The mechanism of controllable dehydrogenation: CPMD study of M(BH₄)_x(NH₃)_y (M = Li, Mg) decomposition

Amine metallic borohydrides were synthesized as a new series of hydrogen-storage materials. Their dehydrogenation can be controlled if appropriate metal centres are chosen. A typical example is LiBH₄NH₃ (ALB) and Mg(BH₄)₂(NH₃)₂ (AMgB) adopt the same symmetries but show totally different appearances when decomposed. Both ALB and AMgB are relatively new compounds designed as candidates for solid-state hydrogen storage. In this study, we have applied a Car-Parrinello molecular dynamic (CPMD) method to simulate the overall processes of their decomposition to figure out the mechanisms behind the difference in post-decomposition appearances. The polarization of Mg²⁺ is almost two times larger than that of Li⁺, making the Mg²⁺ bond with nitrogen and boron stronger compared to that of Li⁺, which improves the appearance of dehydrogenation of AMgB over that of ALB.