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.