AlH3 vacancy induces several phonon modes within these two gaps. We will also compare these vacancy modes for α and γ phases. References 1. H. Gunaydin, K. N. Houk, V. Ozolins, Proc. Natl. Acad. Sci. USA, 105, (2008) 3673-3677. 2. B. C. Wood, N. Marzari, Phys. Rev. Lett., 103, (2009), 185901.

280

Dehydrogenation Behaviour of LiBH4 with the Addition of Pre-Milled Mg-Ni-H Mixtures

W.Yang, D.M. Grant, G.S Walker

Hydrogen Storage Group, Department of Mechanical, Materials, Manufacturing Engineering, University of Nottingham, Nottingham, NG7 2RD, UK

Email: david.grant@nottingham.ac.uk Of the complex hydrides, Lithium Borohydride is often investigated in the search for a high capacity hydrogen storage material with researchers attempting to lower its high dehydrogenation temperature and improve its cycling conditions. Different molar ratios of MgH2+xNi (x=0.5, 1 or 2) were mechanically milled by using high energy SPEX mill for 10 or 20 hours to form Mg2NiH4 prior to mixing with LiBH4 for up to 3h. This is a different approach to that of Li et al who combined the ternary boride with LiH and MgH2 [1]. The 10h-milled (2MgH2+Ni) formed crystalline Mg2NiH4 while 20 h milling was amorphous and the crystalline Mg2NiH4was found to be more effective at lowering the dehydrogenation temperature of the mixture. Specific investigations were undertaken into the dehydrogenation behaviour of (4LiBH4+5Mg2NiH4) mixtures. The endotherm for the LiBH4 orthorhombic-hexagonal phase transition at 120oC was used to measure the amount of LiBH4 remaining after each thermal cycle. Therefore by cycling to different temperatures an indication of the decomposition temperature could be made. Under flowing argon LiBH4 was observed to decompose below its melting point with the majority of hydrogen being released below 290oC, which is 180oC lower than compositions of (2LiBH4+MgH2). TGA analysis indicated ca. 4.5 wt.% hydrogen released from the mixture in the temperature range from 200 to 300oC. The results under both Ar and H2 indicate a destabilisation reaction with the mixture forming the ternary boride, MgNi2.5B2, after decomposing to 585oC. Under 1 bar flowing hydrogen the XRD results indicated the following reaction: 4LiBH4+5Mg2NiH4→2MgNi2.5B2+8Mg+4LiH+16H2 with partial Mg rehydrogenation during cooling to RT. This is because the plateau pressure is beneath 1 bar below 280oC as shown with a DSC exotherm and XRD. The dehydrogenation products formed under flowing Ar formed MgLi α and β alloys. With this composition we would expect only β MgLi [2,3] but there was some loss of Li to LiOH due to contamination resulted in the MgLi being in the two phase α + β region. Other cycling experiments involved dehydrogenation conditions of 350°C under 1 bar flowing hydrogen for complete dehydrogenation and hydrogenation conditions of 350°C at 100 bar for 12 h in a high pressure DSC. The amount of LiBH4 reformed after one cycle was found to be ca. 70%. References 1. Li, W., J.J. Vajo, R.W. Cumberland, P. Liu, S.-J. Hwang, C. Kim, and R.C. Bowman, J Phys Chem Letters, 1, (2009), 69-72. 2.Yu, X.B., D.M. Grant, and G.S. Walker, Chem Commum, 37, (2006), 3906-3908. 3.Walker, G.S., D.M. Grant, T.C. Price, X. Yu, and V. Legrand, J. Power Sources, 194(2), (2009), 1128-1134.

281

Mathematical Model of Metal-Hydride Phase Change

S.Manicheva, I.Chernov, I.Gabis, and A. Voit Karelian State Pedagogical Academy, Petrozavodsk, Russia

Inst. Appl. Math. Res., Karelian Res. Centre, RAS, Petrozavodsk, Russia Phys. Dep. of St-Petersburg State Univ., St-Petersburg, Russia

Email: smanicheva@mail.ru We present a mathematical model for the kinetics of hydriding of metal powders. This model was constructed in [1] for isothermal hydriding under constant pressure and tested on experimental data. Now we develop the model to apply it to varying pressure and non-isothermal hydriding and also to dehydriding [2]. The single powder particle is considered. Its shape is approximated by one of the symmetric ones: sphere, long thin cylinder (wire), or flat thin plate. Our approach is to consider a few concurrent processes instead of choosing a single limiting one. The model equations are derived from the mass conservation law. We consider the case of the “shrinking core” morphology, i.e. formation of the hydride skin on the surface of the particle with subsequent growth of this skin. These stages are mathematically described in different ways. We consider four successive stages of hydriding: nucleation, skin development, skin growth, and final saturation. Each stage is described by its own system of equations. The nucleation stage is considered in order to explain the special S-shape of the experimental curves [3]. The skin formation is described under assumption that the nuclei have the special symmetrical shape. This stage is described by ordinary differential equations; they have simple analytical solution in the isothermal case. The skin growth is described by the diffusion boundary-value problem with a free boundary. We use the model to approximate the series of experimental curves (for successive cycles of hydriding and dehydriding of yttrium) and evaluate the kinetic parameters. Also we show how one can take time-dependent pressure and heat releasing effects into account in the model. In [4] we studied how shape of the powder particles influence the kinetics. To do that we fitted the same experimental curves (for uranium and magnesium) by model ones for different model shapes: sphere, long cylinder, and flat plate. The approximation was comparable for similar kinetic parameters; this shows that the mensioned influence is not significant. We do the same with yttrium experimental data and obtain the same results. We also consider the general three-dimensional model of the phaze change and present arguments that for regular shapes it can be rewritten in the almost shape-independent form, and thus that the shape is not crucial in the general case also. The work has been partially financially supported by the grant 09-03-00947-а “Theoretical and experimental study of kinetics and mechanisms of hydrogen desorption from metal hydrides” of the Russian Foundation for Basic Research. References 1. I. Chernov, I. Gabis, J. Bloch, Int. J. Hydrogen Energy, 33, (2008), 5589-5595. 2. Yu. Zaika, N. Rodchenkova, Applied Math. Modelling, 35(10), (2009), 3776-3791. 3. J. Bloch, J. Alloys and Compounds,361, (2003), 130-137. 4. I. Chernov, I. Gabis, A. Voit, J. Bloch, Int. J. Hydrogen Energy, 35, (2010), 253-258.

282

Synthesis of Amorphous Mg(BH4)2 from MgB2 and H2 at Room Temperature

C. Pistidda,*a S. Garroni,c1 F. Dolci,b2 A. Khandelwal,d E. Gil Bardaji,b3 P. Nolis,e S.

Suriñach,c2 M. Dolores Baró,c3 W. Lohstroh,b4G. Barkhordarian,a2 M. Fichtnerb5and M. Dornheima3

a Institute of Materials Research, Materials Technology, GKSS-Forschungszentrum Geesthacht GmbH, Max-Planck-Straße 1, D-21502 Geesthacht, Germany

bInstitute of Nanotechnology, Forschungszentrum Karlsruhe GmbH Postfach 3640, 76021 Karlsruhe, Germany

c Departament de Física, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain d Dipartimento di Ingegneria Meccanica, Settore Materiali and CNISM,

Università di Padova, Via Marzolo 9, 35131 Padova, Italy e Servei de Ressonància Magnètica Nuclear (SeRMN), Universitat Autònoma de Barcelona,08193 Bellaterra,

Spain Email: claudio.pistidda@gkss.de

Because of their large gravimetric and volumetric hydrogen storage density, borohydrides are considered as potential hydrogen storage materials for mobile applications. However, although LiBH4, NaBH4 and KBH4 are readily available and store large amount of H2, the reaction enthalpy for H2 desorption is too high compared to the desired value of ~ 20 - 30 kJmol-1H2 required for having 1 bar H2 equilibrium pressure at room temperature. By means of empirical evaluations Kuznetsov et al., Sarner and Nakamori et al. [1-3], attributed to magnesium borohydride (Mg(BH4)2) a very attractive decomposition enthalpy value of about 40 kJ/mol-1 H2 which was experimentically confirmed by Matsunaga et al. and Chlopek et al. [4, 5] and which is only slightly above the desired value. This feature, together with a gravimetric hydrogen capacity equal to 14.9 wt.%, has made Mg(BH4)2 one of the very promising materials for hydrogen storage applications. In this work unsolvated amorphous magnesium borohydride is surprisingly obtained for the first time by gas phase loading at room temperature using reactive ball milling of commercial MgB2 in 100 bar hydrogen atmosphere. References 1. V. A. Kuznetsov, T. N. Dymova, Evaluation of the standard enthalpies and isobaric potentials of the formation of certain complex hydrides, Russian Chemical Bulletin, 20, (1971). 2. S. F. Sarner, Propellant chemistry, New York, (1966). 3. Y. Nakamori, K. Miwa, A. Ninomiya, H. W. Li, N. Ohba, S. I. Towata, A. Zuttel, S. I. Orimo, Physical Review B 74, (2006) 9 4. K. Chlopek, C. Frommen, A. Leon, O. Zabara, M. Fichtner, Journal of Materials Chemistry, 17, (2007) 3496-3503. 5. T. Matsunaga, F. Buchter, P. Mauron, A. Bielman, Y. Nakamori, S. Orimo, N. Ohba, K. Miwa, S. Towata, A. Zuttel, J. Alloys Compdounds, 459, (2008), 583-588.

283

Study of Hydride Properties for Hydride Heat Pumps Development

Yu. Shanin and A.Solovey The Federal State Unitarian Enterprise «Scientific Research Institute the Scientific Industrial Association

«Luch», Podolsk, Russia E-mail: syi@luch.podolsk.ru

To select couple of intermetallic compounds is the point of hydride heat pumps (MHHP) development. We use the following technique: 1. The list of the materials allowing to realize a MHHP cycle was defined from published data for chosen range of working pressures and temperatures. 2. A technique [1] was used to restrict candidate pairs. 3. For these hydrides sorption/desorption isotherms were experimentally measured. 4. In pressure-concentration coordinates, the MHHP operating cycle was plotted predicting active hydrogen weight and a coefficient of performance (COP) was determined. The question of hydrides weights ratio in a MHHP was simultaneously solved. 5. Selected intermetallic compounds were melted in quantities 50 … 100 g in process used for melting of alloys for real MHHP. 6. Experimental measurement of chosen hydrides properties and testing of their efficiency was made to determine reached temperatures in imitated boundary conditions of MHHP operation, measurement of heat effects and quantity of acting hydrogen. The work included complex investigations of: 1) kinetics of hydride-hydrogen reactions, 2) cyclic interaction of hydride powders with hydrogen, 3) thermal conductivity of hydride compositions. Brief description of installations, measuring cell designs, experimental techniques and obtained results are presented. Kinetics of metals-hydrogen interaction is the major characteristic influencing on COP of MHHP. Experiments on investigation of powder of LaNi5 interaction with H2, in conditions near to MHHP operation conditions were carried out. Experiments on cyclic interaction were made for hydrides of LaNi5 and ZrCrFe1.2. After more than 10000 cycles, the following effects were observed: 1) increase of equilibrium pressure, 2) deterioration of sorption kinetics, 3) loss of hydrogen capacity. Hydrogen capacity of LaNi5 decreased from 90 to 60% of initial value after increase in number of cycles from 2000 to 10740. The amount of absorbed by ZrCrFe1.2 hydrogen decreased by 50 and 65% after 6250 and 10740 cycles, respectively. Thermal conductivity of various hydride beds (including beds with metal fillers) was measured. Effective thermal conductivity of powders 50…200 microns was (1.25±0.05) W/(m·K). Embedding of corrugated aluminum sheet in a powder bed is capable to increase 3…5 times the effective thermal conductivity of a bed. The results of the work were the basis for: 1) mathematical modelling of MHHP operation [2], 2) further selection of hydride couples and 3) development of real MHHP for various operation conditions. References 1. Yu. Sanin, Int. J.for Alternative Energy and Ecology, No. 3, (2002), 50-53 (in Russian). 2. E. Fedorov, Yu. Sanin, L.Izhvanov, Int. J. Hydrogen Energy, v. 24, (1999), 1027-1032.

284

Li-Al-Borohydride, a New Double-Cation Borohydride I. Lindemanna, R. Domènech Ferrera, Y. Filinchukb, R. Černýc, H. Hagemannc, L. Schultza

and O. Gutfleischa aIFW Dresden, Institute for Metallic Materials, P.O. Box 270016, 01171 Dresden, Germany

bSwiss-Norwegian Beam Lines at ESRF, BP-220, 38043 Grenoble, France cDepartment of Physical Chemistry and Crystallography, University of Geneva, 1211 Geneva, Switzerland

Email: I.Lindemann@ifw-dresden.de Complex hydrides are under consideration for on-board hydrogen storage due to their high hydrogen density. However, up to now conventional borohydrides are either too stable or unstable for applications as in PEM fuel cells. Recently, double-cation borohydride systems have attracted great interest. It was found that the desorption temperature of the borohydrides decreases with increasing electronegativity of the cation.1 Consequentely, it is possible to tailor a feasible on-board hydrogen storage material by the combination of appropriate cations. The stability was found to be intermediate between the single-cation borohydride systems. Li-Al-borohydride shows a desorption temperature suitable for applications (~70°C) combined with an high hydrogen density (17.2 wt.%). It was synthesised via high energy ball milling of AlCl3 and LiBH4. The structure of the compound was obtained from high-resolution synchrotron powder diffraction and shows a unique complex structure within the borohydrides. The material was characterized by means of in-situ-Raman spectroscopy, DSC (Differential Scanning Calorimetry), TG (Thermogravimetry) and thermal desorption measurements to study the decomposition pathway of the compound. The desorption of the new double-cation compound results in the formation of LiBH4 at ~70°C. The high mass loss of about 20% during decomposition points to the release of not only hydrogen but also diborane. Its release is the main problem to solve for the moment. References 1. Nakamori et al., J. Phys. Chem. Solids, 69, (2008), 2292–2296.

285

First-Principles Study of the Phonon Properties of GdFe2 measured utilizing Synchrotron Radiation via Nuclear Resonance

S. Saito 1, M. Katagiri 1, T. Mitsui 2, M. Seto 3, and H. Ogawa 4 1 National Institute for Materials Science, Tsukuba, Japan

2 Japan Atomic Energy Agency, Hyougo, Japan 3 Kyoto University, Osaka, Japan

4 National Institute of Advanced Industrial Science and Technology, Tsukuba, Japan E-mail:SAITO.Shigeki@nims.go.jp

The phonon modes in crystalline alloys and compounds are effective tools to detect structural and thermodynamic stability in the hydrogen-storage process. Recently, nuclear resonant scattering experiments using synchrotron radiation have provided very accurate phonon energy curves for materials scientists [1,2], while first-principles calculations have played an important role in determining the electronic and structural properties at the nanometer scale [3]. In order to clarify the hydrogen storage mechanism of an intermetallic hydride, we performed first principles calculations of phonons [4,5], in nanocrystalline GdFe2, and GdFe2H3 for the nuclear resonant scattering measurement using Spring-8 synchrotron radiation (SR), using the experimental setup shown in Fig. 1. The first principles potential surfaces with a supercell were calculated using the Vienna abinitio simulation program (VASP) [6]. Fig. 2 shows the phonon energy curve of c-GdFe2. The calculation results indicated that the modes around 30 meV include the vibrational amplitudes of Fe atoms in the main, similar to those at 24 meV. The modes at < 17 meV originate from Gd atoms, with slight contributions from Fe atoms. The presentation discusses the interactions between Gd-Fe crystalline atoms and interstitial hydrogens.

Fig. 1 the experimental setup Fig. 2 the phonon energy curve of c-GdFe2

References 1. M. Seto et al., Phys. Rev. Lett., 74, (1995), 3828-3831. 2. B. Fultz et al., Phys. Rev. Lett., 79, (1997), 937-940. 3. K. Mori et al., J. Alloys and Compd., 270, (1998), 35-41. 4. K. Parlinski et al., Phys. Rev. Lett., 78, (1997), 4063-4066. 5. S. Saito et al., Jpn J. Appl. Phys., 45, (2006), 4170-4175.

6. G. Kresse et al., Phys. Rev. B 59, (1999), 1758-1775.

286

LiF−MgB2 System for Reversible Hydrogen Storage

R. Gosalawit1, J. M. Bellosta von Colbe1, T. R. Jensen2, Y. Cerenius3, Christian M. Bonatto1, Maik Peschke1, M. Dornheim1

1Institute of Materials Research, Materials Technology, GKSS-Forschungszentrum Geesthacht GmbH, D-

21502 Geesthacht, Germany, Email:yui_gosalawit@yahoo.com 2Interdisciplinary Nanoscience Center (iNANO) and Department of Chemistry, University of Aarhus,

Langelandsgade 140, DK-800 Aarhus C, Denmark. 3MaXLAB, Lund University, S-22100 Lund, Sweden.

LiF−MgB2 composites are proposed for reversible hydrogen storage. With respect to pure LiBH4, a significantly kinetic destabilization regarding hydrogenation and dehydrogenation is accomplished. The measured reversible hydrogen capacity amounts to 6.4 wt.%. The kinetic properties are improved significantly during cycling. Clear indications for the formation of a hydridofluoride phase (LiBH4-yFy) due to the fluorine anions substitution for hydrogen anions in [BH4]- are observed by synchrotron XRD and ATR-FTIR. Hydrogenation and dehydrogenation mechanisms are described based on the fluorine substitution in LiBH4. References 1. N. Eigen, U. Boesenberg, J. Bellosta von Colbe, T. R. Jensen, Y. Cerenius, M. Dornheim, T. Klassen, R. Bormann, J. Alloys and Compounds, 447, (2009), 76-80.

287

On the Kinetic Inhibition of the Dehydrogenation of AlH3

Lars Ismer, Anderson Janotti and Chris G. Van de Walle Materials Department, University of California, Santa Barbara, CA 93106-5050, USA

Email: ismer@engineering.ucsb.edu Aluminum hydride (AlH3) is a promising material for storing hydrogen. Though thermodynamically unstable at room temperature, it does not decompose on a timescale of years [1]. However, at temperatures above 150 oC, AlH3 rapidly decomposes into Al and H2[2]. The metastable character at room temperature combined with a large hydrogen storage capacity have steered the focus of many research groups towards AlH3 as a viable hydrogen storage material. Recently, an electrochemical cycle has been designed to synthesize AlH3 [3] indicating that efficient large-scale generation of AlH3 is in sight. Still, accelerating the decomposition process of AlH3 at temperatures below 100 oC remains an important issue. In this context, understanding the kinetic effects that inhibit the decomposition of AlH3 at these temperatures is essential. Based on first-principles calculations we propose a microscopic mechanism for the dehydrogenation of AlH3: At dehydrogenation conditions nuclei of the Al phase begin to form within the hydride crystal. The growth of these Al nuclei would eventually drive the AlH3/Al transformation. However, this growth requires mass transport across the bulk, which is, as we will show, the rate-limiting part of the process. Our derived activation energy for this process is 1.5 eV, in excellent agreement with the experimental values [2]. The dehydrogenation flux accross the bulk is therefore practically inactive, explaining why AlH3 does not decompose at room temperature, although it is thermodynamically unstable. References

1. Graetz, J.; Reilly, J. J., Journal of Alloys and Compounds 424, (2006), 262. 2. Herley, P. J.; Christofferson, O. J. Phys Chem. 85, (1981), 1887. 3. Zidan, R. et al., Chem. Commun. (2009), 3717.

288

Investigation on the Nature of Active Species in the CeCl3-doped Sodium Alanate System

Xiu-Lin Fan, Li-Xin Chen∗, Xue-Zhang Xiao, Zhe Wu and Qi-Dong Wang

Department of Materials Science and Engineering, Zhejiang University, Hangzhou, P.R. China Email: lxchen@zju.edu.cn

Complex hydrides have recently received considerable attention as potential hydrogen storage materials since the pioneering studies of Bogdanović and Schwickardi demonstrated that the dehydriding of sodium alanate doped with selected titanium compounds could be kinetically enhanced and rendered reversible under moderate conditions. The understanding of the catalytic mechanism in the catalyzed NaAlH4 system has been a subject of great interest. This presentation provides an investigation on the nature of active species in the CeCl3-doped sodium alanate system.

CeCl3-doped NaAlH4 was directly synthesized in a hydrogenation process using NaH/Al with a few mole percent of CeCl3 under ball-milling. X-ray diffraction was utilized to unveil the nature of Ce during NaAlH4 synthesis process and succedent cycling. It is found that, CeCl3 is reduced in the ball-milling process, causing the formation of NaCl, however, no crystalline Ce-containing phases are detected. After dehydrogenation and succedent hydriding/dehydriding cycles, Al-Ce alloy with a structure of CeAl4 is observed. The catalytic enhancement arising upon doping the ball-milled CeAl4 alloy is impressive, which is quite similar to that achieved in the CeCl3-doped sodium alanate. Because the CeAl4 dopant doesn’t consume the effective hydrogen storage component, the CeAl4-doped NaAlH4 exhibits more hydrogen storage capacity. Besides, the hydrogen storage capacity as well as the reaction rate which remaines stable in CeCl3-doped NaAlH4 with an increasing number of cycles also behaves similarly in the CeAl4-doped NaAlH4. Moreover, CeCl3-doped NaAlH4 and CeAl4-doped NaAlH4 exhibit similar apparent activation energies estimated from Kissinger’s method, suggesting the reactions are all determined by the same rate-limiting step. These results clearly demonstrate that the in situ formed CeAl4 acts as active species to catalyze the reversible dehydriding/rehydriding of NaAlH4.

289

Elaboration and Characterization of Magnesium Substituted A5Ni19 and A2Ni7 (A=Pr, Nd, La) Hydrides Forming Alloys as Active Materials for

Negative Electrode in NiMH Battery

L.Lemorta, M.Latrochea, C.Georgesa, B.Knospb and P.Bernardb a ICMPE, CMTR, CNRS UMR 7182, Thiais, France b SAFT, Direction de la recherche, Bordeaux, France

Email: lemort@icmpe.cnrs.fr

Energy storage will be a major challenge in the future. Metal hydrides offer interesting possibilities as they allow storing energy either chemically or electrochemically. Ni-MH batteries are a promising technology for portable applications and hybrid electric vehicles (HEVs). They offer several advantages such as low toxicity, ability to withstand high charging and discharging currents and are safe. Their performances still need improvements in order to follow the market needs in terms of capacity and cycle-life.

Conventional Ni-MH batteries use mostly AB5 materials as negative electrode material (A= elements with strong affinity for hydrogen such as rare earths; B= elements with low affinity for hydrogen such as transition metals). The discharge capacity is limited around 300 mAh/g.

Based on this family of compounds, a new generation of materials is under development. Their structure can be viewed as intergrowths of the AB5 and A2B4 phases. A2B4 phase has the advantage to allow the substitution of the rare earth by light metal such as magnesium. This substitution improves the properties of the compound and allows to exhibit capacities as high as 400mAh/g [1].

The crystal structure of these compounds can be described as the stacking along the c-axis of n [A2B4] / m [AB5] sub-units. Two of these intergrowths correspond to the compounds A5B19 (n = 1, m = 3) and A2B7 (n = 1, m = 2). Both compounds exist in hexagonal (P63/mmc) and rhombohedral forms (R-3m).

Previous work was done mostly on lanthanum alloys [2]. In this study, we investigate the substitution of lanthanum by other rare earth elements such as neodymium or praseodymium to improve the characteristics of our materials. The substitution of the rare earth by magnesium was investigated to determine the influence of the magnesium amount on the compounds properties.

The crystallographic structure as well as the thermodynamic and electrochemical properties of the hydrogen absorbing compounds have been determined. Thermodynamic properties toward hydrogen uptake (capacity and equilibrium pressure) and electrochemical properties (cycling behavior) in alkaline medium have been measured and compared.

290

Reversibility and Identification of Intermediate Phase in Thermal Decomposition of Ca(BH4)2

1,2Yoonyoung Kim, 3Daniel Reed, 3David Book, 2Hung Nam Han and 1Young Whan Cho

1Materials Science and Technology Research Division,

Korea Institute of Science and Technology, Seoul 136-791, Republic of Korea 2Department of Materials Science and Engineering and Center for Iron and Steel

Research, RIAM, Seoul National University- 56-1, Shinlim-dong, Gwanak-gu, Seoul 151-744, Republic of Korea

3 School of Metallurgy and Materials, University of Birmingham, Edgbaston, Birmingham B15 2TT, United Kingdom

Email: sholangju@kist.re.kr Ca(BH4)2 is one of the potential candidates for hydrogen storage materials because of its high gravimetric and volumetric hydrogen density. However, little has been known regarding its thermal decomposition reaction pathway and the intermediate phase. It has been reported that Ca(BH4)2 undergoes a polymorphic transformation at 440K and decomposes around 640K to form an intermediate compound before it is fully dehydrogenated to CaH2 at higher temperature.1-3 Recently, the intermediate compound of Ca(BH4)2 was identifies as a CaB2Hx 4. However, the reversiblity and the crystal structure of the intermediate phase are still unknown. In an effort to fully understand dehydrogenation sequence of Ca(BH4)2, we have investigated the reversibility and chemical formula of the intermediate phase formed during thermal decomposition of Ca(BH4)2 by using XRD, TG-MS, DSC, Infra-rea and Raman Spectrosopy. References 1. J. H. Kim, S. A. Jin, J. H. Shim, Y. W. Cho, J. Alloy. Compd., 461, (2008), L20- L22. 2. M. D. Riktor, M. H. Sorby, K. Chlopek, M. Fichtner, F. Buchter, A. Zuttel, B.C. Hauback, J. Mater. Chem. 17, (2007), 4939-4942.

3. M. Aoki, K. Miwa, T.Noritake, N. Ohba, M. Matsumoto, H. –W. Li, Y. Nakamori, S. Towata, S. Orimo, Appl Phys A, 92, (2008), 601-605.

4. M. D. Riktor, M.H. Sorby, K. Chlopek, M. Fichtner, B.C. Hauback, J. Mater. Chem, 19, (2009), 2754-2759.

291

Interaction of Ammonia Borane with Li2NH and Li3N

Zhitao Xiong1, Yongshen Chua2, Guotao Wu1, Li Wang2, Richard Ming Wah Wong2, Tom Autrey3, Tim Kemmitt4 and Ping Chen1

1Dalian Institute of Chemical Physics, Dalian, China 116023

2 Department of Chemistry, National University of Singapore, Singapore 117543 3 Pacific Northwest National Laboratory, Richland, Washington 99352 4 Industrial Research Ltd, PO Box 31-310, Lower Hutt, New Zealand

Email: xzt@dicp.ac.cn Efficient on-board hydrogen storage system is one of the demanding technological challenges for PEM fuel cell vehicles. Ammonia Borane (NH3BH3) with a high gravimetric hydrogen density (19.6 wt %) has received significant interest recently1-3. In this study, investigations were focused on the interactions between NH3BH3 and lithium imide (Li2NH) and lithium nitride (Li3N) in tetrahydrofuran. As the nitrogen atom in Li2NH or Li3N is more electron donating than NH3 in NH3BH3, we expected nucleophilic displacement to form Li2NH-BH3 and Li3N-BH3, respectively, However, we observed a completely different reaction pathway involving the apparent metathesis to yield LiNH2BH3 and NH3. In-situ NMR was then used to monitor the chemical shifts of Li and B nuclei in solution to assist a general understanding of reaction mechanism. In a subsequent reaction the ammonia reacts with LiNH2BH3 to evolve ca. 10.5 wt % of hydrogen at a temperature as low as 45°C. References 1. Z. T. Xiong, C. K. Yong, G. T. Wu, P. Chen, W. Shaw, A. Karkamkar, T. Autrey, M.

O. Jones, S. R. Johnson, P. P. Edwards, W. I. F. David, Nat. Mater., 7 (2008), 138. 2. Z. T. Xiong, G. T. Wu, Y. S. Chua, J. J. Hu, T. He, W. L. Xu and P. Chen, Energy

Environ. Sci., 1 (2008) 360. 3. Z. T. Xiong, Y. S. Chua, G. T. Wu, W. L. Xu, P. Chen, W. Shaw, A. Karkamkar, J.

Linehan, T. Smurthwaite and T. Autrey, Chem. Commun., (2008) 5595.

292

Synthesis and Dehydrogenation of Calciumalanate Hydride

Xue-zhang Xiao, Chang-xu Li, Li-xin Chen, Xiu-lin Fan, Hua-qin Kou, Chang-pin Chen, Qi-dong Wang

Department of Materials Science and Engineering, Zhejiang University, Hangzhou 310027, PR China Email: xzxiao@zju.edu.cn

The key factor of realizing hydrogen economy for transportation application is developing cost-effective hydrogen storage materials which can de/hydrogenate under moderate temperature and pressure. Alanates (e.g. NaAlH4, Ca(AlH4)2 and LiAlH4) have been studied for this purpose because they have large hydrogen capacity [1-2]. Moreover, their de/hydrogenation kinetics could be enhanced by doping with suitable catalysts [3]. Ca(AlH4)2 was synthesized by reactive ball milling NaH/Al and CaCl2 with a few CeAl4 catalyst. The synthesis mechanism and dehydriding property of Ca(AlH4)2 were systematically investigated by X-ray diffractometry (XRD), fourier transform infrared spectroscopy (FTIR), simultaneous thermogravimetry (TG)-differential scanning calorimetry (DSC) and mass spectrometry (MS). The synthetic process of Ca(AlH4)2 was found included two steps: the first step was ball milling NaH/Al with CeAl4 under hydrogen to form CeAl4-doped NaAlH4, and the second step was ball milling the as-synthetic CeAl4-NaAlH4 and CaCl2 to form CeAl4-doped Ca(AlH4)2. It is found that the as-synthesized Ca(AlH4)2 can desorb more than 5.0 wt.% hydrogen below 200 °C with a fast reaction kinetics, its dehydriding property is better than that of Ca(AlH4)2 directly prepared by primary NaAlH4 and CaCl2. The reason for improving dehydrogenation of the as-synthesized Ca(AlH4)2 was also discussed in this paper. Keywords: Hydrogen storage; Complex hydride; Ca(AlH4)2; Reactive ball-milling

References 1. J. Yang, S. Hirano, Adv. Mater., 21, (2009), 3023–3028. 2. B. Bogdanović, U. Eberle, M. Felderhoff, F. Schüth, Scr. Mater., 56, (2007), 813–816. 3. X.L. Fan, X.Z. Xiao, L.X. Chen, K.R. Yu, Z. Wu, S.Q. Li, Q.D. Wang, Chem.

Commun., 44, (2009), 6857–6859.

293

Mathematical Modeling of Physical-Chemical Processes in the Metal Hydride Fuel Tank

V.V. Popov

RFNC-VNIIEF, Sarov, Russia arkad@triton.vniief.ru

At present the metal hydride fuel tank use is one of the promising methods of hydrogen storage on vehicle board. The developers of these devices should take into account limitation conditioned by physical-chemical properties of the metal hydride used. The mathematical modeling of the processes which occur in this hydrogen storage equipments allow us to choose more effective design of the specific device, to optimize the structural elements and to choose the operating conditions.

While developing the vehicle metal hydride fuel tank the mathematical model taking into account heat and mass exchange, hydrogenation/dehydrogenation reactions was created and realized. The series of computations were executed to select and optimize the metal hydride fuel tank design. These computations also allowed us to choose operating conditions. This model and computations were checked in the experiments. The mathematical model and computation data will be presented in report.

The work has been performed with financial support of ISTC, the project #3655р.

294

Self-Ignition Combustion Synthesis of LaNi5 Utilizing Hydrogenation Heat of Calcium

Naoto Yasuda, Shino Sasaki, Noriyuki Okinaka, Tomohiro Akiyama

Center for Advanced Research of Energy Conversion Materials, Hokkaido University, Sapporo, Japan E-mail: yasuda_7010@eng.hokudai.ac.jp

The paper describes Self-Ignition Combustion Synthesis (SICS) at pressurized hydrogen to produce LaNi5 using Ni, La2O3 powders as raw materials and Ca grain as a reductant and heat source, in which effect of hydrogen on ignition temperature and hydrogenation properties of the products was mainly examined. In the experiments, La2O3, Ni, and Ca were mixed in molar ratio of 1:10:6, and then were heated up at hydrogen of 1.0 MPa. As soon as the ignition due to the exothermic reaction of Ca+H2→CaH2, the power supply was turned off and the samples were naturally cooled at pressurized hydrogen. For comparison, the same experiments were done at argon of 0.1 MPa. As a result, the ignition temperature was drastically different; 600 K at hydrogen due to hydrogenation of calcium was much lower than 1100 K at argon. The product SICSed at pressurized hydrogen also showed high initial activity, and 1.54 mass% in hydrogen storage capacity as the same as commercial-available one. The SICS proposed offered many benefits for using cost-effective rare-earth oxide, lowering ignition temperature, minimizing operation time, saving productive energy and improving initial activity of the product.

295

References 1. T. Akiyama, H. Isogai, J. Yagi, J. Alloys and Compounds, 252 (1997) 1–4. 2. R. Wakabayashi, S. Sasaki, I. Saita, M. Sato, H. Uesugi, T. Akiyama, J. Alloys and

Compounds, 480, (2009), 592-595.

300

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Fig. 1 Changes in the sample temperature during SICS experiments.

Fig. 2 Hydriding curves of SICSed LaNi5 at different atmospheres at 298K in temperature and 4.1 MPa in initial hydrogen pressure.

Hydrogenation Properties of the Ternary Compounds Mg2-xPrxNi4 and MgRENi4 (0.6 ≤ x ≤ 1.4, RE: La, Ce, Pr, Nd, Sm, Gd)

N. Terashita1, K. Sakaki2, Y. Nakamura2, S. Tsunokake1, E. Akiba2

1 Japan Metals & Chemicals Co., Ltd., Japan 2 National Institute of Advanced Industrial Science and Technology, Japan

terasitan@jmc.co.jp Mg-based alloys have been studied for developing hydrogen storage materials with a larger capacity. Hydrogenation of the ternary compounds MgRENi4 (RE=La, Nd, Gd) have been reported so far [1-4]. Some of the results are in disagreement with others even for similar composition. This is probably because of variation in the quality of the samples, considering that preparation of Mg-based alloys with accurate target compositions needs good technique due to a high vaper pressure of Mg. In this study, we have investigated hydrogenation properties of Mg2-xPrxNi4 (0.6 ≤ x ≤ 1.4) and MgRENi4 (RE: La, Ce, Pr, Nd, Sm, Gd) systematically using a good quality homogeneous samples to understand composition dependence on hydrogenation properties. The compounds were prepared using induction melting techinique under helium atmosphere. The weights of each ingot were approximately 9-10 kilograms. This process has already been successfully industrialized. The Pressure-Composition (p-c) isotherms were measured by automatically operated Sieverts’ apparatus. XRD patterns of samples before and after p-c measurements and hydrides were measured in air. Mg2-xPrxNi4 have a cubic ordered C15b-type Laves phase. Mg1.4Pr0.6Ni4, Mg1.2Pr0.8Ni4 and MgPrNi4 absorbed hydrogen reversibly, and kept the C15b-type structure after desorption. On the other hand, the hydrogenation of both Mg0.8Pr1.2Ni4 and Mg0.6Pr1.4Ni4 led to amorphization. The p-c isotherm of stoichiometric MgPrNi4 at ~30 MPa and 273 K showed distinct two plateaus, while Mg1.4Pr0.6Ni4 and Mg1.2Pr0.8Ni4 have only one plateau. The enthalpies of hydride formation of Mg1.4Pr0.6Ni4, Mg1.2Pr0.8Ni4 and MgPrNi4 were evaluated to be -39.2, -40.3 and -42.4* kJ/mol H2, respectively [*: for the hydride with the smaller hydrogen content]. MgRENi4 (RE: Nd, Sm, Gd) showed similar p-c isotherms with one plateau. Relations among the atomic size of rare-earth elements, lattice constants, and the formation enthalpies were obtained. This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under “Development of technologies for hydrogen production, delivery and storage system” and “HYDRO-STAR”. References 1. H. Oestrreicher, H. Bittner, J. Less-Common Metals, 13 (1980) 339 - 344 2. L. Guenee, V. F-Nicolin, K. Yvon, J. Alloys and Compd, 348 (2003) 129 - 137 3. J-L. Bobet, P. Lesportes, J-G.Roquefere, B. Chevalier, K. Asano, K. Sakaki, E. Akiba, Int. J. Hydrogen Energy, 32 (2007) 2422 - 2428

4. J-N. Chotard, D. Sheptyakov, K. Yvon, Z. Kristallogr, 223 (2008) 690 – 696

296

Preliminary Experimental Study on Titanium Powder and its Application to Tritium Storage Bed Designed

M. Deaconu, T. Meleg, A. Dinu, N. Bidica*, N. Sofilca*

RAAN -Institute for Nuclear Research Pitesti, Romania, e-mail: mariea.deaconu@nuclear.ro

*INC-DTCI – ICSI, Rm. Valcea, Romania

The Nuclear Power Plant Cernavoda, equipped with a Canadian reactor, is the most powerful tritium source, in Europe. A TRF ( Tritium Removal Facility) will be constructed to remove the tritium from heavy water, and this will necessitate the storage of tritium in a special vessel. The titanium metal powder supplied by Alfa Aesar GmbH&Co KG, Karlsruhe (100 mesh, purity 99,4%) was used in this study as a suitable material for tritium immobilization. The samples of titanium powder were tested to examine their hydriding/dehydriding performances. The characteristics of the hydriding/dehydriding reaction over titanium powder have been investigated by means of thermogravimetric analysis(TGA). The morphology of the powder was obtained by scanning electron microscopy (SEM) and the present phases were detected with X-ray diffraction experiments. .The X-ray diffractograms obtained for Ti powder and TiHX powder are shown in Figure 1. The purpose of this paper is to describe the experimental data which supplies the information regarding the practical use of titanium powder for the storage of hydrogen isotopes under different conditions. Titanium powder showed a high hydrogen absorption capacity. Since, the chemical properties of tritium are virtually identical to those of hydrogen, this work has been conducted using hydrogen. The results will be used to evaluate storage vessel design loading limits Using metal hydrides for storage of heavy isotopes in a tritium containing system, can solve many problems arising in the nuclear fuel cycle.

