AlH3-mediated mechanism in hydriding/dehydriding of NaAlH4

By theoretical investigation, we found that the balanced Fermi level in NaAlH4 is pinned by the vacancy pair of its ionic components (VNa− and VAlH4+), which significantly affects the formation enthalpies of other possible charged defects. VNa− and VAlH4+ easily form VNa–AlH40 vacancy complex on surface but not in bulk. This helps the diffusion of VNa− and VAlH4+, but will not induce the decomposition of NaAlH4 directly. In fact, we found that VAlH30 plays a critical role in the decomposition of NaAlH4 and an AlH3-mediated mechanism for the hydriding/dehydriding of NaAlH4 is suggested.