Unravelling the chemical heterogeneity of α-Pu2O3(111) surface with the site-selective adsorption of H2O and CO2

Unravelling the surface physical and chemical properties, especially the surface activity of Pu-oxides (PuO2, α-Pu2O3) toward molecules, is essential to the long-term storage and surface reaction of Pu. Within DFT+U-D3 scheme, we systematically investigate the adsorption behaviors of H2O and CO2 on α-Pu2O3(111) surface, and clarify the different chemical activity of α-Pu2O3(111) surface from PuO2(111), which is due to the distinct coordination and bonding property of the top-layer Pu. There are five- and six-coordinated Pu (Pu5c, Pu6c) on α-Pu2O3(111) surface, among which Pu5c is more reactive with lower work-function than Pu6c. Interestingly, H2O and CO2 present the preferential adsorption at the Pu5c sites rather than Pu6c, namely, the site-selective adsorption. H2O tends to dissociate spontaneously and adsorb in cluster as with the coverages increase, while CO2 keeps the molecular state adsorption. The calculated phase diagram and isotherm indicate that the adsorption quantity and stability of H2O are higher than CO2 at the same (T, P) condition, and CO2 can achieve the multilayer adsorption at high pressure (PCO2). This work reveals the chemical heterogeneity of α-Pu2O3(111) surface and the selective adsorption mechanism of active molecules, which clearly depicts the interactions between environment gaseous and Pu-oxide surfaces.