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Carbon nanomaterials for advanCed energy systems
Carbon nanomaterials for advanCed energy systems
advances in materials synthesis and device applications
Edited by
Wen luJong‐beom baekliming dai
Copyright copy 2015 by John Wiley amp Sons Inc All rights reserved
Published by John Wiley amp Sons Inc Hoboken New JerseyPublished simultaneously in Canada
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Limit of LiabilityDisclaimer of Warranty While the publisher and author have used their best efforts in preparing this book they make no representations or warranties with respect to the accuracy or completeness of the contents of this book and specifically disclaim any implied warranties of merchantability or fitness for a particular purpose No warranty may be created or extended by sales representatives or written sales materials The advice and strategies contained herein may not be suitable for your situation You should consult with a professional where appropriate Neither the publisher nor author shall be liable for any loss of profit or any other commercial damages including but not limited to special incidental consequential or other damages
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Library of Congress Cataloging‐in‐Publication Data
Carbon nanomaterials for advanced energy systems advances in materials synthesis and device applications edited by Wen Lu Jong-Beom Baek Liming Dai pages cm Includes bibliographical references and index ISBN 978-1-118-58078-3 (hardback)1 Electric batteriesndashMaterials 2 Energy harvestingndashMaterials 3 Fullerenes 4 Nanostructured materials 5 Carbon nanotubes I Lu Wen (Materials scientist) II Baek Jong-Beom III Dai Liming 1961ndash TK2945C37C375 2015 62131prime2420284ndashdc23 2015017196Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
List of Contributors xiii
Preface xvii
PARt I synthesIs And ChARACteRIzAtIon of CARbon nAnomAteRIALs 1
1 fullerenes higher fullerenes and their hybrids synthesis Characterization and environmental Considerations 3
11 Introduction 312 Fullerene Higher Fullerenes and Nanohybrids
Structures and Historical Perspective 5121 C
60 Fullerene 5
122 Higher Fullerenes 6123 Fullerene‐Based Nanohybrids 7
13 Synthesis and Characterization 7131 Fullerenes and Higher Fullerenes 7
1311 Carbon Soot Synthesis 71312 Extraction Separation and Purification 101313 Chemical Synthesis Processes 111314 Fullerene‐Based Nanohybrids 12
132 Characterization 121321 Mass Spectroscopy 121322 NMR 131323 Optical Spectroscopy 13
vi CONtENtS
1324 HPLC 141325 Electron Microscopy 141326 Static and Dynamic Light Scattering 14
14 Energy Applications 17141 Solar Cells and Photovoltaic Materials 17142 Hydrogen Storage Materials 19143 Electronic Components (Batteries Capacitors and Open‐Circuit
Voltage Applications) 20144 Superconductivity Electrical and Electronic Properties Relevant
to Energy Applications 20145 Photochemical and Photophysical Properties Pertinent
for Energy Applications 2115 Environmental Considerations for Fullerene Synthesis and Processing 21
151 Existing Environmental Literature for C60
22152 Environmental Literature Status for Higher Fullerenes and NHs 24153 Environmental Considerations 24
1531 Consideration for Solvents 261532 Considerations for Derivatization 261533 Consideration for Coatings 27
References 28
2 Carbon nanotubes 47
21 Synthesis of Carbon Nanotubes 47211 Introduction and Structure of Carbon Nanotube 47212 Arc Discharge and Laser Ablation 49213 Chemical Vapor Deposition 50214 Aligned Growth 52215 Selective Synthesis of Carbon Nanotubes 57216 Summary 63
22 Characterization of Nanotubes 63221 Introduction 63222 Spectroscopy 63
2221 Raman Spectroscopy 632222 Optical Absorption (UV‐Vis‐NIR) 662223 Photoluminescence Spectroscopy 68
223 Microscopy 702231 Scanning tunneling Microscopy and transmission
Electron Microscopy 7023 Summary 73References 73
3 synthesis and Characterization of Graphene 85
31 Introduction 8532 Overview of Graphene Synthesis Methodologies 87
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
Carbon nanomaterials for advanCed energy systems
Carbon nanomaterials for advanCed energy systems
advances in materials synthesis and device applications
Edited by
Wen luJong‐beom baekliming dai
Copyright copy 2015 by John Wiley amp Sons Inc All rights reserved
Published by John Wiley amp Sons Inc Hoboken New JerseyPublished simultaneously in Canada
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Library of Congress Cataloging‐in‐Publication Data
Carbon nanomaterials for advanced energy systems advances in materials synthesis and device applications edited by Wen Lu Jong-Beom Baek Liming Dai pages cm Includes bibliographical references and index ISBN 978-1-118-58078-3 (hardback)1 Electric batteriesndashMaterials 2 Energy harvestingndashMaterials 3 Fullerenes 4 Nanostructured materials 5 Carbon nanotubes I Lu Wen (Materials scientist) II Baek Jong-Beom III Dai Liming 1961ndash TK2945C37C375 2015 62131prime2420284ndashdc23 2015017196Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
List of Contributors xiii
Preface xvii
PARt I synthesIs And ChARACteRIzAtIon of CARbon nAnomAteRIALs 1
1 fullerenes higher fullerenes and their hybrids synthesis Characterization and environmental Considerations 3
11 Introduction 312 Fullerene Higher Fullerenes and Nanohybrids
Structures and Historical Perspective 5121 C
60 Fullerene 5
122 Higher Fullerenes 6123 Fullerene‐Based Nanohybrids 7
13 Synthesis and Characterization 7131 Fullerenes and Higher Fullerenes 7
1311 Carbon Soot Synthesis 71312 Extraction Separation and Purification 101313 Chemical Synthesis Processes 111314 Fullerene‐Based Nanohybrids 12
132 Characterization 121321 Mass Spectroscopy 121322 NMR 131323 Optical Spectroscopy 13
vi CONtENtS
1324 HPLC 141325 Electron Microscopy 141326 Static and Dynamic Light Scattering 14
14 Energy Applications 17141 Solar Cells and Photovoltaic Materials 17142 Hydrogen Storage Materials 19143 Electronic Components (Batteries Capacitors and Open‐Circuit
Voltage Applications) 20144 Superconductivity Electrical and Electronic Properties Relevant
to Energy Applications 20145 Photochemical and Photophysical Properties Pertinent
for Energy Applications 2115 Environmental Considerations for Fullerene Synthesis and Processing 21
151 Existing Environmental Literature for C60
22152 Environmental Literature Status for Higher Fullerenes and NHs 24153 Environmental Considerations 24
1531 Consideration for Solvents 261532 Considerations for Derivatization 261533 Consideration for Coatings 27
References 28
2 Carbon nanotubes 47
