The role of vacancy, impurity, impurity–vacancy complex in the kinetics of LiNH₂ complex hydrides: a first-principles study

This paper studies first-principles plane-wave pseudopotential based on density functional theory of hydrogen vacancy, metal impurity, impurity–vacancy complex in LiNH₂, a promising material for hydrogen storage. It finds easy formation of H vacancy in the form of impurity–vacancy complex, and the rate-limiting step to the H diffusion. Based on the analysis of the density of states, it finds that the improvement of the dehydrogenating kinetics of LiNH₂ by Ti catalysts and Mg substitution is due to the weak bonding of N–H and the new system metal-like, which makes H atom diffuse easily. The mulliken overlap population analysis shows that H vacancy leads to the H local diffusion, whereas impurity–vacancy complexes result from H nonlocal diffusion, which plays a dominant role in the process of dehydrogenation reaction of LiNH₂.