Effect of atomic iron on hydriding reaction of magnesium: Atomic-substitution and atomic-adsorption cases from a density functional theory study

Abstract

Fe atoms doping in form of adsorption and substitution can improve the hydriding performance of Mg for hydrogen storage, but the underlying mechanism is still unclear. In this work, density functional theory calculation is applied to study the effect of atomic Fe on the hydriding reaction of Mg crystal. The H2 adsorption calculation suggests that the adsorbed and substituted Fe atoms can both enhance the sorption performance of H2 molecule on Mg(0001). The H2 dissociation calculation suggests that the adsorbed Fe is more beneficial for H2 dissociation, in which the electron donation of Fe dz2 orbital and back donation of Fe dxy orbital are helpful to transfer electrons from bonding orbital of H2 to antibonding orbital to weaken H-H bond. The H diffusion calculation suggests that the substituted Fe can promote H atom penetration through Mg surface, which makes bulk diffusion from tetrahedral interstice to octahedral interstice the rate-limiting step. This work clarifies the catalytic mechanism of atomic Fe of different doping types on Mg hydriding, which should contribute to design high quality Mg-Fe system for hydrogen storage.