First-principles study of water decomposition and hydrogen evolution on MgZn2 Laves phase

Abstract

Second phase strengthening has been widely applied in Mg alloy designs, many of which however have been reported to aggravate the galvanic corrosion of Mg alloys. In this study, the hydrogen evolution reaction (HER) on MgZn2 Laves phase, which serves as a local cathode, is investigated by first-principles calculations based on density functional theories. We first calculated the surface energy of MgZn2 and found (0001) surface with Mg-rich termination to be the most stable one, and the favored adsorption sites for relevant molecule species were further identified. By using Nudged Elastic Band (NEB) method, the reaction pathway and energy barriers of H2O molecule decomposition, H adatom diffusion, and H2 molecule recombination were obtained, among which hydrogen recombination is thermodynamically unfavored. This study provides fundamental insights into the cathodic reaction on Mg alloys, from determining the cathode, identifying the most stable surface, obtaining reaction energy barrier, to comparing corrosion property among different intermetallics, which may be a guidance to the corrosion-resistant Mg alloys design.