Insight into enhanced dehydrogenation of LiBH4 modified with Bi and S/Se/Te from first-principles calculations

Abstract

A systematic study for the dehydrogenation of LiBH4 modified with Bi and S/Se/Te was performed by first-principles density functional theory calculations. It is found that Bi-for-Li and S/Se/Te-for-H co-substitution allow lower occupation energy and total energy for Bi + S/Se/Te co-doped LiBH4, compared to Bi-for-Li and S/Se/Te-for-B co-substitution. Thus, corresponding compounds Li7BiB8XH31 (X = S, M1; X = Se, M2; X = Te, M3), as well as pristine compound Li8B8H32 (M0), are selected as representatives for hydrogen desorption energies and electronic structures calculations. Our calculated results show that Bi + S/Se/Te co-doping yields a destabilized LiBH4 with enhanced dehydrogenation performance, with the atomic and molecular hydrogen desorption energies (Ed-H and Ed-H2) and the scaled bond order between B-H (BOsB-H) all decreasing in the order of M0 > M3 > M2 > M1. This destabilization of LiBH4 using Bi + S/Se/Te is attributed to the decrease of B-H covalent interactions, the formation of Li-S/Se/Te bonds, and the stronger electronegativity of Bi (relative to Li atom) and S/Se atoms (relative to H atom). Bi + S addition can lower the hydrogen desorption energies to −0.511 eV (Ed-H) and 1.061 eV (Ed-H). However, LiBH4 with Bi + S additives may generate S-H interactions for H2S formation, causing a loss of reversibility for hydrogen storage. For this fact, Bi + Se co-doping should be beneficial for LiBH4 decomposition.