Excess Electrons on Reduced AnO₂ (111) Surfaces (An = Th, U, Pu) and Their Impacts on Catalytic Water Splitting
2019
Wang, Gaoxue | Batista, Enrique R. | Yang, Ping
Excess 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 article, we present a first-principle study of the electronic structure of excess electrons from oxygen vacancies on AnO₂ (111) surfaces (An = Th, U, Pu). The low-energy solutions for the excess electrons are searched via U-ramping and occupation matrix control. The excess electrons are found to localize at the vacancy site on ThO₂ and move to the metal 5f orbitals on the PuO₂ surface, with UO₂ as the intermediate case. This change significantly affects the catalytic properties of the AnO₂ surfaces. In the presence of water, the excess electrons lead to the exothermic splitting of H₂O and formation of molecular H₂ on ThO₂ and UO₂ surfaces, while on the PuO₂ surface the formation of H₂ is thermodynamically unfavorable. This work has vital implications in the surface chemistry and corrosion of AnO₂ and hence the handling and long-term storage of spent nuclear fuels.
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