First-principles investigation of water adsorption and dissociation on the Al/Y-doped Mg (0001) surface

The poor corrosion resistance of Mg alloys affects their large-scale application. The cathodic hydrogen evolution reaction (HER) is one of the reasons for the rapid corrosion rate of Mg alloys, which mainly involves the adsorption and dissociation of water molecules. During these processes, H and OH were gradually formed and adsorbed on the Mg surface. This caused the H atoms that were attracted to each other to form H₂ and escape from the surface, while OH remained on the surface to form Mg(OH)₂ with the Mg atom, which has a significant impact on Mg corrosion. In this work, the effects of Al and Y elements on the adsorption and dissociation of water on the Mg (0001) surface have been investigated using first-principles calculations. By calculating the adsorption free energy of H₂O, H-OH, OH, and the reaction energy for hydrolysis, we determined their stable adsorption sites and the most likely dissociation pathway of water molecules on the surface. In addition, by calculating the charge distribution state of the water adsorption and dissociation process on the Al/Y-doped Mg (0001) surface, we revealed the influence of doped atoms (Al and Y) on the stable adsorption sites of water molecules on the Mg (0001) surface. These results indicated that doped atoms could redistribute surface electrons, which changed the adsorption free energies and sites of H₂O, H, and OH during the water adsorption and dissociation process, regulating the HER of Mg. Interestingly, the Y element can promote the adsorption and dissociation of water molecules on the Y-doped Mg (0001) surface, inducing the formation of Y(OH)₃ and Mg(OH)₂ to enhance the Mg corrosion resistance.