Temporal and spatial imaging of hydrogen storage materials: watching solvent and hydrogen desorption from aluminium hydride by transmission electron microscopyw

There are extensive efforts underway worldwide to develop inexpensive and practical hydrogen storage materials for the implementation of a hydrogen-based energy economy. Perhaps the most promising candidates are light metal hydrides and their complexes. Amongst these, the binary hydride of aluminium, alane (AlH3)x, is increasingly recognised as a leading candidate, satisfying most of the requirements laid out by the US Department of Energy. Alane demonstrates impressive gravimetric and volumetric hydrogen content (around 10 wt% H and 150 kg H m ), acceptable H2 release kinetics, and a low dehydrogenation temperature (60–150 1C). Conventionally, AlH3 is prepared by the method of Brower et al., involving formation of an ethereal intermediate (eqn (1)) that is converted to the polymeric hydride on annealing (eqn (2)). Alane is a kinetically stable hydride, with an equilibrium dissociation pressure of B10 bar at ambient temperature, and the removal of the ether solvent (eqn (2)) converts the material from a gelatinous paste into a fine, dry powder. In contrast to many metal hydride systems, the dehydrogenation of alane is a chemically simple process, yielding aluminium metal and hydrogen gas in a single step (eqn (3)).