First-principles study of water adsorption and dissociation on the UO₂ (1 1 1), (1 1 0) and (1 0 0) surfaces

The adsorption and dissociation behaviors of water molecule on the UO₂ (1 1 1), (1 1 0) and (1 0 0) surfaces were investigated using first-principles methods within the DFT+U framework. For a single water molecule at 1/4 ML coverage, the molecular adsorption exhibits comparable adsorption energies with the dissociative adsorption on the (1 1 1) surface, while it is far less stable than the dissociative adsorption on the (1 1 0) and (1 0 0) surfaces. We find that the adsorbed molecular and dissociative water tend to cluster on low-index UO₂ surfaces by forming hydrogen-bond networks. The adsorption stability of water depends on the synergistic effect of hydrogen bonding interaction and steric effect between adsorbates. The mixed adsorption configuration of molecular and dissociative water in 1:1 mol ratio is found to be thermally more stable on the UO₂ (1 1 1) and (1 1 0) surfaces