21 Synthesis of Carbon Nanotubes 47211 Introduction and Structure of Carbon Nanotube 47212 Arc Discharge and Laser Ablation 49213 Chemical Vapor Deposition 50214 Aligned Growth 52215 Selective Synthesis of Carbon Nanotubes 57216 Summary 63
22 Characterization of Nanotubes 63221 Introduction 63222 Spectroscopy 63
2221 Raman Spectroscopy 632222 Optical Absorption (UV‐Vis‐NIR) 662223 Photoluminescence Spectroscopy 68
223 Microscopy 702231 Scanning tunneling Microscopy and transmission
Electron Microscopy 7023 Summary 73References 73
3 synthesis and Characterization of Graphene 85
31 Introduction 8532 Overview of Graphene Synthesis Methodologies 87
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
Carbon nanomaterials for advanCed energy systems
advances in materials synthesis and device applications
Edited by
Wen luJong‐beom baekliming dai
Copyright copy 2015 by John Wiley amp Sons Inc All rights reserved
Published by John Wiley amp Sons Inc Hoboken New JerseyPublished simultaneously in Canada
No part of this publication may be reproduced stored in a retrieval system or transmitted in any form or by any means electronic mechanical photocopying recording scanning or otherwise except as permitted under Section 107 or 108 of the 1976 United States Copyright Act without either the prior written permission of the Publisher or authorization through payment of the appropriate per‐copy fee to the Copyright Clearance Center Inc 222 Rosewood Drive Danvers MA 01923 (978) 750‐8400 fax (978) 750‐4470 or on the web at wwwcopyrightcom Requests to the Publisher for permission should be addressed to the Permissions Department John Wiley amp Sons Inc 111 River Street Hoboken NJ 07030 (201) 748‐6011 fax (201) 748‐6008 or online at httpwwwwileycomgopermissions
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Library of Congress Cataloging‐in‐Publication Data
Carbon nanomaterials for advanced energy systems advances in materials synthesis and device applications edited by Wen Lu Jong-Beom Baek Liming Dai pages cm Includes bibliographical references and index ISBN 978-1-118-58078-3 (hardback)1 Electric batteriesndashMaterials 2 Energy harvestingndashMaterials 3 Fullerenes 4 Nanostructured materials 5 Carbon nanotubes I Lu Wen (Materials scientist) II Baek Jong-Beom III Dai Liming 1961ndash TK2945C37C375 2015 62131prime2420284ndashdc23 2015017196Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
List of Contributors xiii
Preface xvii
PARt I synthesIs And ChARACteRIzAtIon of CARbon nAnomAteRIALs 1
1 fullerenes higher fullerenes and their hybrids synthesis Characterization and environmental Considerations 3
11 Introduction 312 Fullerene Higher Fullerenes and Nanohybrids
Structures and Historical Perspective 5121 C
60 Fullerene 5
122 Higher Fullerenes 6123 Fullerene‐Based Nanohybrids 7
13 Synthesis and Characterization 7131 Fullerenes and Higher Fullerenes 7
1311 Carbon Soot Synthesis 71312 Extraction Separation and Purification 101313 Chemical Synthesis Processes 111314 Fullerene‐Based Nanohybrids 12
132 Characterization 121321 Mass Spectroscopy 121322 NMR 131323 Optical Spectroscopy 13
vi CONtENtS
1324 HPLC 141325 Electron Microscopy 141326 Static and Dynamic Light Scattering 14
14 Energy Applications 17141 Solar Cells and Photovoltaic Materials 17142 Hydrogen Storage Materials 19143 Electronic Components (Batteries Capacitors and Open‐Circuit
Voltage Applications) 20144 Superconductivity Electrical and Electronic Properties Relevant
to Energy Applications 20145 Photochemical and Photophysical Properties Pertinent
for Energy Applications 2115 Environmental Considerations for Fullerene Synthesis and Processing 21
151 Existing Environmental Literature for C60
22152 Environmental Literature Status for Higher Fullerenes and NHs 24153 Environmental Considerations 24
1531 Consideration for Solvents 261532 Considerations for Derivatization 261533 Consideration for Coatings 27
References 28
2 Carbon nanotubes 47
21 Synthesis of Carbon Nanotubes 47211 Introduction and Structure of Carbon Nanotube 47212 Arc Discharge and Laser Ablation 49213 Chemical Vapor Deposition 50214 Aligned Growth 52215 Selective Synthesis of Carbon Nanotubes 57216 Summary 63
22 Characterization of Nanotubes 63221 Introduction 63222 Spectroscopy 63
2221 Raman Spectroscopy 632222 Optical Absorption (UV‐Vis‐NIR) 662223 Photoluminescence Spectroscopy 68
223 Microscopy 702231 Scanning tunneling Microscopy and transmission
Electron Microscopy 7023 Summary 73References 73
3 synthesis and Characterization of Graphene 85
31 Introduction 8532 Overview of Graphene Synthesis Methodologies 87
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
Copyright copy 2015 by John Wiley amp Sons Inc All rights reserved
Published by John Wiley amp Sons Inc Hoboken New JerseyPublished simultaneously in Canada
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Library of Congress Cataloging‐in‐Publication Data
Carbon nanomaterials for advanced energy systems advances in materials synthesis and device applications edited by Wen Lu Jong-Beom Baek Liming Dai pages cm Includes bibliographical references and index ISBN 978-1-118-58078-3 (hardback)1 Electric batteriesndashMaterials 2 Energy harvestingndashMaterials 3 Fullerenes 4 Nanostructured materials 5 Carbon nanotubes I Lu Wen (Materials scientist) II Baek Jong-Beom III Dai Liming 1961ndash TK2945C37C375 2015 62131prime2420284ndashdc23 2015017196Printed in the United States of America
10 9 8 7 6 5 4 3 2 1
Contents
List of Contributors xiii
Preface xvii
PARt I synthesIs And ChARACteRIzAtIon of CARbon nAnomAteRIALs 1
1 fullerenes higher fullerenes and their hybrids synthesis Characterization and environmental Considerations 3
11 Introduction 312 Fullerene Higher Fullerenes and Nanohybrids
Structures and Historical Perspective 5121 C
60 Fullerene 5
122 Higher Fullerenes 6123 Fullerene‐Based Nanohybrids 7
13 Synthesis and Characterization 7131 Fullerenes and Higher Fullerenes 7
1311 Carbon Soot Synthesis 71312 Extraction Separation and Purification 101313 Chemical Synthesis Processes 111314 Fullerene‐Based Nanohybrids 12
132 Characterization 121321 Mass Spectroscopy 121322 NMR 131323 Optical Spectroscopy 13
vi CONtENtS
1324 HPLC 141325 Electron Microscopy 141326 Static and Dynamic Light Scattering 14
14 Energy Applications 17141 Solar Cells and Photovoltaic Materials 17142 Hydrogen Storage Materials 19143 Electronic Components (Batteries Capacitors and Open‐Circuit
Voltage Applications) 20144 Superconductivity Electrical and Electronic Properties Relevant
to Energy Applications 20145 Photochemical and Photophysical Properties Pertinent
for Energy Applications 2115 Environmental Considerations for Fullerene Synthesis and Processing 21
151 Existing Environmental Literature for C60
22152 Environmental Literature Status for Higher Fullerenes and NHs 24153 Environmental Considerations 24
