The potential of hydrogen hydrate as a future hydrogen storage medium

Hydrogen is recognized as the "future fuel'' and the most promising alternative of fossil fuels due to its remarkable properties including exceptionally high energy content per unit mass (142 MJ/kg), low mass density, and massive environmental and economical upsides. A wide spectrum of methods in H-2 production, especially carbon-free approaches, H-2 purification, and H-2 storage have been investigated to bring this energy source closer to the technological deployment. Hydrogen hydrates are among the most intriguing material paradigms for H-2 storage due to their appealing properties such as low energy consumption for charge and discharge, safety, cost-effectiveness, and favorable environmental features. Here, we comprehensively discuss the progress in understanding of hydrogen clathrate hydrates with an emphasis on charging/discharging rate of H-2 (i.e. hydrate formation and dissociation rates) and the storage capacity. A thorough understanding on phase equilibrium of the hydrates and its variation through different materials is provided. The path toward ambient temperature and pressure hydrogen batteries with high storage capacity is elucidated. We suggest that the charging rate of H-2 in this storage medium and long cyclic performance are more immediate challenges than storage capacity for technological translation of this storage medium. This review and provided outlook establish a groundwork for further innovation on hydrogen hydrate systems for promising future of hydrogen fuel.