Ab initio thermodynamic and kinetic modeling of molecular adsorption and reaction properties on PuO2(111) surface under exposure to environmental gases

Abstract

Adsorption and reaction properties of environmental gases including O2, H2, and H2O on the PuO2(111) surface were studied via density functional theory simulations along with thermodynamic and kinetic analysis. Simulation results show that the stoichiometric PuO2(111) remains intact under O2 atmosphere and extremely low or high O2 pressure is required to form oxygen vacancy or adsorbed-O on the surface. The H2O prefers to stay as molecular state when adsorbing on PuO2(111) and a relatively high humidity is required for H2O to be stably binding on the surface. For H2 interaction with PuO2, the dissociative adsorption of H2 molecule induces reduction of Pu(IV) ions to Pu(III), and remains thermodynamically stable at H2 pressure as low as ∼10−35 bar under room temperature. Kinetic modeling shows that at temperature below 350 K, the PuO2(111) surface is mainly covered by OH species when exposing to H2 environment while bare metal sites appear with increased temperature and reaction time.