Fig.1.X-ray diffraction analysis Key words: titanium powder, hydride,tritium, x-ray diffraction, tritium . References 1. H.R.Z. Sandim, B. V. Morante, P. A. Suzuki, Materials Research, Vol.8. No.3, 293-297, 2005

297

Quasi-Classical and Quantum Dynamics of H2 Dissociation on c(2×2)-Ti/Al(100) Surface with a Physisorption Well

Jian-Cheng Chen, Juan Carlos Juanes-Marcos, Mark Somers,

Cristina Diaz, Roar A. Olsen, and Geert-Jan Kroes

Leiden Institute of Chemistry, Gorlaeus Laboratories, Leiden University jcheng@chem.leidenuniv.nl One of the open questions remaining in hydrogen storage is how catalysts like Ti improve the kinetics and reversibility of hydrogen absorption in and release from the complex metal hydride sodium alanate (NaAlH4). A recent paper by us [1] has shown that the most energetically favorable model for H2 dissociation is on a 1 ML Ti covered c(2×2)-Ti/Al(100) surface with Ti in the first and third layers. A six-dimensional potential energy surface (PES) has been built using a periodic representation of the surface and employing the GROW method [2]. The PES has been used to compute the dissociation probability of H2 using both the quasi-classical trajectory and the time-dependent wave packet (TDWP) [3] methods. In the GROW method, Bayesian analysis is implemented to define a confidence radius when the interpolation of the potential energy value is needed. In the quantum TDWP method, the time-dependent Schrodinger equation is solved by split the six dimensional Hamiltonian to get small errors O(Δt3), which is call split operator (SPO). Meanwhile, the wave function is expanded by orthogonal basis sets for X, Y, Z, r, θ and φ, in which, the degrees of freedom in X, Y, Z, r use plane-wave basis sets (Fourier representations) and the degrees of freedom in θ, φ, use spherical harmonics of the Legendre polynomials (Gauss-Legendre representations). Our calculations show that large r grids are needed in the TDWP method, due to the first H-H vibration excitation v=1, identified by a node in the wave function. The reaction probability obtained by quantum dynamics is larger than the quasi-classical one by 5%, at the tested high incident energy range from 0.30 – 0.85 eV. References 1. J. C. Chen, J.C. Juanes-Marcos, A. Al-Halabi, R.A. Roar and G.J. Kroes, J. Phys. Chem. C 113, (2009) 11027. 2. M. A.Collins, Theor. Chem. Acc., 108, (2002) 313. 3. G. J. Kroes, Prog. Surf. Sci. 60, (1999) 1.

298

Effect of Deformation on Hydrogen Absorption and Desorption Properties of Titanium

Hiroshi Suzuki, Hisashi Taniguchi, Nobuko Hanada, Kenichi Takai, and Yukito Hagihara

Sophia University, 7-1 Kioi-cho, Chiyoda-ku, Tokyo 102-8554, Japan h-suzuki@me.sophia.ac.jp

Titanium absorbs fair amount of hydrogen forming hydride, while requires high temperature to release hydrogen as a result of decomposition of hydride under atmospheric pressure. It is desirable to explore ways to desorb hydrogen at ambient condition while accelerating absorption. This study analyses the effect of deformation on hydrogen absorption and desorption properties as a method to improve these properties. Hydrogen is introduced to commercial purity (99.5%) Ti by means of electrochemical method. The amount of hydrogen and its existing state are examined using hydrogen desorption curves, which are obtained by thermal desorption spectroscopy.

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The amount of absorbed hydrogen increases parabolically with charging time. Hydrogen absorption is promoted by applying tensile deformation prior to charging that leads to formation of hydride at shorter charging time. The role of dislocation and twin on hydrogen absorption is analyzed by experiments controlling amount of twin under a fixed strain. The amount of hydrogen absorbed does not change until volume fraction of twin is about 0.2 as shown in Fig. 1. It is found that hydrogen is mainly trapped by dislocation to form hydride, while twin boundary works as a barrier to cause accumulation of dislocation, thus promote hydride formation. The role of compressive stress on hydride decomposition is assessed by applying in-plane compression to plate specimens at room temperature by means of bending hydrogen charged thin plate. Figure 2 shows a relation between amount of hydrogen after deformation and reciprocal of bending diameter, together with hydrogen content after charging. Almost half of charged hydrogen is released as the reciprocal of diameter becomes higher, corresponding to higher compressive stress, that shows effect of compressive stress on hydrogen desorption from charged Ti.

Fig. 1 Relation between volume fraction of twin and hydrogen content of pure titanium under a fixed total strain.

Fig. 2 Change of hydrogen content of pure titanium after bending with reciprocal of diameter of bend.

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Green, Greener, Greenest: on Interaction of Hydrides and Borohydrides with CO2 for Reuse of a Greenhouse Gas

Tomasz Jaroń 1, and Wojciech Grochala 1, 2

1 Faculty of Chemistry, The University of Warsaw, Pasteura 1, 02093 Warsaw, Poland. 2 ICM, The University of Warsaw, Pawińskiego 5a, 02106 Warsaw, Poland.

E-mail: tjaron@chem.uw.edu.pl During the last decades the problem of anthropogenic climate change via greenhouse gases emmission attracted increasing attention. Recently, the topic has been highlighted and numerous physicochemical routes have been proposed for CO2 capture and storage [1, 2]. The search for novel routes of chemical activation of CO2 to various products is becoming more and more intense nowadays. In this contriubution, we present our study on reactions of simple binary hydrides (LiH, NaH [3], and CaH2) as well as borohydrides (LiBH4, NaBH4 [4], and Y(BH4)3) with CO2. We perfomed systematic analysis of reactivity of these compounds to CO2 and kinetic measurements in various experimental conditions. Binary hydrides activate carbon dioxide at ambient (when diethyl ether is applied as a solvent) or slightly elevated temperatures (above ca. 80 oC, without a solvent) leading to metal formates as main products. Reaction of metal borohydrides with CO2 is more complex and chemical identity of actual products depends strongly on the reaction conditions. In this case, the complete reduction of CO2 may lead to methanol – an important fuel and industrial precursor.

References 1. Carbon Capture and Sequestration, Science, 325 (2009) 1641–1659. 2. IPCC, 2005: IPCC Special Report on Carbon Dioxide Capture and Storage. Prepared by Working Group III of the Intergovernmental Panel on Climate Change [Metz, B., O. Davidson, H. C. de Coninck, M. Loos, and L. A. Meyer (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA, 442 pp. 3. H. Moissan, Ann. Chim. Phys., 8 (1905) 289. 4. T. Wartik, and R. K. Pearson, J. Inorg. Nucl. Chem., 7 (1958) 404.

300

New Tool for Hydrogen Storage Characterization: In-Situ Raman Cell to Measure in Hydrogen Pressure and Temperature

R. Domènech-Ferrer, R. Voigtländer, S. Klod, I. Lindemann, C. Rongeat, L. Dunsch. L.

Schultz and O. Gutfleisch. IFW, Institute for Metallic Materials, Dresden, Germany.

Email: R.domenech.ferrer@ifw-dresden.de A pressure cell has been designed for in-situ Raman measurements as function of hydrogen pressure and temperature. It is able to work in 200bar pressure and at temperatures up to 400°C. The cell has been built with swagelock and vition o-ring connections that ensure a perfect sealing and it allows easy sample transfer from the glovebox. The cell incorporates a cooling water system to keep its body at room temperature while the sample is annealed. Temperature is controlled with an external heat controller and a K-type thermocouple placed just below the sample. Raman cell has been tested with different compounds (LiBH4, NaAlH4 and Li4Al3(BH4)13). LiBH4 was employed to monitor the phase transformation from orthorhombic to hexagonal structure [1]. NaAlH4 doped with TiCl3 was measured in different hydrogen pressures to check the effect of the atmosphere in the decomposition temperature. As expected, the decomposition temperature increased with the hydrogen pressure. Also the novel double complex hydride Li4Al3(BH4)13 was measured along its decomposition pathway in Ar and H2 atmosphere. The in-situ Raman spectroscopy is found to be an excellent tool to characterize complex hydrides and their decomposition pathways, since these compounds have very strong Raman active modes. References 1. S. Gomes, H. Hagemann, and K. Yvon, J. Alloys Compd. 346, 206 (2002)

301

Novel Mixed–Cation Amidoborane of Lithium and Sodium – Not a Simple Solid Solution of LiNH2BH3 and NaNH2BH3

Karol J. Fijałkowskia, Armand Budzianowkib, Tomasz Jarońa and Wojciech Grochalaa,b

a Faculty of Chemistry, University of Warsaw, Pasteura 1, 02-093 Warsaw, Poland. b ICM, University of Warsaw, Pawińskiego 5a, 02-106 Warsaw, Poland

e-mail: fijalkowski@chem.uw.edu.pl Amidoboranes exhibit large hydrogen capacity and low temperature of H2 release thus partlialy fulfilling DOE’s targets for H storage materials. Recently amidoboranes were synthesized of alkali metals (Li, Na),[1,2,3,4,5] alkali earth metals (Ca)[6] and transition metals (Y)[7]. However, a system containing two different cations in the crystal lattice, has not yet been reported. We succeeded in synthesis and characterization of the first mixed-cation amidoborane of lithium and sodium, LiNa(NH2BH3)2, achieved via one-step mechanochemical reaction: LiH + NaH + NH3NH3 → LiNa(NH2BH3)2 + 2H2↑ The title compound is not a simple solid solution of single-cation amidoboranes of lithium and sodium crystallizing in the Pbca space group, since its X-ray diffraction pattern points out to a triclinic cell (Z=2). The NH & BH stretching regions in FT-IR spectrum of LiNa(NH2BH3)2 are not simple combinations of the corresponding bands of the single-cation phases; chemical environments of Li+ and Na+ cations are different for LiNa(NH2BH3)2 than for single-cation phases. Judging from differences between Lewis acidity of Na+ and Li+ cations, LiNa(NH2BH3)2 could be best described as and Na+[Li(NH2BH3)2

–]. Theoretical hydrogen capacity is 11.1 wt.%, but substantial contamination of the evolved H2 with NH3 is seen during thermal decomposition.

Fig. 1 Comparison of (left) X-ray powder diffraction patterns and (right) FT-IR spectra for

LiNa(NH2BH3)2 and amidoboranes of Li and Na. References 1 H. I. Schlesinger and A. B. Burg, J. Am. Chem. Soc., 1938, 60, 290 2 A. G. Myers, B. H. Yang, D. J. Kopecky, Tetrahedron Lett., 1996, 37, 3623. 3 Z. Xiong, C. K. Yong, G. Wu, P. Chen, W. Shaw, A. Karkamkar,T. Autrey, M. O. Jones,

S. R. Johnson, P. P. Edwards and W. I. F. David, Nat. Mater., 2008, 7, 138 4 Z. Xiong, G. Wu, Y. S. Chua, J. Hu, T. He, W. Xu and P. Chen, Energy Environ. Sci.,

2008, 1, 360. 5 K. J. Fijalkowski and W. Grochala, J. Mater. Chem., 2009, 19, 2043. 6 J. Spielmann, G. Jansen, H. Bandmann, S. Harder, Angew. Chem. Int. Ed., 2008, 47, 1. 7 R. Genova, K. J. Fijalkowski, W. Grochala, J Alloys Comp, in press 2010.

302

Hydrogen Absorption in CexGd1-x Alloys

J. Bloch1, M. Bereznitsky2, M. Yonovich1, D. Schweke1, M. H. Mintz1, 2 and I. Jacob2 1. Nuclear Research Center-Negev, P. O. Box 9001, Beer Sheva 84190, Israel.

2. Ben Gurion University of the Negev, P. O. Box 653, Beer Sheva, Israel. Email: matveyb@bgu.ac.il

The effect of alloying on the thermodynamics of hydrogen absorption was studied for CexGd1-x alloys (0.05≤x≤1) at temperatures between 600oC and 800oC. The phase diagram of the Cerium-Gadolinium (Ce-Gd) system exhibits an intermediate Sm-type (delta) phase below 720°C around the concentration Ce0.3Gd0.7 (x=0.3). Pressure-composition isotherms of hydrogen absorption were measured as a function of x for the pressure range 10-2 - 102 Pa and were compared to those of pure Gd and Ce from the literature. The hydrogen solubilities as well as the plateau pressures for the hydride formation were obtained from the isotherms. The terminal solubility of hydrogen in Gd is approximately four times higher than in Ce in the temperature range between 800 and 1000 K. At a given temperature, the hydrogen terminal solubility was found to decrease monotonically with increasing x. This behavior differs from that in substitutional solutions of the vanadium and the titanium groups, for which the hydrogen terminal solubility increases with increasing solute concentrations. Partial molar enthalpies and entropies of dissolution as well as heats and entropies of the dihydride formation were evaluated as a function of the hydrogen concentration. Comparison of isotherms of the alloys with different x values and analysis of the thermodynamic quantities in the solid solution regime provide information concerning hydrogen interaction parameters and the maximum number of interstitial sites available for hydrogen occupation. The heat of formation of the dihydride exhibits a pronounced maximum around x=0.3. This observation correlates with the presence of intermediate Sm-type (delta) phase around this composition. It is concluded that the hydride associated with the delta phase is considerably more stable than both cerium and gadolinium dihydrides.

303

First-Principles Study on LiNH2BH3 (LiAB) and LiNH2BH3·NH3BH3 (LiAB·AB)

W. Li *†, G. T. Wu‡, R. H. Scheicher§, C. M. Araújo§, A. Blomqvist§, R. Ahuja§, Y. P. Feng † and P. Chen‡

‡Dalian Institute of Chemical Physics, Chinese Academy of Sciences, Dalian, P.R. China †Department of Physics, National University of Singapore, Singapore

§Condensed Matter Theory Group, Department of Physics and Astronomy, Uppsala University, Uppsala, Sweden

*Email: yuliwenshu@gmail.com Ammonia borane (NH3BH3, AB) has attracted considerable attention as a hydrogen storage material because of its high hydrogen storage capacity (19.6 wt. %). However, the relatively poor kinetics of AB during dehydrogenation in combination with the environmentally unfriendly toxic borazine as byproduct make it unsatisfactory as a useful hydrogen storage material1-2. One of the approaches to overcome this problem is to substitute an H atom in the [NH3] group by alkali metal or alkaline earth element to form metal amidoborane such as LiNH2BH3 (LiAB)3-6, NaNH2BH3 (NaAB)4,7, or Ca(NH2BH3)2 4,6. More recently, a new AB derivative, LiNH2BH3·NH3BH3 (LiAB·AB), was formed, which has high hydrogen storage capacity (14.8 wt. %) and lower dehydrogenation temperature (on set at 58 ℃ and first peak at 80 ℃) 8. In this study, we employed first-principles calculations to investigate the crystal and electronic structures of LiAB·AB. The results show that Li+ cations destabilize H atoms in a more efficient way in LiAB·AB due to the alternate [LiAB]-[AB] layered structure. With weaker B-H and N-H bonds, the dissociation of N-Hδ+ and B-Hδ– and the subsequent combination of Hδ+ and Hδ– become energetically favorable in LiAB·AB, which could explain the lower dehydrogenation temperature of LiAB·AB compared with those of AB and LiAB. References 1. F. H. Stephens, V. Pons and R. T. Baker, Dalton Transactions, (2007), 2613-2626. 2. T. B. Marder, Angewandte Chemie-International Edition, 46, (2007), 8116-8118. 3. Z. T. Xiong, Y. S. Chua, G. T. Wu, W. L. Xu, P. Chen, W. Shaw, A. Karkamkar, J. Linehan, T. Smurthwaite and T. Autrey, Chemical Communications, (2008), 5595-5597. 4. Z. T. Xiong, C. K. Yong, G. T. Wu, P. Chen, W. Shaw, A. Karkamkar, T. Autrey, M. O. Jones, S. R. Johnson, P. P. Edwards and W. I. F. David, Nature Materials, 7, (2008), 138-141. 5. P. Wang, S. Orimo, K. Tanabe and H. Fujii, Journal of Alloys and Compounds, 350, (2003), 218-221. 6. H. Wu, W. Zhou and T. Yildirim, Journal of the American Chemical Society, 130, (2008), 14834-14839. 7. Z. T. Xiong, G. T. Wu, Y. S. Chua, J. J. Hu, T. He, W. L. Xu and P. Chen, Energy & Environmental Science, 1, (2008), 360-363. 8. C. Wu, G. Wu, Z. Xiong, X. Han, H. Chu, T. He and P. Chen, Chemistry of Materials, 22, (2009), 3-5.

304

Temperature and Concentration Dependence of the Diffusion Constants of H and D in the β-phase of Palladium Hydride(Deuteride).

David Wilkinson1, David Moser1, Keith Ross1 and Drew Bailey2

1. Physics and Materials Research Centre, School of Computing, Science and Engineering University of Salford, Manchester M5 4WT, UK.

2. AWE, Aldermaston, Reading. RG7 4PR Email: D.Wilkinson@pgr.salford.ac.uk

We report on recent measurements of hydrogen and deuterium diffusion in the beta phase of palladium hydride (deuteride) – PdH(D)c - using a gravimetric technique at temperatures between -100oC and +100oC and for concentrations between 0.6<c<0.9. The equilibration time following a change in applied pressure is related to the Fick’s Law Diffusion Coefficient DF(c,T)= Chemical diffusion coefficient, by the equation DF(c,T) = <r2> /6 Δt(c) where <r2> is the mean square value of the linear dimension of the micron scale particle of palladium used and c is the concentration (assuming that the rate of adsorption is not surface limited). By presenting DF(c,T) data for specific concentrations on an Arrhenius Plot, the activation energy for diffusion has been determined as a function of concentration. In this system, we can write DF = {<l2>/6τ(c) kT}. dμ/dx where l is the distance between adjacent octahedral sites, τ(c) is the mean time between jumps at concentration, c and μ(c) is the chemical potential which is proportional to the log of the equilibrium hydrogen pressure = kB T ln (p/p0) [1,2,3]. As the equilibrium pressure in this system is well approximated by an exponential form, dμ/dx is more or less independent of pressure in the β-phase of PdD, so we can estimate the concentration dependence of τ(c) at a given temperature. QENS measurements from Pd/D (coherent and incoherent), Monte Carlo and ab initio calculations of the H-H near neighbour interactions, giving rise to μ(c) and the mean time between jumps, are in hand. References 1. S.K.Sinha and D.K.Ross, Physica B 149 (1988) 51 2. D.K.Ross, Physica B 182 (1992) 318-322 3. P.R.Stonage, M.J.Benham and D.K.Ross, Mainwaring, C and Harris I.R.Z. Physik. Chemie 181 (1993) 125-131

305

Structural and Magnetic Properties of PrPdInH and NdPdInH Hydrides.

K. Koźlaka, Ł.Gondeka, J. Przewoźnika, H. Figiela and A.Szytułab a AGH-UST, Faculty of Physics and Applied Computer Science, Al.Mickiewicza 30, 30-059 Kraków,

Poland Email: kkozlak@agh.edu.pl

b M. Smoluchowski Institute of Physics, Jagiellonian University, Reymonta 4, 30-059 Kraków, Poland It is well known that many intermetallic compounds may absorb hydrogen under certain conditions. However, the amount of stored hydrogen is still not satisfactory for common usage. Switendick’s criterion for H-H distance in the crystal lattice (2.1 Å) is one of the limiting factors in development of intermetallic compounds for hydrogen storage. However, it was recently reported that there are some compounds which can break this criterion. Namely, for some compounds of ZrNiAl-type crystal structure a very short distance between hydrogen atoms were evidenced (~1.5 Å) [1]. Full understanding of this mechanism can provide new ideas for hydrogen storage. In this work we report investigation of PrPdIn and NdPdIn intermetallics, which possess the ZrNiAl-type structure (Space group P-62m). There are some R3T2 bipyramids (R- rare earth, T- transitional metal) in the lattice with 2 sites for hydrogen atoms available. When both sites are fully occupied, RTInH1.33 hydride is obtained. RTInH0.67 is formed when only one of the sites is occupied. Hydrogenation of PrPdIn and NdPdIn was performed under H2 pressure of 50 bar and temperature 2000C. Two hydrides of RPdInH stoichiometry were obtained. The total volume expansion of 1.68% for R = Pr and 3.00% for R = Nd were observed. For PrPdInH magnetometric measurements data reveal no magnetic ordering down to 2 K. The reciprocal magnetic susceptibility follows the Curie-Weiss law within the investigated range in contradiction to the pure PrPdIn sample. For NdPdInH a magnetic ordering at about 5 K for was noticed. Apart from significant lowering of the ordering temperature (from 30 K for NdPdIn) a change of the type of magnetic ordering was observed. The base compound exhibits ferromagnetic ordering, while its hydride behaves as an antiferromagnet. Such changes of the magnetic properties are in agreement with lowering of the RKKY exchange interactions between localized 4f magnetic moments and the conduction band. The another factor that should be taken into account is a change of crystal electric field, that influences strongly the magnetic properties of the ternary RTX intermetallics [2]. References 1. V.A. Yartys , R.V. Denys , B.C. Hauback , H. Fjellvag , I.I. Bulyk , A.B. Riabov , Ya.M. Kalychak, J. Alloys and Compounds, 330-332, (2002), 132-140. 2. Ł. Gondek, A. Szytuła, D. Kaczorowski, K. Nenkov, Solid State Communications 142 (2007) 556–560

306

Volumetric Expansion of LaNi5 Hydride During

Absorption - Desorption Cycles S. Mellouli, H. Dhaou, F. Askri, A. Jemni, S. Ben Nasrallah Laboratoire d’Etudes des Systèmes thermiques et Energétiques (LESTE)

Ecole Nationale d’Ingénieurs de Monastir, (ENIM) Avenue Ibn El Jazzar, 5019 Monastir, Tunisia

mellouli-sofiene@ yahoo.fr

Using a metal hydride is one of the promising solutions when the key question of the storage of hydrogen is considered. Hydrogenation is an exothermic process associated to a change of volume. Therefore the design of a metal hydride tank should include thermal and mechanical aspects. Thermal aspects are now well known and it is now possible to predict the time evolution of the temperatures in the tank during hydrogenation [1]. This paper focuses on the question of volumetric expansion of the powder during sorption. This question, which is of fundamental importance to determine the mechanical strains on the container walls, has been studied by C.A.Chung et al. and F. Qin et al. [2, 3].

An experimental LaNi5 tank has been equipped with a visualisation window for measuring the phenomenon of expansion / contraction of the metal hydride powder during the processes of absorption and desorption. Doing so, it is found the expansion rate can reach a value of 18%. References 1 S. Mellouli, F. Askri, H. Dhaou, A. Jemni, S. Ben Nasrallah. Numerical study of heat exchanger effects on charge/discharge times of metal–hydrogen storage vessel. International Journal of Hydrogen Energy 34 (2009) 3005 – 3017. 2 C.A. Chung, Ci-Jyun Ho. Thermal–fluid behavior of the hydriding and dehydriding processes in a metal hydride hydrogen storage canister. International Journal of Hydrogen Energy 34 (2009) 4351-4364. 3 F. Qin, L.H. Guo, J.P. Chen, Z.J. Chen. Pulverization, expansion of La0.6Y0.4Ni4.8Mn0.2 during hydrogen absorption–desorption cycles and their influences in thin-wall reactors. International Journal of Hydrogen Energy 33 (2008) 707 – 717.

307

Effect of Transition-Metal Halids on the Hydrogen Storage Properties of CaBH4-MgH2 System

Jianfeng Mao,1 Zaiping Guo,1 Huakun Liu,1 and Xuebin Yu2

1Institute for Superconducting and Electronic Materials, University of Wollongong, NSW, 2522, Australia 2Department of Materials Science, Fudan Universtiy, Shanghai 200433, China

Email: jm975@uow.edu.au Ca(BH4)2 is a promising hydrogen storage material due to its high gravimetric hydrogen density of 11.5 wt %. However, a relatively hight kinetic and thermodynamic barries have to be overcome before it becomes a pratical on-board hydroen storage material.1 CaBH4-MgH2 system shows a better hydrogen storage properties than solo CaBH4 due to its thermodynamic properties altered through changing its decompostion path by adding MgH2.2 In this study, different transition-metal halids such as TiF3, ZnCl2, CoCl2 and NiCl2 were doped to the CaBH4-MgH2 system for further improving its properties. It was found that all the halids additives exhibited positive effect on the host material. Among them, NiCl2 exhibited the most positive effect on the kinetic improvement. Results show that the NiCl2-doped CaBH4-MgH2 system can release nearly 3.8 wt % hydrogen wihin 1 h at 315 °C, while the neat system only release 0.97 wt % hydrogen at the same conditions. The reversibility of CaBH4-MgH2 system was also improved after addint NiCl2, the undoped system can absorb 1.62 wt % hydrogen at 400 °C and 40 bar for 8 h,while the NiCl2-doped system can absorb 1.82 wt % hydrogen at the same conditons. References 1. J. F. Mao, Z. P. Guo, C. K. Poh, A. Ranjbar, Y. H. Guo, X. B. Yu, H. K. Liu, Submitted to J. Alloys and Compounds, (2010). 2. Y. Kim, D. Reed, Y. S. Lee, J. Y. Lee, J. H. Shim, D. Book, Y, W, Cho, J. phys. Chem. C 113, (2009) 5865-5871.

308

Ageing Characterisation of Intermetallic Compounds for the Development of Hydrogen Storage Reactors.

N. Michel and P. Dantzer Université Paris-Sud - UMR8000

Laboratoire de Thermodynamique et Physico-Chimie d'Hydrures et Oxydes Bâtiment 415, 91405 Orsay Cedex, france

e-mail : Pierre.Dantzer@u-psud.fr A common feature of all the means of hydrogen production is the need for storage. It is particularly true when safety or purity aspects have to be taken into account. The influence of the impurities on the storage properties was the subject of deepened research, on the other hand the literature contains few studies on the ageing of hydrogenated materials. Let us emphasize that the evolution of the behaviour of the hydrides compounds on the long run controls their technological future and thus represents an important economic issue. If one does not take account a degradation initiated by the presence of impurities, then two parameters remain to consider for the studies of ageing: the temperature range of use of the compound and the necessary time to perform a full loading and unloading cycle with hydrogen. The temperature range is fixed by the thermodynamic parameters whereas the cycle time is imposed by i)the dynamics of the transformation (kinetic aspects), ii)the heat transfer capacities of the reactor, and iii)the type of application considered. The objective of this research consists in carrying out several hundreds of cycles by imposing the driving force during the phase of formation or decomposition of a hydrogenated compound. The transfers are performed in a closed mode in order to avoid any possibility of degradation by impurities. A closed system also makes it possible simultaneously to follow the behaviour of material under isothermal conditions and as a function of the temperature. The evolution of the properties have been quantified by comparison between the isotherm obtained after N cycles and the initial isotherm, this isotherm of reference being defined as the first reproducible isotherm measured after the phase of activation. A specific bench was assembled and dedicated to this research. This report contains the brief description of the equipments, the description of the method, the thermodynamic of the activation of the compounds and the synthesis of the experiments of ageing. This work has been carried out on the Ti0.4Zr0.6Cr0.85Fe0.7Ni0.2Mn0.25Cu0.03 -H2 system.

309

Reaction Pathways in the Reactive Composite Mg(NH2)2 + LiH

Deniz Cakir1, Gilles A. de Wijs2 and Geert Brocks1 1 Computational Materials Science, Faculty of Science and Technology and MESA+ Research

Institute, University of Twente, P.O. Box 217, 7500 AE Enschede, The Netherlands. Email: D.Cakir@tnw.utwente.nl

2 Electronic Structure of Materials, Institute for Molecules and Materials, Faculty of Science, Radboud University Nijmegen, Heyendaalseweg 135, 6525 AJ Nijmegen, The Netherlands. In 2002, Chen et al [1] reported reversible hydrogen storage in a mixture of LiH + LiNH2 with a storage capacity of 6.5 wt %. However, this system requires an operating temperature in excess of 250 C to achieve a hydrogen pressure of 1 bar. Several efforts including cation substitution have been considered in order to improve the operating conditions, which is necessary for onboard applications. For instance, replacing LiH with MgH2 markedly reduces the operating temperature through the reaction MgH2 + 2LiNH2 → Li2Mg(NH)2 + 2H2 ↔ Mg(NH2)2 + 2LiH. Recent experimental results however indicate that the latter is not a simple one-step reaction and full hydrogenation of Li2Mg(NH)2 occurs in a two step sequence via an intermediate Li2Mg2(NH)3 [2,3]. In this work we examine the stability and structure of possible intermediates compounds, namely Li2-2xMgxNH, Li1-2xMgxNH2, LixMg(NH2)2-x(NH)x, and Li2-xMg(NH)2-x(NH2)x, by means of first-principles DFT calculations. In order to get stability of these compounds, formation enthalpies are calculated from total energy differences. We include the vibrational zero point energies in order to get accurate results. All intermediate compounds are thermodynamically stable with respect to the elements. Next we consider possible reaction steps involving these intermediate imides/amides. We find that the intermediate amides Li1-2xMgxNH2 or mixed imide-amides LixMg(NH2)2-x(NH)x and Li2-xMg(NH)2-

x(NH2)x, are energetically not favorable. In contrast, the hydrogenation reaction of Li2Mg(NH)2 via the intermediate imides Li2-2xMgxNH is possible. However, we do not find a clear preference for one specific composition, as all compounds Li2-2xMgxNH with ½ ≤ x ≤ ¾ lead to a similar reaction enthalpy. We predict that all compounds within this composition range are likely to occur as intermediates. The experimentally proposed composition, x = ⅔, lies within this range. References 1. P. Chen, Z. Xiong, J. Luo, and K. L. Tan, Nature 420, 302 (2002). 2. J. Hu, Y. Liu, G. Wu, Z. Chiong, and P. Chen, J. Phys. Chem. C 111, 18439 (2007). 3. E. Weidner, F. Dolci, J. Hu, W. Lohstroh, T. Hansen, D. J. Bull, and M. Fichtner, J. Phys. Chem. C 113, 15772 (2009).

310

Hydrogenation of Ti25V35Cr40 Alloy Doped with Interstitial Boron and Carbon

Chia-chieh Shen1, 2, Shay-Chih Lee2, and Tsong-Pyng Perng3

1Department of Mechanical Engineering, Yuan Ze University, Taiwan 2Gradual School of Renewable Energy and Engineering, Yuan Ze University, Taiwan

3Department of Chemical Engineering and Materials Science, Yuan Ze University, Taiwan Email: ccshen@saturn.yzu.edu.tw

Doping of minor interstitial elements B and C into a BCC-type Ti25V35Cr40 alloy to

raise effective desorption hydrogenation capacity was investigated. Ti25V35Cr40Mx alloys (M = B or C and x = 0, 0.1, 1, or 5) were prepared by arc-melting followed by homogenization treatment. X-ray diffraction (XRD) results show that as-cast specimens are crystalline with a BCC structure, but they contain some amount of precipitate that increases with the doping concentration of B and C. The doping-induced precipitates can be greatly eliminated by annealing treatment at 1200 oC, indicating that B and C elements have been partially dissolved into the interstitial sites in the BCC lattice of Ti25V35Cr40 alloy. With the doping of C, the second plateau pressure of as-annealed Ti25V35Cr40 in the PCI curves at T = 30 oC significantly increases with the amount of C, but the maximum hydrogenation capacity is reduced. On the other hand, the second plateau pressure and maximum hydrogenation capacity are only slightly affected by the B doping. Under optimum doping conditions, the effective H-desorption capacities of Ti25V35Cr40 increase from 0.80 H/M to 0.86 H/M and 0.87 H/M for Ti25V35Cr40B１and Ti25V35Cr40C0.1, respectively. The improvement in the effective capacity is ascribed to the increase in second plateau pressure caused by difficult dissolving of H atoms into the lattice sites of Ti25V35Cr40 containing interstitial B or C. Keywords: TiCrV; Hydrogenation; Boron; Carbon; Pressure-composition isotherm References 1. M. Okada, T. Kuriiwa, T. Tamura, H. Takamura and A. Kamegawa, “Ti-V-Cr bcc

alloys with high protium content,” J. Alloys Comp., 330-332 (2002) 511-516.

2. E. Akiba and M. Okada, “Metallic hydrides III: body-centered-cubic solid-solution alloys,” MRS Bulletin, (2002) 699-703.

3. M. Uno, K. Takahashi, T. Maruyamy, H. Muta and S. Yamanaka, “Hydrogen solubility of BCC titanium alloys”, J. Alloys Comp., 366 (2004) 213-216.

4. S. W. Cho, J. H. Yoo, G. Shim, C. N. Park and J. Choi, “Effect of B addition on the hydrogen absorption-desorption property of Ti0.32Cr0.43V0.25 alloy”, Int. J. Hydrogen Energy, 33 (2008) 1700-1705.

5. S. M. Lee and T.P. Perng, “Effects of B and C on the hydrogenation properties of TiFe and Ti1.1Fe, ” Int. J. Hydrogen Energy, 25 (2000) 831-836.

6. J. Y. Lee, J. H. Kim, S. I Park and H. M. Lee, “Phase equilibrium of the Ti–Cr–V ternary system in the non-burning β-Ti alloy region”, J. Alloys Comp., 291 (1999) 229-238.

311

NMR Study of Metal-Hydrogen Systems for Hydrogen Storage

M. Shelyapina1, V. Kasperovich1, N. Skryabina2, D. Fruchart3, S. Miraglia3, P. de Rango3 1 Department of Physics, St Petersburg State University, 1 Ulyanovskaya st., Petrodvorets, 198504,

St. Petersburg, Russia 2Faculty of Physics, Perm State University, 15 Bukireva st., 614990, Perm, Russia

3 Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France marinashelyapina@mail.ru

During the last decades metal hydrogen systems as hydrogen storage materials were subject of intensive studies. Despite a considerable amount of both experimental and theoretical works, a fundamental and comprehensive understanding of intrinsic mechanisms that govern the thermodynamics and hydrogen kinetics in these hydrides still merits complementary investigations. In such perspectives, deeper knowledge on local structure and hydrogen mobility are helpfully required. Appreciable enlightening of main characteristics (static and dynamics) can be provided using nuclear magnetic resonance (NMR) method which is a especially a powerful tool to investigate metal hydride systems. In the present report contribution we will provide a review of NMR studies of different metal hydrides of interest for reversible hydrogen storage applications. Then we will present and discuss results gained from more recent 1H NMR study of disordered Ti-V-Cr metal hydrides. The Ti-V-Cr alloys belong to a class of body centred cubic systems and exhibit potentially high characteristics of hydrogen storage properties with maximum uptake of more then 3.5 wt% hydrogen for the most appropriate compositions. 1H NMR pulses have been applied to study the hydrogen mobility in those pseudo-ternary hydrides. Thermal dependence of both of the spin-lattice τ1 and the spin-spin τ2 relaxation times have been analysed within the modified Bloembergen-Purcell-Pound model assuming: (i) an activation energy distribution and (ii) a fast exchange between mobile and lattice bonded hydrogen species. The results are discussed in terms of reversible hydrogen storage specificities close to room temperature. This work is granted by RFBR-CNRS, contract No 07-08-92168 and developed under the IAEA project No 15933. We also grateful for a financial support of NoE INSIDEPORES (6th PCR - Europe) for stay of M.S. and N.S. at Institut Néel Grenoble.

