Theoretical study on the hydrogen distribution and diffusion at the PuO₂/α-Pu₂O₃ interface

The interface is a region in the crystal that significantly changes various characteristics. There must be an interface between oxides of different valence states in the surface oxide layer of plutonium. In this work, a first principles approach based on DFT was used to study the hydrogen distribution and diffusion at the PuO₂/α-Pu₂O₃ interface systematically. Our research reveals that at the interface, hydrogen can be captured by the O atoms of PuO₂ and by the oxygen vacancies (OVs) of α-Pu₂O₃, and the capture of OVs is more energetically advantageous. On the PuO₂ side, the cost of H atom diffusion towards the interface gradually increases. On the α-Pu₂O₃ side, the cost of H atoms diffusing inward from the interface gradually increases. OVs that already contain H atoms are more conducive to capturing H atoms. The formation of the interface has little effect on the hydrogen capture ability of O in PuO₂, but it will reduce the capture ability of OVs in α-Pu₂O₃. Overall, the formation of interfaces has no disruptive impact on the behavior of hydrogen in the two plutonium oxides. This is closely related to the fact that α-Pu₂O₃ originates from PuO₂ under anaerobic conditions. The difference in hydrogen behavior comes from the changes in the atomic environment and ion valence state caused by the OVs. This work supports further understanding of the behavior of hydrogen in plutonium oxides and provides a reference for further research on plutonium corrosion prevention.