1531 Consideration for Solvents 261532 Considerations for Derivatization 261533 Consideration for Coatings 27
References 28
2 Carbon nanotubes 47
21 Synthesis of Carbon Nanotubes 47211 Introduction and Structure of Carbon Nanotube 47212 Arc Discharge and Laser Ablation 49213 Chemical Vapor Deposition 50214 Aligned Growth 52215 Selective Synthesis of Carbon Nanotubes 57216 Summary 63
22 Characterization of Nanotubes 63221 Introduction 63222 Spectroscopy 63
2221 Raman Spectroscopy 632222 Optical Absorption (UV‐Vis‐NIR) 662223 Photoluminescence Spectroscopy 68
223 Microscopy 702231 Scanning tunneling Microscopy and transmission
Electron Microscopy 7023 Summary 73References 73
3 synthesis and Characterization of Graphene 85
31 Introduction 8532 Overview of Graphene Synthesis Methodologies 87
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
Contents
List of Contributors xiii
Preface xvii
PARt I synthesIs And ChARACteRIzAtIon of CARbon nAnomAteRIALs 1
1 fullerenes higher fullerenes and their hybrids synthesis Characterization and environmental Considerations 3
11 Introduction 312 Fullerene Higher Fullerenes and Nanohybrids
Structures and Historical Perspective 5121 C
60 Fullerene 5
122 Higher Fullerenes 6123 Fullerene‐Based Nanohybrids 7
13 Synthesis and Characterization 7131 Fullerenes and Higher Fullerenes 7
1311 Carbon Soot Synthesis 71312 Extraction Separation and Purification 101313 Chemical Synthesis Processes 111314 Fullerene‐Based Nanohybrids 12
132 Characterization 121321 Mass Spectroscopy 121322 NMR 131323 Optical Spectroscopy 13
vi CONtENtS
1324 HPLC 141325 Electron Microscopy 141326 Static and Dynamic Light Scattering 14
14 Energy Applications 17141 Solar Cells and Photovoltaic Materials 17142 Hydrogen Storage Materials 19143 Electronic Components (Batteries Capacitors and Open‐Circuit
Voltage Applications) 20144 Superconductivity Electrical and Electronic Properties Relevant
to Energy Applications 20145 Photochemical and Photophysical Properties Pertinent
for Energy Applications 2115 Environmental Considerations for Fullerene Synthesis and Processing 21
151 Existing Environmental Literature for C60
22152 Environmental Literature Status for Higher Fullerenes and NHs 24153 Environmental Considerations 24
1531 Consideration for Solvents 261532 Considerations for Derivatization 261533 Consideration for Coatings 27
References 28
2 Carbon nanotubes 47
21 Synthesis of Carbon Nanotubes 47211 Introduction and Structure of Carbon Nanotube 47212 Arc Discharge and Laser Ablation 49213 Chemical Vapor Deposition 50214 Aligned Growth 52215 Selective Synthesis of Carbon Nanotubes 57216 Summary 63
22 Characterization of Nanotubes 63221 Introduction 63222 Spectroscopy 63
2221 Raman Spectroscopy 632222 Optical Absorption (UV‐Vis‐NIR) 662223 Photoluminescence Spectroscopy 68
223 Microscopy 702231 Scanning tunneling Microscopy and transmission
Electron Microscopy 7023 Summary 73References 73
3 synthesis and Characterization of Graphene 85
31 Introduction 8532 Overview of Graphene Synthesis Methodologies 87
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
vi CONtENtS
1324 HPLC 141325 Electron Microscopy 141326 Static and Dynamic Light Scattering 14
14 Energy Applications 17141 Solar Cells and Photovoltaic Materials 17142 Hydrogen Storage Materials 19143 Electronic Components (Batteries Capacitors and Open‐Circuit
Voltage Applications) 20144 Superconductivity Electrical and Electronic Properties Relevant
to Energy Applications 20145 Photochemical and Photophysical Properties Pertinent
for Energy Applications 2115 Environmental Considerations for Fullerene Synthesis and Processing 21
151 Existing Environmental Literature for C60
22152 Environmental Literature Status for Higher Fullerenes and NHs 24153 Environmental Considerations 24
1531 Consideration for Solvents 261532 Considerations for Derivatization 261533 Consideration for Coatings 27
References 28
2 Carbon nanotubes 47
21 Synthesis of Carbon Nanotubes 47211 Introduction and Structure of Carbon Nanotube 47212 Arc Discharge and Laser Ablation 49213 Chemical Vapor Deposition 50214 Aligned Growth 52215 Selective Synthesis of Carbon Nanotubes 57216 Summary 63
22 Characterization of Nanotubes 63221 Introduction 63222 Spectroscopy 63
2221 Raman Spectroscopy 632222 Optical Absorption (UV‐Vis‐NIR) 662223 Photoluminescence Spectroscopy 68
223 Microscopy 702231 Scanning tunneling Microscopy and transmission
Electron Microscopy 7023 Summary 73References 73
3 synthesis and Characterization of Graphene 85
31 Introduction 8532 Overview of Graphene Synthesis Methodologies 87
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
CONtENtS vii
321 Mechanical Exfoliation 90322 Chemical Exfoliation 93323 Chemical Synthesis Graphene from Reduced Graphene Oxide 97324 Direct Chemical Synthesis 102325 CVD Process 102
3251 Graphene Synthesis by CVD Process 1033252 Graphene Synthesis by Plasma CVD Process 1093253 Grain and GBs in CVD Graphene 110
326 Epitaxial Growth of Graphene on SiC Surface 11133 Graphene Characterizations 113
331 Optical Microscopy 114332 Raman Spectroscopy 116333 High Resolution transmission Electron Microscopy 118334 Scanning Probe Microscopy 119
34 Summary and Outlook 121References 122
4 doping Carbon nanomaterials with heteroatoms 133
41 Introduction 13342 Local Bonding of the Dopants 13543 Synthesis of Heterodoped Nanocarbons 13744 Characterization of Heterodoped Nanotubes and Graphene 13945 Potential Applications 14646 Summary and Outlook 152References 152
PARt II CARbon nAnomAteRIALs foR eneRGy ConveRsIon 163
5 high‐Performance Polymer solar Cells Containing Carbon nanomaterials 165
51 Introduction 16552 Carbon Nanomaterials as transparent Electrodes 167
521 CNt Electrode 168522 Graphene Electrode 169523 GrapheneCNt Hybrid Electrode 171
53 Carbon Nanomaterials as Charge Extraction Layers 17154 Carbon Nanomaterials in the Active Layer 178
541 Carbon Nanomaterials as an Electron Acceptor 178542 Carbon Nanomaterials as Additives 180543 DonorAcceptor Functionalized with Carbon Nanomaterials 183
55 Concluding Remarks 185Acknowledgments 185References 185
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
viii CONtENtS
6 Graphene for energy solutions and Its Printable Applications 191
61 Introduction to Graphene 19162 Energy Harvesting from Solar Cells 192
621 DSSCs 193622 Graphene and DSSCs 195
6221 Counter Electrode 1956222 Photoanode 1986223 transparent Conducting Oxide 1996224 Electrolyte 200
63 OPV Devices 200631 Graphene and OPVs 201
6311 transparent Conducting Oxide 2016312 BHJ 2036313 Hole transport Layer 204
64 Lithium‐Ion Batteries 204641 Graphene and Lithium‐Ion Batteries 205
6411 Anode Material 2056412 Cathode Material 209