312

First Principles Study of the LiNH2 / Li2NH Transformation

G. Miceli,1,2 C. Cucinotta,2 M. Bernasconi,1 M. Parrinello2 1 Dipartimento di Scienza dei Materiali, Universitità di Milano-Bicocca, Via R. Cozzi 53, I-20125, Milano,

Italy 2 Department of Chemistry and Applied Biosciences, ETH Zurich, USI Campus, Via Giuseppe Buffi 13, 6900

Lugano, Switzerland Lithium amide (LiNH2) has been extensively studied in recent years as a promising material for hydrogen storage.1 Hydrogen release occurs in the mixture LiNH2/LiH via a reversible solid state decomposition reaction into lithium imide (Li2NH) and molecular hydrogen (LiNH2+LiH→Li2NH+H2). Although the thermodynamical decomposition temperature is probably too high for on-board applications, the amide decomposition reaction is under deep scrutiny since this material represents a prototypical, relatively simple system, which could shed light on the mechanisms of reversible H-release in the more complex, and more promising, reactive hydrides made of mixtures of amides, borohidrides and/or alanates. In spite of a substantial amount of experimental work, the detailed mechanism of amide decomposition is still matter of debate. Aiming at providing theoretical support to the decomposition mechanism and clarifying the role of the surfaces in this process, we performed ab-initio calculations of activation energies of elementary steps that we hypothesize to be crucial for ammonia mediated transformation path.2 We first analyzed the formation of ammonia via a proton transfer between two NH2- groups in the presence or in the absence of a Li Frenkel pair in the bulk and at the surface of LiNH2. Diffusivity of H+ (i.e. NH3 via a Grohttus mechanism), H+ vacancy (NH2-) and Li+ species in LiNH2 and Li2NH were then computed to contrast the alternative scenarios presented in Refs. 3,4. The H+ and Li+ transfer across the LiNH2/Li2NH interface was also investigated as well as the ammonia desorption at the Li2NH and LiNH2 surfaces. Ions diffusivity in the high temperature phase of Li2NH has been also monitored directly by means of ab-initio molecular dynamics simulations. The scenario for the decomposition mechanism of LiNH2 emerging from the simulations actually suggests that the transformation path depends on the surface-to-volume-ratio. The formation of sub-stoichiometric phases3 is possibly favored in bulky material with a small surface-to-volume ratio, while the direct formation of imide is favored in the presence of small crystallites (large surface-to-volume ratio) which transform according to the core-shrinking model of Ref. 4. Furthermore, by a deep analysis of our dynamical simulations we propose a low temperature structure for Li2NH which solves the contradictions of previous proposals. References 1. P. Chen et al., Nature 420, 302 (2002) 2. T. Ichikawa, et al, J. Phys. Chem. B 108, 7887 (2004) 3. W. I. F. David et al., J. Am. Chem. Soc 129, 1594 (2007) 4. L. L. Shaw et al., J. Power Sources 177, 500 (2008)

313

Prototype Hydrogen Source Based on Hydride Forming Materials

F. Mangiarotti1, G. Bertolino1,2, A. Baruj1,2 and G. Meyer1,2

1 Instituto Balseiro y Centro Atуmico Bariloche, CNEA, 8400, S. C. de Bariloche, Argentina 2 Consejo Nacional de Investigaciones Cientнficas y Tйcnicas (CONICET), Argentina

E-mail: gmeyer@cab.cnea.gov.ar We have designed and constructed a prototype of a portable solid state hydrogen source. It is based on the use of hydride forming materials for low pressure gas storage during transportation plus in-situ compression during operation. The device was primarily conceived to provide hydrogen to experiments outside the main hydrogen laboratory, like simultaneous pressure-composition isotherms (PCI) and X-ray diffraction (XRD) measurements. We have selected LaNi5 as hydride forming alloy because it provides an outlet pressure range between 3 bar and 60 bar for source temperatures between 22oC and 150oC. This alloy has additional advantages: it is fairly stable against cyclic degradation and, once degraded by cycling, it can be reconstituted by a simple thermal treatment. We have selected 316L stainless steel for the source vessel, considering that it has to stand elevated hydrogen pressures during its service life. The vessel design was the result of mechanical, heat transfer, weight and cost considerations. Preliminary mechanical and thermal models were tested and further optimized by using finite element modeling. One of the main limitations during operation is related to the low thermal conductivity of LaNi5

powder, which was addressed by mixing the powdered alloy with Cu wires. In this way, enhanced device sorption kinetics was obtained. We characterized the prototype experimentally using a dynamic absorption/desorption technique in a home-made volumetric equipment. In addition, we have successfully used the prototype in simultaneous PCI-XRD experiments.

314

In-Situ NMR Observation of Hydrogen Absorption and Desorption Behavior for Metal Hydrides

H. Takamura, T. Takahara, R. Ohkura, M. Ando and H. Maekawa

Graduate School of Engineering, Tohoku University, Sendai 980-8579, Japan Email: takamura@material.tohoku.ac.jp

Nuclear magnetic resonance (NMR) is a useful technique for analyzing a local structure and dynamics of metal hydrides. Recently, our group has succeeded in developing an NMR system for in-situ analysis of hydrogen storage materials under high temperature and pressurized atmospheres. The system comprises of three parts; 1) pressure/ow-rate control system, 2) high-temperature probe with low 1H back- ground, and 3) compact pressure-proof sample holder. The system can precisely control the pressure of H2, D2, and/or Ar within the range of 14 Pa to 1 MPa. The high-temperature probe, which can stand for maximum temperature of 350 oC, can be used not only for 1H but also for 7Li, 11B, and 27Al. By using a Cu-Be alloy for the pressure-proof sample holder, a resolution of _ 0.1 ppm (FWHM for 1H) was achieved for a standard sample of TMS. In addition, because of low 1H background, 1H NMR spectrum of H2 gas was observed even for 0.1 MPa-H2. The signal intensity linearly increased with increasing H2 pressure up to 1 MPa. By using the in-situ NMR system, hydrogen absorption and desorption behaviors are observed for a variety of metal hydrides such as Laves-type alloys and LiBH4. For the Laves-type alloys, ZrMn2:3, TiMn1:5, TiCr2, and ZrCr2 were prepared by an arc-melting technique followed by homogenizing treatment. Figure 1 shows 1H NMR spectra for ZrCr2 taken at room temperature. At 0.6 MPa-H2, a sharp peak attributed to pressurized H2 gas is observed. As pressure increases up to 1 MPa-H2, in addition to that, a broad peak, which can be attributed to H in ZrCr2 emerges at around -144 ppm. The peak still remains after depressurizing down to 0.1 MPa-H2.

Fig. 1: 1H NMR spectra of ZrCr2

under pressurized H2 at RT Desorption process of the ZrCr2 hydride under evacuated atmosphere was also monitored by using the in-situ NMR. Corresponding to dehydrogenation at around 100 oC, the peak at around -144 ppm disappeared. A peak remained even at 300 oC seems to be attributed to the presence of stable hydrides such as ZrH2. In the presentation, in-situ NMR observation of hydrogen absorption and desorption behavior for several metal hydrides will be presented. Acknowledgement This work has been supported by New Energy and Industrial Technology Development Organization (NEDO) under \Advanced Fundamental Research Project on Hydrogen Storage Materials".

315

Hydrides Formation in Mg-Fe-H2 System.

A.Demkin, I.Konstanchuk Institute of Solid State Chemistry and Mechanochemistry SB RAS, Novosibirsk, Russia

Email: irina@solid.nsc.ru The ternary hydride Mg2FeH6 is considered as an attractive material for practical application due to its extremely high volumetric hydrogen capacity (1022 H atoms/cm3 or 150 g/l). The synthesis of Mg2FeH6 is complicated by the lack of appropriate intermetallic compounds forming hydride. Moreover, the mutual solubility of magnesium and iron is very low as well as solubility of hydrogen both in magnesium and in iron. This leads to a low yield of ternary hydride even at severe experimental conditions such as a temperature 400-500° C and hydrogen pressure of hundred bars. As it was shown in [1-2] Mg2FeH6 can be formed as a result of reacvtion of MgH2 with Fe or by direct interaction of Mg, Fe depending on experimental conditions. These two reaction ways are compared in this work with the aim to achieve the higher yield of ternary hydride. References 1. I. Konstanchuk, E.Ivanov, B.Darriet, M.Pezat, V.Boldyrev, P.Hagenmüller, J. Less-Common Met., 131 (1987) 181-189. 2. I.G.Konstanchuk, A.A.Stepanov, J. Phys. Chem., 63 (1989) 3123-3127 (in Russ.).

316

Phase Structure and Hydrogen Absorbing Property in Ti-Fe-Al System

J.Matsuda, Y.Nakamura and E.Akiba National Institute of Advanced Industrial Science and Technology(AIST), Tsukuba, Ibaraki, Japan

Email: junko.matsuda@aist.go.jp Th6Mn23-type alloys especially rare earth (RE) containing phases form hydrides, RE6M23{H,D}x. Hydrogen and deuterium atoms preferentially occupy the octahedral sites in the Th6Mn23-structure. Among Ti-M-Al (M=transition metal) alloys with Th6Mn23- or Mg6Cu16Si-type structures (space group Fm-3m), only Ti47Co28Al33 absorbed hydrogen with the content of 0.8 mass%1. In this study, we have focused on Ti4-x-yFexAly (2~x,y~1) alloys, which are expected as new hydrogen storage materials in a low cost, and investigated phase relations and hydrogen absorbing properties. Samples were prepared by arc melting from elemental sticks or ingots with minimal purity of 99.9 %. Hydrogen absorbing properties were evaluated from Pressure –Composition (P-C) isotherms (298K) measured using the Sieverts method. X-ray powder diffraction data were collected for both the samples before and after the P-C measurements in order to determine crystal structures. As a result, nominal compostion Ti43Fe24Al33 absorbed hydrogen with the maximum content of 0.4 H/M. But this alloy slightly desorbed hydrogen at room temperature. XRD patterns revealed that the main phase in this Ti43Fe24Al33 sample was a C14 Laves phase with lattice parameters, a of 0.501 nm and c of 0.810 nm, which increased after hydrogen absorption. Increasing of Fe contents in the ternary system resulted in decreasing of lattice parameters and the hydrogen capacity in the Laves phase. Furthermore, TiFe-based (B2) phase increased with increasing of Ti content. Main phase in TiFeAl2 was the Th6Mn23-type structure, but this sample did not absorb hydrogen. Crystal structures and microstructures will be discussed based on the Rietveld refinement of X-ray diffraction profile and TEM observetion. This work was supported by The New Energy and Industrial Technology Development Organization (NEDO) under Advanced Research on Hydrogen Storage Materials (HYDRO-STAR). References 1. A. Grytsiv, J. J. Ding, P. Rogl, F. Weill, Bernard Chevalier, J. Etourneau, G. A ndre, F. Bouree, H. Noel, P. Hundegger, G. Wiesinger, Intermetallics, 11, (2003), 603-605.

317

Hydrogen Storage Properties of Mn-based Borohydride Compounds

Ruixia Liu, Daniel Reed, David Book School of Metallurgy and Materials, University of Birmingham, Birmingham, UK

Email: rxl883@bham.ac.uk Complex hydrides have attracted a lot of interest due to their high gravimetric hydrogen storage densities. In particular, the structures and properties of a number of transition metal-based borohydrides have been investigated [1-2]. Recently, Jensen’s group has prepared mixed-metal borohydrides of zinc with lithium or sodium and the detailed sturctures of these new compounds have been identified as LiZn2(BH4)3, NaZn2(BH4)3 and NaZn(BH4)3 by NMR and SR-PXD [3]. However, the reversibility has not yet been demonstrated for this type of materials. In this work, a series of manganese-based borohydride compounds – AxMny(BH4)x+2y (A=Li, Na) – were synthesized by mechanochemical milling Li(or Na)BH4 and MnCl2 (with 2:1 and 3:1 molar ratios) under argon. The characterization of the milled samples was carried out by x-ray diffraction (XRD) and Raman spectroscopy measurements. Under optimal milling conditions, no XRD peaks were observed for the starting materials. In addition to the XRD peaks for LiCl (or NaCl), when LiBH4 was used, relatively weak peaks were found at around 20° that have been attributed to the trigonal Mn(BH4)2 compound [4]. In the Raman spectra of the milled mixtures, two typical spectra regions for the BH4 functional group were observed: the bond bending band and stretching mode; and the overtones and combination bands. The thermal stability and decomposition properties of the newly synthesized products were investigated by differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) coupled with mass spectrometry (MS). By comparison with that of LiBH4 (or NaBH4), much lower decomposition temperatures (e.g. 115-175°C) were observed for new compounds, accompanying the evolution of 6-9 wt % hydrogen and trace diborane. The possible reversibility of these new compounds is under investigation. The investigation of decomposition behaviour at variable temperatures by XRD and Raman has revealed that during the decomposition process a ternary chloride compound formed for NaBH4-MnCl2 system, and then the borohydride compounds decomposed to form B and B-metal species. References 1 S. Orimo, Y. Nakamori, J. R. Eliseo, A. Züttel, and C. M. Jensen, Chem. Rev., 107 (10), (2007), 4111. 2. D.B. Ravnsbœk, L. H.Sorensen, Y. Filinchuk, D. Reed, D. Book, H.J.Jakobson, F. Besenbacher, J. Skibsted, T. R. Jensen, European Journal of Inorganic Chemistry, 2010, in press. 3. D.B. Ravnsbœk, Y. Filinchuk, Y. Cerenius, H. J. Jakobsen, F. Besenbacher, J. Skibsted, T.R. Jensen, Angew. Chem. Int. Ed, 48 (2009), 6659. 4. R. Cerny, N. Penin, H. Hagemann, Y. Filinchuk, J. Phys. Chem. C, 113, (2009), 9003.

318

In Situ Raman Studies of the Thermal Decomposition of Lithium Borohydrides.

D. Reed and D. Book School of Metallurgy and Materials, University of Birmingham, Birmingham, B15 2TT, UK

Email: D.Reed@bham.ac.uk With gravimetric hydrogen capacities above 10 wt%, and decomposition temperatures ranging from below ambient to 550°C borohydrides have attracted interest as potential hydrogen storage media. However, evolution of diborane and difficulty in recombination limit the potential applications. It is hoped that a greater understanding of the decomposition and reformation mechanisms, may lead to the development of borohydride based materials that can absorb and desorb hydrogen under acceptable conditions. Currently, most in-situ investigations have used x-ray diffraction (XRD) or neutron diffraction however these cannot readily give information on non-crystalline or liquid phases. The preparation of samples measured ex situ via XRD, NMR [1] and Raman [2] have shown the reaction products and stable intermediates during the thermal decomposition, however, it is very difficult to detect short lived intermediate (or byproduct) species. Raman spectroscopy has the advantages that: materials with only short-range order can be analysed; and by focusing the laser on regions in a sample the reaction path can be monitored with changing temperature with a rapid scan rate. With a number of intermediates and reaction products being predicted and observed, this work used ex situ and in situ investigations was performed. After heating lithium borohydride through its phase change and melting point, shifts in peak position and peak width were observed, which agreed with other studies [3]. Temperature-dependent Raman measurements of LiBH4 show that on heating under argon, the phase change from orthorhombic to hexagonal was observed as an increase in symmetry at 120°C and melting was observed at 320°C as a change in focus height and peak-width. Decomposition products of Li2B12H12 and amorphous boron were observed to begin to form as a precipitate within the liquid LiBH4 at 350°C and 380°C. Upon cooling, both these phases were still present at room temperature. Recombination of LiBH4 should be possible at 600°C in 350 bar hydrogen[4]. References 1. Her, J.H., M. Yousufuddin, W. Zhou, S.S. Jalisatgi, J.G. Kulleck, J.A. Zan, S.J. Hwang, R.C. Bowman, and T.J. Uclovict. Crystal Structure of Li2B12H12: a Possible Intermediate Species in the Decomposition of LiBH4. Inorganic Chemistry, 2008. 47 (21): p. 9757-9759. 2. Miwa, K., N. Ohba, S. Towata, Y. Nakamori, and S. Orimo. First-principles study on lithium borohydride LiBH4. Physical Review B, 2004. 69 (24): p. 245120. 3. Gomes, S., H. Hagemann, and K. Yvon. Lithium boro-hydride LiBH4 II. Raman spectroscopy. Journal of Alloys and Compounds, 2002. 346 (1-2): p. 206-210. 4. Orima, S., Y. Nakamori, G. Kitahara, K. Miwa, N. Ohba, S. Towata, and A. Zuttel. Dehydriding and rehydriding reactions of LiBH4. Journal of Alloys and Compounds, 2005. 404: p. 427-430.

319

Alanates-LiBH4 Systems for Hydrogen Storage: Role of Al in LiBH4 Charge/Discharge Performance.

J. Purewal1, S. Hwang2, C. Kim2, R. C. Bowman, Jr.3, C. Ahn1 1Division of Engineering and Applied Science, California Institute of Technology,Pasadena, CA 91125,

USA. 2The division of Chemistry and Chemical Engineering, California Institute of Technology, Pasadena, CA

91125, USA. 3 Oak Ridge National Laboratory, USA.

Ball milled mixture of Alanates-LiBH4 systems were studied for hydrogen charge and discharge reactions. Stoichiometric mixtures of Ca(AlH4)2 +2 LiBH4 or AlH3 +2 LiBH4 were prepared and milled at 300 rpm for 1 h. About a half gram of material was tested for kinetic desorption up to 400 ̊C and rehydrogenated at 400 ̊C under ~ 60 bar of H2 back pressure. XRD and multinuclear high resolution solid state NMR were used to characterize the samples after reactions. Two desorption steps were common for both cases due to separate desorption of alnates and LiBH4 while the desorption of LiBH4 appeared to be largely dependent to alanates. Addition of Ca(AlH4)2 resulted in nearly complete decomposition of LiBH4 to amorphous boron and more than 70% of LiBH4 was recovered by rehydrogenation. CaH2 and Al metal were remained unreacted. Use of AlH3 in the other case, decomposition of LiBH4 was found to be heavily incomplete at the same desorption condition, yielding significant amount of reaction intermediate including Li2B12H12. The subsequent rehydrogenation of the decomposed powder allowed limited recovery of LiBH4. After the desorption, the formation of AlB2 was not confirmed by XRD or NMR. XRD revealed unidentifiable peaks and NMR also indicated formation of AlxBy type of composite. The catalytic role of Al for LiBH4 recovery and the spectroscopic features of the unidentified phase will be discussed in detail.

320

Prototype Hydrogen Source Based on Hydride Forming Materials F. Mangiarotti1, G. Bertolino1,2, A. Baruj1,2 and G. Meyer1,2

1 Instituto Balseiro y Centro Atуmico Bariloche, CNEA, 8400, S. C. de Bariloche, Argentina 2 Consejo Nacional de Investigaciones Cientнficas y Tйcnicas (CONICET), Argentina

E-mail: gmeyer@cab.cnea.gov.ar We have designed and constructed a prototype of a portable solid state hydrogen source.It is based on the use of hydride forming materials for low pressure gas storage during transportation plus in-situ compression during operation. The device was primarily conceived to provide hydrogen to experiments outside the main hydrogen laboratory, like simultaneous pressure-composition isotherms (PCI) and X-ray diffraction (XRD) measurements. We have selected LaNi5 as hydride forming alloy because it provides an outlet pressure range between 3 bar and 60 bar for source temperatures between 22oC and 150oC. This alloy has additional advantages: it is fairly stable against cyclic degradation and, once degraded by cycling, it can be reconstituted by a simple thermal treatment. We have selected 316L stainless steel for the source vessel, considering that it has to stand elevated hydrogen pressures during its service life. The vessel design was the result of mechanical, heat transfer, weight and cost considerations. Preliminary mechanical and thermal models were tested and further optimized by using finite element modeling. One of the main limitations during operation is related to the low thermal conductivity of LaNi5

powder, which was addressed by mixing the powdered alloy with Cu wires. In this way, enhanced device sorption kinetics was obtained. We characterized the prototype experimentally using a dynamic absorption/desorption technique in a home-made volumetric equipment. In addition, we have successfully used the prototype in simultaneous PCI-XRD experiments.

321

Chemical Hydrogen Storage in NHXBHX Materials

A. Karkamkar Pacific Northwest National Laboratory, Richland, WA 99354

abhi.karkamkar@pnl.gov The NHxBHx class of materials may be classified as complex hydrides and/or chemical hydrogen storage materials. Chemical hydrogen storage materials are of great interest for hydrogen storage because they are capable of providing large quantities of hydrogen (up to 19 wt.% hydrogen) with rapid kinetics at moderate temperatures. Our group has been working on developing an in-depth understanding of the chemical and physical properties of amine borane materials for solid state hydrogen storage. Hydrogen is released at low temperatures through a series of moderate exothermic reactions. In this work we present experimental and computational studies designed to elucidate mechanistic details about how di-hydrogen bonding interactions affect the release of hydrogen from these novel compounds. This approach provides insight into controlling rates of hydrogen release, enhancing purity of hydrogen and providing a rational design for regeneration of spent fuel materials. Pacific Northwest National Laboratory is operated for the DOE by Battelle.

322

Investigation of the 2LiH + MgB2 System by In- and Ex-Situ Neutron Diffraction

M. Crossley, E. Gray, J. Webb, Queensland Micro- and Nanotechnology Centre, Griffith University, Brisbane, Australia

Email: s2172580@student.griffith.edu.au The lithium-hydride/magnesium-diboride system has been the subject of much investigation due to its potential for light-weight hydrogen storage. While its weight (11.4 wt%) and volume densities of hydrogen are favourable, it has been found to react at unfavourably high temperatures. Performance improvements have been made through the use of additives and micro-/nano-structuring [1,2]. In this work we report a study of the reaction 2LiH + MgB2 + 4H2 ↔ 2LiBH4 + MgH2 by neutron diffraction. This required the replacement of natural boron with 11B. Magnesium-diboride was synthesised using 11B and commercial LiD was obtained. The forward (hydrogenation) reaction was studied with samples consisting of a 2:1 molar ratio of LiH to MgB2, ball-milled with or without 5 at% VCl3 or titanium-isopropoxide under deuterium pressures up to 500 bar. In-situ time-of-flight neutron diffraction was undertaken (Polaris, ISIS, United Kingdom) for both the forward and back reaction. The absorption reaction was carried out at the unusually low temperature of 250°C to ensure the formation of solid Li11BD4, and so be able to observe its formation directly using diffraction. During D absorption the lattice parameters of Li11BD4

were found to change as the reaction progressed, indicating an unexpected level of complexity in the reaction mechanism. The in-situ results were supplemented by a subsequent high-resolution ex-situ study (Echidna, OPAL, Australia) of the absorption reaction to elucidate the phases present, relating primarily to potential reactions between the additive and the base materials. The diffraction results and their implications for the reaction mechanism will be discussed in our presentation. References 1. S. Bosenberg, S. Doppiu et al., Acta Materialia , 55, (2007), 3951–3958 2. X. Wan, T. Markmaitree, W. Osborn, L.L Shaw, J. Phys. Chem. C , 2008, 112, 18232– 18243

323

5-Year Review of the DOE Metal Hydride Center of Excellence

L.E. Klebanoff Sandia National Laboratories, Livermore California, USA

Email: lekleba@sandia.gov For the past five years, the US Department of Energy (EERE) has funded the Metal Hydride Center of Excellence (MHCoE) to perform applied research in metal hydride hydrogen storage materials. The MHCoE is led by Sandia National Laboratories, and includes researchers from five other US national laboratories, 10 universities and two industry partners. The purpose of the research has been to find hydrogen storage materials that satisfy the DOE targets (gravimetric density, volumetric density, other) for light-duty vehicles. This presentation will review the structure of the MHCoE, and selected highlights from the R&D program the past five years. Among the highlights will be advances made in off-board regeneration of AlH3 and LiAlH4, investigations of Mg(BH4)2, as well as theoretical advances in our understanding of complex metal hydrides.

324

Interaction of NdNi4M with Hydrogen. A.N.Kazakov, S.V.Mitrokhin

Chemistry Department Moscow State University, Leninskie gory 1/3 119991Moscow, Russian Federation

Intermetallic hydrides are prospective for use in metal-hydride compressors and heat pumps. It is known that NdNi5 may absorb about 6 H atoms per formula unit and exhibit rather high dissociation pressure even at room temperature. Substitution of components in NdNi5 can change significantly thermodynamic parameters of reaction with hydrogen. However there is some uncertainty in literature data on enthalpies of reactions for NdNi4M (M = Al, Fe, Ni) systems.Using the prediction model developed in our laboratory we designed several compositions of NdNi5 based alloys suitable for use in metal-hydride compressors - NdNi4Co0.45Al0.55, NdNi4.1Co0.4Al0.5, Nd0.4Ce0.6Co3.0Ni1.9Mn0.1. Phase composition of alloys was determined by X-ray analysis. The PC-isotherms were measured in standard Sieverts type device (up to 100 atm) and in high pressure installation (upto 2000 atm). It was shown that NdNi4.4Al0.5Sn0.1 exibit rather good absorption-desorption properties and may be recommended for use in metal-hydride compressors. The prediction model proved to be useful for design of compositions with predetermined thermodynamic characteristics.

This work was supported in part by RFBR Grant 09-08-01075.

325

Hydrogen Generating Composites Based on Aluminum Hydride

M.Dulyaa, B.Tarasova, B.Bulychevb and V.Yartysc

a Institute of Problems of Chemical Physics of RAS, Chernogolovka, Russia b Chemistry Department Moscow State University, Moscow, Russia

c Institute for Energy Technology, Kjeller, Norway Email: tarasov@icp.ac.ru

One of the most perspective materials for portable metal hydride hydrogen generators of the thermolysis type is aluminum hydride. This compound has high content of hydrogen (as much as 10 mass %, 150 kg/m3) [1, 2]. It is known that the aluminum hydride is not thermodynamically stable and might decompose at room temperature, however due to kinetic impediments its noticeable decomposition starts at 90–100°C and vast decomposition — at 150–170°C. To reduce the thermodynamic stability of the aluminum hydride it may be modified by doping of hydrides of alkali metals in a planetary ball mill. But the nature and mechanism of this effect has not been investigated so far.

In the present work we found that during the treatment of aluminum hydride in a planetary ball mill under inert atmosphere the initial substance was amorphized and decomposed with release of hydrogen. The same treatment under hydrogen atmosphere allowed us to save the content of the hydride and decrease the temperature threshold of its decomposition by about 20°C. Additions of LiH to AlH3 in the ball mill leaded to the formation of the alanate phase and lowered the decomposition temperature threshold down to 100–125°C. In the composites of aluminum hydride with magnesium hydride the thermodynamic stability reduced for both AlH3 and MgH2. Additions of TiH~2 and ZrH~2 in the ball mill lowered the thermal stability of AlH3 catalyzing the decomposition of the hydride even at small doses of mechanical energy. Under the same conditions the addition of VH~1 did not change the thermal stability of AlH3, preserving high hydrogen content (~7 mass %). The mechanochemical treatment of aluminum hydride with titanium containing additives sharply reduced the stability of the alane and favored the decomposition of the hydride, but influences of Ti, TiO2, and TiH2 substantially differed, with the addition of titanium hydride having the most destabilizing effect. The addition of LiNH2 destabilized AlH3 with release of up to 5 mass. % H2 at 140–160°C and formation of the adduct of the aluminum hydride with ammonia. Mechanochemical treatment of mixtures of aluminum hydride with carbon materials leaded to reduction of the thermal stability of the hydride phase.

We ascertained the possibility of regulation of the temperature and rate of hydrogen release from the composites based on aluminum hydride which is important for elaboration of free-running chemical sources of hydrogen of the thermolysis type intended for low-temperature hydrogen-air fuel cells. We shown possibility of repetitive formation of AlH3 under high hydrogen pressures over the composites obtained during the dehydrogenation of mixtures of AlH3 with magnesium and vanadium hydrides, subjected to ball-milling. References 1. G. Sandrock, J. Reilly, J. Graetz, Wei-Min Zhou, J. Johnson, J. Wegrzyn, J. Alloys and Compounds, 421, (2006), 185-189. 2. S.K. Konovalov, B.M. Bulychev, Inorganic Chemistry, 34, (1995), 172-175.

326

Hydrogen Storage, Optical and Magnetic Properties of Nano Structured Pd and Pd/Mg Thin Films

Yogendra K.Gautam1, 2

, R.D. Agarwal1 and Ramesh Chandra

2

1. Department of Metallurgical and Materials Engineering, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand -247667 (India)

2. Nano Science Laboratory, Institute Instrumentation Centre, Indian Institute of Technology Roorkee, Roorkee, Uttarakhand -247667 (India)

E-mail address: ykg82dmt@iitr.ernet.in

Storing hydrogen in metals in the form of metal hydride shows potential to solve the hydrogen storage challenges. Thin films offer an opportunity to grow new samples fast with novel structures. as the grains are refined, the bulk diffusion distance of hydrogen atoms in the material for achieving uniform distribution becomes smaller, and rate of absorption/desorptoion of hydrogen can be increased. The optical changes, caused by the hydrogenation and dehydro- generation of the metal film with the aid of the catalytic action of Pd is very interesting in thin film technology. They have attracted much attention for their potential applications in smart windows, displays, optical switches, etc. Hydrogen also significantly affects magnetic properties of nano structured coatings and hydrogen based switchable optical mirrors and low dimensional magnetic systems are very useful in sensor applications. In this present work the hydrogen storage, optical and magnetic properties of metal hydride thin films had been investigated. The nano structured Pd and Pd caped Mg thin films/ multilayers had been prepared by DC magnetron sputtering on Si (100) and glass substrate. The samples were hydrogenated/dehydrogenated in a steel chamber at different temperatures for different time durations in H

2 atmosphere. The as deposited and

hydrogenated/dehydrogenated samples had been characterized by XRD, AFM, FE-SEM for their structural (phases & crystallite size) and surface morphological study respectively. The optical properties of the samples had been observed by UV-VIS-NIR spectrophotometer and it was found that the Mg based hydride thin films/multilayers presented transparent state while as deposited sample presented mirror state properties. The elastic recoil detection analysis (ERDA) and super conducting quantum interference device (SQUID) were used to study the hydrogen storage capacity (at %) and magnetic properties of the samples respectively.In Pd thin film the size dependence of the magnetic saturation component reveals that the ferromagnetic ordering occurs only the facets of the particles of the top most two to five layers from the surface. These surface layers contribute to the ferromagnetism with a magnetic moment ( 10

−4 emu).

Reference 1. E. Shalaan, H. Schmitt, Mg nanoparticle switchable mirror films with improved absorption–desorption kinetics Surf. Sci.600, (2006),3650–3653. 2. R. Domenech-Ferrer, M. Gurusamy Sridharan, G. Garcia, F. Pi, J. Rodriguez- Viejo,. Microchip power compensated calorimetry applied to metal hydride characterization. J. Power Sources. 169, (2007)117–122 3. I.P. Jaina, Babita Devia, P. Sharmaa, A. Williamsona, Y.K. Vijaya, D.K. Avasthib, A. Tripathib,Hydrogen in FeTi thin films by ERDA with Ag

107 ions, International Journal of

Hydrogen Energy, 25 (2000) 517-521 4. M. Tischer et al., Phys. Rev. Lett, 75, (1995). 1602-1604.

327

Improved Hydrogenation-Dehydrogenation of the Nanostructured Melt-Spun Mg-Ni-Mm Alloys

Y. Wua,b*, M.V. Lototskyc,d, J.K. Solbergb, V. A Yartysb,c

aSchool of Materials Science and Engineering, Shanghai Institute of Technology, No. 120, Cao Bao Road, Shanghai, 200235, P.R. China

bDepartment of Materials Technology, Norwegian University of Science and Technology, NO-7491 Trondheim, Norway

cInstitute for Energy Technology, P.O. Box 40, N-2027 Kjeller, Norway dUniversity of the Western Cape, South Africa

* Email: science2008@live.cn Magnesium is an attractive material for hydrogen storage applications benefiting from high hydrogen storage capacity, low density and cost, and rich natural resources. However, slow hydrogenation kinetics and high dehydriding temperatures limit its actual use. The reaction kinetics of Mg with H2 is improved by additives of transition and rare earth metals. In our earlier study we have observed that hydrogen absorption /desorption rates in Mg-based alloys are dramatically enhanced by nanoprocessing [1]. Rapid solidification (RS) technique is an efficient process in improving the hydrogen storage properties of Mg-based alloys as different nanocrystalline microstructures can be obtained by controlling the solidification rate. In the present study, melt-spun Mg-10Ni-2Mm (at.%) ribbons were obtained by a single roller melt-spinning technique using copper quenching discs in an argon gas. Microcrystalline and nanocrystalline microstructures were synthesised by applying copper wheel surface velocities of 300 or 1000 rpm, respectively. The grain size of the melt-spun ribbons containing a three-phase mixture Mg-Mg2Ni-MmMg12, was remarkably refined by increasing the solidification rate. From TEM studies we have found that MmMg12 intermetallic nucleates at the grain boundaries of Mg and Mg2Ni, thus, providing paths for H exchange. The interface between MmMg12 and Mg2Ni is semi-coherent, with an ordered repetition of the consistent atomic arrangements. Prior to the studies of the hydrogen storage properties, the ribbon-type samples were milled in H2 by application of planetary milling in order to synthesise corresponding hydrides. The kinetics of H-absorption/desorption is improved in the refined microstructures due to the fast hydrogen diffusion in the nanograins. TEM studies showed (a) stability of the nano-sized grains in the samples that underwent cycling of hydrogen desorption and absorption during their heating to 350 °C; (b) formation of MmH3-x hydride from MmMg12 and its preferential location at grain boundaries of MgH2. Clearly, MmH3-x and Mg2NiH4 act as nucleation centers to initiate the formation of MgH2; this, in turn, promotes hydrogen absorption by the Mg alloys. Pressure-Composition-Temperature graphs show the presence of two plateaux, Mg-MgH2 and Mg2Ni-Mg2NiH4. The MgH2 plateau showed no hysteresis and practically no slope, while the plateau for Mg2NiH4 showed both a pronounced hysteresis and a pronounced slope, particularly for the nanocrystalline samples. Enthalpy and entropy changes measured from the van’t Hoff plots were in good agreement with earlier reported literature data. The maximum hydrogen storage capacity of the nanocrystalline sample was slightly higher than that of the microcrystalline one.

Reference 1. Y. Wu, M.V. Lototsky, J.K. Solberg, V. A. Yartys, W. Han, S.X. Zhou. J. Alloys

Compd. 477 (2009), 262-266.

328

The Influence of Ball Milling Process on Hydrogenation Properties of MgH2 – FeTi Composites

Z. Zaranski1, T. Czujko

Faculty of Advanced Technology and Chemistry, Military University of Technology, Kaliskiego 2 St, 00-908 Warsaw, Poland

1Email: zzaranski@wat.edu.pl Magnesium hydride is well known material which has been considered a hydrogen storage medium for more than two decades. Unfortunately, large enthalpy of fromation and high desorption temperature of the magnesium hydride (∼ 300 °C) exclude its usage in practical applications. However, it has been shown that compositing of MgH2 with some intermetallic alloys can decrease the decomposition temperature of MgH2 [1-3]. In this work, the MgH2-FeTi composite hydrides were synthesized in a wide range of compositions by controlled reactive/mechanical (ball) milling in a magneto-mill. The phase structure and morphology were investigated by XRD and SEM. The hydrogen desorption characteristics of obtained composites were measured by differential scanning calorimetery (DSC) and a volumetric Sievert’s apparatus. It is shown that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems, decreases linearly with increasing volume fraction of the constituent having lower desorption temperature. Recently, we have shown that described composite behaviour of hydride mixtures is observed in metal, intermetallic and comlex hydride systems [4,5]. Moreover, it is demonstrated that the hydrogen desorption temperature in the magnesium-intermetallic hydride composites is afftected not only by the phase composition but also by milling parameters. The particle size of composite constituent is related to the amount of additive and milling parameters, especialy milling time. Our results clearly show that there is a considerable catalytic effect of the FeTi intermetallic additive on the hydrogen desorption temperature of MgH2 and both, absorption and desorption kinetics. The obtained nanocomposite exhibits a good reversibility. The catalytic element introduced into the system from decomposing an intermetallic hydride, does not dramatically reduce the total capacity of the composite system. References 1. N. E. Tran, M. A. Imam, C.R. Feng, J. Alloys and Compounds 359, (2003) 225–229. 2. M. Khrussanova, E. Grigorova, J.-L. Bobet, M. Khristov, P. Peshev, J. Alloys and Compounds 365, (2004) 308–313. 3. R. Vijay, R. Sundaresan, M.P. Maiya, S. Srinivasa Murthy, Y. Fu, H.-P. Klein, M. Groll, J. Alloys and Compounds 384, (2004) 283–295. 4. R.A. Varin, T. Czujko, R. Pulz, Z. Wronski, J.Alloys.Compd., 483, (2009), 252-255. 5. T. Czujko, R.A. Varin, Z.S. Wronski, Z. Zaranski, The Canadian Metallurgical Quarterly, 1, (2009), 11-26.

329

Composite Behaviour of Nanostructured Hydride Mixtures Synthesized by Ball Milling

T. Czujko1, Z. Zaranski, I. E. Malka

Faculty of Advanced Technology and Chemistry, Military University of Technology, Kaliskiego 2 St, 00-908 Warsaw, Poland

1Email: tczujko@wat.edu.pl The search for materials that match the DOE criteria for hydrogen storage materials to be used in automobile applications has been largely focused on hydride composites in the past ten years. In particular, since the work of Vajo et al. [1, 2] on LiBH4-MgH2 mixture, there have been a number of publications devoted to complex and metal hydrides that are thermodynamically or catalytically destabilized by ball milling with others hydrides [3-5]. In this work, the following composite hydride systems: MgH2-FeTiH2, MgH2–VH0.81, MgH2–LiAlH4 and NaBH4–MgH2, were synthesized in a wide range of compositions by controlled reactive/mechanical (ball) milling in a magneto-mill. The phase structure and morphology were investigated by XRD and SEM. In effect, composites having nanometric grain sizes of the constituent phases (nanocomposites) were produced. The hydrogen desorption characteristics of obtained composites were measured by differential scanning calorimetery (DSC). It is shown that the hydrogen desorption temperature of the composite constituent with the higher desorption temperature in the systems, decreases linearly with increasing volume fraction of the constituent having lower desorption temperature. It is also shown that the linear behaviour can break down due to an ineffective milling of a composite. It is demonstrated that the hydrogen desorption in the complex, metal or intermetallic hydride composites involves two steps: first, the lower temperature hydride decomposes to metal, intermetallic or complex hydride + metal and H2 and in a subsequent step, these intermediary compounds, most likely, catalyse or thermodynamically change the decomposition of the high temperature hydride. The catalytic or reactive element introduced into the system from decomposing a simple metal or intermetallic hydride, even with a high content of H2, does not dramatically reduce the total capacity of the composite system. The thermodynamic destabilization can be an effect of solid solution or intermediate intermetallic phase formation. Some times both phenomenon, catalytic influence and intermetalic phase formation can be observed. In particular, this work shows clearly that the formation of MgB2 intermetallic phase during decomposition of both hydride constituents in NaBH4–MgH2 system is not the only factor responsible for the thermal destabilization of NaBH4. References 1. J.J. Vajo, S.L. Skeith, F. Mertens, J. Phys. Chem. C, 109, (2005), 3719-3722. 2. J.J. Vajo and G.L. Olson, Scripta Materialia, 56, (2007), 829–834 3. T. Czujko, R.A.Varin, Z. Wronski, Z. Zaranski, T. Durejko, J.Alloys.Compd., 427, (2007), 291-299. 4. R.A. Varin, T. Czujko, R. Pulz, Z. Wronski, J.Alloys.Compd., 483, (2009), 252-255. 5. T. Czujko, R.A. Varin, Z.S. Wronski, Z. Zaranski, The Canadian Metallurgical Quarterly, 1, (2009), 11-26.

