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Dehydrogenation mechanism of LiBH4 by Poly(methyl methacrylate)
Journal of Alloys and Compounds 645 (2015) S100–S102
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Dehydrogenation mechanism of LiBH4 by Poly(methyl methacrylate) Jianmei Huang a,b, Yurong Yan a, Liuzhang Ouyang a,b,c,⇑, Hui Wang a,b, Min Zhu a,b,⇑ a School of Materials Science and Engineering, and Key Laboratory of Advanced Energy Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, People’s Republic of China b China-Australia Joint Laboratory for Energy & Environmental Materials, South China University of Technology, Guangzhou 510641, People’s Republic of China c Key Laboratory for Fuel Cell Technology in Guangdong Province, South China University of Technology, Guangzhou 510641, People’s Republic of China
a r t i c l e
i n f o
Article history: Available online 29 January 2015 Keywords: Hydrogen storage Lithium borohydride PMMA Confinement
a b s t r a c t We investigated the dehydrogenation properties and mechanism of Poly(methyl methacrylate) (PMMA) confined LiBH4. Thermal stability of LiBH4 was reduced by PMMA, with a decrease in dehydrogenation temperature by 120 °C. At 360 °C, the composite showed fast dehydrogenation kinetics with 10 wt.% of hydrogen released within 1 h. The improved dehydrogenation performance was mainly attributed to the reaction between LiBH4 and PMMA forming Li3BO3 as a final product. Furthermore, the presence of electrostatic interaction between B atom of LiBH4 and O atom in the carbonyl group of PMMA may weaken the BAH bonding of [BH4] and lower the hydrogen desorption temperature. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Hydrogen is considered as a promising alternative energy carrier owing to its high-energy density, abundance, light weight and pollution-free burning [1]. Developing a safe and efficient hydrogen storage material is one of the key challenges for the mobile application of hydrogen [2–4]. Due to the high gravimetric (18.5 wt.%) and volumetric (121 kg H2/m3) hydrogen density, lithium borohydride (LiBH4) has been acknowledged as a potential candidate for hydrogen storage materials [5–7]. However, due to the unfavorable high thermal stability (e.g. decomposition peak temperature of 470 °C), the practical utilization of LiBH4 as hydrogen storage medium is hampered [8]. Hence, several approaches including reactant destabilization, catalyst/additive introduction, nanostructuring, and anion/cation substitution have been applied to decrease the dehydrogenation temperature and accelerate the kinetics [7,9]. Nanoconfinement is a viable way to improve the dehydrogenation performance by decreasing diffusion path lengths and increasing surface areas [10–16]. For example, confining LiBH4 in highly ordered nanoporous carbon with 2 nm average diameter was reported to decrease the onset desorption temperature from 460 to 220 °C [12]. Recently, we encapsulated LiBH4 in a flexible material, PMMA, where the onset hydrogen evolution temperature was ⇑ Corresponding authors at: School of Materials Science and Engineering, and Key Laboratory of Advanced Energy Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, People’s Republic of China. E-mail addresses: [email protected] (L. Ouyang), [email protected] (M. Zhu). http://dx.doi.org/10.1016/j.jallcom.2014.12.268 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.
reduced close to room temperature [17]. Furthermore, the confinement in PMMA improves the air resistance of LiBH4 due to the protection from gaseous O2 and H2O. In present work, we investigated the dehydrogenation mechanism of the PMMA confined LiBH4. Li3BO3 was observed as a final product, indicating that the improved dehydrogenation performance was mainly attributed to the reaction between LiBH4 and PMMA.
