Theoretical insights into the hydroxyl-promoted H2 releasing reaction after H2O splitting on Pu-oxide surfaces

Abstract

Within DFT+U-D3 scheme, we systematically investigate the reaction of H2O on Pu-oxide surfaces to reveal the effects of *H/*OH produced by water splitting on subsequent H2 releasing and surface oxidation. We find that both *H and *OH can promote H2 releasing, especially when PuO2 reduced to α-Pu2O3, but the micro mechanisms of *H/*OH driven H2 releasing process on PuO2(111) are different from α-Pu2O3(111) surface. On PuO2(111) surface, the adsorbed H2O and *H/*OH show a dynamic coupling with the localized electron/hole polarons induced by *H/*OH. Due to the significant heterogeneity of surface structure and Pu-coordination of α-Pu2O3(111), *H and *OH produce non-localized and localized electron polarons respectively, and notably facilitate the first-round exothermic H2 releasing process. After the first-round reaction, the residual surface O prefers to migrate into the inner layer to oxidize the α-Pu2O3 matrix, then the surface is recovered with *OH and ready for further H2 releasing reaction. Thus, we predict the eventual cyclic reaction on α-Pu2O3(111) surface, H2O + Pu2O3→*OH H2(g) + Pu2O3+, which can continually emit H2. In sum, our study provides new insights into the effects of surface structure and polarons on H2 releasing reaction, which we believe is of value to the Pu corrosion science.