H₂O‑Dissociative Adsorption on Mg(0001) SurfaceCorrosion Process under Atmospheric Conditions

The high susceptibility to corrosion of metallic magnesium, the lightest structural metal with great application potential, limits its practical use, and the corrosion mechanism, especially under atmospheric conditions, remains unclear. In this work, reactions of H₂O on the Mg(0001) surface under atmospheric conditions along with the influence of oxygen on the H₂O-Mg-(0001) interaction were investigated by DFT calculation. Electronic structure analyses (PDOS, COHP, and Bader charge) were conducted to provide a fundamental atomic-level explanation for the adsorption and reaction. Results show that molecular H₂O adsorption on pure Mg(0001) is weak, dissociative adsorption is favored kinetically and thermodynamically, and the formed H* and OH* prefer surface sites, while O* prefers subsurface sites from low to high coverage for deep oxidation. Surface oxygen O* atoms, readily formed from the dissociation of O₂ or H₂O atoms, significantly enhance water dissociative adsorption. The oxidized surface layers saturated with hydroxyl layers, which will hinder the further reaction of the compounds of O₂ and H₂O on the surface, are protective under certain conditions.