AIP Conference Proceedings 1914, 030020 (2017); https://doi.org/10.1063/1.5016707 1914, 030020

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Characterization of nanocomposites forhydrogen storageCite as: AIP Conference Proceedings 1914, 030020 (2017); https://doi.org/10.1063/1.5016707Published Online: 15 December 2017

Amanda D. Oliveira, Cesar A. G. Beatrice, Fabio R. Passador, and Luiz A. Pessan

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Characterization of Nanocomposites for Hydrogen Storage Amanda D. Oliveiraa*, Cesar A. G. Beatriceb, Fabio R. Passadorc, Luiz A. Pessanb

aFederal University of Pelotas, Centre of Technology Development, Pelotas – RS, Brazil bFederal University of São Carlos, Department of Materials Engineering, São Carlos – SP, Brazil

cFederal University of São Paulo, Institute of Science and Technology, São José dos Campos – SP, Brazil

* Corresponding author’s: amandaoliveira82@gmail.comAbstract. The use of hydrogen as an energy carrier suitable to replace gasoline and other fossil fuels has been widely discussed as a way to sustainably fuel our civilization. However, hydrogen storage is a major barrier in the establishment of infrastructure for hydrogen technology. The incorporation of nanoparticles to the polymer matrix may be an alternative to obtain materials with promising properties for hydrogen storage. In this work, polyetherimide-based Nanocomposites were prepared using carbon nanotubes doped with sodium alanate (NaAlH4) as filler. The sodium alanate content was fixed at 30 wt% and were studied three carbon nanotubes concentrations: 5, 10 and 20 wt%. The nanocomposites were characterized by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Hydrogen sorption measurements.

Keywords: hydrogen, energy, nanoparticles, storage.

INTRODUCTIONHydrogen fuel promises a future of renewable and clean energy. Hydrogen is the most abundant element on the

earth and its oxidation product water is environmentally friendly. However, hydrogen is flammable, particularly explosive, highly diffusive, and its volume density is only one three thousandth of that of gasoline. The main challenges of hydrogen economy include hydrogen production, hydrogen transportation, hydrogen storage and hydrogen application. The largest obstacle for the spread use of hydrogen technology today is neither the production nor how to utilize the hydrogen, but rather effective and safe means of storage. Therefore, the ultimate goal related to hydrogen storage is to develop technologies with high energy density, high efficiency and safety [1, 2].

Several materials including carbon nanotubes, metalorganic frameworks, metal hydrides, graphite and activated carbon and metal/carbon nanostructures show promise as potential materials for hydrogen storage [2, 3]. Large specific surface area materials, such as metalorganic zeolites and carbon nanotubes, can produce hydrogen physisorption, but the storage capacity is very low (about 2 wt%) and generally the storage properties totally disappear at temperatures over 100 K, and can be increased up to about 195 K by pressurizing at 100 bar [2].

The addition of filler materials to the matrix material can be used to tailor an ideal nanocomposite material for hydrogen storage. In this work, nanocomposites with different filler materials at different concentrations were prepared and its effects on the thermal behavior and hydrogen storage capacity were evaluated.

EXPERIMENTAL

Materials

PEI (UltemTM 1000) was purchased from Sabic Innovative Plastics, presents melt flow index of 9g/10min (6.6Kg/337ºC) and density of 1.28 g/cm3. For the modification of the polymer was used a sulfonating agent prepared from N-Methyl-2-pyrrolidinone (NMP) (was distilled before be used), acetic anhydride and sulfuric acid, all commercial grade, in the ratio 20:2:1 (by volume) to form acetyl sulfate reagent.

The MWCNTs used for this study were provided by the Nanostructured and Amorphous Materials Inc., contain 95 wt% purity, diameter less than 8 nm and length of 10 – 30 m. Sodium alanate (NaAlH4) was purchased from Sigma Aldrich. Titanium dioxide (TiO2) was used as a dopant for NaAlH4 particles and was synthetized in our laboratories [4].

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Sulfonation of PEI

Firstly, it was prepared the sulfonating agent. A predetermined amount of acetic anhydride was dissolved in NMP and the solution cooled to a temperature of approximately 0ºC. The solution was magnetic stirred and sulfuric acid was added slowly in the solution, the reaction was conducted for 30 min.

The sulfonation of PEI was carried under nitrogen atmosphere. Six grams of PEI was dissolved in 40 ml of NMP at 80ºC, under constant stirring. Then sulfonating agent was added to the PEI solution gradually and the reaction continued for 1 h. The reaction product was precipitated by slow dripping of ethyl alcohol. The final product was washed with ethyl alcohol and filtered on a funnel of Buchner. The sulfonated polyetherimide obtained was dried in a vacuum oven at 80ºC for 3 days.

Preparation of the PEIS/MWCNT/NaALH4 nanocomposites

Since the sodium alanate is highly reactive with the reaction medium used for the modification of polyetherimide, firstly nanocomposites of PEIS/MWCNT were prepared in situ with subsequent solubilization and mixture with sodium alanate. The amount of 0.25 g of PEIS/MWCNT was dissolved in 5 ml of NMP and then mixed with NaAlH4 and 2 mol % of TiO2, at room temperature. This mixture was magnetically stirred for 30 min, precipitated with acetone and sonicated for 10 min. The mixture was then filtered and dried in a vacuum oven at 80º for 2 days.

For the preparation of the nanocomposites it was used three different MWCNT compositions (5, 10 and 20 wt%) and the sodium alanate content was fixed at 30 wt%.

Composites were also prepared from PEIS/NaAlH4+2 mol %. These composites were prepared using the previously described conditions.

