(111) Surfaces (An = Th, U, Pu) and Their Impacts on Catalytic Water Splitting*

Exess electrons from intrinsic oxygen vacancies play a key role in the surface chemistry and catalytic properties of metal oxides. This effect is particularly critical in actinide dioxides (AnO₂), the most common nuclear fuels, where radiation can induce the formation of vacancies. However, the behavior of excess electrons on AnO₂ surfaces has not been fully explored. In this talk, I will discuss our first-principle study of the electronic structure of excess electrons from oxygen vacancies on AnO₂ (111) surfaces. The low-energy electronic structure is searched via U-ramping and occupation matrix control. The excess electrons are found to localize at the vacancy site on ThO₂, move to the metal 5f orbitals on PuO₂ surface, with UO₂ as an intermediate case. In the presence of water, the excess electrons lead to the exothermic splitting of H₂O and formation of H₂ on ThO₂ and UO₂ surfaces, while on PuO₂ surface the formation of H₂ is thermodynamically unfavorable. This work has important implications in the surface chemistry and corrosion of AnO₂, and hence the handling and long-term storage of spent nuclear fuels.