Promotion Mechanisms of LiBH4 Dehydrogenation Dominated by Charge Redistribution

LiBH4 is a promising solid-state hydrogen storage material, but its complex dehydrogenation reaction mechanism severely hinders the regulation of dehydrogenation barriers and reversibility. To elucidate the micro-mechanism of its dehydrogenation reaction, the potential of mean force, ab initio molecular dynamics, and electronic structure through density functional theory with Grimme D3 dispersion corrections have been conducted for different surfaces of LiBH4. The dehydrogenation barriers of various surfaces typically fall within the range of 110.84 ~ 122.96 kJ/mol. The dehydrogenation barrier can be remarkably reduced from 110.84 to 70.6 kJ/mol, as the concentration of Li vacancy varies from 0 to 12.5%. Besides, doping transition metals (TM) can effectively reduce the dehydrogenation barrier of LiBH4 (74.28 ~ 104.06 kJ/mol). The existence of Li vacancies results in the loss of electrons in the shared electron pairs of B-H bonds and weakens the strength between B-H covalent bonds. The doping TM makes the B-H bonds gain electrons, which occupy the antibonding orbitals and result in weakening the B-H bond strength. Consequently, the dehydrogenation barriers of LiBH4 are significantly reduced. This work reveals two different promotion mechanisms for Li vacancies and TM doping, and provides a new perspective for lowering its dehydrogenation temperature in future experiments.