First-principles study of co-adsorption behavior of O2 and CO2 molecules on δ-Pu(100) surface

Abstract

First principles calculation is performed to study the co-adsorption behaviors of O2 and CO2 on δ-Pu(100) surface by using a slab model within the framework of density functional theory (DFT). The results demonstrate that the most favorable co-adsorption configurations are Tv-C4O7 and Tp1-C2O8, with adsorption energy of –17.296 eV and –23.131 eV for CO2-based and O2-based system, respectively. The C and O atoms mainly interact with the Pu surface atoms. Furthermore, the chemical bonding between C/O and Pu atom is mainly of ionic state, and the reaction mechanism is that C 2s, C 2p, O 2s, and O 2p orbitals overlap and hybridize with Pu 6p, Pu 6d, and Pu 5f orbital, resulting in the occurrence of new band structure. The adsorption and dissociation of CO2 molecule are obviously promoted by preferentially occupying adsorbed O atoms, therefore, a potential CO2 protection mechanism for plutonium-based materials is that in CO2 molecule there occurs complete dissociation of CO2 → C + O + O, then the dissociated C atom combines with O atom from O2 dissociation and produces CO, which will inhibit the O2 from further oxidizing Pu surface, and slow down the corrosion rate of plutonium-based materials.