Insight into the effect of coexistence of CO₂ and H₂ on stoichiometric and defective PuO₂ surfaces hydriding from first-principles study

Studying the effect of coexistence of CO2 and H-2 on plutonium hydriding is of great significance for nuclear safety storage and disposal. In this work, we studied the microscopic adsorption morphology of CO2 and H-2 molecules with low and high coverage on stoichiometric PuO2 (111) and (110) surfaces. The adsorption energy results showed that both CO2 and H-2 have relatively strong reactivity with the (110) surface. The CO2 molecule may be dominant in competitive adsorption with H-2. The influences of the coexistence of CO2 and H-2 on the adsorption and dissociation behavior for H-2 on stoichiometric and defective surfaces were further researched. The CO2 adsorption configuration on the defect surface reveals that the O atom attempts to "heal" the oxygen vacancy. The results show that the presence of CO2 can weaken the interface interaction between H-2 and the surface, and increase the H-2 dissociation energy barrier on the surface from about 0.518 eV to about 0.791 eV. The electronic properties and work function show that the adsorbed CO2 hinders the electron interaction between H-2 and surface resulting in the blocking of hydrogen adsorption and dissociation, which may be the reason for inhibiting the hydrogenation of plutonium. Our study could provide new insights into the CO2 effect on the hydriding process of active metals.