(668a) Understanding the Mechanism of Aqueous Metal Oxidation on the Nanoscale: Vacancy Transport, Energy Barriers, and Rate Predictions

Quantitative understanding of aqueous oxidation of alloys at the atomic scale to the microscale has remained a challenge and can guide in rational materials design. We employed accurate interatomic potentials and available experimental data to analyze the aqueous oxidation mechanism of Ni using a complete thermodynamic cycle, including detailed molecular dynamics simulations of vacancy migration through the nanometer-thick NiO layer. The energy profile of all steps including vacancy formation, charge transfer from metal to oxygen, and cation vacancy diffusion are discussed and quantified. Cation vacancy migration in the NiO film becomes the critical process determining the overall oxidation rate. The effects of oxide film thickness, applied electric fields, and hydroxylated surfaces on the oxidation rates was predicted consistent with experimental observations, and the methods can be applied to models up to several 100 nm size.