642 LindashS and LindashO2 Batteries 211
65 Supercapacitors 212651 Graphene and Supercapacitors 213
66 Graphene Inks 21667 Conclusions 219References 220
7 Quantum dot and heterojunction solar Cells Containing Carbon nanomaterials 237
71 Introduction 23772 QD Solar Cells Containing Carbon Nanomaterials 238
721 CNts and Graphene as tCE in QD Solar Cells 2387211 CNts as tCE Material in QD Solar Cells 2397212 Graphene as tCE Material in QD Solar Cells 240
722 Carbon Nanomaterials and QD Composites in Solar Cells 2417221 C
60 and QD Composites 241
7222 CNts and QD Composites 2447223 Graphene and QD Composites 245
723 Graphene QDs Solar Cells 2477231 Physical Properties of GQDs 2477232 Synthesis of GQDs 2477233 PV Devices of GQDs 247
73 Carbon NanomaterialSemiconductor Heterojunction Solar Cells 249731 Principle of CarbonSemiconductor Heterojunction Solar Cells 249732 a‐CSemiconductor Heterojunction Solar Cells 250733 CNtSemiconductor Heterojunction Solar Cells 252
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
CONtENtS ix
734 GrapheneSemiconductor Heterojunction Solar Cells 25374 Summary 261References 261
8 fuel Cell Catalysts based on Carbon nanomaterials 267
81 Introduction 26782 Nanocarbon‐Supported Catalysts 268
821 CNt‐Supported Catalysts 268822 Graphene‐Supported Catalysts 271
83 Interface Interaction between Pt Clusters and Graphitic Surface 276
84 Carbon Catalyst 281841 Catalytic Activity for ORR 281842 Effect of N‐Dope on O
2 Adsorption 283
843 Effect of N‐Dope on the Local Electronic Structure for Pyridinic‐N and Graphitic‐N 2858431 Pyridinic‐N 2878432 Graphitic‐N 288
844 Summary of Active Sites for ORR 290References 291
PARt III CARbon nAnomAteRIALs foR eneRGy stoRAGe 295
9 supercapacitors based on Carbon nanomaterials 297
91 Introduction 29792 Supercapacitor technology and Performance 29893 Nanoporous Carbon 304
931 Supercapacitors with Nonaqueous Electrolytes 304932 Supercapacitors with Aqueous Electrolytes 311
94 Graphene and Carbon Nanotubes 32195 Nanostructured Carbon Composites 32696 Other Composites with Carbon Nanomaterials 32797 Conclusions 329References 330
10 Lithium‐Ion batteries based on Carbon nanomaterials 339
101 Introduction 339102 Improving Li‐Ion Battery Energy Density 344103 Improvements to Lithium‐Ion Batteries Using Carbon
Nanomaterials 3451031 Carbon Nanomaterials as Active Materials 345
104 Carbon Nanomaterials as Conductive Additives 3461041 Current and SOA Conductive Additives 346
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
x CONtENtS
105 SwCNt Additives to Increase Energy Density 348106 Carbon Nanomaterials as Current Collectors 351
1061 Current Collector Options 351107 Implementation of Carbon Nanomaterial Current Collectors
for Standard Electrode Composites 3541071 Anode MCMB Active Material 3541072 Cathode NCA Active Material 356
108 Implementation of Carbon Nanomaterial Current Collectors for Alloying Active Materials 356
109 Ultrasonic Bonding for Pouch Cell Development 3581010 Conclusion 359References 362
11 Lithiumsulfur batteries based on Carbon nanomaterials 365
111 Introduction 365112 Fundamentals of LithiumSulfur Cells 366
1121 Operating Principles 3661122 Scientific Problems 368
11221 Dissolution and Shuttle Effect of Lithium Polysulfides 369
11222 Insulating Nature of Sulfur and Li2S 369
11223 Volume Change of the Sulfur Electrode during Cycling 369
1123 Research Strategy 369113 Nanostructure CarbonndashSulfur 370
1131 Porous CarbonndashSulfur Composite 3711132 One‐Dimensional CarbonndashSulfur Composite 3731133 two‐Dimensional Carbon (Graphene)ndashSulfur 3751134 three‐Dimensional Carbon PaperndashSulfur 3771135 Preparation Method of SulfurndashCarbon Composite 377
114 Carbon Layer as a Polysulfide Separator 380115 Opportunities and Perspectives 381References 382
12 LithiumndashAir batteries based on Carbon nanomaterials 385
121 MetalndashAir Batteries 385122 LindashAir Chemistry 387
1221 Aqueous Electrolyte Cell 3871222 Nonaqueous Aprotic Electrolyte Cell 3891223 Mixed AqueousAprotic Electrolyte Cell 3911224 All Solid‐State Cell 391
123 Carbon Nanomaterials for LindashAir Cells Cathode 393124 Amorphous Carbons 393
1241 Porous Carbons 393
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
CONtENtS xi
125 Graphitic Carbons 3951251 Carbon Nanotubes 3951252 Graphene 3981253 Composite Air Electrodes 400
126 Conclusions 403References 403
13 Carbon‐based nanomaterials for h2 storage 407
131 Introduction 407132 Hydrogen Storage in Fullerenes 408133 Hydrogen Storage in Carbon Nanotubes 414134 Hydrogen Storage in Graphene‐Based Materials 419135 Conclusions 427Acknowledgments 428References 428
Index 439
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
LIST OF COnTrIbuTOrS
nirupam Aich Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
Paola Ayala Faculty of Physics University of Vienna Vienna Austria and Yachay Tech University School of Physical Sciences and Nanotechnology Urcuquiacute Ecuador
Marcella bini Department of Chemistry University of Pavia Pavia Italy
Doretta Capsoni Department of Chemistry University of Pavia Pavia Italy
Zhongfang Chen Department of Chemistry Institute for Functional Nanomaterials University of Puerto Rico San Juan PR USA
Wonbong Choi Department of Materials Science and Engineering University of North Texas Denton TX USA
Vishnu T Chundi Department of Materials Science and Metallurgy University of Cambridge Cambridge UK
Liming Dai Center of Advanced Science and Engineering for Carbon (Case4Carbon) Department of Macromolecular Science and Engineering Case Western Reserve University Cleveland OH USA
Santanu Das Department of Materials Science and Engineering University of North Texas Denton TX USA
Stefania Ferrari Department of Chemistry University of Pavia Pavia Italy
Michael W Forney NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
xiv LIST OF CONTRIbUTORS
Matthew J Ganter NanoPower Research Laboratory Rochester Institute of Technology Rochester NY USA
Lorenzo Grande Helmholtz Institute Ulm Ulm Germany
Yong Soo Kang Department of Energy Engineering Hanyang University Seoul South Korea
Takahiro Kondo Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
brian J Landi NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
Fen Li Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Xinming Li School of Materials Science and Engineering Tsinghua University and National Center for Nanoscience and Technology beijing China
Jun Liu State Key Laboratory of Polymer Physics and Chemistry Changchun Institute of Applied Chemistry Chinese Academy of Sciences Changchun China
Piercarlo Mustarelli Department of Chemistry University of Pavia Pavia Italy
Junji nakamura Faculty of Pure and Applied Sciences University of Tsukuba Tsukuba Japan