330

Microstructural Development and Hydriding Kinetics of Ball-Milled Nanocrystalline MgH2 Powders

Á. Révész1,*, D. Fátay1 and T. Spassov2

1Department of Materials Physics, Eötvös University, Budapest, H-1518, P.O.B. 32, Budapest, Hungary 2Department of Chemistry, University of Sofia “St.Kl.Ohridski”, 1 J.Bourchier str., 1164 Sofia, Bulgaria

*correspondin.author. E-mail: reveszadam@ludens.elte.hu Repeated dehydriding/hydriding cycles of ball-milled nanocrystalline MgH2 powders were carried out in a Sievert’s-type apparatus. The microstructural changes during cycling were characterized by high resolution X-ray diffraction. Using the Convolutional Multiple Whole Profile (CMWP) fitting procedure, several microstructural parameters, i.e. the average grain size and the grain size distribution of the as-milled and treated samples were determined. It was obtained that the as-milled MgH2 powder exhibits a homogeneous microstructure with an average grain size of 9nm. The first cycle results in a coarsened microstructure (20 nm) and a narrow grain-size distribution. Further dehydriding/hydriding treatment destroys the homogeneity, while the average grain size remains unchanged. Based on the shrinking core model, the significant difference between the microstructures obtained after the first and repeated cyclings was interpreted. In order to characterize the microstructural changes during a complete MgH2→Mg→MgH2 transformation, the fourth desorption and subsequent absorption were interrupted at different hydrogenation stages. According to the CMWP results, it was obtained that the initial value of the MgH2 grain size remains practically unchanged (20 nm) up to 40 % of desorption; however, at the final stage of the MgH2→Mg transformation the remaining small amount of MgH2 forms very small nanoclusters with an average diameter of 3 nm. This kind of transformation can be ascribed by instantaneous MgH2→Mg conversion of randomly selected particles which is the main characteristics of classical Johnson-Mehl-Avrami (JMA) model. On contrary, a different grain size evolution takes place during the Mg→MgH2 transformation, i.e. ⟨D⟩ increases almost linearly up to 19 nm. The increasing hydride size assumes a contracting volume (CV-type) transformation. The kinetics of hydride formation and decomposition described by semi-empirical models generally does not involve particle and grain-size dependence. Taking into account the size dependence, a total reacted function has been introduced for a nanocrystalline powder agglomerate and has been applied for surface controlled, contracting volume and JMA type of sorption processes. We showed that the shape of the measured reaction fraction curves do not determine unambiguously the rate controlling mechanism of hydrogen sorption, since the kinetics is strongly affected by the microstructure. References 1. D. Fátay, Á. Révész, T. Spassov, J. Alloys and Compounds 399 (2005) 237-241. 2. Á. Révész, D. Fátay, submitted, J. Power Sources (2010). 3. Á. Révész, D. Fátay, T. Spassov, J. Mater. Res. 22 (2007) 3144-3151. 4. D. Fátay, T. Spassov, P. Delchev, G. Ribárik, Á. Révész, Int. J. Hydrogen Energy 32 (2007) 2914-2919. 5. Á. Révész, Japanese Applied Physics 48 (2009) 076511.

331

LiBH4 and Ti-Catalyzed Nanocrystalline MgH2 Composite for Hydrogen Storage

H. Shao, M. Felderhoff, C. Weidenthaler and F. Schüth Department of Heterogeneous Catalysis, Max-Planck-Institut für Kohlenforschung, Mülheim an der Ruhr,

Germany shao@mpi-muelheim.mpg.de

A MgH2 nanocrystalline sample doped with titanium was obtained by a homogenously catalyzed synthesis which had been developed several decades ago1. The obtained sample contains two MgH2 phases: 84% of tetragonal β-MgH2 and 16% of the orthorhombic high-pressure modification γ-MgH2. The average crystallite size is 30 nm, as determined from XRD measurement line broadening and high resolution TEM. The nanostructured sample has a large BET surface area of 108 m2/g. Such MgH2 samples show hydrogen desorption temperatures more than 100℃ lower than commercial MgH2. After desorption, the Ti-catalyzed nanocrystalline sample absorbs hydrogen with a fast kinetics starting at 200℃. Both the Ti catalyst and the nanocrystalline structure with correspondingly high surface area play important roles in the improvement of hydrogen storage properties. The formation enthalpy and entropy values of catalyzed MgH2 nanocrystalline sample are -77.7 kJ/mol H2 and -138.3 J/K·mol H2, respectively. Thermodynamic properties do not change with nanostructure and catalyst, as expected for particles in this size range.

332

Figure 1. Temperature-programmed-desorption curves of 2LiBH4/Ti-catalyzed nanocrystalline MgH2 (red lines) and 2 LiBH4/commercial MgH2 (blue lines) composite samples (decomposition into vacuum). Composites of 2LiBH4 and Ti-catalyzed nanocrystalline MgH2 on the one hand and 2LiBH4/commercial MgH2 on the other were prepared by ball milling. From Figure 1, it can be seen that 2LiBH4/Ti-catalyzed nanocrystalline MgH2 composite sample starts to rapidly desorb hydrogen from 270℃ on, where LiBH4 is still solid. After heat-up to 385℃ and holding this temperature for 5 hours, this composite sample desorbs 9.5mass% hydrogen. The 2LiBH4/commercial MgH2 composite sample starts to desorb hydrogen only at a temperature higher than 350℃. The desorption processes of these two composite samples against different hydrogen pressures were studied and the reaction mechanisms in various temperature and pressure conditions are discussed. References 1. B. Bogdanović, S. Liao, M. Schwickardi, P. Sikorsky, B. Spliethoff, Angew. Chem., Int. Ed. Engl. 19, (1980), 818-819.

(a) (b)

Study on Hydrogen Storage Materials by TEM

Shigehito Isobe, Yongming Wang, Naoyuki Hashimoto, Somei Ohnuki Graduate School of Engineering, Hokkaido University, Sapporo, Hokkaido, Japan

Email: isobe@eng.hokudai.ac.jp For utilizing hydrogen as one of the secondary energies, it is necessary to establish high performance hydrogen storage technologies. Three hydrogen storage ways of liquid hydrogen, high–pressure gas hydrogen and absorbed hydrogen in hydrogen storage materials are considered as hydrogen storage tanks for fuel cell vehicles. Among them, hydrogen storage materials can store more hydrogen than highpressure gas or liquid hydrogen [1, 2]. We have studied on microscopic reaction mechanism of hydrogen storage materials such as MgH2, MH-NH3, NH3BH3, and NaAlH4 by means of transmission electron microscope (TEM) with controlling temperature and gas atmosphere. By using a high voltage electron microscope (HVEM), we can observe lattice image of these materials during the reaction. For example, we have observed the hydrogen desorption process of MgH2 with Nb2O5 catalyst at the temperature range from R.T. to 250 °C. As shown in Figure, decomposition of MgH2 occurred at the boundary between MgH2 and catalyst of Nb2O5. With increase of temperature, the phase of Mg is growing.

References 1. L. Schlapbach, and A. Züttel, Nature 414, 353 (2001). 2. W. Grochala, and PP. Edwards, Chem. Rev. 104, 1283 (2004).

Nb2O5

MgH2

Mg

Figure. High resolution image of boundary between MgH2 and Nb2O5 by HVEM

333

Magnesium-Graphite Composites for Hydrogen Storage with Tailored Heat Conduction Properties

C. Pohlmann1,*, L. Röntzsch2, S. Kalinichenka1, T. Hutsch2 and B. Kieback1,2 1 Institute of Materials Science, Dresden University of Technology, Dresden, Germany

2 Fraunhofer Institute for Manufacturing and Advanced Materials (IFAM), Dresden, Germany * Email: Carsten.Pohlmann@mailbox.tu-dresden.de

A key challenge of establishing a hydrogen-based energy cycle is the efficient and safe storage of the energy carrier. Due to a high gravimetric hydrogen storage density of up to 7.6 wt.%-H in the case of pure MgH2, Mg-based solid-state storage materials have attracted remarkable attention over the last decades [1]. Major emphasis has been put on enhancing the kinetic of such systems by introducing catalytically active elements and by nanoscale crystal structuring via ball-milling [2] or rapid solidification [3]. In view of the dynamics of a hydrogen storage tank system, a further important physical property of the storage material itself is its heat transfer characteristics in order to manage the reaction enthalpies during de-/hydrogenation. Due to the inferior heat conduction properties of most hydrides, composite materials containing hydrides and expanded natural graphite (ENG) have been investigated demonstrating impressive enhancement for various hydride systems [4; 5; 6]. In this contribution, compact composites of a melt-spun magnesium nickel alloy [3] and ENG were produced to tailor the heat conduction properties. At first, the melt-spun ribbons were chopped to accomplish a powder-like feedstock. Secondly, the thereby produced magnesium alloy flakes were mixed with various amounts of ENG and compacted to cylindrical pellets. For comparison, composites of magnesium hydride powder and ENG were investigated at equal processing parameters. All sets of specimens were investigated regarding their thermal conductivities in radial and axial direction, their microstructure and phase fractions. It was found that the heat transfer characteristics can be tailored in a wide range without deteriorating storage capacities beyond given targets [8]. Pure magnesium alloy compacts with a thermal conductivity of 6 W·m-1·K-1 were advanced up to 46.7 W·m-

1·K-1 using 25.5 wt.% ENG. The values of the hydride-based system vary within the range from 1 W·m-1·K-1 to 50 W·m-1·K-1. Thus, a hydrogen storage material with homogeneous heat transfer properties independent of the charging state can be anticipated. Furthermore, the hydrogenation/ dehydrogenation of the compact composites as well as their dimensional stability upon cycling will be discussed in view of their used in cylindrical hydride storage tanks. References: 1. L. Schlapbach, A. Züttel, Nature, 414, (2001), 353-358. 2 M. Dornheim, S. Doppiu, G. Barkhordarian, U. Boesenberg, T. Klassen, O. Gutfleisch, R. Bormann, Scr. Mater., 56, (2007), 841-846. 3. S. Kalinichenka, L. Röntzsch, B. Kieback, Intl. J. Hydrogen Energy, 34, (2009), 7749-7755. 4. A. Chaise, P.d. Rango, P. Marty, D. Fruchart, S. Miraglia, R. Olivès, S. Garrier, Intl. J. Hydrogen Energy, 34, (2009), 8589-8596. 5. H.-P. Klein, M. Groll, Intl. J. Hydrogen Energy, 29, (2004), 1503-1511. 6. A.R. Sánchez, H.-P. Klein, M. Groll, Intl. J. Hydrogen Energy, 28, (2003), 515-527. 7. D. Vojtech, P. Novák, J. Cízkovský, V. Knotek, F. Prusa, J. Phys. Chem. Solids, 68, (2007), 813-817. 8. C. Pohlmann, L. Röntzsch, S. Kalinichenka, T. Hutsch, B. Kieback, submitted to Intl. J. Hydrogen Energy.

334

Space-Confined NaAlH4 in Mesoporous Carbon for Hydrogen Storage: Enhancing Cycling Performance

Y.T. Li, F. Fang, Y. Song, and D. Sun Department of Materials Science, Fudan University, Shanghai, China

Email: 081030012@fudan.edu.cn

Sodium alanate (NaAlH4) has been considered as a candidate material for solid-state hydrogen storage since the pioneering discovery by Bogdanović that using Ti-containing compounds as doping agents to NaAlH4 can realize the hydrogen uptake and release reversibly under mild conditions.1 However, its practical application is still blocked by poor reversibility on multiple de-/re-hydrogenation cycles.2 An alternative approach to improve the hydrogen storage properties is a reduction of complex hydrides to nanoscale,3 but how to maintain the nanostructure upon multiple cycling is a challenge. To alleviate this problem, in the present work the space-confined NaAlH4 in mesoporous carbon was synthesized by two-step method of thermal melting impregnation and regeneration. It is found that the confined NaAlH4 shows faster dehydrogenation kinetics than that of the pristine NaAlH4. Moreover, an enhanced cycling performance is also proved that the capacity decay slightly from the first to sixth cycle, and keep invariant (up to 80%) with a further de-/re-hydrogenation up to fifteenth cycle. These improvements are attributed to the synergistic effects of both nanoconfinement and catalytic effect caused by mesoporous carbon.

Fig.1 Evolutions of normalized hydrogen release capacity of pristine NaAlH4 and confined NaAlH4 in mesoporous carbon.

References 1. B. Bogdanović, M. Schwickardi, J. Alloys and Compounds, 253–254, (1997), 1–9. 2. S. Orimo, Y. Nakamori, R. E. Jennifer, A. Züttel, C. M. Jensen, Chemical Reviews, 107, (2007), 4111–4132. 3. C. P. Baldé, B. P. Hereijgers, J. H. Bitter, K. P. de Jong, J. American Chemical Society, 130, (2008), 6761–6765.

335

Spin-Charge Conjunction Quantum Fluctuations Of Hydrogen in Nonequilibrium Nanosystem

M.Zhukovsky and S.Beznosyuk

Chemistry Department Altai State University, Barnaul, Russia Email: bsa1953@mail.ru

The new treatment of the nature of hydrogen atoms in nonequilibrium nanosystem is offered. The approach to the given problem is under construction on the basis of consideration specific sub-femtosecond bi-ionic and bi-radical relativistic quantum fluctuations hydrogen atoms in nonequilibrium nanosystem as effects of activation of internal quantum relativistic degrees of freedom of electron spin-charge conjunction at Fermi's level of nanoparticles. Occurrence of quantum-dimensional effect in compact nanoparticles of atoms in the condensed state essentially changes electrodynamic properties such discrete nanosystem [1]. Electrodynamical vacuum conditions change also a role relativistic spin-charge conjugating quasielectron- quasiholes pairs (е-е +) – quasipositroniums, which are born as sub-femtosecond bi-ionic and bi-radical relativistic quantum fluctuations at hydrogen atoms. These compound of quantum relativistic quasiparticles are born and disappear in the field of Fermi's electronic level of nonequilibrium nanoparticles in the condensed state. In the conditions of course of physical and chemical processes the quasipositronium dynamics property as quantum fluctuation at Fermi's level is defined by small energy of their formation. Really, inside nanoparticle its energy δε = (ε+ + ε-)/2 in the order of size makes nearby 7.5 eV [2]. As a result in case of 2δε = 15.0 eV a time of the quasipositronium life reaches sub-femtoseconds: Δτ ≤ ħ/2δε ≈ 0.04 fs. Thus the spatial area of relativistic transitions quasipositronium quantum fluctuation reaches: λ = сΔτ = ħс/δε ≈ 13 nm. This size is typical for nonequilibrium nanoparticles. These sizes and these intervals of life times of relativistic quasipositroniums (е-е+) set characteristic existential scale of areas of existence of nonequilibrium relativistic nanoparticles in the condensed state. Computer simulation of self-assembling confinement of single electron as a result of its entanglement with relativistic quasipositronium pair (е-е+) in compact subspace of H-atom illustrates theory. It is shown that finite electron wave function of the confined H-atom includes two parts: an electrodynamics kink-mode and an electrostatic cusp-mode. It is found out that there are two equilibrium states of hydrogen atom in the condensed state. One of them corresponds to infinite H-atom. Another state describes finite H-atom. Difference between them lies in that infinite wave function includes only electrostatic 1s-cusp-mode. Finite wave function, besides the 1s-cusp-mode, includes small addend of the kink-mode of entangled bi-ionic and bi-radical compound (e-е- + e-е+). The addition seriously changes features of H-atom. Equilibrium radius decreases from infinity to 3.1 a0. The “collapse” of H-atom is accompanied by appearance of specific changing in chemical features, which could be using for understanding of hydrogen behavior in nanostructures. References 1. S. Beznosjuk, B. Minaev, R. Dajanov, Z. Muldachmetov, Int. J. Quant. Chem., 38, (1990), 779-797. 2. S. Beznosyuk, D. Mezentzev, M. Zhukovsky, T. Zhukovsky, NATO Science Series: II Mathematics, Physics and Chemistry, 172, (2004), 531-538.

336

Hydrogen Storage Behaviours of Nanocrystalline and Amorphous Mg2Ni1-xMnx (x = 0-0.4) Alloys Prepared by Melt Spinning

Yang-huan Zhang a, b*, Dong-liang Zhaoa, Bao-wei Li b, Hui Yong a, b, Shi-hai Guo a, Xin-lin Wang a

a Department of Functional Material Research, Central Iron and Steel Research Institute, Beijing 100081, China

b School of Material, Inner Mongolia University of Science and Technology, Baotou 014010, China Email: zhangyh59@163.com or zyh59@yahoo.com.cn

The Mg2Ni-type compounds have been expecting to be used as hydrogen storage materials or negative anode electrode in Ni-MH batteries. However, their practical application to hydrogen suppliers has been limited mainly due to their sluggish hydriding/dehydriding kinetics as well as high thermodynamic stability of their corresponding hydride. In order to improve the hydriding and dehydriding kinetics of the Mg2Ni-type alloys, Ni in the alloy was partially substituted by element Mn, and the nanocrystalline and amorphous Mg2Ni-type Mg2Ni1-xMnx (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by the melt-spinning technique. The as-spun ribbons with a continuous length, a thickness of about 30 μm and a wideness of about 25 mm were obtained. The microstructures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system. Electrochemical impedance spectroscopy (EIS) spectra, Tafel polarization curves and H diffusion coefficient were measured using electrochemical workstation (PARSTAT 2273). The results show that all the as-spun alloy (x=0) hold typical nanocrystalline structure, whereas the as-spun alloy (x=4) displays a nanocrystalline and amorphous structure, confirming that the substitution of Mn for Ni significantly enhances the glass forming ability of the Mg2Ni-type alloy. The hydrogen absorption capacity of the alloys first increases and then decreases with rising Mn content, but the hydrogen desorption capacity of the alloys always grows with increasing Mn content. Furthermore, the substitution of Mn for Ni significantly improves the electrochemical hydrogen storage performances of the alloys, involving both the discharge capacity and the electrochemical cycle stability. Furthermore, the high rate dischargeability (HRD), electrochemical impedance spectrum (EIS) and potential-step measurements all indicate that the electrochemical kinetics of the alloy electrodes first increases then decreases with rising the percent of Mn substitution. Keywords: Mg2Ni-type alloy; Mn substitution; Melt spinning; Structures; Hydrogen

storage behaviours References 1. Kazuhide T, Journal Alloys and Compounds, 450, (2008), 432–439. 2. Ren H P, Zhang Y H, Li B W, Zhao D L, Guo S H, Wang X L, International Journal of

Hydrogen Energy, 34, (2009), 1429–1436.

337

Direct Synthesis of Sodium Alanate with Novel Catalytics TiB2

L.Li Y.J.Wang* Y.P.Wang Q.L.Ren L.F.Jiao and H.T.Yuan Institute of New Energy Material Chemistry of Nankai University, Key Laboratory of Energy-Material

Chemistry (Tianjin) and Engineering Research Center of Energy Storage & Conversion (Ministry of Education), Tianjin, PR China Email: wangyj@nankai.edu.cn

TiB2 as a novel catalyst was used in preparing TiB2-doped sodium aluminum hydride by ball-milling NaH/Al mixture with TiB2 powder under a lower hydrogen pressure. The X-ray diffraction (XRD) revealed that TiB2 particles synthesized by chemical reduction method were crystalline. NaAlH4 can be prepared by using TiB2 as catalyst in about 55 h at 1 MPa hydrogen pressure. It shows that TiB2 has a remarkable catalytic effect, enhancing the performances of hydrogen storage and release. The sample doped with 8 mol% TiB2 presented large amount of hydrogen release. It demonstrates that TiB2 particles synthesized by chemical reduction method is a promising catalyst for enhancing hydrogen release in light-metal complex hydrides. References 1. N. Eigen, M. Kunowsky, T. Klassen, R. Bormann, J. Alloys and Compounds, 430, (2007), 350–355. 2. X. Z. Xiao, X. L. Fan, K. R. Yu, S. Q. Li, C. P. Chen, Q. D. Wang, L. X. Chen, J. Phys. Chem. C, 113, (2009), 20745–20751. 3. X. P. Zheng, S. L. Liu, D. L. Li, Int. J. Hydrogen Energy, 34, (2009), 2701–2704 4. R. A. Zidan, S. Takara, A. G. Hee, C. M. Jensen, J. Alloys and Compounds, 285, (1999), 119–122.

338

Deuterium Desorption From Nano-Crystalline Magnesium Thin Films

R.Checchetto, N. Bazzanella and A.Miotello Department of Physics, University of Trento, Trento, Italy

P. Mengucci Department of Physics, Università Politecnica delle Marche, Ancona, Italy

Email: checchet@science.unitn.it Decreasing the particle size and distorting the crystalline lattice has been shown to influence the hydrogen desorption temperature in metal hydride. To study this point Pd capped nanocrystalline magnesium deuteride ultrathin films (thickness in the 100 nm range) with the β-MgH2 structure were prepared by vacuum evaporation of a Mg target and thermal annealing in 0.15 MPa D2 atmosphere at 373 K [1,2,3]. Different nanostructures of the deposited Mg films (columnar or nanocrystalline grains) were obtained by changing the substrate and by adding transition metal atoms to the growing Mg layers [4,5]. Here we report on the deuterium sorption kinetics and structural evolution of the Mg- based thin films as studied by thermal desorption spectroscopy (TDS), isothermal desorption kinetics, X-rays diffraction spectroscopy (XRD) and transmission electron microscopy (TEM). Analysis have been carried out to have indications on: i) preferential Mg nucleation sites in the MgD2 to Mg phase transition, ii) relation between the structure of the Mg thin films and thermal stability of the deuteride phase. References 1. R. Checchetto, N. Bazzanella, A. Miotello, R. S. Brusa, A. Zecca and P. Mengucci, J. Appl. Phys. 95, 1989 (2004) 2. R. Checchetto, R. S. Brusa, N. Bazzanella, G.P. Karwasz, M. Spagolla and A. Miotello, . Mengucci and A. Di Cristoforo, Thin Solid Films, 469-470, 350 (2004) 3. G. Siviero, V. Bello, G. Mattei, P. Mazzoldi, G. Battaglin, N. Bazzanella, R. Checchetto, A. Miotello, Int. Journal of Hydrogen Energy 34, 4817 (2009) 4. P. Mosaner, N. Bazzanella, R. Checchetto, A. Miotello, Mat. Sci. Eng. B 108, 33 (2004) 5. N. Bazzanella, R. Checchetto, A. Miotello, C. Sada, P. Mazzoldi and P.Mengucci, Appl. Phys. Lett. 89, 014101 (2006)

339

Nano-Confinement Effect on Hydrogen Sorption Properties of Metal Particles Embedded in a Porous Material

C. Zlotea a, P. Dibandjo b, D. Heurtaux c, F. Cuevas a, V. Paul-Boncour a, E. Leroy a, R. Gadiou b, C. Serre c C. Vix-Guterl b, and M. Latroche a

a Institut de Chimie et des Matériaux Paris Est (ICMPE), UMR 7182, CNRS, Thiais, France b Institut de Science des Matériaux de Mulhouse (IS2M), LRC 7227, CNRS, Mulhouse, France

c Institut Lavoisier, 45 Avenue des Etats Unis, 78035 Versailles, France Email: Claudia.Zlotea@icmpe.cnrs.fr

The downscaling and control of the metal particle sizes is an important issue for the design of new solid-state hydrogen storage materials. Materials with small crystal and particle size have improved kinetics of hydrogen sorption [1]. Moreover, theoretical calculations have stated that the thermodynamic properties of the Mg hydride can be destabilized when the metal clusters become smaller than 1.3 nm [2]. Hydrogen sorption properties of ultra-small Pd nanoparticles (2.5 nm) embedded in a porous material (carbon template-CT or metal-organic-frameworks-MIL) have been determined and compared to bulk system. Downsizing the Pd particle size introduces significant modifications of the hydrogen sorption properties. The total amount of stored hydrogen in nanosized Pd particles is decreased as compared to bulk Pd. The hydrogen absorption in Pd nanoparticles induces a phase transformation from fcc to icosahedral structure, as proven by in situ XDS and EXAFS measurements. This phase transition is not encountered in bulk since the fivefold symmetry is non-translational. The kinetics of hydrogen desorption from hydrogenated Pd nanoparticles is faster than in bulk Pd, as demonstrated by TDS investigations. Moreover, the presence of Pd nanoparticles embedded in CT strongly affects the desorption of physisorbed hydrogen, which occurs at higher temperature in the hybrid material as compared to the pristine carbon template (figure 1). In conclusion, this study clearly confirms that downsizing the Pd particle dimensions dramatically changes the interaction with hydrogen relative to bulk system.

Figure 1. Comparison of the TDS signals from CT/nanoPd (line), CT (dashed line) and bulk Pd (dotted line) between 22 and 310 K (0.42 K min-1). References 1. M. Fichtner, Nanotechnology 20 (2009) 204009. 2. R. W. P. Wagemans, J.H. van Lenthe, P. E. de Jongh, A. J. van Dillen, and K. P. de

Jong, Journal of the American Chemical Society 127 (2005) 16675.

50 100 150 200 250 300

chemisorption

bulk Pd

CT/nanoPd

Temperature (K)

TDS

sign

al (a

.u.)

CTphysisorption

340

Hydrogen Desorption Kinetics of Melt-Spun and Hydrogenated Mg-Based Alloys Using in Situ Synchrotron X-ray Diffraction and

Thermogravimetry

S. Kalinichenka1, L. Röntzsch2, C. Baehtz3 and B. Kieback1,2

1Institute for Materials Science, Dresden University of Technology, Helmholtzstraße 7, 01069 Dresden, Germany

2 Fraunhofer Institute for Manufacturing Technology and Applied Materials Research, Winterbergstraße 28, 01277 Dresden, Germany

3 Institute of Ion Beam Physics and Materials Research, Forschungszentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany

Email: siarhei.kalinichenka@tu-dresden.de

Magnesium alloys are favourable materials for the solid-state storage of hydrogen due to high gravimetric hydrogen storage densities of up to 7.6 wt.%-H in the case of MgH2, low specific weight, cycle stability, a comparatively high abundance in the earth's crust and comparatively low cost [1]. Nevertheless, the slow hydrogen sorption kinetics is still a challenge in view of practical applications. To overcome the kinetic and thermodynamic limitations of bulk Mg, nanostructured Mg alloys which contain catalytic elements like transition metals, metal oxides or rare earths are widely used [2].

In this study, a high-yield synthesis technology for nanocrystalline Mg-rich alloys was employed, namely melt spinning [3]. Mg-rich alloys with different compositions were prepared, e.g. Mg-Ni, Mg-Ni-Y, Mg-Cu-Ni-Y. They were characterized regarding their microstructure and cyclic (de-)/hydrogenation properties using SEM, TEM, EELS, in situ synchrotron XRD, DSC and TGA. Thermogravimetry using a magnetic suspension balance shows that these alloys can reach reversible gravimetric hydrogen storage capacity of up to 5.3 wt.%-H2. The hydrogenation rates and the maximum hydrogen storage capacity of the alloys at 20 bar H2 are comparably high even at 150 °C. However, dehydrogenation at this temperature is too slow due to thermodynamic reasons at pressures of 1 bar H2 and more. In order to understand the dehydrogenation reactions of the hydrogenated melt-spun Mg-based alloys and the role of catalysts in this processes, the desorption properties were studied by in situ synchrotron X-ray diffraction (SR-XRD) performed at European Synchrotron Radiation Facility (ESRF) in Grenoble as well as by thermogravimetric analysis and differential scanning calorimetry (DSC). It was found that the kinetics of hydrogen de-sorption is controlled by different mechanisms for both alloys. According to the results ob-tained by DSC and SR-XRD both alloys undergo a two-step desorption with different de-sorption kinetics [4]. References 1. B. Sakintuna, F. Lamari-Darkrim, M. Hirscher, Intl. J. Hydrogen Energy 32 (2007) 1121-

1140. 2. G. Liang, J. Huot, S. Boily, A. van Neste, R. Schulz, J. Alloys Compd. 292 (2005) 247-252. 3. S. Kalinichenka, L. Röntzsch, B. Kieback., Intl. J. Hydrogen Energy 34 (2009) 7749-7755. 4. S. Kalinichenka, L. Röntzsch, C. Baehtz, B. Kieback, J. Alloys Compd. (2010), in press,

DOI: 10.1016/j.jallcom.2010.02.128.

341

Tayloring NaAlH4 Towards Realistic Operation Conditions

T.Schmidt, L.Röntzsch, C.Pohlmann and B.Kieback Fraunhofer IFAM, Dresden Branch Lab, Hydrogen Technology Group, Dresden, Germany

Email: thomas.schmidt@ifam-dd.fraunhofer.de NaAlH4, doped with transition metal catalysts is a promising material for hydrogen storage [1,2]. Both hydrogen desorption and reabsorption can be carried out under moderate temperature. Cycle stability has been proven as well. However, available studies in literature usually fail to adress the technically interesting conditions, namely desorption against hydrogen back-pressure and dehydrogenation-rehydrogenation cycles at constant temperature. A further problem is the extremely low heat conductivity of the hydride, which increases with the size of the storage tank. A promising attempt to circumvent problems with heat transfer is the introduction of lightweight carbon material with a high heat conductivity as has been demonstrated for Mg-based systems [3,4]. Very recently, we were able to demonstrate efficient hydrogen desorption of Ti-Zr codoped NaAlH4 at 150°C against a hydrogen pressure of 4 bar [5], which is the considered bach-pressure for high temperature PEM fuel cells [6]. Furthermore, we could reversibly store and release 4 wt.% hydrogen under isothermal conditions (125°C). In our contribution we present detailed investigations of the effect of hydrogen back pressure on the desorption kinetics of Ti-Zr codoped NaAlH4. The influence of temperature, catalyst concentration and the ratio of Ti and Zr on the absorption and desorption rate will be adressed. The effect of enhanced natural graphite on the thermal conductivity of compacted NaAlH4 samples will be discussed. Those data are of utmost importance for the development of hydrogen storage devices, based on transition metal-doped NaAlH4. The results indicate that Ti-Zr codoped NaAlH4 is a promising material for hydrogen storage, which should ideally be used in combination with a high temperature PEM fuel cell. References 1. F.Schüth, B.Bogdanovic, M.Felderhoff, Chem. Commun. 2004, 2249-2258. 2. S.Orimo, Y.Nakamori, J.R.Eliseo, A.Züttel, C.M.Jensen, Chem. Rev. 107 (2007), 4111-4132. 3. A.Chaise, P.de Rango, P.Marty, D.Fruchart, S.Miraglia, R.Olives, S.Garrier, Int. J. Hydr. En. 34 (2009), 8589-8596. 4. C.Pohlmann, Diploma thesis, University of Dresden, 2009. 5. T.Schmidt, L.Röntzsch, "Reversible hydrogen storage in Ti-Zr codoped NaAlH4 under realistic operation conditions", accepted for publication in J. Alloys Compd. 6.http://www1.eere.energy.gov/hydrogenandfuelcells/storage/pdfs/targets_onboard_hydro_storage.pdf

342

Effect of Activated Carbons Derived from Agricultural by- Products on the Hydrogen Storage Properties of Magnesium

E. Grigorovaa, Ts. Mandzhukovaa, M. Khristova, B. Tsyntsarskib and P. Tzvetkova

a Institute of General and Inorganic Chemistry, Bulgarian Academy of Sciences, bl.11, Acad. G. Bonchev str.

1113 Sofia, Bulgaria b Institute of Organic Chemistry, Bulgarian Academy of Sciences, bl.9, Acad. G. Bonchev str., 1113 Sofia,

Bulgaria Email: egeorg@svr.igic.bas.bg

The absorption-desorption characteristics towards hydrogen of composite 95wt.%

Mg-5wt.% activated carbons derived from bean pods and apricot stones obtained by ball milling under argon atmosphere were investigated. Hydriding measurements of the composites were performed at temperatures 573 K and 473 K and pressure of 1 MPa and dehydriding at T = 623 K and P = 0.15 MPa. The activated carbons used as additives to magnesium were prepared by steam pyrolysis. The specific surface area values obtained by BET analysis are 960 m2/g for the activated carbon derived from apricot stones and 260m2/g for the activated carbon derived from bean pods. Comparing the hydrogen sorption data it was established that the activated carbon with higher specific surface area reflects more favorably the hydrogen sorption kinetics of magnesium. At T = 573 K and P = 1 MPa the absorption capacity values are 5.43 wt.% for the composite containing activated carbon derived from bean pods and 6.13 wt.% for the one containing activated carbon from apricot stones. The highest rate of dehydriding showed the latter composite which desorbs 50% of its maximum hydrogen absorption capacity within 16 min. Besides the specific surface area other characteristics of activated carbons as surface chemistry and porosity have to be also taken into account. The phase composition and morphology of the composites were characterized by X-ray diffraction analysis, scanning electron microscopy and laser particle size analysis. The scanning electron microscopy images after hydriding showed the formation of some cracks on the surface of the composites. After ball milling particles in the range of 20 µm to 50 µm and small particles of the order of few µm could be distinguished while after hydriding the size and the shape of the particles are similar. The data on particle size distribution of the composites confirm the SEM results. The hydriding/dehydriding characteristics of the studied composites were compared with those of pure magnesium. It was established that the activated carbons derived from bean pods and apricot stones improved the hydrogen sorption kinetics of magnesium.

343

Using X-ray Photoelectron Spectroscopy in Investigation of Mg-Based Thin Film Hydrides

I.J.T. Jensen,1* S. Diplas,2,3 O.M. Løvvik,1,2 H. Schreuders, 4 and B. Dam, 4

1Department of Physics, University of Oslo, P/O box 1048 Blindern, 0316 Oslo, Norway

2SINTEF Materials and Chemistry, P/O box 124 Blindern, 0314 Oslo, Norway 3Department of Chemistry and Center for Materials Science and Nanotechnology, P/O box 1126 Blindern,

0318 Oslo, Norway 4Materials for Energy Conversion or Storage (MECS), DelftChemTech, Faculty of Applied Science,

Technical University Delft, P/O Box 5045, NL-2600 GA Delft, The Netherlands *Corresponding author (i.j.t.jensen@fys.uio.no)

Mg is an interesting material in a hydrogen storage perspective due to its low weight, and its intriguing change in optical properties upon hydrogenation makes Mg-based thin films a good candidate for a variety of other applications as well. These applications cover a wide range, from coatings on solar collectors and smart windows to optical hydrogen sensors and semiconductor devices. Despite the importance of electronic structure in this context, there has been limited work done on these (or any) hydride systems using spectroscopic techniques like X-ray photoelectron spectroscopy (XPS). In this work XPS using monochromatic Al Kα radiation (hν =1486.6 eV) was employed to investigate different Mg and Mg-Ti thin film samples, with and without hydrogen. The spectra from hydrogenated samples were compared to those from metallic samples, and efforts were made to identify specific contributions from the Mg-H bonds. Issues regarding electronic structure and atomic arrangement are discussed on the basis of the experimental results.

344

Thermal Stability of Gas Phase Magnesium Nanoparticles for Hydrogen Storage: a TEM Study

Gopi Krishnan, G. Palasantzas , B.J. Kooi. Zernike Institute for Advanced Materials and Materials Innovation Institute, University of Groningen,

Nijenborgh 4, 9747 AG Groningen, The Netherlands.

