A general picture for water dissociation on uranium dioxide surfaces

Despite extensive theoretical and experimental studies, there is still no universal picture for water dissociation on actinide dioxide surfaces. Based on ab initio molecular dynamics studies, we systematically investigated the influences of surface morphology and stoichiometry of the UO2 (001) surface on the adsorption behavior of a water molecule. We find that the critical factor corresponding to water dissociation is the existence of surface actinide atoms. On the normal UO2 (001) surface, surface U atoms are ready to bond with dissociated hydroxyl groups and the adsorbed water molecules dissociate spontaneously upon approaching. Comparatively, the surface U atoms on the oxygen-over surface are fully bonded with oxygen atoms, and the approaching water molecule do not dissociate. On a more realistic trench UO2 surface, we find that approaching water molecules can steadily adsorb in the trench area after weakly bonding with two oxygen atoms in the trench. Our work reveals the vital role of surface actinide atoms in dissociating approaching water molecules, which is meaningful for macroscopic modellings of actinide corrosion.