Mg/MgO interfaces as efficient hydrogen evolution cathodes causing accelerated corrosion of additive manufactured Mg alloys: A DFT analysis

Abstract

The corrosion rates of additive-manufactured Mg alloys are higher than their as-cast counterparts, possibly due to increased kinetics for the hydrogen evolution reaction on secondary phases, which may include oxide inclusions. Scanning Kelvin Probe Force Microscopy demonstrated that MgO inclusions could act as cathodes for Mg corrosion, but their low conductivity likely precludes this. However, the density of state calculations through density functional theory using hybrid HSE06 functional revealed overlapping electronic states at the Mg/MgO interface, which facilitates electron transfers and participates in redox reactions. Subsequent determination of the hydrogen absorption energy at the Mg/MgO interface reveals it to be an excellent catalytic site, with HER being found to be a factor of 23x more efficient at the interface than on metallic Mg. The results not only support the plausibility of the Mg/MgO interface being an effective cathode to the adjacent anodic Mg matrix during corrosion but also contribute to the understanding of the enhanced cathodic activities observed during the anodic dissolution of magnesium.