Vasile Vn Obreja National RampD Institute for Microtechnology (IMT bucuresti) bucharest Romania
Toshiyuki Ohashi Fundamental Technology Research Center Honda RampD Co Ltd Wako Japan
Jaime Plazas‐Tuttle Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
reginald E rogers NanoPower Research Laboratory and Department of Chemical Engineering Rochester Institute of Technology Rochester NY USA
navid b Saleh Department of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
P Sudhagar Department of Energy Engineering Hanyang University Seoul South Korea
Toma Susi Faculty of Physics University of Vienna Vienna Austria
Di Wei Nokia RampD UK Ltd Cambridge UK
Xiaowei Yang School of Material Science and Engineering Tongji University Shanghai China
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
LIST OF CONTRIbUTORS xv
Yuegang Zhang Suzhou Institute of Nano‐Tech and Nano‐bionics Chinese Academy of Sciences Suzhou China
Jijun Zhao Laboratory of Materials Modification by Laser Electron and Ion beams and College of Advanced Science and Technology Dalian University of Technology Dalian China
Tianshuo Zhao Department of Material Science and Engineering University of Pennsylvania Philadelphia PA USA
Hongwei Zhu School of Materials Science and Engineering and Center for Nano and Micro Mechanics Tsinghua University beijing China
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
Preface
The global energy consumption has been accelerating at an alarming rate due to the rapid economic expansion worldwide increase in world population and ever‐increasing human reliance on energy‐based appliances It was estimated that the world will need to double its energy supply by 2050 Consequently the research and development of sustainable energy conversion and storage technologies have become more important than ever Although the efficiency of energy conversion and storage devices depends on a variety of factors their overall performance strongly relies on the structure and property of the materials used The recent development in nanotech-nology has opened up new frontiers by creating new nanomaterials and structures for efficient energy conversion and storage Of particular interest carbon nanomate-rials have been cost‐effectively structured into various nanostructures with a high surface area and energy conversionstorage capacities This book will focus on advances in the research and development of carbon nanomaterials for advanced energy systems
Carbon has long been known to exist in three forms amorphous carbon graphite and diamond However the Nobel Prize‐winning discovery of buckminsterfullerene C
60 in 1985 has created an entirely new branch of carbon chemistry The subsequent
discoveries of carbon nanotubes in 1991 and graphene in 2004 opened up a new era in materials science and nanotechnology Since then carbon nanomaterials with unique size‐surface‐dependent electrical thermal optical and mechanical prop-erties have been demonstrated to be useful as energy materials and tremendous progress has been achieved in developing carbon nanomaterials for high‐performance energy conversion and storage systems This is a field in which a huge amount of literature has been rapidly generated with the number of publications continuing to increase each year Therefore it is very important to cover the most recent develop-ments in this field in a timely manner
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
xviii PrefACe
This book deals with the synthesis fundamentals and device applications of a wide range of carbon nanomaterials In order to cover the multidisciplinary field of such diversity Carbon Nanomaterials for Advanced Energy Systems provides a collection of chapters written by top researchers who have been actively working in the field and the text has been divided into three major parts The first part consisting of Chapters 1ndash4 Synthesis and Characterization of Carbon Nanomaterials deals with the synthesis and basic science of various carbon nanomaterials including ful-lerenes carbon nanotubes graphene and their multidimensionalmultifunctional derivatives In the second part Carbon Nanomaterials For Energy Conversion Chapters 5ndash8 present an overview of carbon nanomaterials for various energy conversion systems such as solar cells fuel cells and thermoelectric devices A large variety of carbon‐based energy storage devices ranging from supercapacitors through batteries to energy‐related gas storage systems are then described in the final part (Chapters 9ndash13) Carbon nanomaterials for energy storage of the book The above approach will allow the readers to first review the scientific basis of carbon nanomaterials and then extend the basic knowledge to the development construction and application of functional devices many of them are of practical significance
The readers who are new to the field will be exposed to many self‐explanatory illustrations that could provide an overview understanding even before a serious reading In the meantime the large number of updated references cited in each of the chapters should enable advanced readers to quickly review the multidisciplinary and challenging field with information on the latest developments Therefore Carbon Nanomaterials for Advanced Energy Systems is an essential reference on carbon nanomaterials for energy systems to scientists engineers teachers and students who are new to the field experienced academic and industrial professionals can use this book to quickly review the latest developments in this challenging multidisciplinary field and broaden their knowledge of carbon nanomaterials for developing novel devicessystems for advanced energy conversion and storage
finally we wish to express our sincere thanks to Dr edmund H Immergut Ms Anita Lekhwani Ms Cecilia Tsai and their colleagues at Wiley and Wiley‐VCH for their very kind and patient cooperation during the completion of this book project without which this book would never have been appeared We would also like to thank all of the chapter contributors authors whose work was cited and our colleagues who contributed in one way or the other to the book Last but not the least we thank our families for their love unceasing patience and continuous support
Wen Lu Jong‐Beom Baek Liming DaiNovember 2014
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
PART I
SynTheSIS And chARAcTeRIzATIon of cARbon nAnomATeRIAlS
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
Carbon Nanomaterials for Advanced Energy Systems Advances in Materials Synthesis and Device Applications First Edition Edited by Wen Lu Jong-Beom Baek and Liming Dai copy 2015 John Wiley amp Sons Inc Published 2015 by John Wiley amp Sons Inc
1Fullerenes HigHer Fullerenes and tHeir Hybrids syntHesis CHaraCterization and environmental Considerations