2. Experimental Lithium borohydride solution (2.0 M LiBH4 in tetrahydrofuran) (abbreviate as LiBH4/THF here and after) was purchased from Sigma–Aldrich Co. PMMA (MW 120,000) was supplied by Alfa-Aesar. All these reagents were used without any further purification and were stored and handled in a glove box equipped with an Ar recirculation system with water and hydrogen below 3 ppm so that prevent them from oxidation. In a typical experiment, 5 ml LiBH4/THF solution containing 0.218 g of LiBH4 was added to 0.1452 g PMMA in a glass bottle under argon, resulting in a 3/2 mass ratio between LiBH4 and PMMA. The suspension was vigorously stirred using a magnetic stirrer at room temperature until all the PMMA dissolved. The obtained solution was dried by freeze drying at least 72 h to remove all the THF and finally, the PMMA confined LiBH4 (labelled 60LP), with a loading ratio of 60 wt.%, was prepared. The phase structures of samples were characterized on rotation anode X-ray diffractometer (a Philips X’Pert MPD) using graphite monochromatized Cu Ka radiation as the light source. The samples for measurement were loaded on a glass sheet and wrapped with a 3 M film to protect them from air and moisture during the measurement process. A scanning rate of 0.02° s 1 was applied to record the patterns in the 2h range of 10–90°. The chemical bonds of the species were identified via a Fourier transform infrared spectrometer (FT-IR, Vector 33) in the range of 400–4000 cm 1 with 32 scans. The tested samples were pressed with potassium bromide (KBr) powder. Zeiss-Supra 40 scanning electron microscope (SEM) was employed to characterize sample morphology. The hydrogen release was
J. Huang et al. / Journal of Alloys and Compounds 645 (2015) S100–S102
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Fig. 1. (a) XRD results of pure PMMA, LiBH4 and 60LP; (b) SEM image for 60LP.
Fig. 2. (a) MS hydrogen signals of PMMA, LiBH4 and 60LP; (b) isothermal TPD results of 60LP at different temperatures. The hydrogen capacity is referred to pure LiBH4. determined by a mass-spectrometer (MS, Hiden, Qic 20) at a heating rate of 4 K min 1 under a flowing Ar atmosphere. Isothermal dehydrogenation properties of samples were measured by Setaram PCT-Pro 2000 apparatus at various temperatures. The sample chamber and the gas reservoir were evacuated before measuring. The volume of gas reservoir is 163 ml. Sample was quickly heated to target temperature and desorbed hydrogen amount was recorded to measure the dehydrogenation capacity and kinetics.
3. Results and discussion 3.1. Phase structure and morphology X-ray diffraction (XRD) patterns of pure LiBH4, PMMA and 60LP are shown in Fig. 1a. PMMA shows a broad halo at 2h = 17° and LiBH4 shows a low-temperature (orthorhombic) phase. No reflections of LiBH4 were observed in 60LP, implying that LiBH4 is in amorphous state. In Fig.1b, the SEM image of 60LP shows a porous structure with pore diameters ranging from 60 to 300 nm, implying that the sizes of LiBH4 particles in 60LP are within 60 to 300 nm.
3.2. Dehydrogenation properties The dehydrogenation properties of PMMA, pure LiBH4 and 60LP were investigated by MS (Fig. 2a). No hydrogen release from PMMA was observed up to 500 °C. The major desorption of pure LiBH4 occurred at 470 °C. The temperature of major desorption was reduced to 350 °C in 60LP. The isothermal hydrogen desorption of 60LP was shown in Fig. 2b. Noticeable hydrogen release was observed at 150 °C (1.1 wt.%), 200 °C (1.4 wt.%) and 260 °C (2.6 wt.%), respectively, within 5 h. At 360 °C, approximately 11 wt.% of hydrogen was
released within 5 h. In contrast, pure LiBH4 released limited hydrogen below 400 °C. 3.3. Reaction mechanism To elucidate the dehydrogenation mechanism for 60LP, the samples after dehydrogenation at different temperatures were characterized by FT-IR (Fig. 3a) and XRD (Fig. 3b). 60LP shows BAH vibrations modes at 2210–2400 and 1080 cm 1 from LiBH4. The BAH vibrations faded when the dehydrogenation temperature increased up to 260 °C, and disappeared at 360 °C. The absorption band of the BAO appeared at 260 °C and dominated at 360 °C. In Fig. 3b, the reflections of LiBH4 were observed after heating at 150 °C and became even stronger when dehydrogenation temperature increased to 200 and 260 °C. This can be explained that the LiBH4 in 60LP crystallized upon heating. The reflections of LiBH4 disappeared after dehydrogenation of 60LP at 360 °C. Li3BO3 started to form at 260 °C and dominated after dehydrogenation at 360 °C, which is in accordance with observation by FT-IR spectra (Fig. 3a). Based on the above FT-IR and XRD results, the hydrogen desorption of 60LP mainly went through the reaction between LiBH4 and PMMA forming Li3BO3 as the final product. Pure LiBH4 is known to decompose via Li2B12H12 and finally into boron [18]. Possibly due to the formation of Li3BO3, the reaction pathway of LiBH4 was altered leading to the lower desorption temperature and faster desorption kinetics of 60LP. However, the formation of Li3BO3 may be not favorable for the on-boarding charging of LiBH4. The nanosize effect by the confinement in PMMA may not play an important role in the improvement of desorption properties, since the particle sizes of LiBH4 in 60LP are within the range of 60– 300 nm (Fig. 1b).
