Formation and Stability of Ternary Imides in the Li-Mg-N-H Hydrogen Storage System

The thermodynamic nature of the mixtures consisting of Mg(NH(2))(2) and LiH determines the reaction sequence and pathways between the components. That is, the reaction resulting in the formation of Li(2)Mg(NH)(2) and H(2), which is useful for on-board hydrogen storage, first takes place in the mixtures in spite of various stoichiometries. By varying the molar ratio of Mg(NH2)2 to LiH in the proximity of 1:2, a maximal amount of H(2) release and low level of ammonia generation were observed for the mixture of Mg(NH(2))(2) and LiH at a 1:2 molar ratio. When LiH was in deficit (<2), severe ammonia evolution occurred concomitantly during dehydrogenation. On the other hand, excess in LiH (higher than 2) lowered the hydrogen storage efficiency. In the molar ratio range from 1:1.5 to 1:2.7 of Mg(NH(2))(2) to LiH, both dynamic and quasi-equilibrium dehydrogenation resulted in the formation of the ternary imide Li(2)Mg(NH)(2), indicating the ternary imide is a thermodynamically favored dehydrogenation product in this hydrogen storage system and may explain the cyclic stability of this system.