Role of oxygen vacancies in the surface evolution of H at CeO₂(111): A charge modification effect

Diffusion processes and reactions of H at stoichiometric and reduced CeO₂(111) surfaces have been studied by using density functional theory calculations corrected by on-site Coulomb interactions (DFT + U). Oxygen vacancies on the surface are determined to be able to significantly affect the behavior of H by modifying the charge of surface lattice O through the occurrence of Ce³⁺. It has been found that, at the reduced CeO₂(111) surface, the adsorption strength of H as well as the H coupling barrier can be dramatically reduced compared to those at the stoichiometric surface, while H₂O formation barrier is not significantly affected. Moreover, the diffusion of H at the reduced surface or into the bulk can occur more readily than that at stoichiometric CeO₂(111).