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J. Huang et al. / Journal of Alloys and Compounds 645 (2015) S100–S102
Fig. 3. (a) FT-IR and (b) XRD results of 60LP after synthesis and dehydrogenation at various temperatures.
Additionally, we observed that the stretching vibration of C@O from PMMA shift from 1730 cm 1 for pure PMMA to 1718 cm 1 in 60LP, which indicates the presence of interaction between LiBH4 and C@O in PMMA [19]. This interaction may result in the hydrogen release at a lower temperature. For example at 150 °C, we observed the hydrogen release of 60LP (Fig. 2b) and meanwhile the C@O vibration of PMMA in 60LP disappeared (Fig. 3a). It is known that B atom in the LiBH4 molecule is electropositive and O atom in C@O group of PMMA is an electron-donor. The electrostatic interaction between B atom and O atom may weaken the BAH bonds and lower the hydrogen release temperature.
51271078), the Key Project of DEGP (cxzd1010) and by GDUPS (2014). References [1] [2] [3] [4] [5] [6] [7]
4. Conclusion The PMMA confined LiBH4 was successfully prepared by a solution method. By confinement in PMMA, the temperature of major hydrogen desorption of LiBH4 was reduced to 350 °C and faster desorption kinetics was achieved, e.g., 11 wt.% of hydrogen released within 5 h. The enhanced dehydrogenation performance is mainly attributed to the formation of Li3BO3. Electrostatic effect between B atom of LiBH4 molecule and O atom in C@O group of PMMA may weaken the BAH bonding and lower the dehydrogenation temperature. This work also provides a general dehydrogenation pathway of LiBH4 in the system with carbonyl group.