Characterization of the materials

The nanocomposites were characterized employing differential scanning calorimetry (DSC), thermogravimetric analysis (TGA) and Hydrogen sorption measurements. Differential scanning calorimetry (DSC) was done on a Q2000 equipment, from TA Instruments and thermograms were obtained from room temperature up to 250 °C under nitrogen flow and heating rate of 10 °C/min. Thermogravimetric analysis (TGA) were carried on a Q50 equipment, also from TA Instruments, under nitrogen atmosphere and heating rate of 20°C/min from room temperature up to 800 °C.

Hydrogen Sorption measurements

Kinetic measurements of hydrogen absorption were performed in a volumetric device (Sievert´s Apparatus) built and designed in the Laboratory of Hydrogen in Metals of the Materials Engineering Department of the Federal University of São Carlos. The absorption measurement was performed at 32 bar of hydrogen and at fixed temperature of 120 °C. The amount of material loaded for hydrogen sorption measurements corresponds to approximately 100 mg.

RESULTS AND DISCUSSION

Figure 1 shows the DSC curves of the PEIS, PEIS/NaAlH4 (70/30%) and PEIS/MWCNT/NaAlH4nanocomposites.

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FIGURE 1. DSC curves for: (a) PEI and PEIS; (b) PEIS/MWCNT/NaAlH4. PEI has a glass transition temperature (Tg) of approximately 216 ºC, after the sulfonation a decrease in Tg to

190 oC is observed, probably due to the introduction of sulfonic groups, which increases the free volume between polymeric chains. In the presence of sodium alanate another endothermic peak can be observed, which is correlated to the melting of NaAlH4. The addition of carbon nanotubes (PEIS/MWCNT/NaAlH4) promoted a reduction in the intensity of the peak of fusion of the sodium alanate and increasing the amount of nanotube an enlargement of this peak was observed. For the composition PEIS/10MWCNT/30NaAlH4 the melting peak is absent. It is also observed in Figure 1 that the nanocomposite with 10 wt% of carbon nanotube has lower glass transition temperature than the PEIS, approximately 177ºC.

Figure 2 shows the thermal stability of the PEIS/NaAlH4 (70/30%) and PEIS/MWCNT/NaAlH4 nanocomposites.

FIGURE 2. TGA curves for PEIS/MWCNT/NaAlH4.

The degradation for all samples occurred in two stages. The first one corresponds to the degradation of the sulfonic chains and the second stage, around of 440 ºC, corresponding the degradation of the PEI chain. The first stage also receives the contribution of the mass loss of NaAlH4, which after melting begins the decomposition and release of gaseous molecules, at temperatures close to 200 °C. It is also observed in Figure 2 that the residues at the end of the analysis increases when increasing the MWCNT content, since the carbon nanotubes remains thermally stable up to higher temperatures.

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Figure 3 shows the hydrogen sorption measurements of TiO2-doped PEIS/NaAlH4 composite and PEIS/20MWCNT/30NaAlH4. Hydrogen sorption of the mixtures was performed at 120ºC and lower pressures of 32 bar. For both samples it can be observed that hydrogen sorption increases with the increase of hydriding time from 0.5h to 10h. It can also be observed in Figure 3 that the TiO2-doped PEIS/NaAlH4 composites and PEIS/20MWCNT/30NaAlH4 can absorb 1.1 and 1.2 wt% of hydrogen in 12 h, respectively. As the hydriding time decrease to 6 h, the hydriding capacity reduces to 0.5 for the TiO2-doped PEIS/NaAlH4 and to 0.9 for the PEIS/20MWCNT/30NaAlH4. These results show that the materials developed in this work can be used for hydrogen storage as compared to results from the literature.

0 1 2 3 4 5 6 7 8 9 10 11 12 13

0,0

0,2

0,4

0,6

0,8

1,0

1,2 PEIS/NaAlH

4

PEIS/20 MWCT/30NaAlH4

Cap

acity

(wt.%

H2)

t (h) FIGURE 3. Hydrogen sorption for PEIS/NaAlH4 composite with 2 mol % of TiO2 and PEIS/20MWCNT/30NaAlH4.

CONCLUSION

The hydriding properties and thermal of sulfonated polyetherimide nanocomposite material were investigated. Carbon nanotubes and sodium alanate added to the polymer matrix reduced the glass transition temperature of polymer. Hydrogen sorption tests were carried and it was shown that TiO2-doped PEIS/NaAlH4 can store 1.1 wt% hydrogen at 120ºC. The addition of carbon nanotubes to the composite PEIS/NaAlH4 has small effect on the hydrogen sorption capabilities of the material, though the increase in porosity of the material causes a slight increase in its hydrogen sorption capabilities.

ACKNOWLEDGMENTS

The authors would like to FAPESP (São Paulo Research Foundation) for the financial support. The authors thank Prof. Dr. Daniel Leiva and Prof. Dr. Tomaz Ishikawa (Federal University of São Carlos, Department of Materials Engineering, Laboratory of Hydrogen in Metallic Materials, Brazil) for their help with the hydrogen sorption measurements.

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REFERENCES

1. M. P. Brown and K. Austin, The New Physique, Publisher City: Publisher Name, 2005, pp. 25-30. 2. M. P. Brown and K. Austin, Appl. Phys. Letters 85, 2503-2504 (2004). 3. R. T. Wang, “Title of Chapter,” in Classic Physiques, edited by R. B. Hamil, Publisher City: Publisher Name, 1999, pp. 212-

213. 4. C. D. Smith and E. F. Jones, “Load-Cycling in Cubic Press” in Shock Compression of Condensed Matter-2001, edited by M.

D. Furnish et al., AIP Conference Proceedings 620, American Institute of Physics, Melville, NY, 2002, pp. 651-654.

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https://doi.org/10.1063/1.1786365