Development and Application of a ReaxFF Reactive Force Field for Cerium Oxide/Water Interfaces

Ceria (CeO₂) is a well-known catalytic oxide with many environmental, energy production, and industrial applications, most of them involving water as a reactant, byproduct, solvent, or simple spectator. In this work, we parameterized a Ce/O/H ReaxFF for the study of ceria and ceria/water interfaces. The parameters were fitted to an ab initio training set obtained at the DFT/PBE0 level, including the structures, cohesive energies, and elastic properties of the crystalline phases Ce, CeO₂, and Ce₂O₃; the O-defective structures and energies of vacancy formation on CeO₂ bulk and CeO₂ (111) surface, as well as the absorption and reaction energies of H₂ and H₂O molecules on CeO₂ (111). The new potential reproduced reasonably well all the fitted properties as well as the relative stabilities of the different ceria surfaces, the oxygen vacancies formation, and the energies and structures of associative and dissociative water molecules on them. Molecular dynamics simulations of the liquid water on the CeO₂ (111) and CeO₂ (100) surfaces were carried out to study the coverage and the mechanism of water dissociation. After equilibration, on average, 35% of surface sites of CeO₂ (111) are hydroxylated whereas 15% of them are saturated with molecular water associatively adsorbed. As for the CeO₂ (100) surface, we observed that water preferentially dissociates covering 90% of the available surface sites in excellent agreement with recent experimental findings.