Potential and Reaction Mechanism of Li−Mg−Al−N−H System for Reversible Hydrogen Storage

Complex metal hydrides are attracting much attention as a class of candidate materials for hydrogen storage. Lithium-based complex hydrides, including lithium aluminum hydrides (LiAlH_4 and Li_3AlH_6), are among the most promising materials, owing to their high hydrogen contents. In the present work, we investigated the dehydrogenation/rehydrogenation reactions of a combined system of Li_3AlH_6 and Mg(NH_2)_2, which has a theoretical hydrogen capacity of 6.5 wt %. Thermogravimetric analysis of hydrogenated 2/3Al−Li_2Mg(NH)2 (doped with 4 wt % TiCl_3) indicated that a large amount of hydrogen (∼6.2 wt %) can be stored under 300 °C and 172 bar of hydrogen pressure. The FT-IR and NMR results showed that the reaction between Li_3AlH_6 and Mg(NH_2)_2 is reversible. Further, a short-cycle experiment has demonstrated that the new combined material system of alanates and amides can maintain its hydrogen storage capacity upon cycling of the dehydrogenation/rehydrogenation reactions.