Theoretical Study of Water Molecule Dissociation on Surfaces of Ce, CeN, and CeH₂

Cerium (Ce) has unique electronic structural properties, making it an ideal model for studying surface reaction mechanisms of plutonium (Pu)-based materials. This study employed density functional theory (DFT) to systematically investigate the adsorption and dissociation kinetics of water molecules on Ce, CeN, and CeH₂ surfaces. By conducting geometric optimization and energy calculations, the impact of different surface structures on the adsorption energy and configuration of water molecules was quantitatively analyzed. It is found that the most stable adsorption of water molecules on all three surfaces occurs at the bridge-site adsorption configuration, but there are still differences in adsorption energy and geometric parameters. The adsorption energy of water molecules on the Ce, CeN, and CeH₂ surfaces is −0.81, −0.92, and −0.93 eV, respectively. Furthermore, through electron structure analysis methods such as the electron localization function (ELF) and crystal orbital bond index (COBI), the impact of charge distribution and bonding characteristics at active surface sites on the cleavage of water’s O-H bonds was explored. The ELF results show that the electron structure of water molecules changes significantly after interacting with the surface, weakening the original O-H bond strength. The COBI analysis reveals that the O-H bond order decreases in the Ce-H₂O, CeN-H₂O, and CeH₂-H₂O systems, while the O-Ce bond order increases. The transition-state search results demonstrate that the Ce metal surface promotes water dissociation. In the CeN and CeH₂ systems, the negatively charged N and H atoms induce surface charge rearrangement, further facilitating water dissociation. The dissociation processes on these three surfaces are different. On the Ce surface, the dissociation process is a multi-step reaction with a total reaction energy barrier of 0.80 eV for the second O-H bond cleavage, and the overall process is exothermic by 3.34 eV. On the CeN surface, the first O-H bond breaks without a potential barrier, and the second O-H bond cleavage is the rate-determining step with an energy barrier of 0.98 eV, and the total heat release is 3.54 eV. On the CeH₂ surface, the first O-H bond also breaks spontaneously without a potential barrier, and the second O-H bond cleavage requires crossing an activation energy barrier of 0.72 eV, with a total heat release of 4.99 eV. In conclusion, this study systematically reveals the adsorption and dissociation mechanisms of water molecules on the surfaces of Ce, CeN, and CeH₂. It provides a systematic comparison of the dissociation kinetics among the three surface systems, which can complement experimental observations and offer valuable guidance for further research on the surface reaction mechanisms of Pu-based materials.