[8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Acknowledgements [18]
This work was supported by the National Natural Science Foundation of China Projects (Nos. 51431001, U1201241 and
[19]
I.P. Jain, Int. J. Hydrogen Energy 34 (2009) 7368–7378. L. Schlapbach, A. Zuttel, Nature 414 (2001) 353–358. J. Yang, A. Sudik, C. Wolverton, D.J. Siegel, Chem. Soc. Rev. 39 (2010) 656–675. S.-I. Orimo, Y. Nakamori, J.R. Eliseo, A. Züttel, C.M. Jensen, Chem. Rev. 107 (2007) 4111–4132. A. Züttel, P. Wenger, S. Rentsch, P. Sudan, P. Mauron, C. Emmenegger, J. Power Sources 118 (2003) 1–7. A. Zuttel, S. Rentsch, P. Fischer, P. Wenger, P. Sudan, P. Mauron, C. Emmenegger, J. Alloys Comp. 356 (2003) 515–520. C. Li, P. Peng, D.W. Zhou, L. Wan, Int. J. Hydrogen Energy 36 (2011) 14512– 14526. I. Saldan, Cent. Eur. J. Chem. 9 (2011) 761–775. H.-W. Li, Y. Yan, S.-I. Orimo, A. Züttel, C.M. Jensen, Energies 4 (2011) 185–214. A. Remhof, P. Mauron, A. Züttel, J.P. Embs, Z. Łodziana, A.J. Ramirez-Cuesta, P. Ngene, P. de Jongh, J. Phys. Chem. C 117 (2013) 3789–3798. Z.Z. Fang, P. Wang, T.E. Rufford, X.D. Kang, G.Q. Lu, H.M. Cheng, Acta Mater. 56 (2008) 6257–6263. X.F. Liu, D. Peaslee, C.Z. Jost, E.H. Majzoub, J. Phys. Chem. C 114 (2010) 14036– 14041. P. Ngene, P. Adelhelm, A.M. Beale, K.P. de Jong, P.E. de Jongh, J. Phys. Chem. C 114 (2010) 6163–6168. T. Sun, J. Liu, Y. Jia, H. Wang, D.L. Sun, M. Zhu, X.D. Yao, Int. J. Hydrogen Energy 37 (2012) 18920–18926. W. Sun, S. Li, J. Mao, Z. Guo, H. Liu, S. Dou, X. Yu, Dalton Trans. 40 (2011) 5673– 5676. A.F. Gross, J.J. Vajo, S.L. Van Atta, G.L. Olson, J. Phys. Chem. C 112 (2008) 5651– 5657. J. Huang, Y. Yan, L. Ouyang, H. Wang, J. Liu, M. Zhu, Dalton Trans. 43 (2014) 410–413. Y. Yan, A. Remhof, S. Hwang, H. Li, P. Mauron, S. Orimo, A. Züttel, Phys. Chem. Chem. Phys. 14 (2012) 6514–6519. J. Zhao, J. Shi, X. Zhang, F. Cheng, J. Liang, Z. Tao, J. Chen, Adv. Mater. 22 (2010) 394–397.
Contents lists available at ScienceDirect
Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jalcom
Dehydrogenation mechanism of LiBH4 by Poly(methyl methacrylate) Jianmei Huang a,b, Yurong Yan a, Liuzhang Ouyang a,b,c,⇑, Hui Wang a,b, Min Zhu a,b,⇑ a School of Materials Science and Engineering, and Key Laboratory of Advanced Energy Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, People’s Republic of China b China-Australia Joint Laboratory for Energy & Environmental Materials, South China University of Technology, Guangzhou 510641, People’s Republic of China c Key Laboratory for Fuel Cell Technology in Guangdong Province, South China University of Technology, Guangzhou 510641, People’s Republic of China
a r t i c l e
i n f o
Article history: Available online 29 January 2015 Keywords: Hydrogen storage Lithium borohydride PMMA Confinement
a b s t r a c t We investigated the dehydrogenation properties and mechanism of Poly(methyl methacrylate) (PMMA) confined LiBH4. Thermal stability of LiBH4 was reduced by PMMA, with a decrease in dehydrogenation temperature by 120 °C. At 360 °C, the composite showed fast dehydrogenation kinetics with 10 wt.% of hydrogen released within 1 h. The improved dehydrogenation performance was mainly attributed to the reaction between LiBH4 and PMMA forming Li3BO3 as a final product. Furthermore, the presence of electrostatic interaction between B atom of LiBH4 and O atom in the carbonyl group of PMMA may weaken the BAH bonding of [BH4] and lower the hydrogen desorption temperature. Ó 2015 Elsevier B.V. All rights reserved.