Nirupam Aich Jaime Plazas‐Tuttle and Navid B SalehDepartment of Civil Architectural and Environmental Engineering University of Texas Austin TX USA
11 introduCtion
The search for alternative and renewable energy sources has become one of the major thrusts of the twenty‐first‐century researchers due to the increasing demand for energy Innovations and development of photovoltaics dye‐sensitized or polymer solar cells high‐efficiency lithium ion batteries supercapacitors transshyparent conductors hydrogen productions and storage systems microbial fuel cells catalyst‐driven proton exchange membrane fuel cells thermoelectric power genershyation etc have come to the forefront in alternative energy research [80 149] In quest of effective energy transfer distribution and storage improved materials are being synthesized since the 1990s Nanoscale manipulation of materials has fueled such development [11] Improved surface area at the nanoscale and targeted molecshyular placement or alteration in nanomaterials resulted in desired band gap tuning and effective electron transfer storage and surface activity [111] One of the key challenges that eluded energy researchers for decades was an efficient photoelecshytron acceptor with high structural stability and chemical reactivity a spheroidal
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
4 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
carbon allotrope known as fullerene addressed this critical gap in alternative energy research and development [31 111]
Sixty carbon atoms organized following isolated pentagon rule (ie 20 hexagons and 12 pentagons) forming a truncated icosahedron structure is known as buckminsterfullerenemdashthe first member of the fullerene family discovered by Sir Harry Kroto Robert Curl and Richard Smalley in 1985 [136] Fullerenesrsquo ability to effectively function in donoracceptor heterojunctions has popularized its synthesis derivatization and supramolecular assembly for photovoltaic applications [31] Later detection and effective isolation of higher‐order fullerenes [121] that is C
70
C76
C82
C84
etc have encouraged their studies and uses in energy applications Changes in holeelectron‐pair generation ability and electronic band gap with the changing number of atoms in the fullerene structures have continued to evoke interest in these higher fullerenes [61 169] Electronic structure could be further tuned by conjugation of fullerenes with other carbon allotropes for example carbon nanoshytubes (CNTs) graphene etc which has encouraged synthesis of hierarchical assemblages of fullerenes with other nanoscale structures resulting in nanoscale hybrid (NH) materials [3 146 201 212 272]
C60
s especially its polymeric derivative [66]‐phenyl‐C61
‐butyric acid methyl ester (PCBM) has been known to be the most effective electron acceptor for organic photovoltaics [31] Recent advances in this field have proposed a novel donoracceptor blend for holeelectron transfer By photoexciting the donor electron moves from the lowest unoccupied molecular orbital (LUMO) of the donor to the acceptor where the hole gets transported to the donor C
60rsquos excellent electron‐accepting ability
has presented it as an ideal candidate for photovoltaic solar cell construction Their applications in organic field‐effect transistors [9] and lithium or hydrogen storage [42] also depend on its high electron affinity and high charge transferability C
60s also
act as promising catalytic composites and electrode materials for Nafion‐based proton exchange membrane fuel cells [243] Similarly higher‐order fullerenes such as C
70 C
76 C
84 and C
90 and their derivatives are also being utilized as higher‐
efficiency transistors and have shown promising solar cell efficiencies [128 221 244] Moreover hybridization of fullerenes to formulate concentric fullerene clusters or carbon nano‐onions [90] fullerene nanopeapods [146] or nanobuds (fullerenendashCNT hybrids) [245 255] and endohedral metallofullerenes [263] enhances their promises in energy storage devices However such demand of fullerenes requires higher quantity to be synthesized and purified Such high demand for this material requires unique synthesis and preparation processes which in conjunction with fullerenesrsquo inherent attributes can invoke toxic responses to the environment hence necessitating careful consideration [200]
C60
and its derivatives such as C‐3 fullerol C60
(OH)24
bis‐methanophosphonate fullerene tris carboxyl fullerene adduct tris‐C
60 dendritic C
60 monoadduct malonic
acid C60
tris adduct etc are found to be responsible for inducing toxicological impacts in soil and aquatic microbes [41 73 114 151 259] invertebrates [276] and fish [276] as well as in human cell lines [78 196 205] and rats and mice [71] Such environmental and biological toxic potentials are known to have resulted from fullershyenesrsquo ability to penetrate cell membranes and generate oxidative stresses Similarly
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
FULLERENE HIGHER FULLERENES AND NANOHYBRIDS 5
C70
s have also shown to adversely affect aquatic species when C70
‐gallic acid derivative at less than quantifiable concentration causes significant reduction in Daphnia magna fecundity after 21‐day exposure It has also demonstrated generation of oxidative stress through inhibition of enzymatic activities [211] The demonstrated toxicity of fullerenes resulted in systematic evaluation of its fate transport and transshyformation in natural environment which include fundamental aggregation [164] deposition and transport in porous media [270] photoinduced transformation [104] etc C
60s synthesized using different techniques [32 150] have been studied to
evaluate role of synthesis on their potential risk However very few studies have focused on systematic investigations of higher fullerenes and fullerene‐based NHrsquos fate transport transformation and toxicity [2 3 200 201]
This book chapter discusses synthesis characterization and application of fullerenes higher fullerenes and their NHs The chapter will identify potential risk of these carbon allotropes when used in energy applications and discuss possible strategies for pursuing green synthesis of these materials The discussion in this chapter will potentially highlight the relevant risk of using fullerenes in energy applishycations and help establish an understanding of environmental considerations
12 Fullerene HigHer Fullerenes and nanoHybrids struCtures and HistoriCal PersPeCtive
121 C60 Fullerene
C60
fullerene is an all‐carbon and perfectly symmetric molecule made from 60 carbon atoms (Fig 11a) It was the first ever discovered regular truncated icosahedral molshyecule [197 242] The carbon atoms on the vertices of the polygons in C
