Editorial on the Research Topic
Metal Hydride-Based Energy Storage and Conversion Materials
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Energy storage and conversion materials are of critical importance in the development and utilization of new renewable clean energies ( Li et al., 2016 ). Hydrogen, as an ideal energy carrier that can be transportable, storable, and convertible, has the potential to become a solution to energy security, resource availability, and environmental compatibility ( Martin et al., 2020 ). Storing hydrogen in a safe, effective and economic way, however, is a great challenge in the development of a hydrogen-based economy, because of the extremely low volumetric density (0. 0899 kg m −3 ) at ambient condition ( Schlapbach and Züttel, 2001 ). Compared to pressurizing gaseous or liquefying hydrogen, storing hydrogen in metal hydride has definite advantages in terms of gravimetric and volumetric density, safety, and energy efficiency, for both mobile and stationary applications ( Wu, 2008 ; He et al., 2019 ; Ouyang et al., 2020 ). Criteria developed by the US Department of Energy (DOE) for onboard hydrogen storage for light-duty fuel cell vehicles include 6. 5 wt% of systematic gravimetric density and 50 kg H 2 m −3 of volumetric density along with other stringent properties such as operating temperature (<85°C), extended cycle-life, fast kinetics, safety, and cost. Therefore, in the last decade tremendous efforts have been devoted to the research and development of light metal hydrides, including MgH 2 , alanates, borohydrides, amides/imides, which hold sufficiently high hydrogen capacity ( Orimo et al., 2007 ; Hansen et al., 2016 ; Yu et al., 2017 ; Liu et al., 2018 ; Schneemann et al., 2018 ; Zhou et al., 2019 ; Hirscher et al., 2020 ).
This special issue of Metal Hydride-Based Energy Storage and Conversion Materials is focused on the synthesis, catalyst development, and nano-structuring of light metal hydrides (MgH 2 , AlH 3 , NaAlH 4 , and LiBH 4 ) as hydrogen storage media. The eight contributions to this special issue highlight that metal hydrides are promising candidates for high density hydrogen storage.
Catalysts prove effective in reducing the reaction energy barriers for hydrogen absorption and desorption in Mg-based materials. Ding et al. report the catalytic activity of Co-Ni nanocatalyst with different compositions and morphology for hydrogen storage reaction of MgH 2 . The partial replacement of Ni by Co induced a change in the morphology from spherical to plate-like, which is found to be less effective toward catalytic activity, presumably due to reduced surface contact. Zeng et al. prepared Ni and TiO 2 co-anchored on reduced graphene oxide [(Ni-TiO 2 )@rGO], which showed superior catalytic effects on the hydrogen desorption, as evidenced by the release of 1. 47 wt% H 2 by MgH 2 within 120 min at 225°C. Wang and Deng ameliorated the performance of MgH 2 by using a core-shell [email protected] carbon (CoNC) based catalyst. In their work, the MgH 2 -5 wt% CoNCo composites released up to 6. 58 wt% of H 2 in 5 min at 325°C. Liu Y. et al. present that Pd-decorated Mg nanoparticles, ranging from 40 to 70 nm, started releasing H 2 at 216. 8°C and absorbed 3. 0 wt% hydrogen in 2 h at 50°C. In addition, Wu et al. investigated the effects of CeH 2. 73 /CeO 2 composites on the desorption properties of Mg 2 NiH 4 . The onset dehydrogenation temperature and activation energy of Mg 2 NiH 4 were largely reduced when CeH 2. 73 /CeO 2 composite with the same molar ratio of hydride and oxide were used as a catalyst.
Hirscher, M., Yartys, V. A., Baricco, M., von Colbe, J. B., Blanchard, D., Bowman, R. C., et al. (2020). Materials for hydrogen-based energy storage – past, recent progress and future outlook. J. Alloys Compd . 827: 153548. doi: 10. 1016/j. jallcom. 2019. 153548
Liu, Y. F., Ren, Z. H., Zhang, X., Jian, N., Yang, Y. X., Gao, M. X., et al. (2018). Development of catalyst-enhanced sodium alanate as an advanced hydrogen-storage material for mobile applications. Energy Technol . 6, 487–500. doi: 10. 1002/ente. 201700517
Martin, A., Agnoletti, M. F., and Brangier, E. (2020). Users in the design of Hydrogen Energy Systems: a systematic review. Int. J. Hydrogen Energy 45, 11889–11900. doi: 10. 1016/j. ijhydene. 2020. 02. 163
Schneemann, A., White, J. L., Kang, S. Y., Jeong, S., Wan, L. F., Cho, E. S., et al. (2018). Nanostructured metal hydrides for hydrogen storage. Chem. Rev . 118, 10775–10839. doi: 10. 1021/acs. chemrev. 8b00313
Yu, X. B., Tang, Z. W., Sun, D. L., Ouyang, L. Z., and Zhu, M. (2017). Recent advances and remaining challenges of nanostructured materials for hydrogen storage applications. Prog. Mater. Sci . 88, 1–48. doi: 10. 1016/j. pmatsci. 2017. 03. 001
Zhou, H., Wang, X. H., Liu, H. Z., Gao, S. C., and Yan, M. (2019). Improved hydrogen storage properties of LiBH4 confined with activated charcoal by ball milling. Rare Metals 38, 321–326. doi: 10. 1007/s12598-018-1067-1