Email: G.Krishnan@student.rug.nl Magnesium nanoparticles have attracted strong interest as high capacity hydrogen storage materials in order to improve the poor kinetics of H adsorption/desorption and reduce the high thermal stability of MgH2 due to nanoscale size effects. Here we present a unique transmission electron microscopy study of the stability of gas phase synthesized Mg nanoparticles (∼10-80 nm in size) during thermal annealing. Hydrogenation of Mg nanoparticles at 280 oC for 40 hours results in void formation in each Mg core with development of a relatively thin MgH2 phase around the void. The results indicate void formation prior to MgH2 formation. In fact, Mg nanoparticles with an MgO shell (~3 nm thick) annealed at 300 0C show evaporation, void formation and void growth in the Mg core both in vacuum and under various high pressure gas environments This is mainly due to the outward diffusion and evaporation of Mg with the simultaneously inward diffusion of vacancies leading to void growth (Kirkendall effect associated with evaporation). The rate of Mg evaporation and void formation depends on the annealing conditions. In vacuum, and at T=300 0C, the complete evaporation of the Mg core takes place (within a few hours) for sizes ∼15-20 nm, Void formation and growth has been observed for particles with sizes ∼20-50 nm, while stable Mg nanoparticles were observed for sizes > 50 nm. Furthermore, even at relative low temperature, as low as 60 0C, the effect of annealing in vacuum shows void formation and its growth in 15-20 nm sized Mg nanoparticles, indicating that voiding will be even more dominant for nanoparticles smaller than 10 nm. Therefore, our findings confirm that Mg evaporation and void formation in nanoparticles with sizes less than 50 nm present formidable barriers for their applicability in hydrogen storage. However, results on Mg-Ni based nanoparticle show an improved thermal stability compared to pure Mg nanoparticles. References 1. G.Krishnan, B.J.Kooi, G.Palasantzas, Y.Pivak, B.Dam, J. Applied Physics, 107, (2010), 053504 .

345

Hydrogenation and Microstructural Study of Melt-Spun Ti0.8V0.2 S. Suwarno a, J.K.Solberg a, V.A. Yartys a,b

a Department of Materials Science and Engineering, NTNU, NO-7491, Trondheim, Norway b Institute for Energy Technology, P.O. Box 40, NO-2027, Kjeller, Norway

Email: suwarno@material.ntnu.no Hydrides of titanium, vanadium and their alloys have gravimetric and volumetric hydrogen densities of up to 4.01 wt. % H and 150 kg H/m3. Ti and V also release significant amount of heat during the hydrogen uptake. Therefore, their alloys have an application potential for both hydrogen and heat storage systems. In this work we utilized the melt spinning process to synthesize a nanostructured Ti-V alloy. The aim was to improve the kinetics of hydrogen exchange in the material. A Ti0.8V0.2 pre-alloy (BCC structure; a =3.2315 Å) was first produced by argon arc melting. Ribbons were solidified from the melt using two different wheel spinner velocities; 1000 rpm (Ti0.8V0.2 MS1000) and 3000 rpm (Ti0.8V0.2 MS3000). LOM, SEM, EPMA were utilized to examine the microstructures of the ribbons and their corresponding hydrides. Hydrogen absorption and desorption were performed using a TDS technique. The metal alloys and the hydride structures were further characterized by SR XRD at SNBL, ESRF, Grenoble. Hydrides of the pre-alloy, Ti0.8V0.2 MS1000, and Ti0.8V0.2 MS3000, were found to crystallize in an FCC crystal structure having lattice parameter of 4.4340 Å, 4.4216 Å, and 4.4224 Å, respectively. Rapid solidification (RS) resulted in very small grains, so the average grain size of the hydrogenated Ti0.8V0.2 MS3000 alloy was smaller than 200 nm (see Figure 1a). The thermal stability of the hydrides correlated very well with the RS solidification rate. For the hydride of Ti0.8V0.2 MS3000, a decrease in the thermal stability was observed (the temperature for the peak of H desorption was 79 centigrades lower than for the pre-alloy, see Figure 1b). Thus, nanostructuring achieved by the melt spinning process yields improvements in the hydrogen storage behavior of the present Ti-V alloy.

(a)

igure. (a) Microstructure of the hydride of melt spun Ti0.8V0.2 MS3000; S spectra and

(b)

F(b) Temperatures of the main peak of hydrogen evolution in the TD intensities of the desorption peaks. We note decreasing peak temperature with increasing spinner speed.

346

Preparation and Characterization of Porous Carbon Spheres with Controlled Micropores and Mesopores Xiaoping Jiang, Xin Ju* and Miaofeng Huang

Department of Physics, University of Science and technology Beijing, 100083 Beijing, China *Email: jux@ustb.edu.cn

In order to solve the current energy and environmental problems caused by fossil fuels, hydrogen has received considerable attention as a clean energy[1]. Porous carbon materials as a major candidate for hydrogen storage have attracted many scientific interests because of its light weight, abundant natural precursors, low cost, and high surface area. Tailored pore systems of the porous carbon materials for hydrogen storage is an urgent matter[2,3]. In recent years, template carbonization was applied to produce porous carbons with tunable pore size distributions through the selection of templates, carbon sources, infiltration methods, and filling degree of the carbon precursor in the pore system of templates[4]. In this article, porous carbon spheres were prepared by carbonization of resorcinol–formaldehyde (RF) aerogel spheres at a high temperature under an argon atmosphere. Commercial hollow polystyrene spheres were used as templates and microreactors for polymerization of resorcinol and formaldehyde monomers in the synthesis. The carbon dioxide activation was applied to further control the pore structures and textures of the porous carbon spheres which closely associated with the hydrogen storage properties. Small angle X-ray scattering (SAXS) using synchrotron radiation as X-ray source was employed to characterize the microstructure and the specific surface area of the porous carbon spheres. Within certain limits, the specific surface area increases with the higher concentration of RF precursor solution. The atomic concentration and chemical shift on the surface of the porous carbon spheres were measured using X-ray photoelectron spectroscopy technique. The results reveal that carbonization temperature has obvious effect on surface composition and function species of carbon spheres. References 1. L. Schlapbach, A. Züttel, Nature, 414, (2001), 353-358. 2. M. Hirscher, B. Panella, J. Alloys and Compounds, 404-406, (2005), 399-401. 3. H. Wang, Q. Gao, J. Hu, J. American Chemical Society, 131, (2009), 7016-7022. 4. A.-H. Lu, F. Schüth, Advanced Materials, 18, (2006), 1793-1805.

347

The Effects of Mg-Ti Compound on the Hydrogen Temperature Ranges of Desorption

I.Neklyudov, N.Lomino, O.Morozov, V.Kulish, V.Zhurba, V.Ovcharenko, O.Kuprin National Science Center “Kharkov Institute of Physics and Technology”, Kharkov, Ukraine

Email: morozov@kipt.kharkov.ua At the present stage of materials science development special interest is caused with materials in nanocrystalline state which it is expected will open new opportunities in achievement of hydrogen high concentration and its low temperatures desorption. One of materials production method in nanocrystalline state is introduction nanoforming addition. To nanoforming elements it is necessary to carry of chemical elements which do not form binary phases with components alloy and show negligible solubility. At the present stage of solubility studying of chemical compounds in system Mg-Ti is not revealed. Production by physical methods magnesium - titanium of composites with the various composition a component and research of their hydrogen storage properties is of interest. Production magnesium-titanium of composites was carried out by a method of plasma evaporation - sputtering a component on molybdenum. Deuterium saturation of Ti-Mg composites was realized through 24 keV D ion implantation at temperatures of ~110 К to doses ranging between 1×1017 and 5×1018 D/cm2. In the course of deuterium ion implantation the concentration of deuterium in the implanted layer, Y/ΔD, was measured using the nuclear reaction method. After implantation of the preset deuterium dose, the temperature ranges of deuterium desorption in zirconium were determined by the thermal desorption spectroscopy technique.

2+

Researches of concentration influence of the titanium on temperature ranges desorption deuterium from a Ti-Mg composite have shown. Contents of the titanium below 67at.% lead to significant downturn of temperature desorption deuterium. At the same time excess of this concentration is accompanied by slight increase of temperature desorption deuterium in comparison with allocation from pure Mg. Dependence of maxima temperature desorption deuterium peak from composition a component magnesium - titanic composites (see fig. 1) evidently shows quantum character of temperature allocation of the same doses implanted deuterium depending on component magnesium - titanium composite.

Fig.1. Dependence of maxima temperature desorption maxima deuterium peak from component Ti-Mg composites A deuterium dose ~7.3×1017D/см2

Indisputable interest represents area of structure magnesium - titanic composites with the maintenance of magnesium above 50 ат. %. On the basis of the received data on десорбции hydrogen on an example of compositions Mg-Ti it is drawn a conclusion on perspectives of search of materials of hydrogen storage which have nanoforming elements.

348

Hydrogen Absorption/Desorption Properties and Catalytic Mechanisms of the NaOH-added Mg(NH2)2-2LiH System

Yongfeng Liu, Chu Liang, Ying Jiang, Zhijun Wei, Mingxia Gao, and Hongge Pan Department of Materials Science and Engineering, Zhejiang Univeristy, Hangzhou 310027, China

Email: hgpan@zju.edu.cn The Mg(NH2)2-2LiH system has attracted intensive attention due to its relatively higher hydrogen storage capacity (5.6 wt%) and favorable thermodynamics (~39 kJ/mol-H2). However, the high operating temperature for hydrogen desorption prevents it from practical applications. In this work, NaOH was introduced into the Mg(NH2)2-2LiHsystem for improving the hydrogen desorption kinetics. The effects of NaOH addition on the hydrogen storage properties of the Mg(NH2)2-2LiH system were systematically studied, and the catalytic mechanisms were elaborated. The operating temperatures for hydrogen absorption/desorption of the Mg(NH2)2-2LiH system were significantly lowered by the addition of NaOH as a 35 ºC reduction in the onset temperature for hydrogen desorption from the Mg(NH2)2-2LiH-0.5NaOH sample was attained relative to the pristine sample. Mechanistic analyses showed that NaOH first reacted with Mg(NH2)2 and LiH to convert to MgO, NaH, and LiNH2 during ball milling, and then their synergistic catalysis played an important role on the improvement of the hydrogen storage performances of the Mg(NH2)2-2LiH system.

349

Fig. 1 TPD curves of the post-36h milled samples with/without addition of NaOH.

References 1. P. Chen, Z.T. Xiong, J.Z. Luo, J.Y. Lin, K.L. Tan, Nature, 420, (2002), 302-304. 2. Z.T. Xiong, G.T. Wu, J.J. Hu, P. Chen, Adv. Mater., 16, (2004), 1522-1525. 3. W.F. Luo, J. Alloys Compd., 381, (2004), 284-287. 4. T.K. Mandal, D.H. Gregory, Annu. Rep. Prog. Chem., Sect. A, 105, (2009), 21-54. 5. Y.F. Liu, K. Zhong, K. Luo, M.X. Gao, H.G. Pan, Q.D. Wang, J. Am. Chem. Soc.,

131, (2009), 1862-1870.

25 50 75 100 125 150 175 200 225 250 275

Inte

nsity

(a.u

.)

Temperature (°C)

Mg(NH2)2-2LiH Mg(NH

2)2-2LiH-0.1NaOH

Mg(NH2)2-2LiH-0.3NaOH

Mg(NH2)2-2LiH-0.5NaOH

192186

178

154

Hydrogen Addition to Local Defects in CNT

A.Popov and E.Zheleznyak Department of Education Quality Control Southern Federal University, Rostov-on-Don, Russia

Email: nanosys@mail.ru The attempt of theoretical research of hydrogen joining to defects in nanotubes is undertaken. As is clear the defect region should be chemically more active, than faultless regions of nanotubes. This assumption has received acknowledgement in results of the calculations executed in the framework of a semi empirical PM3-method [1-4]. The computations of equilibrium configuration, total energy, heat of formation, ionization potential and IR spectra for fragment of (9, 0) tube C198 with the different kinds of local vacancies and one or two hydrogen atoms added to them are performed in the framework of semi empirical PM3 method. To get a possibility of direct comparison with experimental data there are calculated IR spectra also for all of the objects. Essential reconstruction of IR spectra in the region of high frequency collective vibrations of a carbon cage is observed. Besides, the additional lines with frequency of considerably exceeding frequencies of collective vibrations of a carbon cage appear also in IR spectra. This line corresponds to longitudinal vibrations CH bond. The frequency of these vibrations allows indirectly estimate the strength of CH bond. Joining of hydrogen with defects in nanotubes leads to change DOS in the nearest neighborhood of Fermi's level energy, and also to essential change of IR spectra in the region of high-frequency collective vibrations of a carbon cage and to occurrence in IR spectra additional lines corresponding to longitudinal vibrations of CH bond. References 1. M.J.S. Dewar, W. Thiel. J. Am. Chem. Soc. 99, 4899 (1977). 2. J. J. P. Stewart. J. Comput. Chem. 10, 209 (1989). 3. J. J. P. Stewart. J. Comput. Chem. 10, 221 (1989). 4. T. Clark, A.Breindl, G.Rauhut, J. Mol. Model., 1, 22 (1995).

350

Structural Investigation of LiAl(NH2)4 on Thermal Decomposition

Taisuke Ono1), Keiji Shimoda2), Masami Tsubota2), Takayuki Ichikawa1,2), Ken-ichi Kojima3), Masataka Tansho4), Tadashi Shimizu4), and Yoshitsugu Kojima1,2)

1) Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima 739-8530, Japan, 2) Instutite for Advanced Materials Research, Hiroshima University, Higashi-Hiroshima 739-8530, Japan, 3) Division of Environmental Siences, Graduate School of Integrated Arts and Sciences, Hiroshima University, Higashi-Hiroshima 739-8521, Japan, 4) National Institute for Materials Science, 3-13 Sakura,

Tsukuba 305-0003 Email: two4one619@hiroshima-u.ac.jp

A composite technique is quite useful to improve gas desorption properties for chemical

hydrides,. Recently, Janot et al. focused on lithium aluminum amide LiAl(NH2)4, and they reported that the composite of LiH and LiAl(NH2)4 released more than 5 mass% H2 below 130 °C [1]. Thermal decomposition pathway of the composite was also proposed. However, the composite become amorphous during decomposition, and the detailed reaction products are still unclear. Therefore, it is important to clarify the NH3 desorption mechanism of pristine LiAl(NH2)4 for better understanding the complex thermal reaction of the composite. In the present study, we have investigated the detailed structural properties of the decomposition products by using in situ synchrotron X-ray diffraction, in situ infrared spectroscopy, and solid-state nuclear magnetic resonance spectroscopy as well as the thermal gas desorption properties by thermogravimetry-mass spectroscopy, and then, have reexamined the thermal decomposition pathway of LiAl(NH2)4.

351

Fig. 1 In situ X-ray diffraction patterns

LiAl(NH2)4 was synthesized by milling the mixture of LiH and Al in liquid NH3. The results of the thermal analysis indicated that the NH3 desorption from LiAl(NH2)4 proceeds in two-step process. The results of high temperature in situ X-ray diffraction measurement showed that LiAl(NH2)4 became amorphous phase with NH3 desorption above 135 °C (Fig. 1). The results of in situ infrared spectroscopy indicated that the sharp amide peaks in LiAl(NH2)4 immediately disappeared during the first decomposition stage (≤ 125 °C), and imide-like units became dominant species with the decreasing nitrogen and hydrogen atoms by the NH3 desorption. 27Al MAS NMR results indicated that tetrahedral Al site (AlN4) maintained from RT to 400 °C. These results propound another decomposition model that the tetrahedral Al clusters were polymerized to make up for released N as Al-NH-Al or N-Al3, where the nitrogen is bound with two Al and one H or three Al, respectively. These polymerized compounds which have the wide-ranged bonding angle and length might give the amorphous features in X-ray diffraction profiles. Acknowledgement This work was partially supported by NEDO under “Advanced Fundamental Research Project on Hydrogen Storage Materials”. Reference 1. R. Janot, J. Eymery, J. Tarascon, J. Phys.

Chem. C, 111, (2007), 2335-2340. of LiAl(NH2)4 up to 400 °C

Hydrogen Diffusion in Bulk Metallic Glasses Zr-Cu-Al-Pd

A. Gradišek, T. Apih, A. Kocjan, P. Jeglič, S. Vrtnik and J. Dolinšek Jozef Stefan Institute, Jamova 39, SI-1000 Ljubljana, Slovenia

Email: anton.gradisek@ijs.si We report on the direct determination of the hydrogen self-diffusion coefficient D in a series of hydrogen-storage bulk metallic glasses Zr50Cu39Al10-xPdx using the technique of nuclear magnetic resonance diffusion in a static fringe field of a superconducting magnet. Magnetic field gradient was 68 T/m. For all the samples, the H/M ratio was around 0.2. In the investigated temperature interval between 380 K and 420 K, D is in the range 10-8–10-9 cm2/s and obeys Arrhenius form, D = D0 exp(-Ea/kBT), indicating classical over-barrier-hopping hydrogen diffusion with the activation energy Ea = 576 ± 15 meV. Additionally, 27Al, 63Cu and 65Cu and NMR spectra were measured on all the samples before and after loading with hydrogen. The spectra were analyzed using a model for amorphous solids. After loading, the crystal lattice expands. This results in the narrowing of the spectral lines, which are mainly determined by the quadrupolar interaction. The expansion of the lattice, obtained from the NMR measurements, is consistent with the X-ray measurements.

352

Kinetics and Modeling Study of Magnesium Hydride with Various Additives at Constant Pressure Thermodynamic Driving Forces

S. T. Sabitu and A. J. Goudy

Department of Chemistry, Delaware State University, Dover, DE 19901 Email: agoudy@desu.edu

Magnesium hydride has been extensively studied for hydrogen storage because it has a high hydrogen-holding capacity of 7.6 wt%. A major obstacle to its usefulness for hydrogen storage is the high temperature required for it to release hydrogen and its relatively slow reaction rates. Researchers have attempted to lower the desorption temperature and increase reaction rates by using additives such as metal oxides and transition metals. In this research a series of mixtures were made in which MgH2 was ball milled with 4 mol% of TiH2, Nb2O5 and Mg2Ni or combinations of these. The goal was to compare the effects of these additives on the reaction kinetics of MgH2. This comparison was made using a novel procedure in which the ratio of the equilibrium plateau pressure (Pm) to the opposing pressure (Pop), defined as the N-value, was the same in all cases. This represents the first time that this method has been used to study the kinetics of the magnesium hydride system. Since the Gibbs free energy change is proportional to Ln(Pm/Pop), it was concluded that these experiments were carried out under constant pressure thermodynamic driving forces. Temperature programmed desorption (TPD) analysis showed that the addition of 4 mole percent of the various additives to MgH2 resulted in a reduction of the onset temperature of MgH2 by as much as 190 oC. By doing TPD analyses at several different scan rates, it was possible to obtain the data necessary to construct Kissinger plots. These plots were used to obtain activation energies for the mixtures. The kinetic data were fitted to models for a moving boundary mechanism, a diffusion controlled process, and nucleation and growth in order to determine which of these processes controlled the reaction rates. References

1. A. Ibikunle, A. J. Goudy, and H. Yang, J. Alloys and Compounds, 475 (2009) 110-115.

2. H. Yang, A. Ojo, P. Ogaro and A. J. Goudy, J. Phys Chem C, 113 (2009) 14512-14517.

353

Catalytically Enhanced Dehydrogenation of Hydide-Amidoborane Composite Materials for Hydrogen Storage

Yu Zhang, Keiji Shimoda, Takayuki Ichikawa and Yoshitsugu Kojima

Institute for Advanced Materials Research, Hiroshima University Email: tichi@hiroshima-u.ac.jp

Ammonia borane (AB) has been considered as one of the most important candiates in

hydrogen storage materials during the last decade.[1] However, its practical application is greatly retarded by the sluggish dehydrogenation kinetics at below 100 ºC and the release of trace quantities of borazine, diborane and ammonia. To solve this terrible problem, novel alkali-metal amidoboranes, such as LiNH2BH3 and NaNH2BH3 (MAB), are recently proposed to release approximately 10.9 mass% and approximately 7.5 mass% hydrogen, respectively.[2] Unfortunately, the hydrogen purity still suffers from concurrent release of ammonia,[3] which is extremely detrimental for fuel cell operation even at trace level (NH3 would poison the noble Pt catalyst).[4] From the above points of view, obtaining of truly pure hydrogen at ever lower temperature is of great importance. Here, we proposed a novel method to activate MAB by hybrid alkaline-metal hydrides (LiH and NaH) and AB (hydride:AB = n:1, n>1). Alkali-metal amidoboranes and hydide-amidoborane compsite materials were prepared by ball milling AB and alkali-metal hydrides under H2 atmosphere for 1 h at 200 rpm. The products were characterized by means of X-Ray Diffraction(XRD), Thermalgravimetry combined with Mass Spectroscopy(TG-MS), Nuclear Magnetic Resonance(NMR)

It is found that MAB can be successfully activated by the excess of alkaline-metal hydride (NaH) via a dihydrogen bond between hydridic hydrogen of NaH and protonic hydrogen of MAB. The desorption results showed this activation strategy can significantly decrease the dehydrogenation temperature, and furthermore can successfully suppress ammonia gas release and volume expansion, which are of great importance for fuel cell application from the viewpoint of system design and running cost. This advantage may come from tuning the reactivity of B-H, N-H and B-N bonds through inducing polar species such as strong electropositive cations. This successful strategy for obtaining truly pure hydrogen at rather low temperature would propel the realization of hydrogen economy.

This work was partially supported by the project “Advanced Fundamental Research on Hydrogen Storage Materials” of the New Energy and Industrial Technology Development Organization (NEDO). References 1. F. H. Stephens, V. Pons, R. T. Baker, 25, Dalton Trans. (2007), 2613-2626. 2. Z. Xiong, C. K. Yong, G. Wu, P. Chen, 1, Nat. Mater, (2008), 360-363. 3. K. J. Fijalkowski, W. Grochala, 19, J. Mater. Chem. (2009), 2043-2050. 4. N. Rajalakshmi, T. T. Jayanth, K. S. Dhathathreyan, 3, Fuel cells. (2003), 177-180.

354

Hydrogen Desorption from Destabilized LiBH4

Bin Hong Liua, Bang Jie Zhanga, Zhou Peng Lib a: Dept. of Materials Science and Engineering, b: Dept. of Chemical Engineering

Zhejiang University, Hangzhou 310027, P.R. China Email: liubh@zju.edu.cn

LiBH4 is of interest as a promising hydrogen storage material due to its high gravimetric and volumetric hydrogen densities [1-2]. It contains 18.4wt% hydrogen and is among a few chemicals with the highest hydrogen capacities. The decomposition of LiBH4 is proposed to be as follows: LiBH4 = LiH + B + 3/2H2 (1) In the above reaction, 13.6wt% hydrogen can be achieved. However, the reversible hydrogen storage in LiBH4 is found to be tough. The dehydrogenation temperature is well over 400oC and the re-hydrogenation temperature is above 600oC under 7MPa H2 [1]. Some oxides and halides like SiO2, TiO2, TiCl3 were found to effectively promote hydrogen release from LiBH4 [2]. Vajo et al. [3] reported that the mixture of LiBH4 +1/2 MgH2 showed reversible hydrogen storage under milder conditions than pure LiBH4. In this work, we report our research on hydrogen desorption from LiBH4 destabilized by halides of some transition metals and rare earth metals. The dehydrogenation temperature of the mixtures of LiBH4 and halides was considerably decreased to 230oC-300oC. Ball milling treatment for the mixtures could further decrease the hydrogen desorption temperature. In some cases, diborane was detected through a coupled DSC-TG-MS analysis. The mechanisms of LiBH4 destabilization and diborane formation were discussed.

References 1. A. Zuttel, P. Wenger, S. Rentsch, P. Sudan, Ph. Mauron, Ch. Emmenegger, J. Power Sources, 118, (2003), 1-7. 2. S. Orimo, Y. Nakamori, J.R. Eliseo, A. Zuttel, C.M. Jensen, Chem. Rev., 107, (2007), 4111-4132. 3. J.J. Vajo, S.L. Skeith, F. Mertens, J. Phys. Chem. B, 109, (2005), 3719-3722.

355

Adsorbtion and Storage Hydrogen in Graphene-Based Carbon Nanotubes

Synthesized in Pores of Inorganic Membranes A.P. Soldatov, O.P. Parenago and M.V. Tsodikov

Topchiev Institute of Petrochemical Synthesis RAS, Moscow, Russia E-mail: Soldatov@ips.ac.ru

Now, much attention is paid to the synthesis and investigations of materials composed of nanosized particles. Among these works, studies of carbon nanostructures (nanocrystallites, nanotubes, nanofibers, graphenes, etc.), which have extraordinary adsorption and electron emission properties, hold a special place.

The new technique of synthesis of new carbon nanostructires is proposed: the oriented carbon nanotubes with graphene walls (OCNTG). To synthesize these structures the consistent covering of surface of pores of ultrafiltration inorganic membranes (Dav.= 50 and 90 nm) with monolayers of graphenes was held. These monolayers were formed during pyrolysis of the definite quantity of methane.

Formation of the monolayer of graphenes was identified with the help of X-ray photoelectron spectroscopy (XPS), which was performed on the spectrometer PHI 5500 ESCA (Perkin Elmer) using Mg K radiation (hν = 1253.6 eV). α

Formation of OGCNTs in the membrane pores was carried out under Knudsen diffusion conditions (deposition over the whole pore depth). The depth of covering with monolayer was controlled with scanning electron microscope (SEM).

Investigation of regularities of adsorption, storage and desorption of hydrogen in OCNTG were carry out. It was shown that quantity of the adsorbed hydrogen reached 14,0% from mass of OCNTG. Adsorption of hydrogen in OCNTG was identified for the first time using thermogravimetric analysis (TGA) coupled with mass-spectrometric analysis, and it was

found that its desorption at atmospheric pressure occurs at temperature of ~ 1750C. Fig. 1 (on the left) represent change of mass (1) and ion current (2) at m/e =2.

The new effect of hydrogen variation of performance (HVP) was found; this effect consists in that fact that hydrogen adsorbed in OCNTG influences in transport properties of membranes decreasing their performance on liquids in 4-26 times which fact is the indirect confirmation of its high activity which rides probably on dissociative mechanism of hydrogen adsorption. Fig. 2 represent change of performance for membranes with Dpores=90 nm versus quantity of hydrogen adsorbed in OCNTG.

Thus, new carbon nanostructures were synthesized, namely, oriented single- and multiwall carbon nanotubes with walls formed of graphenes. They turned out to be able to adsorb and store molecular hydrogen and their adsorption capacity is in line or larger than similar value of traditional carbon nanotubes. This ability of OGCNTs can be of interest for solving the problem of hydrogen storage for fuel cells. These structures are also good

candidates for another end-use application: membrane nanororeactors, in which one of the reagents (hydrogen) will be stored in OGCNTs and will desorb as required to enter into the reaction.

Work was supported in part by the Russian Fond Fundamental Investigation, Grant 09-03-00089-a.

356

Hydrogen Storage Properties of Spark Generated Magnesium Nanoparticles

Anca Anastasopol1, Vincent Vons2, Tobias Pfeiffer2, Andreas Schmidt-Ott2, Walter

Legerstee1, Fokko Mulder1, and Stephan Eijt1

1Fundamental Aspects of Materials and Energy, Department of Radiation, Radionuclides & Reactors, Faculty of Applied Sciences, Delft University of Technology

2Nanostructured Materials, Department of Chemical Engineering, Faculty of Applied Sciences, Delft University of Technology

A.Anastasopol@tudelft.nl

Magnesium nanoparticles and mixtures of magnesium nanoparticles with palladium or niobium nanoparticles as catalysts were synthesized using spark discharge generation as an interesting new method for metal hydride nanoparticle generation [1]. The distribution of the catalyst was examined by transmission electron microscopy (TEM). Rietveld refinement on the X-ray diffraction (XRD) patterns revealed the presence of crystalline Mg, as well as Nb and traces of NbO2 for the case of the Nb-catalyzed sample. The size of the agglomerated as-produced magnesium nanoparticles was found to be about 15-20nm, consistent with the TEM results. The particle sizes grow to 45-70nm after 5-10 hydrogen cycles. The formation of Mg6Pd was identified in the XRD patterns of the palladium catalyzed magnesium sample after a few cycles of absorption and desorption. The hydrogen storage properties of the nanocomposites were studied with thermal desorption spectroscopy (TDS). Hydrogen capacities of up to 6.7 wt% were measured for the magnesium nanoparticle samples. The TDS spectra are characterized by a broad thermal desorption peak which starts at relatively low temperatures of about 350 K and extends to beyond 700 K. This indicates the presence of a broad range of apparent activation energies, possibly related to the particle size distribution or to the presence of thin magnesium oxide shells of up to a few nanometers in thickness as observed by TEM. The apparent average activation energy extracted by Kissinger analysis for samples consisting of magnesium nanoparticles only was about 90kJ/molH2, comparable to bulk MgH2. The rate of desorption of the palladium catalyzed magnesium is comparable to the niobium catalyzed magnesium, and faster than for uncatalyzed Mg nanoparticles. References 1. V.A. Vons, H. Leegwater, W.J. Legerstee, S.W.H. Eijt, A. Schmidt-Ott, “Hydrogen storage Properties of Spark Generated Palladium Nanoparticles”, International Journal of Hydrogen Energy (accepted).

357

Hydrogen Storage through Alloys Nanoparticles heterogeous Nucleation within Carbonaceous Foams

T.Bibiennea,b, J-L. Bobeta

and R. Backovb

a CNRS, Université de Bordeaux, ICMCB, 87 Avenue du Docteur Albert Schweitzer, 33608 Pessac Cedex, France

b CNRS, Université de Bordeaux, CRPP, 115 Avenue du Docteur Albert Schweitzer, 33600 Pessac, France

First, the synthesis of Si-HIPE is performed through combining TEOS (tetraethoxy

orthosilane), a tretramethyltrimethylammonium bromide (TTAB) as a surfactant and HCl to catalyse sol-gel reaction. In a second step dodecane is added drop by drop to the above prepapred contninuous hydrophilic phase, leading to a direct concentrated emulsion (High Internal Phase Emulsion1). Final solid foams are labelled Si-HIPE and are bearing porosity hierarchically organized.

Secondly using the as-synthesied Si-HIPE as hard templates, Carbon-HIPE are obtained through impregnation of phenolic resin dissolved in THF within the Si-HIPE foams. After reticulation and pyrolysis of the carbon precursor the silica scaffold is vanished through HF dissolution. Final carbonaceous foams are called Carbone-HIPE. These monolith-type foams are bearing macro- and mesoporosity possessing thereby high surface area2.

The aim of this work is to induce heterogeneous nucleation and growth of metallic nanoparticles (Pd, PdNi, Mg,…) inside these carbonaceous foams. For instance, porous Carbon are impregnated with an acid solution of H2PdCl4 under dynamic vacuum3. Then reduction is promoted under H2/Ar flow, at 300°C. Final materials will be investigated with MEB, TEM, DRX, ATG under H2 flow (1Bar) and hydrogenation test (PCT). The first results show the presence of crystalline nanopalladium, which is very encouraging. We have extrapoled to other metallic or intermetallic and the results will be presented there. References 1. N.R. Cameron, D.C. Sherrington, Advances in Polymer Science, 126, (1996), 163. 2. N. Brun, S. Prabaharan, M. Morcette, G. Précastaings, A. Derré, A. Soum, H. Deleuze, M. Birot, R. Backov, Advanced Functional Materials, 19, (2009), 1-10. 3. R. Campesi, F. Cuevas, R. Gadiou, E. Leroy, M. Hirscher, C. Vix-Guterl, M. Latroche, Carbon, 46, (2008), 206-214.

358

Performance Tests of a Small Hydrogen Reservoir Based on Mg-Al Pellets

G. Capurso, F. Agresti, A. Maddalena, G. Principi

Settore Materiali, Dipartimento di Ingegneria Meccanica, Università di Padova, Italy S. Lo Russo

Dipartimento di Fisica, Università di Padova, Italy A. Cavallari, C. Guardamagna

ERSE, Milano, Italy giovanni.capurso@gmail.com

On the basis of previously acquired experience on scaling up issues regarding the use of magnesium hydride as base material for solid state hydrogen storage, a small reactor containing about 10 g of catalyzed magnesium hydride powder mixed with 5 wt% aluminium powder and pressed in the form of cylindrical pellets has been designed and tested in different operating conditions. Heat flow is managed by means of an oil circulation system. Carbon paper is used to ensure a good heat conductivity between the pellets and the inner wall of the reactor and between one pellet and the other. A number of hydrogen absorption and desorption cycles at different temperatures and pressures has been carried out to compare the behaviour of the storage device with laboratory data obtained on small amounts (fractions of grams) of powders and pellets. Data acquisition for gas flow, pressure and temperature in different positions of the reactor allow a good understanding of internal dynamics. The results in terms of hydrogen absorption/desorption kinetics and of stability to ongoing cycles are very encouraging, so that the tested small storage device can be taken as base element for multielement hydrogen reservoirs of larger size. References 1. M. Verga, F. Armanasco, C. Guardamagna, C. Valli, A. Bianchin, F. Agresti, S. Lo Russo, A. Maddalena, G. Principi, Scaling up effects of Mg hydride in a temperature and pressure controlled hydrogen storage device, Int. J. Hydrogen Energy 34 (2009) 4602-4610. 2. A. Glage, R. Ceccato, I. Lonardelli, F. Girardi, F. Agresti, G. Principi, A. Molinari, S. Gialanella, A powder metallurgy approach for the production of a MgH2–Al composite Material, J. Alloys. Compd. 478 (2009) 273-280. 3. A. Khandelwal, F. Agresti, G. Capurso, S. Lo Russo, A. Maddalena, S. Gialanella, G. Principi, Pellets of MgH2-based composites as practical material for solid state hydrogen storage, Int. J. Hydrogen Energy (in press).

359

Dehydrogenation Kinetics of LiBH4 Dispersed on Carbonaceous Nanosupports

F. Agresti, G. Capurso, A. Maddalena, G. Principi

Settore Materiali, Dipartimento di Ingegneria Meccanica, Università di Padova, Italy S. Lo Russo

Dipartimento di Fisica, Università di Padova, Italy filippo.agresti@unipd.it

The solvent infiltration technique has been used with the aim of improving the dehydrogenation kinetics of LiBH4 dispersed on high specific surface area (SSA) ball milled graphite and microporous carbon. A systematic study has been carried out on samples having different SSA of the supporting material and different LiBH4 to support ratio content. A Sievert’s apparatus has been used to perform thermal programmed desorption measurements and pressure composition isotherms at different temperatures in order to estimate the kinetics and the thermodynamics of the dehydrogenation process. According to our previous findings [1], it has been observed that the dispersion of the LiBH4 leads to a lower dehydrogenation temperature compared to unsupported LiBH4. Moreover, a further decrease of the dehydrogenation temperature is observed by increasing the SSA of the support. The use of graphite as nanosupport having SSA comparable with that used in [1] (MWCNTs) shows a further improvement in the dehydrogenation kinetics. The improvement could be explained by a heterogeneous nucleation process on the carbon surface of decomposition products or intermediate phases from liquid LiBH4. The curvature of the supporting medium is supposed to influence the observed effect. References 4. F. Agresti,A. Khandelwal, G. Capurso, S. Lo Russo, A. Maddalena, G. Principi, Improvement of dehydrogenation kinetics of LiBH4 dispersed on modified multi-walled carbon nanotubes, Nanotechnology 21 (2010) 065707.

360

EXAFS Study of the Structure Evolution in Mg-Ti Multilayer Thin Films Q. Zheng

1,2, A. M. J. van der Eerden

2, A. Baldi

1, H. Schreuders

1, J. H. Bitter

2, P. E. de

Jongh2, B. Dam

1

1Chemical Engineering, Delft University of Technology, Julianalaan 136, 2628 BL Delft, The Netherlands

2Inorganic Chemistry and Catalysis, Debye Institute for Nanomaterials Science, Utrecht University,

Sorbonnelaan 16, 3584 CA Utrecht, The Netherlands Email: q.zheng@tudelft.nl

Mg and Ti are immiscible in bulk materials as a result of their positive enthalpy of mixing. However, during a non-equilibrium preparation process, such as magnetron sputter deposition, they can form metastable alloys. In a recent optical, electrical and structural study on co-sputtered Mg-Ti thin films, it was shown that this alloy is composed of chemically segregated Mg and Ti domains [1]. Since multilayers are attractive models to study interface energy effects, the aim of our EXAFS study is to investigate the local structure around Ti in Mg-Ti multi-layers with an identical overall composition but with different thicknesses of the individual Ti and Mg layers. In this way we established a critical thickness at which individual Ti layers can be discerned. Below this critical thickness the multilayer develops the same disorder parameter as the co-deposited thin film. References 1. A. Baldi, R. Gremaud, D. M. Borsa, C. P. Balde, A. M. J. van der Eerden, G. L. Kruijtzer, P. E. de Jongh, B. Dam, R. Griessen, Int. J. Hydrogen Energy, 34, 1450 (2009).