1. Introduction Hydrogen is considered as a promising alternative energy carrier owing to its high-energy density, abundance, light weight and pollution-free burning [1]. Developing a safe and efficient hydrogen storage material is one of the key challenges for the mobile application of hydrogen [2–4]. Due to the high gravimetric (18.5 wt.%) and volumetric (121 kg H2/m3) hydrogen density, lithium borohydride (LiBH4) has been acknowledged as a potential candidate for hydrogen storage materials [5–7]. However, due to the unfavorable high thermal stability (e.g. decomposition peak temperature of 470 °C), the practical utilization of LiBH4 as hydrogen storage medium is hampered [8]. Hence, several approaches including reactant destabilization, catalyst/additive introduction, nanostructuring, and anion/cation substitution have been applied to decrease the dehydrogenation temperature and accelerate the kinetics [7,9]. Nanoconfinement is a viable way to improve the dehydrogenation performance by decreasing diffusion path lengths and increasing surface areas [10–16]. For example, confining LiBH4 in highly ordered nanoporous carbon with 2 nm average diameter was reported to decrease the onset desorption temperature from 460 to 220 °C [12]. Recently, we encapsulated LiBH4 in a flexible material, PMMA, where the onset hydrogen evolution temperature was ⇑ Corresponding authors at: School of Materials Science and Engineering, and Key Laboratory of Advanced Energy Storage Materials of Guangdong Province, South China University of Technology, Guangzhou 510641, People’s Republic of China. E-mail addresses: [email protected] (L. Ouyang), [email protected] (M. Zhu). http://dx.doi.org/10.1016/j.jallcom.2014.12.268 0925-8388/Ó 2015 Elsevier B.V. All rights reserved.
reduced close to room temperature [17]. Furthermore, the confinement in PMMA improves the air resistance of LiBH4 due to the protection from gaseous O2 and H2O. In present work, we investigated the dehydrogenation mechanism of the PMMA confined LiBH4. Li3BO3 was observed as a final product, indicating that the improved dehydrogenation performance was mainly attributed to the reaction between LiBH4 and PMMA.
2. Experimental Lithium borohydride solution (2.0 M LiBH4 in tetrahydrofuran) (abbreviate as LiBH4/THF here and after) was purchased from Sigma–Aldrich Co. PMMA (MW 120,000) was supplied by Alfa-Aesar. All these reagents were used without any further purification and were stored and handled in a glove box equipped with an Ar recirculation system with water and hydrogen below 3 ppm so that prevent them from oxidation. In a typical experiment, 5 ml LiBH4/THF solution containing 0.218 g of LiBH4 was added to 0.1452 g PMMA in a glass bottle under argon, resulting in a 3/2 mass ratio between LiBH4 and PMMA. The suspension was vigorously stirred using a magnetic stirrer at room temperature until all the PMMA dissolved. The obtained solution was dried by freeze drying at least 72 h to remove all the THF and finally, the PMMA confined LiBH4 (labelled 60LP), with a loading ratio of 60 wt.%, was prepared. The phase structures of samples were characterized on rotation anode X-ray diffractometer (a Philips X’Pert MPD) using graphite monochromatized Cu Ka radiation as the light source. The samples for measurement were loaded on a glass sheet and wrapped with a 3 M film to protect them from air and moisture during the measurement process. A scanning rate of 0.02° s 1 was applied to record the patterns in the 2h range of 10–90°. The chemical bonds of the species were identified via a Fourier transform infrared spectrometer (FT-IR, Vector 33) in the range of 400–4000 cm 1 with 32 scans. The tested samples were pressed with potassium bromide (KBr) powder. Zeiss-Supra 40 scanning electron microscope (SEM) was employed to characterize sample morphology. The hydrogen release was
J. Huang et al. / Journal of Alloys and Compounds 645 (2015) S100–S102
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Fig. 1. (a) XRD results of pure PMMA, LiBH4 and 60LP; (b) SEM image for 60LP.
Fig. 2. (a) MS hydrogen signals of PMMA, LiBH4 and 60LP; (b) isothermal TPD results of 60LP at different temperatures. The hydrogen capacity is referred to pure LiBH4. determined by a mass-spectrometer (MS, Hiden, Qic 20) at a heating rate of 4 K min 1 under a flowing Ar atmosphere. Isothermal dehydrogenation properties of samples were measured by Setaram PCT-Pro 2000 apparatus at various temperatures. The sample chamber and the gas reservoir were evacuated before measuring. The volume of gas reservoir is 163 ml. Sample was quickly heated to target temperature and desorbed hydrogen amount was recorded to measure the dehydrogenation capacity and kinetics.
