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

Ceria (CeO) 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 training set obtained at the DFT/PBE0 level, including the structures, cohesive energies, and elastic properties of the crystalline phases Ce, CeO, and CeO; the O-defective structures and energies of vacancy formation on CeO bulk and CeO (111) surface, as well as the absorption and reaction energies of H and HO molecules on CeO (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 CeO (111) and CeO (100) surfaces were carried out to study the coverage and the mechanism of water dissociation. After equilibration, on average, 35% of surface sites of CeO (111) are hydroxylated whereas 15% of them are saturated with molecular water associatively adsorbed. As for the CeO (100) surface, we observed that water preferentially dissociates covering 90% of the available surface sites in excellent agreement with recent experimental findings.