60s possess sp2
hybridization and become bonded through 66 double bond between hexagons and 65 bonds between hexagons and pentagons [87] One carbon atom is bonded to 3 other carbon atoms with a bond length of 014 nm The total spherical diameter of a C
60 molecule becomes 071 nm giving rise to the perfect symmetric cage [95]
Though such molecules possess high structural stability [162 197 228 242] these were found to be highly reactive where acceptance of electrons makes them strongly reductive [99 100] Such conjugate reactivity and structural stability help them to produce various derivatives as shown in Figure 11b
The discovery of fullerene was rather extraordinary [130] A research lab in Exxon group in 1984 had first seen carbon soot presenting similar time of flight (TOF) mass spectra for even numbers of carbon atoms starting from 40 to 200 [198] however they were unable to identify the abundance of C
60s in that mixture In similar time frame
while searching for the mechanism of interstellar long‐chain carbon molecule formation an unusual TOF spectral signature of carbon soot was observed by Sir Kroto Smalley and Curl while synthesizing carbon soot through laser irradiation of graphite [136] at Rice University in 1985 The group hypothesized that the spectral signature was generated due to the formation of C
60s the probable aromatic icosaheshy
dron structure with remarkable stability Later on nuclear magnetic resonance (NMR)
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
6 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
experiments were performed to conclude that the molecules obtained by Kroto and others truly resulted in C
60 molecules [230] Kratschmer Huffman and Fostiropoulos
on the other hand came up with synthesis technique for macroscopic amount of C60
and C
70 in 1989 [132] In 1995 Harry Kroto Richard Smalley and Robert Curl were
awarded Nobel Prize in Chemistry for the discovery of C60
The aforementioned scishyentists later named the first discovered carbon allotrope as ldquobuckminsterfullerenerdquo or ldquofullerenerdquo to pay homage toward the renowned American architect Buckminster Fuller who designed geodesic dome‐shaped structures resembling fullerenes
122 Higher Fullerenes
Members of fullerene family possessing more than 60 carbon atoms are known as higher‐order fullerenes (Fig 11c) They are generally found in the same carbon soot obtained during C
60 synthesis C
70 being the first member of the higher‐order
fullerene family is always found in abundance with the C60
s However the other members that is C
76 C
78 C
84 and C
92 (up to fullerenes with more than a hundred
carbon atoms) are found in much smaller quantities in the soot Diederich et al first
(a)
(c)
(b)
C28 C32
C60C50
C70
C240
(i)
(ii) (iii)
(d)
CF3CF3CF3
CF3CF3 CF3
CF3
CF3
CF3CF3
CF3
(ii)
(i)
O
OCH3
F3C
C84
Figure 11 (a) Fullerenes (b) Fullerene derivatives (i) C60
derivative [66]‐phenyl‐C
61‐butyric acid methyl ester (PCBM) and (ii) trifluoromethyl derivative of C
84 ([C
84](CF
3)
12)
(c) Higher‐order fullerenes (d) (i) Nanobud (fullerenes covalently bound to the outer sidewalls of single‐walled carbon nanotube) (ii) peapod (fullerenes encapsulated inside a single‐walled carbon nanotube) and (iii) nano‐onion (multishelled fullerenes) (See insert for color represen-tation of the figure)
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
SYNTHESIS AND CHARACTERIZATION 7
found mass spectroscopic evidence for existence of C76
C78
and C84
and isolated them through extraction technique employment during reproduction of the Kratschmer method for producing C
60 and C
70 fullerenes [59] During the same time theoretical
prediction of their existence isomerism and chemical stability was presented by Fowler and Manolopoulos [20 74 155 156] With the help of the newer chromatographic techniques fullerenes with a wide range of composition that is C
20
to C400
were extracted isolated and characterized alongside with identification of isomeric forms of several higher‐order fullerenes [121 189 214]
123 Fullerene‐based nanohybrids
When C60
and higher fullerenes are conjugated either exohedrally or endohedrally with carbon‐ and metal‐based nanomaterials the ensemble materials are known as fullerene‐based nanohybrids (NHs) (Fig 11d) [3 201] The overall scope of this book will limit the discussion to carbon NHs only Endohedral NHs can be formed via fullerene and higher fullerene encapsulation within CNTs and larger fullerene structures These strucshytures are called peapods [218] and carbon nano‐onions [219] respectively (Fig 11d) Nanopeapods prepared in 1998 by Luzzi et al was one of the first NHs synthesized [218] Growing interests in fullerene and NH chemistry encouraged development of other NH assemblages either with CNTs [174] or graphene [194] The conjugation is performed using both nonspecific short‐ranged interaction [257] and via covalent bonding [148 174] with the use of functional linking molecules or polymers
13 syntHesis and CHaraCterization
131 Fullerenes and Higher Fullerenes
Commercial production of C60
s and higher fullerenes involves a two‐step process [63] First carbon soot containing fullerene mixtures is synthesized via carbon vapor genershyation methods Second fullerene separation and purification from the carbon soot are performed to obtain individual fractions of the carbon allotropes Based on the raw materials and precursors vaporization methods and processing techniques various soot generation processes have been developed Most of the synthesis techniques were developed during the 1985ndash1995 time line when fullerene discovery and techniques for primary isolations and separation were innovated [130] Later chemical synthesis processes to form fullerenes from aromatic hydrocarbons were developed [207] A brief discussion on the major fullerene and higher fullerene production techniques is described in this section Figure 12 shows a flow diagram demonstrating steps involved in carbon soot synthesis and fullerene extraction and purification
1311 Carbon Soot Synthesis
Arc Vaporization Methods Arc vaporization methods are the most effective ones for carbon soot synthesis The process of resistive heating of graphite rods in helium environment developed by Kratschmer et al was the first step to produce carbon
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
8 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
