Thermal destabilization of binary and complex metal hydrides by chemical reaction: A thermodynamic analysis

Some alkali and alkali-earth metal hydrides and their complex hydrides have very high hydrogen storage capacities and reversibility. Unfortunately, most of them have decomposition temperatures that are too high. This must be overcome before these hydrides can be considered seriously as practical hydrogen storage materials for on-board applications. In the present study, the CALPHAD approach has been adopted to evaluate thermodynamically the possibility of destabilizing these high temperature binary ionic hydrides and ternary complex hydrides by reacting them with light elements or other hydrides. The MgH₂+Si, LiBH₄+MgH₂, and LiBH₄+Al systems are predicted to show a significant decrease in decomposition temperature. On the other hand, the decrease in the decomposition temperatures of the MgH₂+Al and NaBH₄+Al systems is relatively small. The LiH+Si system also presents a considerable destabilization effect, which is consistent with experiment.