Oxygen Vacancy Formation and Water Adsorption on Reduced AnO2{111}, {110}, and {100} Surfaces (An = U, Pu): A Computational Study

Abstract

The substoichiometric {111}, {110}, and {100} surfaces of UO2 and PuO2 are studied computationally using two distinct yet related approaches based on density functional theory (DFT): the periodic electrostatic embedded cluster method and Hubbard-corrected periodic boundary condition DFT. The first and the second layer oxygen vacancy formation energies and geometries are presented and discussed; the energies are found to be substantially larger for UO2 versus PuO2, a result that traced to the substantially more positive An(IV)/An(III) reduction potential for Pu and hence relative ease of Pu(III) formation. For {110} and {100} surfaces, the significantly more stable dissociative water adsorption seen previously for stoichiometric surfaces (J. Nucl. Mater. 2016, 482, 124–134; J. Phys. Chem. C 2017, 121, 1675–1682) is also found for the defect surfaces. By contrast, the vacancy creation substantially changes the most stable mode of water adsorption on the {111} surface, such that the almost degenerate molecul...