soot containing fullerenes in macroscopic amounts [131] The method was furthered into AC‐ or DC‐arc‐based carbon vaporization processes to produce gram quantities of fullerenes [4] this technique reduced loss of carbon rods through complete heating of the electrodes Figure 13 shows a typical arc process for fullerene soot generation Two graphite rods are separated from each other by 1ndash10 mm in a helium‐filled chamber under 100ndash200 torr pressure An arc is discharged to generate 100ndash200 amp current at a voltage of 10ndash20 V This process causes the graphite rods to evaporate and form soot containing fullerene products Copper jacket covering the chamber wall and circulating cooling water control the temperature to allow carbon soot vapors to conshydense and deposit on the chamber walls which can later be extracted for purification and processing Modifications of these methods were performed to achieve several advantages Such modifications include arc via contacting with the graphite [93 214] or demineralized coal electrodes [186] employment of plasma discharge for high yield [189 210] application of DC power rather than AC [93 186 214] and low current rather than high AC current [126] to achieve better fullerene yield formation of tapered apparatus for gravity‐based collection of carbon soot [126] etc
Laser Ablation Method This technique was first adopted by the Smalley group in 1985 [136] which involves a laser such as neodymium‐doped yttrium aluminum garnet (NdYAG) irradiated on a graphite rod causing the carbons to evaporate via
Stage 1 Stage 2
Fullerene Synthesis
Fullerenemixtureextraction
Carbonsootsynthesis
Isolation ofindividualfullerenes
Solvent methodor soxhlet
Solvent-based liquidchromatography
Sublimation usingtemperature gradient
Fullerene separation and puricationCarbon soot containing fullerenes
Sublimation technique
Resistive heating
Laser ablation
Arc vaporization
Plasma discharge
Inductive heating
Combustion of benzene
Carbon sputtering
Electron beam sputtering
Figure 12 Flow diagram showing steps for fullerene synthesis via carbon soot formation and fullerene separation and purification
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
SYNTHESIS AND CHARACTERIZATION 9
heating and produce carbon plasma Afterward controlled cooling of the carbon plasma takes place to form fullerene clusters Later ablation at elevated temperature or inside of heated furnace resolved the issue by slowing down the cooling process [59 147] Around 1000ndash1200degC was found to be most efficient for fullerene cluster formation [147] A high‐temperature furnace containing such laser ablation arrangeshyment is shown in Figure 14 Operating parameter modulation such as changing laser intensity wavelength buffer gas pressure and temperature in the furnace can offer better control over fullerene formation and yield
Other Methods Versatility in fullerene synthesis processes has been achieved through adoption of different innovative approaches A thermal vaporization method by inducshytively heating the graphite rods in a high‐frequency furnace at 2700degC was developed
Heliumgas
Reactionchamber
Electrodes+ ndash
Vacuum
Deposited sootcontainingfullerenes
ArcdischargeWater-
cooledwall
Graphiterods
Figure 13 Arc discharge process for fullerene synthesis Adapted and modified from Refs 93 and 147
Furnace
Quartztube
Graphite rod +(Ni + Co)
Water-cooled Cucollector
Heating coil
Heating coil
Argongas
Nd-YAGlaser
Deposited sootcontainingfullerenes
Plasma
Target
Figure 14 Laser ablation process for fullerene synthesis Adapted and modified from Ref 147
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
10 FULLERENES HIGHER FULLERENES AND THEIR HYBRIDS
for soot production at large quantities [190] Moreover combustion method was employed where laminar flames of premixed benzene and oxygen with argon diluents were used to produce C
60 and C
70 [102 103] Gram quantities of fullerenes were
produced using this process with potential for easy scale‐up continuous process operations easy dopant addition in the flame mixture and changes in flame properties for controlling the fullerene size distribution [102 147] Efficient production of a large quantity of higher fullerene soot with minor C
60 presence was developed by Bunshah
et al in 1992 [36] Two different experimental setups were devisedmdashone for carbon sputtering and the other for electron beam sputtering In the carbon sputtering method a magnetron sputtering cathode was attached to a graphite target and carbon black was sputtered from the target by helium ions In the other method an electron beam was used to evaporate carbon from a graphite target Efficiencies of fullerene synthesis methods along with their extraction methods yields and operating conditions such as pressure temperature mode etc have been summarized in several review papers [188 216]
1312 Extraction Separation and Purification Fullerene extraction and purishyfication involve a two‐step process [63] First fullerene mixtures are isolated from the carbon soot using a solvent extraction followed by a separation of individual fullerene molecules using chromatography or sublimation processes Details of these processes are described in the following
Fullerene Mixture Extraction from Carbon Soot In the solvent extraction method fullerene mixtures along with some soluble hydrocarbons from the soot are dissolved in toluene or similar solvents and then filtered or decanted to remove the insoluble residue to recover extractable fullerenes at 10ndash44 mass [216] Toluene‐soluble extracts generally contain 65 C
60 30 C
70 and 5 higher fullerenes [216]
Tetrahydrofuran (THF) is also used to ultrasonicate soot at room temperature followed by filtration [58] Evaporation of the filtrate in a rotary evaporator is employed to obtain fullerene powder mixture A Soxhlet apparatus can also be used for efficient solubilizashytion of fullerenes [63 189] In this process the solvent is first boiled and evaporated which is condensed down through a carbon soot matrix extracting the fullerenes The cycle is repeated for maximizing the fullerene extraction [189] Sublimation process in contrast involves heating the raw soot in a quartz tube under helium gas or in vacuum followed by condensing the mixture [241] Fullerene mixtures accumulate at the bottom leaving the residue products from soot in the vapor phase
Separation and Purification of Individual Fullerenes from Mixture There are two major processes for purification or isolation of individual fullerenes These are solvent‐based liquid chromatography (LC) and sublimation using temperature gradient
lc This is the primary technique for separation of individual C60
C70
and other higher fullerenes from the extracted mixture [216] In this process a solution of fullerene mixture is passed through a packed porous column The solution is known as the mobile phase and the solvent as the eluent while the solid surface is called the
top related