A DFT study of the adsorption of O2 and H2O on Al(111) surfaces

Abstract

Using first-principles calculations that are based on density functional theory, the molecular and dissociative adsorptions of O₂ and H₂O on a clean and O pre-adsorbed Al(111) surface were systematically investigated. The van der Waals dispersion correction is considered for the molecular adsorption of H₂O. We found that O₂ dissociates into O atoms which can adsorb on fcc and hcp sites. The stability ranking for O atoms on the clean Al(111) surface is fcc > hcp. The energy barriers for the migration of a single O atom from a hcp to a fcc site on a clean and O pre-adsorbed Al(111) surface are 25.91 kJ mol⁻¹ and 28.67 kJ mol⁻¹, respectively, which means that the pre-adsorbed O atom inhibits the migration of O atoms on the surface. H₂O molecules cannot dissociate on both clean and O pre-adsorbed Al(111) surfaces spontaneously. The pre-adsorbed O atom can strengthen the adsorption of H₂O and promote its deformation. The dissociation adsorption of H₂O, that is, the co-adsorption of OH and H, is much stronger than the molecular H₂O adsorption. The energy barrier of H₂O dissociation is 137.58 kJ mol⁻¹ on a clean Al(111) surface, however, it decreases to 38.18 kJ mol⁻¹ with the aid of a pre-adsorbed O atom, suggesting that a pre-adsorbed O atom can promote the dehydrogenation reaction of H₂O.