361

Microstructural Optimisation of LaMg12 Alloy for Hydrogen Storage

A.A. Poletaev a,b, R.V. Denys b,c, J. K. Solberg a, B.P. Tarasov d, V.A. Yartys a,b

a Norwegian University of Science and Technology, Trondheim, Norway b Institute for Energy Technology, Kjeller, Norway

c Physico-Mechanical Institute / National Academy of Sciences of Ukraine, Lviv, Ukraine d Institute of Problems of Chemical Physics RAS, Chernogolovka, Russai

Email:poletaev@material.ntnu.no

Magnesium alloys reach high gravimetric and volumetric densities of stored hydrogen, but suffer from poor hydrogenation kinetics. Different methods to improve the kinetics have been applied, including microstructure modification by rapid solidification (RS) of the melt. By RS a very fine grain size is obtained, and this increases the hydrogenation rate of the metal. In the present work, the RS technique was applied to a LaMg12 alloy in order to synthesize a material with a small grain size. Thin ribbons were produced by solidifying the melt on a spinning copper wheel in an argon atmosphere. Three different speeds of the copper wheel (3.1 m/s, 10.5 m/s, 20.9 m/s) were applied. The ribbons were analyzed by SR XRD, EPMA, and TEM, and they were subjected to hydrogen absorption-desorption cycling and to TDS. SR XRD and EPMA revealed formation of two phases, LaMg12-x and Mg. From powder SR XRD it was found that, depending on the cooling rate, the LaMg12-x alloy crystallized with three different structural modifications, hexagonal TbCu7 (a = 5.96, c = 5.22 Å; highest cooling rate), tetragonal ThMn12 (a = 10.35, c = 5.96 Å; medium cooling rate) and orthorhombic LaMg11 type (a = 10.34, b = 10.35, c = 77.4 Å; lowest cooling rate) [1]. From the SEM studies, RS was found to cause a significant grain refinement, and for the highest cooling rate, even partially amorphous areas were detected. The particle size of the formed hydride phases varied in the range of 0.2-3 µm and was related to the morphology/RS synthesis of the original alloy. Hydrogen absorption resulted in a two-step disproportionation process; LaMg12 + H2 → LaH3 + Mg → LaH3 + MgH2. Decreasing grain size improved the hydrogenation kinetics. Hydrogen desorption studied by TDS and in situ SR XRD showed a major peak of hydrogen evolution at ~ 370 oC, which for the alloys synthesized at 10.5 m/s and 20.9 m/s was accompanied by an extra desorption event at 415 oC. This extra peak was associated with Mg-assisted low temperature hydrogen desorption from LaH2 proceeding below 450 oC, leading to a recombination process to form the initial intermetallic alloy LaMg12. References 1. Roman V. Denys, Andrey A. Poletaev, Jan Ketil Solberg, Boris P. Tarasov, and

Volodymyr A. Yartys. // Acta Materialia, 58 (7) 2510-2519 (2010).

362

MgH2:B Nanocomposite for Hydrogen Storage: ab Initio Calculations and Experiment

S.Kurko, N.Novakovic, Lj.Matovic, Z.Raskovic, Z.Jovanovic, B.Matovic

J.Grbovic Novakovic Vinča Institute of Nuclear Sciences, P.O.Box 522, 11000 Belgrade, Serbia

E-mail: skumric@vinca.rs

Structural destabilization of MgH2 with ion irradiation is recognized as potential method of improving its hydrogen desorption properties [1, 2]. In attempt to comprehend and improve desorption behavior of MgH2 we have investigated the influence of structural changes introduced by the B3+ ions irradiation within surface layer of MgH2. MgH2 powder samples have been irradiated with 45 keV B3+ ions with different ion fluencies ranging from 1012 to 1016 ions/cm2. Additionally, ab initio electronic structure pseudopotential based calculations as implemented in ABINIT code [3,4] was used to investigate the influence of introduction of B on stability of MgH2 matrix. Irradiation induced modifications of material were characterized with X-ray diffraction (XRD) and particle size analysis, while, hydrogen desorption behavior of MgH2 have been investigated with temperature programmed desorption (TPD) measurements. Our results suggest that there are several mechanisms involved in desorption process, which depend on defect concentration and their interaction and ordering. It has been demonstrated that the changes in near-surface area play the crucial role in hydrogen desorption kinetics. It is also confirmed that there is possibility to control the thermodynamic parameters by controlling vacancies concentration in the systems. Electronic structure calculation suggest the possibility of existence of stable MgH2:B compound with sufficiently low concentrations of boron, and preserved crystal structure of rutile MgH2. Introduction of B also significantly destabilizes MgH2 matrix compared to pure ionic compound. References 1. J. Grbović Novaković, Lj. Matović, S. Milovanović, M. Drvendžija, N. Novaković, D. Rajnović, M. Šiljegović, Z. Kačarević Popović, N. Ivanović, Int. J. Hydrogen Energ., 33, (2008), 1876-1879. 2. Lj. Matović, N. Novaković, S. Kurko, M. Šiljegović, B. Matović, Z. Kačarević Popović, N. Romčević, N. Ivanović, J. Grbović Novaković, Int. J. Hydrogen Energ., 34, (2009), 7275-7282. 3. X. Gonze, B. Amadon, P.-M. Anglade, J.-M. Beuken, F. Bottin, P. Boulanger, F. Bruneval, D. Caliste, R. Caracas, M. Cote, T. Deutsch, L. Genovese, Ph. Ghosez, M. Giantomassi, S. Goedecker, D.R. Hamann, P. Hermet, F. Jollet, G. Jomard, S. Leroux, M. Mancini, S. Mazevet, M.J.T. Oliveira, G. Onida, Y. Pouillon, T. Rangel, G.-M. Rignanese, D. Sangalli, R. Shaltaf, M. Torrent, M.J. Verstraete, G. Zerah, J.W. Zwanziger, Computer Phys. Commun. 180, (2009), 2582-2615. 4. X. Gonze, G.-M. Rignanese, M. Verstraete, J.-M. Beuken, Y. Pouillon, R. Caracas, F. Jollet, M. Torrent, G. Zerah, M. Mikami, Ph. Ghosez, M. Veithen, J.-Y. Raty, V. Olevano, F. Bruneval, L. Reining, R. Godby, G. Onida, D.R. Hamann, and D.C. Allan, Zeit. Kristallogr., 220, (2005), 558-562.

363

Study of the 2LiBH4 + MgH2 Reactive Hydride Composite Doped with Fe and F3Fe for Hydrogen Storage

J.A. Puszkiel, F.C. Gennari, P. Arneodo Larochette

Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET) y Centro Atómico Bariloche, Av. Bustillo km 9,5, R8402AGP, S. C. de Bariloche, Argentina.

Email: jpuszkiel@cab.cnea.gov.ar, gennari@cab.cnea.gov.ar, arneodo@cab.cnea.gov.ar LiBH4 is a promising material to store hydrogen because of its interesting characteristics. It has high hydrogen gravimetric capacity (18.4 wt%) which is far above of the target established by the International Energy Agency (5.0 wt% of hydrogen) and high volumetry capacity (121 kg.m-3 H2) [1–3]. However, the main constraint of LiBH4 is its high thermodynamic stability (ΔHLiBH4= 74 kJ.mol−1 H2) wich consequently results in an elevated dehydrogenation temperature (Tdesorption= 370 ºC at 1 bar) and harsh hydrogenation conditions (600 ºC and 155 bar of hydrogen) [4]. Thus, the physicochemistry of LiBH4 precludes its practical application, for example as a medium to store hydrogen for vehicular purposes. One of the applied concepts to reduce the stability of LiBH4 is the combination with other compounds such as binary hydrides as for example MgH2. This approach leads to the reduction of the enthalpy of the overall reaction (2LiBH4 + MgH2 ↔ MgB2 + 2LiH + 4 H2, ΔH = 40.5 kJ.mol-1 H2) and reversible decomposition of the borohydride via boride compounds formation [5, 6]. Nonetheless, the reacction between LiBH4 and MgH2 may have kinetic restrictions that do not permit to operate at temperatures below 400 ºC as predicted by thermodynamic reaction (Tdesorption= 225 ºC at 1 bar). In order to improve the operative conditions at wich the 2LiBH4 + MgH2 reactive hydride composite uptake/release hydrogen, we add Fe and F3Fe as catalysts. We assess the microestructural and thermal properties before and after hydrogen cycling and the rate of absorption/desorption of hydrogen as well as the hydrogen cycling of 2LiBH4 + MgH2 doped with Fe and F3Fe. Experimental results show that the kinetics of 2LiBH4 + MgH2 is improved by the catalyst addition, reaching reversible capacities of about 10 wt% H, but the operative temperature is above 350 ºC. References 1. L. Schlapbach, A. Zuttel, Nature, 414, (2001), 353-358. 2. A. Zuttel, S. Rentsch, P. Fischer, P. Wenger, P. Sudan, Ph. Mauron, Ch. Emmenegger, J. Power Sources 118, (2003), 1-7. 3. http://www.iea.org/papers/2006/hydrogen.pdf 4. P. Mauron, F. Buchter, O. Friedrichs, A. Remhof, M. Bielmann, C.N. Zwicky, A. Züttel,

J. Phys. Chem. B, 112, (2008) 906–910. 5. J.J.Vajo, S.L. Skeith, J. Phys. Chem. B 109, (2005), 3719. 6. J.J.Vajo, T. T. Salguero, A. F. Gross, S. L. Skeith, G. L. Olson, J. of Alloy Compd. 446–

447 (2007) 409.

364

Enhanced Hydrogen Sorption in Mg/C Nanocomposites T. Spassov, Z. Zlatanova, St. Todorova, M. Spassova

T University of Sofia “St.Kl.Ohridski”, 1 J.Bourchier str., 1164 Sofia, Bulgaria

Email: tspassov@chem.uni-sofia.bg Nanostructured Mg/C based composites have been investigated intensively during the last years due to their suitable combination of improved hydrogen sorption kinetics, lower operational temperature and improved oxidation resistance, compared to pure magnesium. A number of studies have been devoted to the effect of different carbon materials on the hydriding/dehydriding reactions of Mg/MgH2, but the low temperature hydrogen sorption in these materials is still unsatisfactorily analysed.

The present investigation aims at the synthesis of nanostructured magnesium/carbon composites, applying mechanical milling under different milling conditions in order to produce materials with different morphology and microstructure. The effect of various kinds of carbon on the hydrogen absorption/desorption kinetics and on the temperature of hydriding/dehydriding of the nanocomposites have been studied by means of a high pressure DSC and Sievert’s type volumetric method. The particle and crystallite size distribution has been characterized and its influence on the hydrogen sorption properties was analyzed as well. In consequence, new results concerning the low temperature hydriding/dehydriding of the Mg/C composites are presented.

365

Hydrogen Sorption in the CaH2+MgB2 System

B.Schiavo1,2, F.Agresti3, G. Capurso3, C.Milanese4 1 Department of Physics and Related Technologies, University of Palermo, Italy

2 Institute of Advanced Technologies (ITA), Trapani, Italy 3 Department of Mechanical Engeneering - Materials Sector, University of Padova, Italy

4 Department of Physical Chemistry, University of Pavia, Italy Email: benedetto.schiavo@difter.unipa.it

Among materials for hydrogen storage, complex hydrides are being studied because of their high hydrogen storage capacity. Drawbacks are often constituted by severe temperature and pressure conditions needed for hydrogen absorption/desorption, the scarce or null reversibility or, at least, the significant capacity loss already during the first sorption cycles. In recent years Ca(BH4)2 has been indicated and tested as an interesting material for hydrogen storage. Some advantages in the use of combinated systems, such as Ca(BH4)2+MgB2, rather than the borohydride alone have been reported [1], despite a reduction of the theoretical hydrogen capacity. In this frame, we performed kinetics and thermodynamic measurements on mixed/milled CaH2 + MgB2 powders, from which calcium borohydride and magnesium hydride can be synthetized through the hydrogen absorption process [2]. Absorption tests performed at 360°C and 120 bar of hydrogen pressure showed a final capacity of 6,7 wt%. XRD analyses showed the presence of the two hydrides Ca(BH4)2 and MgH2 together with the unaspected phase Ca4Mg3H14, some unreacted MgB2 and a still unknown phase. After desorption, performed at 360 °C under static vacuum XRD results showed precence of Mg in addition to the starting compounds CaH2 and MgB2, thus indicating that some amorphous boron phase, not detected by diffraction, is also present. Absorption/desorption PCI analyses are in progress to characterize the intermediate sorption steps. Ex situ XRD, NMR and Raman measurements will help to clarify the nature of the intermediate phases. The thermodynamic characteristics will be explored also by calorimetric measurements both under hydrogen and under inert atmosphere. References 1. Y. Kim, D. Reed, Y.-S. Lee, J.Y. Lee, J.-H. Shim, D. Book, Y.W. Cho, J. Phys. Chem.

C, 113, (2009), 5865-5871. 2. G. Barkhordarian, T.R. Jensen, S. Doppiu, U. Bösemberg, A. Borgschulte, R.

Gremaud, Y. Cerenius, M. Dornheim, T. Klassen, R. Bormann, J. Phys. Chem. C, 112 (2008), 2743-2749.

366

Pressure-Composition-Isotherm Behavior of Mg-Pb/Zr/TiO3(PZT) composites by Hydrogen Induced Mechanical Alloying

Kyeong-Il Kim and Tae-Whan Hong*

Department of Material Science Engineering/Research Center of Sustainable Eco-Devices and Materials(ReSEM), Chungju National University, Daehak-ro 72, Chungju, Chungbuk, 380-702, South Korea.

*twhong@cjnu.ac.kr Mg and Mg-based materials are lightweight and low cost materials with high hydrogen

storage capacity (7.6wt. %). However, commercial applications of the Mg hydride are currently hinder by its high absorption/desorption operationg temperature, and very slow reaction kinetics. PZT ceramics have known peroveskite structure, was famous for ferroelectrics materials. In ferooelectric materials as temperature rose electrical conductivity increased. PZT ceramics was used application of sensor likely sonar, electrical devices. Therefore Mg and Mg-alloys would be improving kinetics to add PZT ceramics as catalysts. These properties could be increasing hydrogen diffusion and dissociation. In this paper, we tried to improve the hydrogen absorption/desorption properties of Mg.

The effect of ferroelectic materials, such as PZT on the kinetics of the Mg hydrogen absorption reaction was investigated. MgHx-PZT composites have been synthesized by hydrogen induced mechanical alloying. The fabricated powder was characterized by XRD, SEM, EDS and simultaneous TG/DSC analysis. The hydrogenation behaviors were evaluated by using a Sievert's type automatic PCT apparatus. References 1. Kyeong-Il Kim, Tae-Whan Hong, Materials Science Forum, 620-662, (2009), 9-12. 2. W. Oelerich, T. Klassen, R. Bormann, J. Alloys Compd., 322, (2001), L5-9.

367

Catalytic Effect of V2O5 on the Hydriding Properties of Mg Z. Chen, C. Tian, H. B. Yang*

Institute of New Energy Material Chemistry, Nankai University, Tianjin, China E-mail: hb_yang@nankai.edu.cn

Magnesium hydride is recognized to be one of the most promising candidates for hydrogen storage materials due to its higher gravimetric density of hydrogen. However, the sluggish hydrogen sorption kinetics and high thermodynamic stability set a barrier for its commercial applications[1]. Recent extensive researches indicated that the addition of 3d-metal oxides to Mg as catalysts is an effective way to improve its poor hydrogen sorption kinetics[2,3]. Although great achievements have been made, much confusion still arises up because some proposed mechanisms are not in agreement with others. In order to investigate the catalytic mechanism of 3d-metal oxides to Mg, V2O5 was chosen to be ball-milled with Mg to form Mg–xwt.%V2O5(x=0, 5, 20) composites, and their hydriding properties and structure changes have been investigated in this work. The results showed that the hydriding kinetics of Mg was greatly improved after the addition of V2O5. The Mg-5wt.% V2O5 composite had the best hydriding performance and could absorb 3.6wt.% of hydrogen within 100s at 473K and 4.0 wt.% of hydrogen within 50s at 523K. A Rietveld refinement result indicated that V2O5 was reduced by Mg during the milling process. Moreover, V partially substituted for Mg to form an Mg0.45V0.55H2 phase during hydriding and led to the expansion of the crystal lattice of MgH2. This was believed to be responsible for the kinetics improvement after the addtion of V2O5.

Figure 1 XRD pattern of the Mg-20wt.%V2O5 composite (+) The observed intensity, and (-) the calculated intensity. The ticks below the patterns show the Bragg positions of the peaks. The bottom line is the difference between the calculated and observed intensities.

References 1. H. B. Yang, H. T. Yuan et al., J. Alloys Comp., 330-332, (2002), 640. 2. G. Barkhordarian, T. Klassen, R. Bormann, J. Phys. Chem. B, 11020-11024, (2006),

110. 3. A. Patah, A.Takasaki, J. S. Szmyd, Int. J. Hydrogen Energy, 3032-3037, (2009), 34.

368

Effect of Multiwall Carbon Nanotubes on Absorption /Desorption Kinetics in MgH2

M. G. Verón, H. E. Troiani, F. C. Gennari Centro Atómico Bariloche (CNEA) and Instituto Balseiro (UNCuyo), (8400) S.C. de Bariloche, A.

Bustillo km 9.5, Río Negro, Argentina, Email: maria.gisela.veron@cab.cnea.gov.ar Consejo Nacional de Investigaciones Científicas y Técnicas (CONICET)

Metal hydrides are a promising alternative for hydrogen storage in mobile applications. MgH2 is an attractive candidate due to its high storage capacity (7.6wt %), abundance in the earth crust and low cost. However its unfavorable absorption and desorption kinetics has hindered its practical application for on-board hydrogen storage. Various alternatives such as mechanical milling and the addition of catalysts have been applied to solve this difficulty. In the present work, the effect of milling time and of the addition of 5 wt% multiwall carbon nanotubes on the kinetics sorption of MgH2-5wt% Co mixture was studied. With this purpose, 5 wt% multiwall carbon nanotubes (MWCNT) were added to a mixture of MgH2-5wt% Co previously milled for 50 hours in a high energy mill. The microstructure, structure and thermal behavior of the formed phases were investigated by transmission electron microscopy (TEM), X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The hydrogen storage capacity and kinetic properties of the reaction with hydrogen were determined by using a modified Sieverts-type equipment. Improved storage capacity and absortion/desorption kinetics were observed for the sample MgH2-5wt% Co with 5 wt% MWCNT milled for 5 hours (Fig.1). This result canbe attributed to the combined effect of additional diffusion paths provided by carbon nanotubes [1, 2], the catalytic role of Co in the dissociation of hydrogen molecule and the milling time. The correlation between microstructure and nature of the phases formed during hydrogen cycling on the sorption properties of MgH2 for hydrogen storage applications are analyzed.

Fig. 1. Hydrogen absortion kinetics at 300ºC of MgH2-Co mixture with 5wt% MWCNT References 1. Chengzhang Wu, Ping Wang, Xiangdong Yao, Chan Liu, Demin Chen, Gao Qing Lu, and Huiming Cheng, J. Phys. Chem. B 109 , (2005), 22217-22221 2. Babak Shalchi Amirkhiz, Mohsen Danaie and David Mitlin, Nanotechnology, 20, (2009), 204016 (13pp).

369

Nanostructured Composites of Magnesium, Hydride-Forming Additives and Carbon for Hydrogen Storage

M.Lototsky1, M.Williams1, J.Sibanyoni1, J.K.Solberg2, V.A. Yartys2,3 and R.Denys4 1 SA Institute for Advanced Materials Chemistry, University of the Western Cape, Bellville, South Africa

Email: 2438658@uwc.ac.za 2 Norwegian University of Science and Technology, Trondheim, Norway

Email: jan.solberg@material.ntnu.no 3 Department of Energy Systems, Institute for Energy Technology, Kjeller, Norway

Email: volodymyr.yartys@ife.no 4 Physico-Mechanical Institute / National Academy of Sciences of Ukraine, Lviv, Ukraine

Email: rdenys@ipm.lviv.ua This work presents results of detailed experimental studies on synthesis, structure, morphology and hydrogen sorption performances of Mg-based nanocomposites obtained by high-energy ball milling (HRBM) in hydrogen [1,2]. The nanocomposites were synthesized using a planetary ball mill and a high pressure milling vial equipped with gastemperature-monitoring system (Evico Magnetics GmbH). The starting materials contained Mg powder, 10 wt.% of polymetallic hydrogenation catalyst (BCC-V alloy or ZrNi, taken either in hydrogenated or non-hydrogenated state), and / or 5 wt.% of carbon (graphite or multiwall carbon nanotubes, MWCNT). In some experiments the catalyst was surface-modified by fluorination and electroless deposition of Pd [3]. Synthesis was carried out at H2 pressure 25–30 bar, temperature 30 to 70 oC, 500 rpm rotation speed, and balls-to powder ratio 40:1. In-situ monitoring of the HRBM process (see Figure) has shown that all the samples were completely hydrogenated during 1–6 hours of the ball-milling; the agreement between the observed and theoretical maximum hydrogen capacities was within 5%. Significant improvements in H2 charge kinetics were observed via addition of the polymetallic hydrogenation catalyst. Further addition of carbon somewhat slows down the hydrogenation kinetics leading to the appearance of incubation period, but significantly

improves re-hydrogenation performances of the ball-milled nanocomposites. We note that for the MWCNT the incubation period was shorter than that for the graphite (see Figure). The materials were studied by XRD (incl. SR XRD), high-resolution SEM, TEM, BET, TDS. The data were related to the volumetric measurements of re-hydrogenation kinetics. The mechanism behind the improvement of the hydrogen absorption / desorption performance of the nanocomposites will be proposed and dicussed in the presentation. This work is supported by South Africa – Norway Research Cooperation Programme (Project 180344) and Hydrogen and Fuel Cell Technologies RD & Innovation Programme funded by the

Department of Science and Technology in South Africa (project KP3-S04). References 1. Denys R.V., Riabov A.B., Maehlen J.P., Lototsky M.V., Solberg J.K., Yartys V.A., Acta Materialia, 57 (2009): 3989–4000. 2. Lototsky M., Denys R., Yartys V., Int. J. Energy Res., 33 (2009): 1114-1125. 3. Williams M, Lototsky M.V., Linkov V.M., Nechaev A.N., Solberg J.K., Yartys V.A., Int. J. Energy Res., 33 (2009): 1171-1179.

370

Organized Nanoporous Carbon - Metal Composites for Hydrogen Storage

D. Giasafaki1,2, A. Bourlinos1, G. Charalambopoulou1, A. Stubos1 and Th. Steriotis1 1 National Center for Scientific Research “Demokritos”, 15310 Agia Paraskevi, Athens, Greece 2 Department of Material Science Engineering, University of Ioannina, 451 10 Ioannina, Greece

Email: g.dimmy@chem.demokritos.gr Efficient storage has been one of the main topics in hydrogen energy related research. The currently studied methods, i.e. liquid or compressed gaseous hydrogen, chemical storage and physisorption, present inherent limitations and technological problems as well as poor results at ambient conditions. Several high surface area nanoporous solids such as zeolites, activated carbons and Metal Organic Frameworks (MOFs) have received great scientific and technological attention as H2 stores, however due to weak interactions with hydrogen, such materials become efficient only at cryogenic temperatures. Additionally, a series of carbon nanostructures, such as fullerenes, nanotubes (CNTs) and nanofibers (CNFs) have been proposed as H2 adsorbents. In this case even though the initial theoretical and experimental results were exceptionally encouraging, deeper and more careful studies proved that carbon nanostructures are not capable of presenting high storage capacity at ambient temperature. Quite recently, a new family of metal (such as Pd or Pt) - carbon composites, has shown significant H2 storage potential at room temperature, e.g. Pd/CNF (1.38 wt%, 7.7 MPa) [1], Pd/CNT (1.5 wt%, 0.1 MPa, 573 K) [2], Pd/AX-21 (1.8 wt%, 10 MPa) [3], Pt/CNT (2.9 wt%, 10 MPa) [4], Pt/AC/IRMOF-8 (4 wt%, 10 MPa) [5]. H2 sorption on metal doped porous solids, is supposed to involve dissociative hydrogen chemisorption followed by diffusive cascading to various support sites. This mechanism is collectively known as hydrogen spillover. Ordered mesoporous carbon molecular sieves, designated as OMCs, have attracted much attention as sorbents, due to their high specific surface area, large pore volume, uniform and tailored pore sizes, large adsorption capacities, low specific weight, high degree of structural ordering, economical and facile synthesis pathways, high thermal, acid-base and mechanical stability and so forth. These materials are also capable of high dispersions of metal nanoparticles and their nanopore walls can be functionalized with various chemical groups. In this respect, they comprise an excellent “basis” to investigate the alleged hydrogen spillover phenomena. In this work, we have prepared a series of metal-doped ordered mesoporous carbon materials, after casting carbon frameworks in mesoporous silica templates. Furthermore, in order to study the influence of surface oxygen groups in hydrogen storage, the original OMCs, prior to doping, were oxidized at different degrees. The materials were fully characterised and their hydrogen storage properties were systematically studied. References 1. M. Marella, M. Tomaselli, Carbon, 44, (2006), 1404 2. E. Yoo, T. Habe, J. Nakamura, Science and Technology of Advanced Materials, 6,

(2005), 615 3. A.J. Lachawiec, Jr., G. Qi, R.T. Yang, Langmuir, 21, (2005), 11418 4. R. Zacharia, S. Rather, S-W. Hwang, K-S Nahm, Chemical Physics Letters, 434,

(2007), 286 5. Y. Li, R.T. Yang, J. Am. Chem. Soc., 128, (2006), 8136

371

Nanostructured Composites of Mesoporous Carbons and Boranates, as Hydrogen Storage Materials

A. Ampoumogli1, Th. Steriotis1, P. Trikalitis2, D. Giasafaki1,3, E. Gil Bardaji4, M. Fichtner4

and G. Charalambopoulou1 1National Center for Scientific Research "Demokritos", 15310 Ag. Paraskevi Attikis, Greece

2Department of Chemistry, University of Crete, P.O. Box 1470, 71409 Heraklion, Crete 3Department of Material Science Engineering, University of Ioannina, 45110 Ioannina, Greece

4Karlsruhe Institute of Technology, Institute of Nanotechnology, Hermann-von-Helmholtz Platz 1, D-76344 Eggenstein-Leopoldshafen, Germany Email: gchar@chem.demokritos.gr

Complex metal hydrides with high hydrogen content such as boranates are being extensively studied as potential hydrogen storage systems. For such materials, particular emphasis has been placed on upturning their unfavourable kinetic and thermodynamic properties which give rise to significantly high dehydrogenation temperatures far away from the desired application window [1],[2]. Nanoconfinement, based on the incorporation or even synthesis of a hydride within the pore system of an inert (most commonly carbonaceous) matrix, has quite recently emerged as a possibly efficient pathway towards the thermodynamical destabilization of the hydrides and the significant improvement of the respective dehydrogenation/re-hydrogenation kinetics [3]. The reduction of the size of solid state hydride phases down to the nanoscale leads to the dramatic increase of the surface-to-volume ratio compared to the bulk materials, thus facilitating the release and uptake of hydrogen. Furthermore, both experimental and theoretical studies have shown that nanosized hydrides are expected to release hydrogen at lower temperatures due to the decrease of the dehydrogenation enthalpy while confinement of the particles is required to prevent re-agglomeration. Indeed there have been several reports on such nanoconfined systems that exhibit reduced dehydrogenation temperatures both due to confinement and nanosize effects [4],[5]. Prompted by the need for development of a facile process for the preparation of nanoconfined hydrides we synthesized a range of hydride-carbon composites based on NaBH4, Mg(BH4)2 and Ca(BH4)2, using different wet-chemistry routes and hydride loadings. Taking into account that hydrides infiltration/impregnation is expected to be facilitated by porous scaffolds with controlled pore size and high surface area/ total pore volume, we have emphasized on the usage of a set of ordered mesoporous carbons and carbon aerogels offering a variety of pore networks. Preliminary results from thermal desorption-mass spectrometry experiments on the obtained materials have been quite encouraging, as a noticeable decrease of the dehydrogenation temperature (by at least 25%) has been observed for some of the examined systems. References 1.J.J. Vajo, G.L. Olson, Scr.Mater, 56 (2007) 829 2.S. Satyapal, J. Petrovic, C. Read, G. Thomas, G. Ordaz, Catal.Today, 120 (2007) 246 3.H. Wu, ChemPhysChem, 9 (2008) 2157 4.S. Zhang, A. Gross, S.L. Van Atta, M. Lopez, P. Liu, C. Ahn, J. Vajo, C. Jensen,

Nanotechnology, 20 (2009) 204027 5.M. Fichtner, Z. Zhao-Karger, J. Hu, A. Roth, P.Weidler, Nanotechnology, 20 (2009)

204029

372

Dehydriding and Hydriding Properties of 6LiBH4-CeCl3 Composite

F. C. Gennari, L. Fernández Albanesi, J. A. Puszkiel, P. Arneodo Larochette

Centro Atómico Bariloche (CNEA) and Instituto Balseiro (Univ. Nacional de Cuyo), R8402AGP, S. C. de Bariloche, Río Negro, Argentina

Email: gennari@cab.cnea.gov.ar

Solid-state storage of hydrogen as borohydrides or tetrahydroborates has been attracting great interest as potential candidates for advanced hydrogen storage materials. Among them, LiBH4 has the highest theoretical hydrogen storage capacity (18.5 wt%) and desorbs about 13.8 wt% of hydrogen from the reaction LiBH4→ LiH + B + 3/2 H2. However, both the temperature-pressure conditions and rate at which the hydrogen can be incorporated and released from LiBH4 are not suitable for on-board storage for vehicle purpose.

For these reasons, recent efforts have focused on incorporating additives, such as metals, metal halides, oxides and hydrides to thermodinamically destabilize LiBH4 toward improved experimental conditions of reversibility. Recently, it was demonstrated that LiBH4 can be destabilized by mixing with MgH2 [1,2]. During dehydrogenation, the exothermic formation enthalpy of MgB2 stabilizes the dehydronated state, thereby destabilizing both LiBH4 and MgH2 and reducing the dehydriding temperature. Thus, the concept of thermodynamic destabilization appears to provide new possibilities for accessing the high hydrogen content of strongly bound hydrides.

In this context, different LiBH4-based reactive hydrides composites are under investigation. In the present work, we study the hydrogen absorption/desorption properties of 6LiBH4-CeCl3 composite prepared by milling. The chemical interaction between CeCl3 and LiBH4 decreases the dehydrogenation temperature in comparison with as–milled LiBH4 by destabilization via CeH2 formation. Hydrogen desorption starts with the decomposition of Ce(BH4)3 formed during the milling process [3] and proceeds to the final formation of LiH and CeB6, which is confirmed by X-ray diffraction data. After rehydrogenation at 400 ºC under 6.0 MPa for 2 h, LiH and CeB6 are converted back to LiBH4-CeH2. The effect of hydrogen back pressure and microstructural characteristics of the composites on hydrogen absorption/desorption properties is analyzed. References 1. J. J. Vajo, S. L. Skeith and F. Mertens, J. Phys. Chem. B, 109, (2005), 3719-3722. 2. U. Boesenberg, S. Doppiu, L. Mosegaard, G. Barkhordarian, N. Eigen, A. Borgschulte, T.R. Jensen, Y. Cerenius, O. Gutfleisch, T. Klassen, M. Dornheim, R. Bormann, Acta Mater., 55, (2007), 3951-3958. 3. F. C. Gennari and M. R. Esquivel, J. Alloys Compd., 485, (2009), L47-51.

373

Hydrogen Binding in Fe(H)2(H2)(PEtPh2 )3 - Theoretical Predictions

V. Gomzi

Division of Organic Chemistry and Biochemistry / Quantum Organic Chemistry Group, Rudjer Boskovic Institute, Zagreb, Croatia

Email: vgomzi@irb.hr In a number of recent investigations the effort is made to elucidate the possibility of hydrogen storage in materials of high gravimetric storage density ratios. A class of such compounds in which hydrogen is stored in form of dihydrogen molecules (in comparison to hydride form) involves metal centres in which dihydrogen is bound at one of metal ligand positions. The special features of these compounds are relatively low dihydrogen binding energy and the possibility to store and release hydrogen in the form of hydrogen molecules ready to be used in energy transformation appliances. Some time ago, it has been found that one of the metal complexes with dihydrogen-binding capabilities is Fe(H)2(H2)(PEtPh2)3. Recently it has been predicted that this complex actually possesses two dihydrogen binding sites of almost the same energy [1]. The binding of hydrogen molecule to the metal center in the complex has been investigated theoretically. Energy profiles for these processes are obtained and compared to the recent data on the barrier heights for possible materials of applicable use [2,3]. References 1. V. Gomzi et al., (2010), (in preparation). 2. J. Kubas, Chem. Rev. 107(10), (2007), 4152. 3. M. C. Nguyen, H. Lee, J. Ihm, Sol. State Comm. 147, (2008), 419.

374

Electrochemical Synthesis of Magnesium and Aluminum Hydrides in the System of Li-ion Extraction and Insertion

N. Hanada1, H. Suzuki1, A. Kamura1, K. Takai1, T. Ichikawa2 and Y. Kojima2

Department of Engineering and Applied Sciences, Sophia University, Japan Institute for Advanced Materials Research, Hiroshima University, Japan

Email: n-hanada@sophia.ac.jp For a electrochemical synthesis of magnesium and aluminum hydride, the cathode

electrodes of metal (Mg or Al) and lithium hydride are electrochemically charged with Li anode electrode in the system of Li-ion extraction and insertion following reactions, Cathode Mg + 2LiH ↔ MgH2 + 2Li+ + 2e− Al + 3LiH ↔ AlH3 + 3Li+ + 3e− Anode 2Li+ + 2e−↔ 2Li . . 3Li+ + 3e− ↔ 3Li .

Total Mg + 2LiH ↔ MgH2 + 2Li Al + 3LiH ↔ AlH3 + 3Li.

Furthermore the cathode electrodes of MgH2 and AlH3 are discharged with Li anode electrodes to confirm the reversibility of the reactions.

Fig. 1. Voltage composition curve of 2LiH+Mg ball milled for 10 h for charge reaction to 3 V

The ball milled samples of Mg + 2LiH, Al + 3LiH, MgH2 and AlH3 are mixed with Acetylene black and PTFE as cathode electrodes. Lithium metal and EC/EMC (1:1) + LiPF6 (1M) are used as an anode electrode and an electrolyte, respectively. For MgH2 formation, the Voltage-Composition

(VC) curve of Mg + 2LiH ball milled for 10 h shows a plateau voltage at 0.6 V until final

composition of 1.05 Li extraction during charge as shown in Fig. 1. After charging MgH2 phase is observed by the XRD measurement. It indicates that MgH2 is produced by the electrochemical charge from Mg and LiH. On the other hand, MgH2 ball milled for 20 h is discharged with the formation of LiH and Mg phase as a first step and Li3Mg7 phase as a second step until the composition of 1.5 mol Li insertion. Therefore the reversibility of MgH2 formation reaction is confirmed.

375

For AlH3 formation, the VC curve of 3LiH + Al ball milled for 10h shows plateau voltage at 0.8 V until 0.3 mol Li extraction. And finally the curve rises to 3.0 V with final composition of 0.6 mol Li as shown in Fig. 2. In the XRD profile after charging AlH3 phase is not detected although the intensities of Al and LiH decrease compared with these before charging. Furthermore, AlH3 is discharged with the formation of LiH and Al phases as a first step and LiAl phase as a following step until the composition of 2.2 mol Li. It indicates that the decomposition reaction of aluminum hydride: AlH3 + 3Li+ + 3e− → Al + 3LiH proceeds as the first discharge reaction.

Fig. 2. Voltage composition curve of 3LiH+Al ball milled for 10 h for charge reaction to 3 V

Hydrogenation Properties of Mg-IMC-C Composites Prepared by Ball Milling

R.V. Denys, I.Yu. Zavaliy, V.V. Berezovets, V. Paul-Boncour (1) Physico-Mechanical Institute, NAS Ukraine, 5, Naukova St., Lviv, 79601;

(1) ICMPE, CNRS, 2-8 rue Henri Dunant, 94320 Thiais Cedex, France E-mail: zavaliy@ipm.lviv.ua

Practical use of magnesium and its alloys in hydrogen storage systems is limited by slow kinetics and elevated temperatures (above 300°C) of hydrogen absorption-desorption. A lot of recent studies were devoted to the enhancement of these parameters, including preparation of magnesium by reactive ball milling in hydrogen medium (RBM) and its modification by different additions, e.g. oxides, intermetallic compounds (IMC), graphite etc. In our previous work [1] we have studied hydrogen absorption-desorption performance of Mg composite materials with two different types of suboxides: η-Ti4Fe(Ni)2Ox and Zr3NiOx. Substantially improvement of hydrogen absorption-desorption properties was demonstrated for the Mg–Ti4Fe(Ni)2Ox composites prepared by RBM. Further studies devoted to the combination of graphite and IMC additives (η-phase suboxides) in the same Mg-based composite material. The Mg-based composites were hydrogenated by RBM of Mg and initial IMC (with or without graphite) under 2 MPa H2 pressure (Fig.1). The mechanochemical hydrogenation of the selected mixtures demonstrated the highest dynamics for the composites Mg–Ti4Fe2O0.5 and Mg–Ti4Fe2O0.5–graphite. Maximum obtained capacity for these composites after 1 hour of hydrogenation was ~6.5 wt.%. Temperature Desorption Spectroscopy (TDS) was applied to determine the onset temperature for hydrogen release in vacuum for hydrogenated composites. Compared to conventional MgH2, much lower temperatures of hydrogen desorption (a single peak at ~300°C) were observed for both Mg and Mg–C composites prpepared by RBM. But the best desorption parameters (a single peak at ~190-230°C) were obtained for the IMC-containing Mg-based composite materials. The Mg-IMC and Mg-IMC-C composites demonstrated substantial defference during rehydrogenation. C-containing composites were characterised by higher capacity and better stability for absorption-desorption cycling.

Fig.1. RBM hydrogenation (2 МPа H2) of Mg–Ti4Fe2O0.5–C mixtures: 1 – Mg; 2 – Mg–5 wt.% С; 3 – Mg–20 wt.% ІМС; 4 – Mg–20 wt.% ІМС–5 wt.% С.

