Dissociation Mechanism of Water Molecules on the PuO₂(110) Surface: An Ab Initio Molecular Dynamics Study

Reactions between water and plutonium oxide play a key role in determining the oxidation and corrosion rates of plutonium materials. We perform consecutive ab initio molecular dynamics simulations with the DFT + U approach, systematically studying the dissociation dynamics and mechanism of water molecule and small clusters on the PuO 2 (110) surface. The dissociation of water on the surface is found to be a two-step hydroxylation process for both monomer and clusters, but different dissociation mechanisms are revealed. Water monomer dissociation, as the consequence of the hybridizations between the molecular orbitals of water and the electronic state of the surface, needs to overcome a reaction energy barrier of 0.18 eV. In contrast, the dissociations of hydrogen-bonded small water clusters are exothermic by −0.42 eV with no transition energy barrier. Hydrogen-bonding interactions between water molecules facilitate the dissociation process and result in a more stable dissociation state with respect to that of a single molecule. Such interaction also induces a hydrogen-transfer reaction between formed surface hydroxyl group and the remaining water molecule.