3. Results and discussion 3.1. Phase structure and morphology X-ray diffraction (XRD) patterns of pure LiBH4, PMMA and 60LP are shown in Fig. 1a. PMMA shows a broad halo at 2h = 17° and LiBH4 shows a low-temperature (orthorhombic) phase. No reflections of LiBH4 were observed in 60LP, implying that LiBH4 is in amorphous state. In Fig.1b, the SEM image of 60LP shows a porous structure with pore diameters ranging from 60 to 300 nm, implying that the sizes of LiBH4 particles in 60LP are within 60 to 300 nm.
3.2. Dehydrogenation properties The dehydrogenation properties of PMMA, pure LiBH4 and 60LP were investigated by MS (Fig. 2a). No hydrogen release from PMMA was observed up to 500 °C. The major desorption of pure LiBH4 occurred at 470 °C. The temperature of major desorption was reduced to 350 °C in 60LP. The isothermal hydrogen desorption of 60LP was shown in Fig. 2b. Noticeable hydrogen release was observed at 150 °C (1.1 wt.%), 200 °C (1.4 wt.%) and 260 °C (2.6 wt.%), respectively, within 5 h. At 360 °C, approximately 11 wt.% of hydrogen was
released within 5 h. In contrast, pure LiBH4 released limited hydrogen below 400 °C. 3.3. Reaction mechanism To elucidate the dehydrogenation mechanism for 60LP, the samples after dehydrogenation at different temperatures were characterized by FT-IR (Fig. 3a) and XRD (Fig. 3b). 60LP shows BAH vibrations modes at 2210–2400 and 1080 cm 1 from LiBH4. The BAH vibrations faded when the dehydrogenation temperature increased up to 260 °C, and disappeared at 360 °C. The absorption band of the BAO appeared at 260 °C and dominated at 360 °C. In Fig. 3b, the reflections of LiBH4 were observed after heating at 150 °C and became even stronger when dehydrogenation temperature increased to 200 and 260 °C. This can be explained that the LiBH4 in 60LP crystallized upon heating. The reflections of LiBH4 disappeared after dehydrogenation of 60LP at 360 °C. Li3BO3 started to form at 260 °C and dominated after dehydrogenation at 360 °C, which is in accordance with observation by FT-IR spectra (Fig. 3a). Based on the above FT-IR and XRD results, the hydrogen desorption of 60LP mainly went through the reaction between LiBH4 and PMMA forming Li3BO3 as the final product. Pure LiBH4 is known to decompose via Li2B12H12 and finally into boron [18]. Possibly due to the formation of Li3BO3, the reaction pathway of LiBH4 was altered leading to the lower desorption temperature and faster desorption kinetics of 60LP. However, the formation of Li3BO3 may be not favorable for the on-boarding charging of LiBH4. The nanosize effect by the confinement in PMMA may not play an important role in the improvement of desorption properties, since the particle sizes of LiBH4 in 60LP are within the range of 60– 300 nm (Fig. 1b).
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J. Huang et al. / Journal of Alloys and Compounds 645 (2015) S100–S102
Fig. 3. (a) FT-IR and (b) XRD results of 60LP after synthesis and dehydrogenation at various temperatures.
Additionally, we observed that the stretching vibration of C@O from PMMA shift from 1730 cm 1 for pure PMMA to 1718 cm 1 in 60LP, which indicates the presence of interaction between LiBH4 and C@O in PMMA [19]. This interaction may result in the hydrogen release at a lower temperature. For example at 150 °C, we observed the hydrogen release of 60LP (Fig. 2b) and meanwhile the C@O vibration of PMMA in 60LP disappeared (Fig. 3a). It is known that B atom in the LiBH4 molecule is electropositive and O atom in C@O group of PMMA is an electron-donor. The electrostatic interaction between B atom and O atom may weaken the BAH bonds and lower the hydrogen release temperature.