Fig.2. The vacuum TDS traces at 2°C/min heating rate for: 1 – Mg (RBM); 2 – Mg–5 wt.% С; 3– Mg–20 wt.% ІМС; 4 – MgH2 preapared by conventional method.

Reference: 1. R.Denys, I.Zavaliy, V.Beresovets’, V.Paul-Boncour. Proc. of X Int. Conf. ”Hydrogen Materials Science and Chemistry of Carbon Nanomaterials", ICHMS’07, Sudak, Crimea, Ukraine, 22-28 Sept. 2007. P.358-361.

376

Hydriding Ti45Zr38Ni17-xMx (M – 3d metals) Intermetallic Compounds

A. Żywczaka, Daigo Shinyab, Ł. Gondeka, Akito Takasakib and H. Figiela aFaculty of Physics and Applied Computer Science, AGH University of Science and Technology,

Mickiewicza 30, 30-059 Kraków, Poland bDepartment of Engineering Science Mechanics, Shibaura Institute of Technology, Toyosu, Tokyo, Koto-ku,

135-8548, Japan

Ti-based quasicrystals belong to the second largest group of the stable quasicrystals, showing attractive properties as hydrogen storage materials. The Ti45Zr38Ni17 intermetallic compound which is initially amorphous after mechanical milling, after annealing forms the icosahedral (i-phase) structure, in which Ti and Zr atoms possess very good chemical affinity for hydrogen absorption. The structure of Ti45Zr38Ni17 is based on the Bergmann cluster.

The samples were produced by mechanical alloying and easily absorb hydrogen. We modified the Ti45Zr38Ni17 compounds by substituting 3d metals (Fe, Co, Mn) for Ni to obtain amorphous phase. The 3d metals atoms are located in the same positions as nickel atoms. The obtained amorphous phases Ti45Zr38Ni17-xMx (M - Fe, Co, Mn) transform to the i-phase at the similar temperature range as Ti45Zr38Ni17.

The structural characterization was made by means of XRD measurements. Thermodynamic properties were studied by differential scanning calorimetry (DSC) and thermal desorption spectroscopy (TDS). To find the influence of hydrogen and structure type on hyperfine interactions in the samples with Fe the Mössbauer spectroscopy (MS) experiment was made. The magnetic properties were also investigated and no traces of magnetic ordering were found.

The final concentration of absorbed hydrogen depends on the amount of 3d metals. The highest hydrogen concentration we observed for composition with Mn, smallest for compounds with Fe. After hydriding, the amorphous samples decompose into simple metal hydrides, and after dehydrogenation the system does not come back to amorphous phase. Contrarily, quasicrystals with substituted metals after hydrogenation and dehydrogenation retain the quasicrystal structure with increased lattice parameters for hydride compounds.

377

Neutron Study of Nanoscale Metal-Hydrogen Systems

S.Agafonov, V.Glazkov, D.Ibarbia, V.Somenkov, G.Syrykh RRC “Kurchatov institute”, Kurchatov sq., 1, Moscow, Russia

E-mail: agaph@mail.ru

On the basis of neutron researches phase transformations in amorphous and nanocrystalline hydrides, caused by influence of a surface, Laplase pressure and impurity are considered. Presence of the polyamorphous transitions and also occurrence of metastable phases connected with existence of real or virtual crystal analogues was established.

For the answer on a question what transitions are possible in metal hydrides at particles size decreasing methods of neutron and X-ray diffraction were used on well investigated earlier deuterides niobium (NbD0.95 and NbD1.84), tantalum TaD0.75 and vanadium VD0.5, after ballmilling (milling in spherical mills on air and in helium). It was revealed that at such influence in NbD0.95 there is an essential change of diffraction pattern broadening peaks, disappearance of the superstructural peaks corresponding to a star of a wave vector (½½0), occurrence of new superstructural peaks such as (100) and also splitting of structural peaks with с/а ~ 1,07. It is possible to explain the received results because of formation of the ordered phase such as Ме2D with octahedral coordination of hydrogen atoms and residual disordered phase МеD similarly equilibrium diagram of a state of vanadium hydride. Similar change of hydrogen atoms coordination in NbD already was observed earlier with the help of synchrotron radiation at pressures of 10-20 GPa and was predicted at high pressures for other hydrides. However, estimations shows that at the particles size arising in NbD0.95 at ballmilling Laplase pressure isn’t enough for realization of transition thereby the reasons of transition are connected, probably, with influence of gas impurity. In NbD1.84 consisting of NbD2 and impurity NbD0.9, at ballmilling occurs аmorphisation NbD2 and in NbD0.9 – the transitions described above. The situation similar NbD0.95, takes place in TaD0.75, but in VD0.5 at early stages of ballmilling a formation of disordered deuteride with FCC a lattice was detected.

At the same time after ballmilling in helium atmosphere another ordered phase was formed side by side with FCC phase. Correlation between this two phases after ballmilling depends, apparently, on presence or absence of another light elements admixtures.

Structure transitions in the Zr0,7Pd0,3 amorphous alloys after hydrogen treatment (gaseous pressure up to 700 atm and different temperatures in the field of amorphous phase stability) have been studied using a neutron and X-ray diffraction techniques. Samples of alloys were prepared by melt-spinning method. High pressure of hydrogen was created in bomb and than intensified by heating. It have been revealed that under hydrogen pressure exceeding 100 atm a transition of homogenous amorphous alloy occurs, resulting the formation of PdDx hydride with BCC lattice and amorphous hydride of ZrDx. Early phase transitions in metallic matrix (ordering or decomposition) induced by hydrogen have been observed only in crystal alloys. Obtained results show that analogy effects also may occurred in amorphous (nano-scale) systems. Polyamorphous transformation appears reversible, but transformations to metastable phase don’t.

The received results shows that in nanoscale systems phase transitions change of a phase condition, phase boundary and coordination of atoms distinct from transformations into crystal samples are possible.

378

Polymers of Intrinsic Microporosity: Organic Materials That Can be Tailored for hydrogen Storage

S. Teddsa, A. Waltona, N. McKeownb, B. Ghanemb, P. Buddc, D. Booka aSchool of Metallurgy and Materials, College of Engineering and Physical Sciences,

University of Birmingham, Birmingham, B15 2TT, UK bSchool of Chemistry, University of Cardiff, Cardiff, CF10 3AT, UK

cOrganic Materials Innovation Centre, School of Chemistry, University of Manchester, Manchester, M13 9PL, UK

Email: spt291@bham.ac.uk Typically organic polymers possess sufficient conformational flexibility to fill space efficiently and are therefore not microporous. However, McKeown et al. have found polymers that exhibit intrinsic microporosity (PIMs), as they have no rotational freedom within the polymer backbone and that are unable to pack space efficiently.1,2 In this work a series of triptycene-based PIMs have been investigated.

Figure 1. Gravimetric (IGA) hydrogen sorption isotherms for a triptycene-based series of PIMs at 77 K. Each PIM contains a different alkyl chain, which results in different pore

structures. Pressure composition isotherms were measured to assess the hydrogen storage capacities, heats of adsorption, surface area and pore size distributions. It has been shown that the addition of various alkyl groups of different sizes at a bridgehead position to the contorted structure affects the surface area and pore structure, which in turn directly effects the hydrogen storage properties of these materials. The apparent BET surface area of the materials can be tuned up to ca. 1800 m2 g-1. Shorter (e.g. methyl) or branched (e.g. i-propyl) alkyl chains provide the materials of greatest microporosity, whereas longer alkyl chains appear to block the microporosity created by the rigid organic framework.3 References

1. P. M. Budd, N. B. McKeown , D. Fritsch, J. Mater. Chem., 15, (2005), 1977. 2. N. B. McKeown, B. Ghanem, K. J. Msayib, P. M. Budd, C. E. Tattershall, K.

Mahmood, S. Tan, D. Book, H. W. Langmi, A. Walton, Angew. Chem., Int. Ed., 45, (2006), 1804.

3. B. S. Ghanem, K. J. Msayib, N. B. McKeown, K. D. M. Harris, Z. Pan, P. M. Budd, A. Butler, J. Selbie, D. Book, A. Walton, Chem. Commun., (2007), 67.

0

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379

Magnesium Based Composite Materials for Hydrogen Storage

D.N. Borisov, P.V. Fursikov, and B.P. Tarasov Institute of Problems of Chemical Physics of Russian Academy of Sciences, Chernogolovka, Russia

E-mail: tarasov@icp.ac.ru

With respect to the hydrogen gravimetric capacity magnesium and their alloys — Mg-Ni and Mg-La(Mm)-Ni — meet modern requirements imposed on metal hydride systems for hydrogen storage, i.e. more than 5 mass.%. However, high temperature of hydrogen uptake and release, poor sorption/desorption kinetics, and tendency to sintering are impeding factors for their usage in hydrogen accumulators [1,2]. Therefore the elaboration of methods for modification of the magnesium alloys which is capable to decrease the hydrogenation temperature and to raise the rate of hydrogen sorption/desorption is actual. For this in the present work we proposed to form magnesium based composite materials by the mechanochemical treatment of a mixture of the highly dispersed hydride phases (MgH2, MgH2+Mg2NiH4 or MgH2+Mg2NiH4+LaH3) with addition of metal catalysts of hydrogenation (Pd, LaNi5) and/or carbon containing materials (graphite, nanotubes and nanofibers) followed by annealing of the composite obtained [3].

During the investigations we found the optimal compositions and conditions of the mechanochemical formation of polymetallic and metal-carbon composites with high hydrogen sorption performances. It was determined that these composites absorb hydrogen more rapidly and do not exhibit the induction period due to the activation of hydrogen molecules, high dispersion of the magnesium phase, enhanced specific surface area, and contents homogeneity. In addition to that, due to the presence of metal and carbonaceous additives the sintering temperature of the magnesium powders is substantially increased.

On the basis of the obtained magnesium composites with optimal hydrogen sorption characteristics we elaborated prototypes of a middle-temperature hydrogen accumulator and determined their operational performances. Acknowledgements

The work was performed under the financial support of Russian Foundation for Basic Research (Grant No 09-03-01135). References 1. S.Klyamkin, R.Lukashev, B.Tarasov, D.Borisov, V.Fokin, V.Yartys, Materialovedenie (Rus), 9, (2005), 53-57. 2. S.Lǿken, J.K.Solberg, J.P.Mæhlen, R.Denys, M.Lototsky, B.Tarasov, V.Yartys, J. Alloys and Compounds, 446–447, (2007), 114-120. 3. B.Tarasov, M.Lototsky, V.Yartys, Russ. Chem. Journal, 77, (2007), 694-711.

380

Facile Preparation and Good Electrochemical Performance of Chain-Like and Rod-like Co-B Nanomaterials

Q.H.Wang, L.F.Jiao, H.M.Du, W.X.Peng, Y.J.Wang and H.T.Yuan

(Institute of New Energy Material Chemistry, Key Laboratory of Advanced Micro/Nanomaterials and Batteries/Cells (Ministry of Education)�, Nankai University, Tianjin 300071, P.R. China)

Email: yuanht@nankai.edu.cn. Chain-like and rod-like Co-B nanomaterials are prepared by chemical reduction method in cetyltrimethylammonium bromide (CTAB) and polyvinylpyrrolidone (PVP) aqueous solution, respectively. XRD patterns demonstrate that the two materials both have amorphous structures. SEM and TEM images show that the chain-like Co-B constructs of one-by-one tactic ball-like particles with nanoflakes on the surface, whereas the rod-like Co-B alloy possesses a porous nanostructure. The results of electrochemical measurements indicate that, as negative electrode materials of Ni-MH batteries, their electrochemical properties are both better than those of regular Co-B alloy. At the discharge current density 25 mA g-1, the discharge capacities of the chain-like and the rod-like Co-B alloys are 314 mAh g-1 and 292 mAh g-1 after 50 cycles, repectively, which are both higher than that of regular Co-B alloy. The reaction mechanism of the electrodes in alkaline solution is also investigated.

381

a b

Fig.1 SEM images of (a) the chain-like Co-B alloy; (b) Rod-like Co-B alloy.

0 10 20 30 40 500

100

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Fig.2 Cycle life of the Co-B alloys. Fig.3 CV curves of the Co-B alloys.

References 1. Y.D. Wang, X.P. Ai, H.X. Yang, Chem. Mater., 16, (2004), 5194-5197. 2. D.W. Song, Y.J. Wang, Y.P. Wang, L.F. Jiao, H.T. Yuan, Electrochem. Commun., 10, (2008), 1486-1489. 3. Y. Liu, Y.J. Wang, L.L. Xiao, D.W. Song, L.F. Jiao, H.T. Yuan, Electrochem. Commun., 9, (2007), 925-929.

Direct Synthesis of Sodium Alanate with Novel Catalytics TiB2

L.Li Y.J.Wang* Y.P.Wang Q.L.Ren L.F.Jiao and H.T.Yuan Institute of New Energy Material Chemistry of Nankai University, Key Laboratory of Energy-Material

Chemistry (Tianjin) and Engineering Research Center of Energy Storage & Conversion (Ministry of Education), Tianjin, PR China Email: wangyj@nankai.edu.cn

TiB2 as a novel catalyst was used in preparing TiB2-doped sodium aluminum hydride by ball-milling NaH/Al mixture with TiB2 powder under a lower hydrogen pressure. The X-ray diffraction (XRD) revealed that TiB2 particles synthesized by chemical reduction method were crystalline. NaAlH4 can be prepared by using TiB2 as catalyst in about 55 h at 1 MPa hydrogen pressure. It shows that TiB2 has a remarkable catalytic effect, enhancing the performances of hydrogen storage and release. The sample doped with 8 mol% TiB2 presented large amount of hydrogen release. It demonstrates that TiB2 particles synthesized by chemical reduction method is a promising catalyst for enhancing hydrogen release in light-metal complex hydrides. References 1. N. Eigen, M. Kunowsky, T. Klassen, R. Bormann, J. Alloys and Compounds, 430, (2007), 350–355. 2. X. Z. Xiao, X. L. Fan, K. R. Yu, S. Q. Li, C. P. Chen, Q. D. Wang, L. X. Chen, J. Phys. Chem. C, 113, (2009), 20745–20751. 3. X. P. Zheng, S. L. Liu, D. L. Li, Int. J. Hydrogen Energy, 34, (2009), 2701–2704 4. R. A. Zidan, S. Takara, A. G. Hee, C. M. Jensen, J. Alloys and Compounds, 285, (1999), 119–122.

382

Hydrogen Dissociation on Small Aluminum Clusters

I.Pino, M.C.van Hemert and G.J.Kroes University of Leiden, Leiden Institute of Chemistry, Leiden, The Netherlands

Email: i.pino@chem.leidenuniv.nl

It has been found that alanates (complex hydrides containing AlHn-(n-3) anions) exhibit

improved kinetics and low-temperature efficiency in hydrogen absorption/release by decreasing particle size at the nanometric scale level,1 or if they are doped with some metals, such as Ti,2,3 or ball milled with carbon,4,5 or adsorbed on carbon supports.6,7 In this work we investigate the effect of small aluminum cluster size on hydrogen adsorption barriers, since, in absence of Ti doping, hydrogen dissociation could be catalyzed by the presence of very small aluminum clusters with special properties with respect to surfaces. These could be highly correlated to the operative temperature and times, and to the reversibility yield of the process: as recognized earlier, the main elementary reactions involve the formation of chemical bonds between pure aluminum and hydrogen atoms.8 Transition states and reaction paths for a hydrogen molecule dissociating on small aluminum clusters have been calculated using density functional theory. The two lowest spin states have been taken into account for all the considered clusters Aln with n=2-6. The aluminum dimer, which shows a 3Πu electronic ground state, has been also studied at the coupled cluster and configuration interaction level for comparison and to check the accuracy of single determinant calculations in this special case, where two degenerate configurations should be taken into account. The calculated reaction barriers give an explanation of the experimentally observed reactivity of hydrogen on Al clusters of different size9 and reproduce the high reached reactivity of the Al6 cluster. The electronic structure problem was also systematically investigated in order to determine the role played by interactions of specific molecular orbitals for different nuclear arrangements. References 1. C. P. Baldé, B. P. C. Hereijgers, J. H. Bitter, and K. P. de Jong, J. Am. Chem. Soc. 130, 6771 (2008). 2. B. Bogdanović and M. Schwickardi, J. Alloys Compd. 253, 1 (1997). 3. S. S. Srinivasan, H. W. Brinks, B. C. Hauback, D. Sun, and C. M. Jensen, J. Atmos. Chem. 377, 283 (2004). 4. C. Cento et al., J. Alloys Compd. 437, 360 (2007) 5. P. A. Berseth et al., Nano Lett. 9, 1501 (2009). 6. C. P. Baldé, B. P. C. Herijgers, J. H. Bitter, and K. P. de Jong, Angew. Chem. Ind. Ed. 45, 3501 (2006). 7. P. Adelhelm, K. P. de Jong, andP. E. de Jongh, Chem. Comm. 6261 (2009), DOI: 10.1039/b910461e. 8. E. C. Ashby and P. Kobetz, Inorg. Chem. 5, 1615 (1966). 9. D. M. Cox, D. J. Trevor, R. L. Whetten, E. A. Rohlfing, and A. Kaldor, J. Chem. Phys. 84, (1986) 4651

383

Metal-Hydrogen Nanoscale Systems : a Review of Ab Initio Calculations

M. Shelyapina1, D. Fruchart2, P. Wolfers2 1 Department of Physics, St Peterburg State University, 1 Ulyanovskaya st., Petrodvorets, 198504,

St. Petersburg, Russia 2 Institut Néel, CNRS, BP 166, 38042 Grenoble Cedex 9, France

marinashelyapina@mail.ru

In recent years intense research has been going on to study metallic and metal-hydrogen (MH) nanoscale systems, such as clusters and thin films, in order to better understand their physics properties and evolution of bulk transformation. Improved understanding of phenomena of nanosized MH systems is crucial for fundamental aspects as for applications. At that scale, major challenges include both synthesis processing, and characterization of structures and properties. Another important question relates to the theoretical understanding of the electronic properties of nanoscale systems that requires, at various steps, the use of ab initio or molecular dynamics calculations, advanced methods of statistical science, as well as empirical knowledge of chemistry. Among a large number of MH systems MgH2 is more particularly attracting in terms of promising hydrogen storage application, because of its high hydrogen capacity (up to 7.6 wt%), light weight and low cost. However, its particularly slow hydrogen kinetics and a rather high thermal stability were considered breaking effective applications. However, the hydrogenation/dehydrogenation kinetics can be effectively improved either by accreting Mg particles with transition metal such as Ti, V, Nb (or their corresponding oxides) after being nanostructured e.g. by ball milling (BM). Indeed, application of Severe Plastic Deformation treatments (BM, ECAP, Cold Rolling...) does not change noticeably the thermodynamics of the Mg-H system. Presently, ab initio calculations are considered as a valuable tool in the effort to explore effective potentiality of hydrogen storage materials. For example, in order to better understand more specifically the mechanisms of nanostructuration and the role of so called catalyst additives in the improvement of kinetics and thermodynamics of MgH2, numbers of theoretical calculations have been carried out in last few years. In this report we present a review of ab initio studies on Mg-H, Al-H and other M-H nanoscale systems, that lead to better understand the properties of both bulk and microstructured hydrides.

This work is granted by RFBR-CNRS, contract No 07-08-92168 and developed under the IAEA project No 15933. We also grateful for a financial support of NoE INSIDEPORES (6th PCR - Europe) for stay of M.S. at Institut Néel Grenoble.

384

Structural Evolution and Hydrogen Storage Properties of the NaBH4 + MgH2 System

S. Garroni1, C. Milanese2, A. Marini2, D. Pottmaier3, M. Baricco3, F. Dolci4, G.B.M. Vaughan5, M.Orlova5, G. Mulas6, C. Pistidda7, M. Dornheim7, S. Suriñach1 and M.D.

Baró1 1 Departament de Física, Universitat Autònoma de Barcelona, Bellaterra, Spain

2 Dipartimento di Chimica Fisica "M. Rolla", Università di Pavia, Pavia, Italy 3 Dipartimento di Chimica, Laboratorio di Metallurgia, Universita di Torino, Torino, Italy

4 European Commission - JRC Institute for Energy, Petten, The Netherlands 5 ESRF, Grenoble, France

6 Dipartimento di Chimica, Università di Sassari, Sassari, Italy 7 Institute of Materials Research, GKSS Research Centre,Geesthacht, Germany

Email: sebastiano.garroni@campus.uab.cat Hydrogen storage materials based on a mixture of complex and light metal hydrides constitute a promising class of compounds in the field of hydrogen storage for vehicular applications [1]. In particular, the NaBH4-MgH2 system has a high gravimetric capacity, high volumetric hydrogen density and rather low dehydrogenation temperature compared to the single compounds. Moreover, the resistance to moisture and the low price make this system a good model for the more attractive Ca(BH4)2-MgH2 and LiBH4-MgH2 reactive hydride composites. In this work, a detailed study of the sorption properties of the 2NaBH4 + MgH2 and NaBH4 + 2MgH2 composites is reported. It will be demonstrated that complete desorption occurs for both the systems, and that the second composition shows a favourable kinetics compared with the first. For both the mixtures, the re-absorption is rapid but not complete. The formation of the unexpected NaMgH3 phase is observed. The sorption mechanism of the 2NaBH4 + MgH2 composite has been elucidated by in-situ syncrotron radiation X-ray powder diffraction (in-situ XRPD) performed at ESRF, Grenoble, at the beamline ID11. A two-step dehydrogenation process is observed for the system. The first step concerns the desorption of MgH2 to Mg and the second one corresponds to the decomposition of NaBH4, in agreement with the hydrogen release recorded by thermal programmed desorption measurements. After complete desorption, a pure MgB2 phase is obtained. A complementary investigation of the sorption process has been carried out by solid state Nuclear Magnetic Resonance (ss-NMR) spetroscopy and High-Pressure Differential Scanning Calorimetry (HP-DSC). Interestingly, the obtained data show that MgB2 is formed at temperatures below those indicated by XRPD. A plausible model mechanism of the fast re-absorption is discussed.

References 1. S. I. Orimo, Y. Nakamori, J. R. Eliseo, A. Züttel and C. M. Jensen, Chem. Rev., 107, (2007), 4111-4132.

385

Studies of the Addition of the Nb-based Nanocomposites in the Matrix of Mg Processed by Reactive Milling (MR)

R. Floriano, D. R. Leiva,T.T. Ishikawa and W. J. Botta

Department of Materials Science and Engineering, Federal University of São Carlos, São Paulo, Brazil. e-mail: ricardo_fisica@hotmail.com

Magnesium as a light, abundant and low cost metal with a high storage capacity of hydrogen represents a very attractive material for hydrogen storage [1]. Although many studies have shown improvements in desorption kinetics and themodynamic stability with the addition of small quantities of transition metals and their oxides or fluorides, very little is known about the detailed mechanism of this catalytic action [2,3]. In this scenario, the catalytic action of Nb-based nanocomposites has already attracted significant attention [4,5]. In the present work, reactive milling (RM) processing was used to produce nanocomposites Mg-based hydrides containing Nb, Nb2O5 or NbF5. All samples were milled up to 48 h under 3 MPa of hydrogen (H2) in a centrifugal mill with rotational speed of 600 rpm.The crystallographic structure and thermal properties of the resulting powders were analyzed by x-ray diffraction (XRD) and differential scanning calorimetry (DSC). The DSC curves for all the mixtures show a significant decrease in the desorption temperature in comparison with as milled MgH2, indicating an excellent catalyst effect associated with the presence of niobium. The presence of Nb2O5 or Nb were most effective than NbF5 in improving the sorption characteristics. The XRD patterns indicate that Mg was partiality transformed into the β-MgH2 and γ-MgH2 phases, however non-reacted Mg still remained in final product. In particular, the XRD pattern of the mixture Mg + 2 mol% Nb indicates the presence of the phases γ-NbHx and β-NbH2. The MgO phase was indentified in the mixtures Mg+2 mol%Nb, Mg+2 mol%Nb2O5 and as milled MgH2. These results indicates an important effect from the presence of Nb, and the ability of RM to produce metastable phases such as γ-MgH2 and γ-NbHx. A detailed study concerning the decomposition sequence of the phases γ-NbH2 and β-NbHx and the structural characterization of all composite samples is under progress. References

1. O. Friedrichs, T. Klassen, J.C. Sanchez-Lopez, R. Bormann, A. Fernandez, Scripta

Materialia, 54, (2006),1293–1297. 2. G. Barkhordarian, T. K. Bormann, Scripta Materialia, 49, (2003), 213–217. 3. J.F. Pelletier, J. Huot, M. Sutton, A.R. Sandy, L.B. Lurio, S.G.J.Mochrie, Phys.

Rev. B, 63 (2001), 521. 4. J. Huot, J.F. Pelletier, L.B. Lurio, M. Sutton, R. Schulz, J. Alloys and Compounds,

348, (2003), 319–324. 5. J.F.R. de Castro, S.F. Santos, A.L.M. Costa, A.R. Yavari, W.J. Botta F.,T.T.

Ishikawa, J.Alloys Compounds, 376, (2004), 251–256.

386

Electrochemical Study of Conic Carbon Nanotubes as Hydrogen Storage Systems

S.Khantimerov1,2, N.Suleimanov1,2, E.Kukovitsky1, V.Matukhin2, Yu.Sakhratov2

1Zavoisky Physical-Technical Institute of Russian Academy of Sciences, Kazan, Russia 2Kazan State Power Engineering University, Kazan, Russia

Email: khantim@mail.ru Hydrogen is now considered as a versatile energy carrier which in combination with electric energy can provide the change-over to the clean and sustainable power engineering. Carbon-based systems such as carbon nanotubes (CNTs), carbon nanofibers, nanoporous activated carbon and doped carbon materials are among attractive objects for hydrogen storage. At present time intensive investigations of ways to increase hydrogen/carbon ratio take place, in order to proceed at accumulation up to practically comprehensible level for application in fuel cells. The uptake of hydrogen by CNTs is usually performed in two ways: at high gas pressures [1] or electrochemically from aqueous solutions [2]. The originality of the latter method lies in the fact that as a result of electrochemical processes without of application of expensive catalysts the protons appear which can be introduced to CNTs. Previously [3] using NMR-method it was shown that the absorption of hydrogen by multiwalled conic carbon nanotubes took place. In the given work the results of investigation of the storage capacity of the conic carbon nanotubes are presented. Carbon nanotubes were synthesized by catalytic pyrolysis of the granulated polyethylene in helium atmosphere on a nickel plate [4]. The morphology and geometrical parameters of carbon nanomaterial were investigated by TEM. It has been established, that during synthesis “bamboo”- type and “fish bone”- type carbon nanotubes are formed. The main feature of these type of nanotubes is that the majority of their external and internal edges are open, that can essentially simplify process of hydrogen intercalation into the interplane space of nanotubes. Hydrogenation of CNT was carried out by the electrochemical method in a three-electrode cell. As a working electrode the sample with carbon nanotubes grown up on a nickel plate was used. The platinum foil served as an auxiliary electrode, Ag/AgCl electrode was used as a reference electrode. The experiments were carried out both for 3M KOH and 3M H2SO4. The charge-discharge capacity of CNTs was measured in galvanostatic experiments with a current load 0.5 mA during charging and discharging. The hydrogen storage capacity of such samples is being discussed. The work is partially supported by the Ministry of Education and Sciences of the Russian Federation (ADTP №2.1.1/4982) and Russian Foundation for Basic Research (grant №09-08-01099). References 1. H. Kajiura et al. Appl.Phys.Lett., 82, (2003), 1929-1931. 2. I. Lombardi, M. Bestetti et al. Electrochem. Solid-State Letters, 7, (2004), A115-A118. 3. S. Khantimerov, N. Suleimanov et al. XI International Conference "Hydrogen Material Science and Chemistry of Carbon Nanomaterials". Extended abstracts, 620-623. Yalta, Ukraine, 2009. 4. N. Kiselev et al. Carbon, 36, (1998), 1149-1157.

387

Mg2FeH6-Based Nanocomposites with High Capacity of Hydrogen Storage Processed by Reactive Milling

A. A. C. Asselli1*, C. S. Kiminami2, T.T. Ishikawa2, and W. J. Botta2

1 Programa de Pós-Graduação em Ciência e Engenharia de Materiais, Universidade Federal de São Carlos, São Carlos, Brazil.

2 Departamento de Engenharia de Materiais, Universidade Federal de São Carlos, São Carlos, Brazil. Email: asselli@gmail.com

Magnesium is an attractive material to hydride forming due to several advantages, such as its high gravimetric density of H2 (7.6 wt% of H2), its abundance on the Earth and its low cost. However, its main drawbacks are its high stability and low hydrogen sorption kinetics. In this context, the magnesium complex hydrides appear as an interesting alternative, compromising hydrogen capacity for better absorption – desorption kinetics. In this compounds group, the Mg2FeH6 presents the highest known volumetric density of 150 kg of H2/m3, nevertheless, as Mg and Fe do not form any intermetallic compound, the hydride phase is difficult to synthesize. At first, sintering processes of Mg and Fe powders under H2 were used to obtain Mg2FeH6 [1], but high pressures, elevated temperatures and several days were required. A processing route to diminish these severe conditions is the high-energy ball milling of precursory metallic powders, furthermore, a direct synthesis of hydride can be obtained when a hydrogen pressure is applied (Reactive Milling – RM) [2]. This mechanically activated method can reduce the grain and particles sizes to the nanometric scale and improve H-sorption kinetics of hydrides. In the present work, the compound Mg2FeH6 was synthesized from a 2Mg+Fe mixture in a single process by high-energy ball milling under hydrogen atmosphere at room temperature. The complex hydride was prepared from Mg powder and granulated (1-2 mm) or powdered Fe using a planetary mill. The phase evolution during different milling times (up to 72 hours) was investigated by X-rays diffraction (XRD) technique. The dehydrogenation behavior of the so-formed metal hydride was investigated by simultaneous thermal analysis of differential scanning calorimetry (DSC) and thermogravimetry (TGA) coupled with mass spectrometry. Measurements of hydrogen sorption kinetics were made in a Sievert’s apparatus. The use of powdered iron as starting material promoted conversion to complex hydride at shorter milling times than when granulated iron was used, nevertheless, after 12 hours of milling the 2Mg+Fe (powdered or granulated) mixtures presented a similar dehydrogenation behavior. Even though 72 hours of milling, a remaining iron was identified by XRD and the gravimetric capacity of hydrogen was on average 3.2 %, in others words, 60% of the theoretical capacity (5.4 wt% of H2). These XRD results agree with the reaction sequence proposed by Gennari, Castro and Gamboa [3]:

(1) and )(2)(2)( sgs MgHHMg ⇔+ )()(62)()(23 ssss MgFeHMgFeMgH +→+ (2). The reactive milling of 3Mg+Fe mixture was performed and a Mg2FeH6-based nanocomposite with high capacity of hydrogen storage (5.2 wt% of H2) was obtained. References 1. J.-J. Didisheim, P. Zolliker, K. Yvon, P. Fisher, J. Shefer, M. Gubelmann, A. F. Williams, Inorganic Chemistry, 23, (1984), 1953-1957. 2. J. Huot, S. Boily, E. Akiba, R. Schulz, Journal of Alloys and Compounds, 280, (1998), 306-309. [3] F. C. Gennari, F. J. Castro, J.J. Adrade Gamboa, Journal of Alloys and Compounds, 339, (2002), 261-267.

388

Interaction of MIL-101-Based Hybride Materials with Hydrogen at High Pressures

S.Klyamkin, E.Berdonosova, E.Kogan, K.Kovalenkoa), V.Fedina)

Chemistry Department Moscow State University, Moscow, Russia; a) Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia

Email: klyamkin@highp.chem.msu.ru MIL-101, mesoporous chromium (III) terephtalate, is considered as one of the most promising for hydrogen storage among numerous metal-organic frameworks (MOFs). Its sorption capacity with respect to hydrogen exceeds 6 wt.% [1] at 77 K but remains very low at room temperature as well as for other MOFs. The approach proposed to enhance the MIL-101 hydrogen sorption ability consisted in intercalation of polar clusters within the framework pores to provide an additional polarization of the surface inside the hybrid structure. The elaborated technique allowed us to synthesize on the basis of MIL-101 a series of new compounds with incorporated metal guests [2]. In the present work we report the experimental results on sorption behaviour of Re@MIL-101 and W@MIL-101 containing 90 [Re4S4F12]4- and 48 [α-SiW11O39]8- clusters per lattice unit, respectively. XRD analysis made it possible to characterize the new phases as solid solutions based on the rigid framework of chromium terephthalate MIL-101. Measurements of specific surface and porous structure carried out by low-temperature nitrogen sorption shown that some of N2 adsorption sites were blocked by the intercalated clusters. Meanwhile those positions remained accessible to H2: total hydrogen capacity per volume unit was not changed as compared with unmodified MIL-101 matrix. To reveal the effect of metal clusters on specific gas-solid interactions within a wide pressure range excess hydrogen capacity was calculated on the basis of preliminary helium experiments. This parameter is commonly used for mesoporous materials to distinguish surface adsorption from filling of giant pores by gas molecules. For the materials studied the excess capacity reached the maximum at pressures of 25-50 bar (81 K) and 100 bar (298 K) then dropped down to negative values. The point at isotherms corresponding to zero excess capacity indicates the adsorbed layer density. At low temperature this value did not depend on the presence of doping metal clusters but the room temperature experiments shown a remarkable increase of adsorbed hydrogen density for hybride compounds. In the case of Re-containing material hydrogen at the surface was three times tighter as compared with initial MIL-101: 0.03 g/cm3 instead of 0.01 g/cm3. This work was supported in part be Russian Foundation for Basic Researches, grants 09-03-01057 and 09-03-12112. References 1. M. Latroche, S. Surble, C. Serre, C. Mellot-Draznieks, P. L. Llewellyn, J.-H. Lee, J.-S. Chang, S. H. Jhung, G. Férey, Angew. Chem., Int. Ed., 45, (2006), 8227-8231. 2. D. Dybtsev, K. Kovalenko, Yu. Mironov, V. Fedin, G. Férey, N. Yakovleva, E. Berdonosova, S. Klyamkin, E. Kogan, Izvestiya Akad. Nauk, Ser. Khim., (2009), 1576-1579.

389

Effect of LaNi5 on Hydrogen Sorption Properties of MIL-101

E.Berdonosova, S.Klyamkin, N.Rtischeva, K.Kovalenkoa), V.Fedina) Chemistry Department Moscow State University, Moscow, Russia;

a) Nikolaev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia Email: ellenganich@highp.chem.msu.ru

Metal-organic frameworks (MOFs) are considered as a promising media for hydrogen storage. A special interest in such materials is caused by their extremely high specific surface (up to 5000 m2/g), adjustable porosity and wide possibilities of modification. Thousands of MOFs have been synthesized up to now but only few of them (i.e. chromium (III) terephtalate - MIL-101) combine high sorption capacity with thermal and chemical stability in air and in presence of water. Valuable hydrogen uptake in MOFs is realized only at low temperatures (77 K). MIL-101 under those conditions absorbs more then 6 wt.% H2 meanwhile at 298 K its sorption capacity is very low - 0.4 wt.% at 80 bar [1]. One of the strategies to enhance hydrogen sorption ability of MOFs at room temperature and relatively low pressures consists in combination of physical adsorption and chemisorption within the same material.

Hydrides forming intermetallic compounds are known as activators of molecular hydrogen due to their ability to dissociate H2 [2]. In the present work we choose LaNi5, as such an activator and metal-organic polymer MIL-101 as а receptor of atomic hydrogen. To maximize efficiency of the activator a mixture of MIL-101 and LaNi5 with weight ratio 5:1 was treated in a high-energy ball mill for 2 minutes. Hydrogen sorption capacity at 296 K for ball-milled MIL-101 decreased slightly in spite of the framework ific surface and pore volume. LaNi5 addition

affects remarkably the isotherm shape as well as capacity of the material. In the low pressure range the main contribution to hydrogen uptake is related to formation of LaNi5H6 hydride. Total hydrogen content in the composite exceeds the sum of specific capacities of the components by 45%. The effect observed evidences that the approach proposed was fruitful and can be additionally intensified by further optimization of the activating treatment parameters.

390

destruction and a drastic reduction of the spec

This work was supported in part by Russian Foundation for Basic Researches, grants 09-03-01057 and 09-03-12112. References 1. M. Latroche, S. Surble, C. Serre, C. Mellot-Draznieks, P.L. Llewellyn, J.-H. Lee, J.-S. Chang, S.H. Jhung, G. Ferey, Angew.Chem.Int.Ed., 45, (2006), 8227-8231. 2. Yu.F. Shmal’ko, M.V. Lototsky, Ye.V. Klochko, V.V. Solovey, J. Alloys and Compounds, 231, (1995), 856-859.

