First-principles thermodynamical modeling of molecular reactions on α-U (001) and α-UH 3 (001) surfaces and their influence on hydrogen activation

Density functional theory calculations coupled with thermodynamic analysis have been performed to investigate the reactions of hydrogen and impurity gases including O2, 2 , CO2, 2 , CO, N2 2 on alpha-U(001) and alpha-UH3(001) 3 (001) surfaces. Binding strength of adsorbates on alpha-UH3 3 is calculated to be weaker than alpha-U, suggesting enhanced poisoning- resistant properties of U-hydride compared to its metallic state. Surface phase diagrams of U under binary H2 2O2, 2 , H2 2-N2 2 and H2 2-CO gaseous environments show that while N and C elements prefer to stay in their hydrogenated states on the hydride surface, isolated O atoms favorably interact with both alpha-U(001) and alpha-UH3(001), 3 (001), indicating the heavily poisoning effect of impurities containing oxygen. Global optimization of partially oxidized alpha-U(001) slabs induces surface geometry reconstruction and the activity of oxidized surfaces toward hydrogen adsorption can be linearly correlated with local electronic and atomic properties of the adsorption site.