51271078), the Key Project of DEGP (cxzd1010) and by GDUPS (2014). References [1] [2] [3] [4] [5] [6] [7]
4. Conclusion The PMMA confined LiBH4 was successfully prepared by a solution method. By confinement in PMMA, the temperature of major hydrogen desorption of LiBH4 was reduced to 350 °C and faster desorption kinetics was achieved, e.g., 11 wt.% of hydrogen released within 5 h. The enhanced dehydrogenation performance is mainly attributed to the formation of Li3BO3. Electrostatic effect between B atom of LiBH4 molecule and O atom in C@O group of PMMA may weaken the BAH bonding and lower the dehydrogenation temperature. This work also provides a general dehydrogenation pathway of LiBH4 in the system with carbonyl group.
[8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
Acknowledgements [18]
This work was supported by the National Natural Science Foundation of China Projects (Nos. 51431001, U1201241 and
[19]
I.P. Jain, Int. J. Hydrogen Energy 34 (2009) 7368–7378. L. Schlapbach, A. Zuttel, Nature 414 (2001) 353–358. J. Yang, A. Sudik, C. Wolverton, D.J. Siegel, Chem. Soc. Rev. 39 (2010) 656–675. S.-I. Orimo, Y. Nakamori, J.R. Eliseo, A. Züttel, C.M. Jensen, Chem. Rev. 107 (2007) 4111–4132. A. Züttel, P. Wenger, S. Rentsch, P. Sudan, P. Mauron, C. Emmenegger, J. Power Sources 118 (2003) 1–7. A. Zuttel, S. Rentsch, P. Fischer, P. Wenger, P. Sudan, P. Mauron, C. Emmenegger, J. Alloys Comp. 356 (2003) 515–520. C. Li, P. Peng, D.W. Zhou, L. Wan, Int. J. Hydrogen Energy 36 (2011) 14512– 14526. I. Saldan, Cent. Eur. J. Chem. 9 (2011) 761–775. H.-W. Li, Y. Yan, S.-I. Orimo, A. Züttel, C.M. Jensen, Energies 4 (2011) 185–214. A. Remhof, P. Mauron, A. Züttel, J.P. Embs, Z. Łodziana, A.J. Ramirez-Cuesta, P. Ngene, P. de Jongh, J. Phys. Chem. C 117 (2013) 3789–3798. Z.Z. Fang, P. Wang, T.E. Rufford, X.D. Kang, G.Q. Lu, H.M. Cheng, Acta Mater. 56 (2008) 6257–6263. X.F. Liu, D. Peaslee, C.Z. Jost, E.H. Majzoub, J. Phys. Chem. C 114 (2010) 14036– 14041. P. Ngene, P. Adelhelm, A.M. Beale, K.P. de Jong, P.E. de Jongh, J. Phys. Chem. C 114 (2010) 6163–6168. T. Sun, J. Liu, Y. Jia, H. Wang, D.L. Sun, M. Zhu, X.D. Yao, Int. J. Hydrogen Energy 37 (2012) 18920–18926. W. Sun, S. Li, J. Mao, Z. Guo, H. Liu, S. Dou, X. Yu, Dalton Trans. 40 (2011) 5673– 5676. A.F. Gross, J.J. Vajo, S.L. Van Atta, G.L. Olson, J. Phys. Chem. C 112 (2008) 5651– 5657. J. Huang, Y. Yan, L. Ouyang, H. Wang, J. Liu, M. Zhu, Dalton Trans. 43 (2014) 410–413. Y. Yan, A. Remhof, S. Hwang, H. Li, P. Mauron, S. Orimo, A. Züttel, Phys. Chem. Chem. Phys. 14 (2012) 6514–6519. J. Zhao, J. Shi, X. Zhang, F. Cheng, J. Liang, Z. Tao, J. Chen, Adv. Mater. 22 (2010) 394–397.