Practical solid-state hydrogen storage requires materials with high hydrogen densities, fast kinetics, low dehydrogenation enthalpies, and good cycle-life. Although complex metal hydrides such as metal alanates, amides, and borohydrides are considered to be among the most promising classes of materials for reversible hydrogen storage, known bulk materials cannot meet all the requirements for reversible hydrogen storage media due to thermodynamic and/or kinetic limitations. Nanostructuring and nanoconfinement are emerging as useful strategies to enhance their reversibility, increase rates of hydrogen adsorption and desorption, and lower the reaction temperatures. We describe highly porous carbons, whose pore sizes can be tuned during their syntheses, being used as hosts for three high hydrogen-capacity complex hydrides: LiAlH4, Li3N, and Mg(BH4)2. The effects of pore size, pore volume, and heteroatom doping on the thermodynamics and kinetics of hydrogenation and dehydrogenation are discussed. Our work demonstrates that nanostructuring can fundamentally alter both the hydrogenation and dehydrogenation reaction pathways as a direct consequence of differences in hydride nanoparticle surface energies, as well as differences in the energetics of solid-solid nanointerfaces within the material. Efforts toward maximizing the loading of the hydrides and thus the hydrogen mass fraction were also undertaken in order to demonstrate the potential to meet the Department of Energy hydrogen storage targets.

Effect of nanostructuring on hydrogen storage properties of complex metal hydrides confined inside nanoporous carbons

253rd National Meeting (2017)

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