Calcium Borohydride for Hydrogen Storage: A Computational Study of Ca(BH4)2 Crystal Structures and the CaB2Hx Intermediate

Plane wave density functional theory calculations have been performed to study the potential hydrogen storage material Ca(BH 4 ) 2 and the proposed CaB 2 H x dehydrogenation intermediate. It is shown that three different published structures of α-Ca(BH 4 ) 2 are essentially identical. Likewise, four proposed structures of β-Ca(BH 4 ) 2 are the same. The previously proposed CaB 2 H 2 structure of space group P n m a is both structurally unstable and too high in energy to be a Ca(BH 4 ) 2 dehydrogenation intermediate. A direct computational search failed to find a viable CaB 2 H x candidate structure.