Co-adsorption of O₂ and H₂O on Al(111) surface: A vdW-DFT study

Using first-principles calculations based on van der Waals density functional theory, we systematically studied the co-adsorption behavior of H₂O and O₂ on Al(111) surfaces. The study consists of two parts: (i) the adsorption of H₂O molecules on O pre-adsorbed Al(111) surfaces, and (ii) co-adsorption of H₂O and O₂ molecules on a clean Al(111) surface. H₂O adsorbs on O pre-adsorbed Al(111) surfaces in the form of a molecule, while both the adsorption energies and partial density states results prove that the adsorption of H₂O is strengthened with the increasing pre-adsorbed O coverage. An Al atom bonded with H₂O is pulled out of the surface in all adsorbed structures because of the repulsion between pre-adsorbed O atoms and the O atoms of H₂O. For the co-adsorption of H₂O and O₂ on a clean Al(111) surface, H₂O molecules can dissociate into OH and H when both of the two O atoms of O₂ can interact with H atoms of H₂O, or else they will adsorb on the surface keeping the behavior of single adsorption. For the dissociation adsorption of H₂O, the redistribution of charge occurs and the value of charge transfer from the surface and O₂ to H₂O is much larger than that of molecular adsorption, which is larger than 0.1.