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0 5 10 15 20 25 30 35

P, bar

wt%

H2

M IL-101 ball-milled

MIL-101/LaNi5

MIL-101 b.m.+LaNi5

`

Ti-V Based Metal Hydrides for Hydrogen Storage

L. Pickering, A. Bevan and D. Book School of Metallury & Materials, University of Birmingham, Birmingham, B15 2TT, UK.

Email: lxp686@bham.ac.uk The concept of a hybrid hydrogen storage vessel, which places hydrogen storage materials in a high pressure vessel, has been proposed to improve the volumetric density of hydrogen in on-board hydrogen storage for fuel cell vehicles (Takeichi et al, 2003). It has been shown that Ti-V-Mn alloys are candidate materials for a use in such hybrid vessels at 350 bar (Shibuya, Nakamura, Enoki & Akiba, 2008). These alloys showed promising hydrogen storage; effective capacity of 1.9 wt% under H2 pressure from 350 to 1 bar; good hydriding-dehydriding kinetics and easy activation. However, there is a need to increase the storage capacity, improve cyclability, and allow the plateau pressure to be tailored to that required by the hybrid tank. Research into these alloys has identified a range of different phases: C14 Laves, BCC and a minor FCC phase. Further, it has been found that the hydrogenation properties, such as the plateau and hysteresis pressure, can be influenced by the substitution of transition metals such as vanadium (Shibuya, Nakamura & Akiba, 2007). In this work the substitution of niobium (Nb) for vanadium has been investigated. Nb is chemically similar and is also a BCC phase stabiliser (in iron). Elemental Ti, Mn, Nb and V was weighed out into molar ratios of Ti0.5V0.5Mn, Ti0.5V0.45Nb0.05Mn, Ti0.5V0.4Nb0.1Mn and Ti0.5V0.3Nb0.2Mn and arc melted on a water-cooled copper crucible under argon. The as-melted alloys were then heat-treated at 1233 K for 6 hours in a vacuum furnace. It was found that the Ti0.5V0.5Mn, ternary alloy has a hydrogen uptake of just over 1.4 wt% at 268-273 K. The substitution of niobium for vanadium decreases the plateau pressure and storage capacity, but also decreases the enthalpy of formation. Backscattered SEM/EDS analysis shows a light and dark phase to be present in the Nb-containing samples which has tentatively ascribed by XRD to BCC and Laves phases. References 1. Shibuya, M., Nakamura, J., Akiba, E., 2007. Hydrogenation properties and microstructure of Ti-Mn-based alloys for hybrid hydrogen storage vessel. Journal of Alloys and Compounds 466, p 558-562. 2. Shibuya, M., Nakamura, J., Enoki, H., Akiba, E., 2008. High-pressure hydrogenation properties of Ti-V-Mn alloy for hybrid hydrogen storage vessel. Journal of Alloys and Compounds. 3. Takeichi, N., Senoh, H., Yokota, T., Tsuruta, H., Hamada, K., Takeshita, H. T., Tanaka, H., Kiyobayashi, T., Takano, T., Kuriyama, N., 2003. “Hybrid hydrogen storage vessel”, a novel high-pressure hydrogen storage vessel combined with hydrogen storage material. Internation Journal of Hydrogen Energy 28, p1121-1129.

391

Integral Treatment for Materials Synthesized, Improved and Applied to Hydrogen Thermal Compression

1 M.G. Rodriguez and 2,3,4 M.R. Esquivel

1 Instituto Sabato- UNSam y CNEA-Avda. Gral Paz 1499 – Bs. As – Argentina 2 Comisión Nacional de Energía Atómica- Centro Atómico Bariloche – Avda. Bustillo km 9.5 Bariloche- Río

Negro - Argentina. (R8402AGP) 3 Consejo Nacional de Investigaciones Científicas y Técnicas

4 CRUB – UNComa – Quintral 1250 –Bariloche –Río Negro - Argentina Email: esquivel@cab.cnea.gov.ar

In this work, it is achieved an integral treatment consisting in synthesis by mechanical alloying of a mixture of intermetallics, annealing at 600 °C and application to a two stage hydrogen thermal compressor. A mixture of AB5´s of composition LaNi4.60Al0.40 and La0.25Ce0.52Nd0.17Pr0.06Ni5 was mechanically milled 100 h to reach final stage [1,2,3]. The obtained sample of composition La0.62Ce0.12Nd0.08Pr0.03Ni4.70Al0.30 as measured by EDS was annealed at 600 °C for 24 h to improve the microstructural properties i.e to minimize the strain and increase the crystallize size. As an example of the improvement achieved, the strain reduced from 2% to 1% and crystallite size increases from 120 ± 5 Å to 900 ± 5 Å as compared as milled samples to annealed samples. The annealed AB5 was refined using the Rietveld method. The structure crystallizes in P6/mmm space group, with cell parameters a = 4.982 ± 0.005 Å and c = 4.001± 0.005 Å. Lanthanides distribute randomly in Wyckoff positions 1a and Ni in positions 2c and Al in positions 2c and 3g. The occupancy of the OF coincides with that of the chemical composition obtained by EDS. The La0.62Ce0.12Nd0.08Pr0.03Ni4.70Al0.30 is used a one-stage hydrogen thermal compression. In this stage, the hydrogen is absorbed at 1500 ± 10 kPa at 25 °C reaching a maximum capacity of 1.2% mass percent. The system is isolated and the the temperature is elevated up to 90 °C. The hydride is desorbed reaching an hydrogen pressure of 2200 ± 10 kPa. As a result, a one stage hydrogen compression is obtained. Under these conditions, the compression ratio reached is 1.46. These results are currently used in the development of a two-stage hydrogen thermal compressor developed under the same integral program. Acknowledgements The authors thank Comisión Nacional de Energía Atómica of Argentina, Universidad Nacional de Cuyo of Argentina Project 0 and ANPCyT of Argentina (Project PAE-PICT 00158) for partial financial support. References 1. M.R.Esquivel, G. Meyer, J. Alloys Compd., 446-447, 2007, 212-217. 2. M.R. Esquivel, G. Meyer, Mat. Sc. For. 570, 72-77. 3. B.A. Talagañis, M.R. Esquivel, G. Meyer, Int. J.Hydrogen Energy 2009, 34, 2009, 2062-2068.

392

Austenitic Steels: Tensile Tests in 400 Bar H2-Environment, Determination of Surface Oxide Thickness and Near-Surface Carbon

C. Izawa1, S. Wagner1, M. Martin2, S. Weber2 , Anais Bourgeon3, Richard Pargeter3, T. Michler4, and A. Pundt1

1Institut für Materialphysik der Universität Göttingen, Friedrich-Hund-Platz 1, 37077 Göttingen, Germany

2Gemeinsame Forschergruppe, Helmholtz-Zentrum Berlin / Ruhr-Universität Bochum, Universitätsstr. 150 - IA 2/44, D-44801 Bochum, Germany

3TWI Ltd, Granta Park, Great Abington, Cambridge CB21 6AL, United Kingdom 4Adam Opel GmbH, IPC R2-50, GM Alternative Propulsion Center Europe

65423 Ruesselsheim, Germany Email: apundt@ump.gwdg.de

For the safely use of highly compressed gaseous hydrogen as a fuel, steel fittings, tubes and other components are needed that resist to hydrogen embrittlement. Ni-rich austenitic steels show good resistance to hydrogen embrittlement (HE) but Ni is expensive. For commercial applications, low Ni-content austenitic steels are desired. Results on resistence against HE are not unambiguous for some austenitic steels with concentrations below 10 wt-% Ni. For some samples it looks as if there exists a threshold value around 10 wt-% Ni. However, tensile tests in hydrogen environment give opposing results, some alloys show HE while alloys of the same alloy type do not embrittle [1,2]. One theory for this variability is that differences in surface layers may be affecting hydrogen access to the underlying material.

In this paper we adress the local chemistry of the surface of several austenitic steels with Ni-concentrations around the threshold value. Tensile tests are performed in hydrogen gas at 400 bar and 20°C. The surface of the tensile test samples is studied by Scanning Electron Microscopy (SEM) to characterize the fracture type. Secondary Ion Mass Spectroscopy (SIMS) is performed on the tested samples to gain information about the near-surface concentration of Fe, Cr, Ni and C. Because of the cylindrical surface geometry and the constraint of keeping the sample surface in its original quality (no further surface pretreatment is allowed) these measurements are extremely difficult. Surface roughness and surface contaminations hamper proper SIMS analyses. The depth profiles are analysed with regard to the impacts of surface contaminations. Figure 1 shows the lateral elemental distribution maps determined depending on the sample depth. Special care is taken to analyze the element distributions near crack regions.

393

Figure 1. Lateral elemental distribution of Cr+, Fe+, 58Ni+, and fragment ions from

contamination (Si2C5H15O+ and C3F7+) at different depths. (a) at surface and (b) beneath

oxide layer. Financial support of the BMWI via HYDEE-project is gratefully acknowledged.

References 1. A. Barnoush, doctoral thesis, Saarbrücken 2007. 2. A. Pundt and R. Kirchheim, Annu. Rev. Mater. Res., 36 (2007), 555-608.

(a)

(b)

Synthesis, Properties and Mossbauer Study of ZrFe2-xNix Hydrides (x = 0.2 – 0.8)

R.B. Sivov, T.A. Zotov, V.N. Verbetsky, D.S. Filimonov, K.V. Pokholok Chemistry Department, Moscow State University, Moscow, Russia

E-mail: rsivov@mail.ru High pressure hydrides of intermetallic compounds (IMC) were only of scientific

interest up to now. Recently new tanks for storage and transportation of hydrogen compressed to 350 – 800 atm have been developed. However, even at such pressure it is difficult to reserve considerable quantities of the hydrogen. Therefore there is an idea of filling of accumulators with IMC which hydrides possess suitable absorption and desorption pressures and the high hydrogen capacity. This fact attracts attention of auto and energy companies and makes the high pressure hydrides perspective materials for practical applications.

ZrFe2 possesses a relatively high reversible hydrogen capacity of ~1.7 wt.% H2 and high equilibrium absorption and desorption plateau pressures of 690 atm and 325 atm respectively. Besides, it starts to react with hydrogen at pressure near 800 atm while initial hydrogenation [1]. Addition of other 3d-metals instead of iron could change the absorption and desorption pressures. ZrFe2-xNix (x = 0.2, 0.4, 0.6, 0.8) alloys were synthesized and investigated for this purpose. We also studied the effect of hydrogen absorption on local structure and hyperfine magnetic interaction of iron atoms in ZrFe2-xNix.

The composition of alloys was examined by scanning electron microscope (SEM) with energy dispersive X-ray analyzer and powder X-ray diffraction (XRD). The hydrogen sorption properties were studied by measuring PC absorption and desorption isotherms using high hydrogen pressure apparatus at hydrogen pressure below 3000 atm described in [2]. The composition of obtained hydrides defined from absorption and desorption isotherms is near ZrFe2-xNixH3.6, the hydrogen capacity is ~1.8 wt.% H2. Investigated hydrides are pyrophoric but in most cases it was possible to study their structure by XRD. It was found that volume expansion of a sample lattice at hydrogenation is ~25%. From investigation of interaction of hydrogen with ZrFe2-xNix alloys it is defined that increase of Ni content leads to considerable decrease of equilibrium absorption and desorption pressures (from 250 atm for ZrFe1.8Ni0.2 to 110 atm for ZrFe1.2Ni0.8). Phase transition β-hydride → α-solution enthalpies and entropies are calculated for all samples. Mossbauer spectra were taken in the 78 – 300 K temperature range. The correlations between Ni content and parameters of hyperfine interactions of 57Fe nuclei were discussed. It was shown that the isomer shift value (δ = -0.17 mm/s, T = 300 K) is insensitive to Ni content in these IMC, while the Curie temperatures decreased with Ni increase. Absorption of hydrogen leads to significant increase in δ value which was found to be of 0.4 mm/s at 300 K for all the samples. This was attributed to increase of ionicity of these compounds. Besides, embedding of hydrogen affected the magnetic interaction that resulted in Curie temperatures increase. Analysis of Mossbauer spectra of hydrides, which were decomposed at 300 K and 1 atm, revealed a multi-step mechanism of decomposition involving intermediate hydride phase formation.

References 1. Zotov T., Movlaev E., Mitrokhin S., Verbetsky V., J. Alloys Comp., 2008, V. 459, P. 220–224. 2. Mitrokhin S., Zotov T., Movlaev E., Verbetsky V., J. Alloys Comp., 2007, V. 446-447, P. 603-605.

394

Author Index Abe, 65 Adamska, 225 Adelhelm, 27, 99 Agafonov, 234, 378 Agarwal, 327 Agresti, 359, 360, 366 Ahn, 320 Ahuja, 17, 126, 232 Akiba, 25, 53, 57, 179,

192, 296, 317 Akiyama, 295 Aleksanyan, 245 Alexander, 55 Alimov, 40 Aliouane, 84, 269 Amieiro, 256 Ampoumogli, 372 Anastasopol, 357 Ando, 315 André, 144 Andreenko, 234 Andrews, 34 Andrieux, 215 Andrievski, 13 Anikina, 154, 155, 156 Antisari, 110 Antonov, 5, 77, 146 Aoki, 55, 69, 130, 180,

226 Apih, 62, 352 Araújo, 17, 304 Arefev, 229 Ares, 149, 174, 227, 273 Arnold, 22 Asano, 25, 192 Askri, 307 Asselli, 388 Aurora, 110 Autrey, 164, 292 Avdyukhina, 173 Awakura, 137 Aydınol, 241 Aymard, 9, 124 Azofeifa, 227 Babanova, 261

Backov, 358 Badalov, 145, 157 Baehtz, 341 Baikov, 135 Bailey, 305 Baldi, 37, 48, 142, 201,

361 Bardaji, 264, 283 Baricco, 54, 147, 148,

187, 217, 385 Barkhordarian, 30, 283 Barlam, 43 Baró, 187, 385 Barucca, 56 Baruj, 314, 321 Bazhanov, 173 Bazzanella, 56, 339 Beattie, 93 Belitskii, 135 Belonogov, 134 Belosludov, 151 Belov, 150 Berbenni, 250 Berdonosova, 389, 390 Bereznitsky, 114 Berezovets, 376 Bernard, 290 Bernasconi, 313 Bertolino, 314, 321 Besedin1, 42 Besenbacher, 94 Bevan, 391 Beznosyuk, 336 Bibienne, 358 Bidica, 297 Bielmann, 64 Bitter, 361 Blach, 119 Blanchard, 193 Bloch, 46, 47, 303 Blomqvist, 17, 126, 304 Bobet, 9, 66, 81, 124,

278, 358 Bodega, 149, 174, 227,

273

Boelsma, 201 Bogerd, 27 Bolhuis, 116 Bonatto, 287 Bonatto Minella, 30 Bönisch, 61 Book, 291, 318, 319,

379, 391 Borchers, 86 Borgschulte, 21, 64, 75 Borisov, 117, 380 Bormann, 30, 277 Bösenberg, 30, 94, 239 Botta, 111, 386, 388 Bourgeon, 393 Bourlinos, 371 Bowman, 320 Bramant, 200 Brocks, 88, 248, 310 Bruni, 250 Brusa, 50 Buchter, 75 Buckley, 197 Budd, 379 Budzianowki, 302 Bull, 15 Bulychev, 5, 326 Burkhanov, 134, 136,

233 Busnyuk, 40 Bystrzycki, 208 Cagnon, 163 Cai, 89 Callear, 55, 256 Callini, 103 Campesi, 115 Cantelli, 16, 164, 190 Capurso, 359, 360, 366 Castro, 274, 275 Cekić, 262, 263 Celebi, 74 Cerenius, 94, 239, 287 Černý, 14, 44, 162, 165,

177, 237, 285 Chaise, 35

395

Chan, 34 Chandra, 162, 190, 237,

327 Charalambopoulou,

371, 372 Chaudhary, 197 Checchetto, 50, 56, 339 Cheklina, 272 Chen, 76, 106, 126, 198,

214, 238, 254, 289, 292, 293, 298, 304, 368

Cheng, 106 Chernov, 252, 282 Chernyshov, 14 Chevalier, 278 Chiriac, 215 Chistov, 136 Chistyakov, 233 Cho, 240, 271, 291 Chotard, 79 Chou, 279, 280 Chu, 251, 254 Chua, 238, 292 Ćirić, 262, 263 Claessen, 201 Clark, 227 Colbe, 109 Colin, 22, 38 Colognesi, 264 Corno, 147 Costa, 191 Couillaud, 81, 278 Cowgill, 68 Crivello, 64, 237 Crossley, 323 Cucinotta, 313 Cuevas, 8, 9, 124, 273,

340 Culligan, 80 Curtarolo, 47 Czujko, 208, 329, 330 D’Anna, 44 Dahle, 271 Dam, 37, 48, 59, 73,

127, 142, 201, 212, 344, 361

Dantzer, 309

David, 55, 80, 256 Davids, 211 de Jong, 27, 91, 99 de Jongh, 27, 91, 99,

361 de Rango, 35, 128, 163,

167, 191, 312 de Wijs, 248 Deaconu, 297 Degtyareva, 172, 182 Delaplane, 52 Deledda, 84, 114, 269 Delogu, 115 Demkin, 316 Denys, 11, 52, 119, 170,

177, 362, 370, 376 Devyatkina, 155 Dhaou, 307 Diaz, 298 Dibandjo, 340 Didyk, 118 Dinu, 297 Diplas, 344 Dmitriev, 14 Dobrotvorski, 71 Doi, 95 Dolci, 54, 148, 187, 217,

283, 385 Dolinšek, 62, 352 Dollinger, 50 Dolores Baró, 283 Dolukhanyan, 159, 245 Domènech Ferrer, 285 Domènech-Ferrer, 247,

301 Doncov, 134 Dong, 123 Dornheim, 30, 94, 109,

239, 277, 283, 287, 385

Drulis, 186, 210, 228 Du, 381 Dulya, 326 Dunsch, 301 Dupuis, 35 Duś, 203 Dzidziguri, 176 Edwards, 80, 256

Efimchenko, 158 Efimchenko2, 77 Efimov, 176 Egger, 48, 50 Eijt, 48, 116, 357 Ellis, 256 Enoki, 25 Enzo, 217 Er, 88, 248 Ermilova, 138 Esquivel, 392 Eul, 278 Evard, 71, 220, 222 Fabre, 200, 276 Fan, 289, 293 Fang, 335 Fátay, 331 Fateev, 272 Fedin, 389, 390 Fedotov, 158 Fehse, 105 Felderhoff, 332 Feng, 304 Fernandez, 227, 273 Fernández, 149, 174 Fernández Albanesi,

373 Fichtner, 6, 54, 96, 105,

148, 264, 283, 372 Fieg, 277 Figiel, 85, 306, 377 Fijałkowski, 302 Filimonov, 394 Filinchuk, 14, 44, 161,

165, 261, 285 Filipek, 114 Filippi, 212 Finot, 200 Fjellvåg, 28 Floriano, 386 Fokin, 181 Fokina, 181 Fomina, 209 Fonneløp, 84, 269 Friedrichs, 75 Frommen, 84, 269

396

Fruchart, 20, 35, 58, 141, 163, 167, 191, 242, 312, 384

Fruchart2, 128 Fursikov, 117, 380 Fuster, 274, 275 Gabis, 5, 71, 222, 252,

282 Gadiou, 340 Gafurov, 145, 157 Galitskiy, 169 Gao, 27, 99, 113, 349 Garcia, 247 Garrier, 35 Garroni, 148, 187, 283,

385 Gaudin, 81, 278 Gautam, 327 Gemma, 63, 143 Gennari, 364, 369, 373 Georges, 8, 290 Gerasimov, 66 Germanovich, 135, 272 Getzlaff, 221 Ghanem, 379 Giamello, 217 Giannasi, 264 Giasafaki, 371, 372 Gil, 191 Gil Bardaji, 372 Gilles, 248 Girard, 20, 141, 242 Girella, 250 Glazkov, 234, 378 Glazunov, 131 Godart, 162 Goltsova, 41, 140 Gomzi, 374 Gondek, 85, 306, 377 Gorbar, 133 Gorina, 136 Gosalawit, 30, 94, 239,

287 Goutaudier, 215 Gradišek, 62, 352 Graetz, 5, 74 Granroth, 77 Grant, 83, 281

Gray, 34, 119, 171, 323 Greenbaum, 43 Gregoryanz, 182 Gremaud, 21, 59, 212 Grigorova, 343 Grobety, 133 Grochala, 300, 302 Gross, 144 Grove, 84, 269 Guéguen, 257 Guerin, 97, 256 Guillaume, 182 Guillot, 22 Guo, 78, 238, 253, 254,

258, 308, 337 Gupta, 237 Gutfleisch, 70, 285, 301 Hagemann, 14, 44, 261,

285 Hagihara, 299 Han, 291 Hanada, 123, 299, 375 Hapke, 277 Haraki, 101 Harries, 204 Harris, 93 Hashimoto, 207, 219,

333 Hatano, 40 Hattori, 101 Hauback, 84, 96, 114,

129, 161, 175, 218 Havela, 225 Hayashi, 192 Hayden, 97, 256 He, 251, 254 Her, 92 Hermes, 278 Heurtaux, 340 Hino, 95, 123, 236, 259 Hirao, 121, 226 Hirasawa, 207 Hirate, 216 Hirose, 4 Hirscher, 98, 100 Hjörvarsson, 17, 46, 47,

152 Holt, 129

Hong, 367 Honkimaki, 215 Hoshino, 112 Huang, 224, 347 Huot, 58, 82, 111, 245 Hutsch, 334 Hwang, 320 Ibarbia, 378 Ichikawa, 95, 112, 123,

219, 236, 259, 270, 351, 354, 375

Ievlev, 134 Irodova2, 42 Isaev, 150, 153 Ishikawa, 111, 130, 386,

388 Ishikiriyama, 55 Ismer, 288 Isnard, 22, 38, 119 Isobe, 207, 333 Ito, 125 Ivanova, 229 Iwasieczko, 186, 210,

228 Izawa, 393 Izotov, 231 Jacob, 46, 47, 114, 303 Jacobsen, 193 Jain, 108 Janot, 79 Janotti, 288 Jansa, 175 Jaroń, 300, 302 Jeglič, 352 Jemni, 307 Jensen, 14, 94, 103, 161,

165, 171, 239, 287, 344

Jensen1, 240 Jephcoat3, 42 Jepsen, 109 Jian, 238 Jiang, 223, 224, 347,

349 Jiao, 338, 381, 382 Johansson, 153 Johnson, 256 Jones, 55, 80, 256

397

Jorge, 111 Joubert, 12, 257 Jovanovic, 363 Ju, 260, 265, 347 Juanes-Marcos, 298 Kalinichenka, 334, 341 Kamarád, 22 Kamazawa, 55 Kamegawa, 244, 246 Kamura, 375 Karakaya, 241 Karazhanov, 129 Kardjilov, 85 Karkamkar, 164, 322 Karpacheva, 176 Karpenkov, 228 Kasperovich, 312 Kassab, 63 Katagiri, 286 Kataoka, 246 Katayama, 69 Kato, 21, 64 Kawakami, 244 Kawazoe, 76, 151 Kayanuma, 202 Kazakov, 325 Kemmitt, 292 Khaimovich, 169 Khan, 108 Khandelwal, 283 Khantimerov, 387 Khatamian, 60 Khazaei, 76 Kheres, 193 Khomenko, 86 Khristov, 343 Kieback, 334, 341, 342 Kim, 33, 44, 53, 232,

291, 320, 367 Kiminami, 388 Kimmel, 114 Kim-Ngan, 225 Kirchheim, 63, 143, 195 Kita, 130 Klassen, 30, 109, 239 Klebanoff, 266, 324 Klochko, 10 Klod, 301

Klyamkin, 77, 389, 390 Knor, 203 Knosp, 290 Knudsen, 96 Kobayashi, 101 Kocjan, 352 Kockelmann, 55 Kogan, 389 Kojima, 95, 112, 123,

236, 259, 270, 351, 354, 375

Kolesnikov, 77 Kolyago, 135 Kong, 255 Konstanchuk, 66, 316 Kooi, 345 Korzhavyi, 153 Koshkidko, 229 Koteski, 262, 263 Kotur, 178 Kou, 293 Koudriachova, 58 Koval’chuck, 177, 178 Kovalenko, 389, 390 Koźlak, 306 Krexner, 61 Krishnan, 345 Krkljuš, 98, 100 Kroes, 298, 383 Krystian, 61 Kudrevatykh, 233 Kukovitsky, 387 Kulish, 169, 348 Kumar, 89 Kume, 180 Kuprin, 348 Kuriiwa, 244, 246 Kuriyama, 243 Kurko, 363 Kurmaev, 86 Kuroda, 33 Kustov, 166 Kuzovnikov, 146, 158 Kyotani, 202 Lacina, 74 Lakhnik, 104 Lang, 82 Larochette, 364, 373

Latroche, 8, 9, 124, 162, 194, 237, 257, 273, 290, 340

Laversenne, 58, 163, 215

Leardini, 149, 174, 227, 273

Lee, 33, 240, 311 Leegwater, 48 Legerstee, 357 Leiva, 111, 386 Lemort, 8, 290 Leoni, 194 Leonov, 86 Leroy, 340 Leshchinskaya, 136 Levchenko, 77, 144 Levy, 47 Li, 106, 126, 223, 224,

253, 255, 267, 268, 293, 304, 335, 337, 338, 355, 382

Liang, 106, 349 Lieutenant, 84, 269 Lindemann, 285, 301 Linkov, 211 Linsinger, 278 Liu, 78, 113, 223, 224,

258, 308, 318, 349, 355

Livraghi, 217 Livshits, 40 Llamas-Jansa, 84, 218,

269 Lohstroh, 54, 105, 148,

283 Lomino, 348 Lototsky, 10, 211, 328,

370 Løvvik, 344 Lozano, 277 Luo, 68, 128, 266 Lushnikov, 154 Lv, 223, 224 Lyashenko, 160 Lyubimenko, 41 Machida, 31, 69, 180,

226

398

Maddalena, 359, 360 Mæhlen, 119 Maehlen, 5, 52, 129, 170 Maekawa, 72, 315 Majni, 56 Majzoub, 29 Maksimenko, 134 Malka, 208, 330 Mandzhukova, 343 Mangiarotti, 321 Mangiarotti1, 314 Manicheva, 282 Manickam, 100 Mao, 308 Marini, 250, 385 Maronsson, 193 Martin, 393 Marty, 35 Maslova, 209 Matovic, 363 Matsuda, 317 Matsumoto, 39, 137 Matsumura, 65, 67, 205 Matsuo, 72 Matsuoka, 226 Matukhin, 387 Mauron, 21 Mayilyan, 159 Mazet, 38 Mazzolai, 213 McGrady, 93 McKeown, 379 Mei, 128 Meleg, 297 Mellouli, 307 Mengucci, 56 Meyer, 314, 321 Mi, 223, 224 Miceli, 313 Michel, 309 Michler, 393 Migel, 166 Mikhaylushkin, 168 Milanese, 115, 144, 250,

366, 385 Mintz, 43, 303 Miotello, 56, 339 Mirabile Gattia, 110

Miraglia, 20, 35, 58, 141, 163, 167, 191, 242, 312

Mirsaidov, 145, 157 Mirzoyev, 196 Mitrokhin, 325 Mitsui, 286 Miwa, 55, 267, 268 Miyamoto, 101 Miyaoka, 95 Miyazaki, 72 Mizuki, 67 Mizuseki, 76, 107, 151 Mnatsakanyan, 245 Mogilyanski, 114 Mongstad, 129 Montone, 103, 110 Mooij, 127, 142, 201 Mordovin, 138 Moretto, 148 Morinaga, 39, 137, 216 Morita, 207 Morozov, 169, 348 Morozova, 86 Moser, 15, 305 Movlaev, 120 Moysés Araújo, 126 Mulas, 115, 385 Mulder, 116, 357 Myakush, 178 Myronenko, 178 Nagashima, 202 Nakai, 216 Nakamura, 53, 57, 179,

192, 296, 317 Nakatsugawa, 125 Nambu, 39, 137 Napolitano, 115 Nasrallah, 307 Nasrulloeva, 157 Navarra, 164 Neklyudov, 169, 348 Nekrasova, 176 Nemanič, 139 Ngene, 27, 91 Nielsen, 94 Nii, 125

Nikitin, 186, 228, 229, 234

Nishihara, 202 Nishihata, 67 Nolis, 283 Norèus, 15 Noritake, 55 Notkin, 40 Novakovic, 363 Nowakowski, 203 Nowicka, 203 Nuttall, 256 Ogawa, 51, 202, 206,

286 Ohishi, 226 Ohkura, 315 Ohnuki, 65, 333 Okada, 244, 246 Okajima, 67 Okinaka, 295 Olsen, 298 Onanko, 160 Ono, 207, 236, 351 Orekhova, 138 Orimo, 21, 26, 72, 75,

267, 268 Orlova, 54, 148, 187,

385 Ornat, 230 Ortega, 20, 141 Oumellal, 9, 124 Ovcharenko, 348 Ozolins, 29 Öztürk, 241 Paik, 270 Paja, 230 Palasantzas, 345 Palasyuk, 45 Palmisano, 37, 142 Pálsson, 17, 152 Palumbo, 164, 190 Pan, 349 Pankratov, 228 Paolone, 164, 190 Parenago, 356 Pargeter, 393 Parker, 44 Parlouër, 144

399

Parrinello, 313 Paskevicius, 197 Pasquini, 103 Pastushenkov, 229 Paul-Boncour, 22, 38,

340, 376 Pejova, 46, 47 Peng, 106, 381 Penin, 49 Perng, 311 Peschke, 30, 287 Pfeiffer, 357 Phejar, 38 Phung, 206 Pickering, 391 Pinatel, 147 Pinkerton, 87 Pino, 383 Piscopiello, 103 Pistidda, 30, 239, 283,

385 Pivak, 59, 73 Platzer-Björkman, 129 Pohl, 256 Pohlmann, 334, 342 Pokholok, 394 Poletaev, 362 Politova, 228 Ponthieu, 273 Popov, 294, 350 Pospíšil, 225 Pöttgen, 278 Pottmaier, 54, 148, 187,

385 Prat, 141 Price, 83 Prigent, 194 Principi, 359, 360 Prinz, 152 Proctor, 182 Prodaivoda, 160 Proffen, 53 Przewoźnik, 306 Pundt, 63, 195, 393 Purdy, 256 Purewal, 320 Puszkiel, 364, 373 Rabkin, 102

Rahman, 217 Rakitin, 196 Ramirez-Cuesta, 52, 55,

264 Ranong, 277 Rapin, 44 Raskovic, 363 Ravelli, 48, 50 Ravindran, 28 Ravnsbæk, 14, 165 Raybaud, 79 Rector, 73, 212 Reed, 291, 318, 319 Reilly, 5, 74 Remhof, 21, 75 Ren, 253, 338, 382 Révész, 331 Revkevich, 173 Riabov, 170, 178 Richter, 14, 240 Riktor, 175, 193 Rispoli, 164, 190 Rodchenkova, 188 Rodriguez, 392 Rodríguez-Viejo, 247 Roehm, 264 Rohr, 194 Rongeat, 70, 301 Rönnebro, 190 Röntzsch, 334, 341, 342 Roshan, 134, 136 Ross, 15, 305 Roth, 96, 105 Rougier, 9, 124 Roupcová, 235 Rtischeva, 390 Rud, 104 Rude, 161 Rush, 92 Russo, 360 Sabitu, 353 Sahara, 76, 107 Saito, 183, 286 Saitoh, 69 Sakai, 243 Sakaki, 57, 179, 296 Sakharov, 77, 158 Sakhratov, 387

Salamova, 229, 233 Saldan, 30, 239 Sánchez, 149, 174, 227,

273 Sartori, 84, 96 Sasaki, 180, 295 Sato, 268 Saxena, 45 Scheicher, 126, 232, 304 Schiavo, 366 Schlichtenmayer, 100 Schmidt, 342 Schmidt-Ott, 357 Schneweiss, 235 Schreuders, 37, 73, 127,

142, 201, 344, 361 Schultz, 70, 285, 301 Schulze, 239 Schut, 48 Schüth, 332 Schweke, 303 Segard, 276 Seki, 130 Selvaraj, 85 Serre, 340 Setman, 61 Seto, 286 Shamir, 19 Shanin, 284 Shao, 332 Shekhtman, 245 Shelyapina, 167, 242,

312, 384 Shen, 311 Sheppard, 197 Sheptyakov, 79 Shida, 243 Shimizu, 180, 226, 351 Shimoda, 236, 351, 354 Shimojo, 112 Shimura, 180 Shinohara, 65 Shinya, 377 Shneck, 43 Sholl, 44 Sibanyoni, 370 Sidorova, 176 Sidorovich, 135

400

Siekhaus, 199 Silenkov, 272 Singh, 116 Sivov, 120, 394 Skokov, 228, 229 Skripnyuk, 102 Skripov, 23, 189, 261 Skryabina, 20, 141, 163,

167, 191, 312 Slaman, 37, 73, 127, 142 Slovetskii, 136 Smith, 97 Sofilca, 297 Solberg, 211, 328, 346,

362, 370 Soldatov, 356 Soloninin, 189, 261 Soloveichik, 36 Solovey, 284 Somenkov, 90, 154, 234,

378 Somers, 298 Sommariva, 55 Song, 335 Sørby, 84, 161, 175 Soulié, 49, 97, 256 Spassov, 331, 365 Spassova, 365 Srepusharawoot, 126 Stavila, 92, 266 Steriotis, 371, 372 Stevens, 256 Stojadinović, 133 Stojić, 262, 263 Streppel, 100 Stubos, 371 Suarez, 30, 239 Subbotin, 151 Sugiyama, 55, 125 Suleimanov, 387 Sulic, 89 Sun, 78, 335 Suriñach, 283, 385 Sutrisna, 65 Suwarno, 346 Suzuki, 123, 202, 299,

375 Syrykh, 378

Szytuła, 306 Taira, 205 Takahara, 315 Takai, 123, 299, 375 Takamura, 72, 315 Takasaki, 33, 183, 377 Takeichi, 243 Takemura, 180 Tal-Gutelmacher, 143 Tan, 241 Tanaka, 243 Taniguchi, 299 Taniuchi, 205 Tansho, 351 Tao, 106 Tarasov, 5, 117, 181,

231, 326, 362, 380 Tatiparti, 27 Taube, 239 Tedds, 379 Teng, 259 Teraoka, 204 Terashita, 57, 296 Tereshchenko, 138 Tereshina, 228, 233 Thiébaut, 12, 276 Thøgersen, 129 Thundat, 200 Tian, 368 Tkacz, 45, 146, 158 Tode, 204 Todorova, 365 Towata, 55, 267, 268 Trikalitis, 372 Troiani, 369 Tsubota, 236, 270, 351 Tsunokake, 57, 296 Tsyntsarski, 343 Tzvetkov, 343 Uchida, 65, 101, 195 Udovic, 92 Uesugi, 125 Ugliengo, 147 Ulivi, 264 Urretavizcaya, 274, 275 Utsumi, 65, 205 Vajeeston, 28 Van de Walle, 288

van der Eerden, 361 van Hemert, 383 van Leeuwen, 127 Van Setten, 212 Varin, 249 Vasquez, 227 Vaughan, 54, 148, 187,

385 Vazhenin, 209 Vekilov, 150 Venkataramanan, 76,

107 Verbetsky, 120, 154,

155, 156, 186, 233, 234, 394

Verdal, 92 Verkuijlen, 99 Verón, 369 Vigva, 160 Villeroy, 162 Vinogradskaya, 222 Vix-Guterl, 340 Vogt, 133 Voigtländer, 301 Voit, 71, 282 Volkert, 143 von Colbe, 239, 277,

287 Vons, 357 Voyt, 220, 222 Vrtnik, 352 Vyas, 108 Wagner, 393 Wakasugi, 207, 219 Walker, 83, 281 Walton, 59, 379 Wan, 260, 265 Wang, 207, 219, 223,

224, 253, 260, 265, 279, 280, 289, 292, 293, 333, 337, 338, 381, 382

Watanuki, 180 Webb, 34, 119, 171, 323 Weber, 393 Wegrzyn, 74 Weidenthaler, 332 Westerwaal, 127

401

402

Wijs, 88, 310 Wilczynska, 118 Wilkinson, 305 Williams, 10, 211, 370 Wirth, 144 Wisniewski, 118 Wolfers, 384 Wong, 292 Wu, 214, 238, 251, 254,

289, 292, 304, 328 Xiao, 214, 289, 293 Xiong, 198, 238, 251,

254, 255 Xiong1, 292 Yamane, 112 Yamauchi, 18 Yamazaki, 179 Yan, 255, 260, 265, 267,

268 Yang, 243, 281, 368 Yao, 207 Yaropolov, 186, 234

Yartys, 5, 10, 11, 52, 119, 170, 211, 326, 328, 346, 362, 370

Yasuda, 295 Yeheskel, 114 Yildirim, 92 Yokoyama, 183 Yong, 337 Yonovich, 303 Yoshigoe, 204 Yousufuddin, 92 Yu, 78, 258, 308 Yuan, 338, 381, 382 Yukawa, 39, 137, 216 Yvon, 49 Zaïdi, 9, 124 Zaika, 188 Zajec, 139 Zakaznova-Herzog,

132, 133 Zaranski, 329, 330 Zavalij, 177 Zavaliy, 177, 376 Zbroniec, 249

Zehetbauer, 61 Zemtsov, 176 Zepon, 111 Zhang, 8, 9, 113, 124,

162, 223, 253, 279, 280, 337, 354, 355

Zhao, 106, 337 Zhao-Karger, 96 Zheleznyak, 350 Zheng, 198, 254, 361 Zhirov, 140 Zhou, 29, 92, 128 Zhukovsky, 336 Zhurba, 169, 348 Zidan, 24 Zlatanova, 365 Zlotea, 340 Znovets, 135 Zoppi, 264 Zotov, 120, 394 Žumer, 139 Züttel, 21, 75, 132, 133 Zvyagintseva, 184, 185 Żywczak, 377