Elucidating the Initial Oxidation of Pt(111) Using Large-Scale Atomistic Thermodynamics: A ReaxFF Study

In situ scanning tunneling microscopy experiments on the initial oxidation of Pt(111) found complex intermediary platinum surface oxides, consisting of spoke wheel and stripe structures [Nat. Commun.2017, 8, 429]. While the stripes have been investigated extensively in the following, the spoke wheels are poorly understood because of their size and complexity. Here we employ atomistic thermodynamics based on an established reactive force field to investigate the structure and stability of spoke wheels at the elevated temperature (>530 K) and pressure (1–4 bar) conditions of the in situ experiments. At those conditions, the thermodynamic stability of the structural model for the spoke wheel is similar to that of the stripes, while the degree of surface oxidation is much lower. The spoke wheel is found to be much more stable than partially formed stripes with a similar degree of oxidation. These results are consistent with experimental findings, where the spoke wheel is observed first, at slightly lower oxygen pressures. They thus provide a better understanding of the oxidation pathway for Pt(111)-based catalysts in the context of oxidative catalysis.