First-principles investigation of H2O2 adsorption and dissociation on the UN (001) surface: thermodynamic effects of temperature and pressure

The interaction between UN and H₂O₂, a key product in high radiation fields, plays a crucial role in understanding the corrosion and stability of UN as an accident-tolerant fuel (ATF). In this study, we investigated the adsorption and dissociation behavior of H₂O₂ on the UN (001) surface using DFT + U and ab initio atomic thermodynamic simulations. The adsorption configurations for one to nine H₂O₂ molecules were analyzed under varying temperature and pressure conditions, providing insight into surface reactions relevant to high-radiation environments. Results show that the most stable adsorption sites for H and O atoms are hollow sites, while OH groups favor U-top sites. For a single H₂O₂ molecule, the adsorption energies for the most stable molecular, partially and fully dissociative states are -7.18 eV, -7.07 eV and -6.89 eV, respectively. Spontaneous decomposition (H₂O₂→2OH) occurs, with one of the OH groups to dissociate into O and H atoms requiring a significant energy barrier of 1.74 eV, followed by further dissociation into O and H atoms with a smaller barrier of 0.50 eV. Increasing H₂O₂ coverage promotes dissociation into H₂O and O atoms. Additionally, the stability of H₂O₂ adsorption is strongly influenced by temperature and pressure, with higher temperatures leading to lower coverages and higher pressures favoring more stable adsorption configurations. These findings provide important insights into the behavior of UN in environments relevant to nuclear reactors, contributing to the development of more stable and corrosion-resistant ATF materials.