Effects of Li doping on the dehydrogenation properties of MgH2(110) surface: Insights from first-principles Calculations

Elemental doping is commonly used to improve the dehydrogenation thermodynamic and kinetic properties of MgH2. Compared with transition metals, Li doping can keep the hydrogen gravimetric density of MgH2. In this work, we present the density functional theory calculations of MgH2(110) surface to explore the influence on dehydrogenation by Li doping. Both the Li substitution doping and interstitial doping are considered. The bond length, charge density difference and Bader charge are investigated to understand the effects of Li doping on local lattice structure and bonding property of MgH2(110) surface. Both atomic hydrogen and molecular hydrogen desorption are considered. The atomic hydrogen desorption energies decrease significantly upon Li doping, which suggests that Li favors the dehydrogenation of MgH2. Moreover, the activation energy barriers for molecular hydrogen desorption from pure and Li-doped MgH2(110) surfaces are predicted via one-step direct dehydrogenation manner. It is found that a significant reduction in the activation barrier when Li substitutes Mg while interstitial Li has no apparent catalytic effect on the activation barrier.