Unraveling oxygen-driven surface segregation dynamics in platinum-gold alloys

In this study we use high-energy resolution and fast X-ray Photoelectron Spectroscopy (XPS) measurements combined with Density Functional Theory (DFT) calculations to investigate the interplay between surface segregation and bulk migration of Pt atoms on Au(111) in an oxygen environment. We demonstrate that the segregation of Pt atoms is significantly influenced by the oxygen partial pressure and identify a range of O2 pressure where PtAu surface alloy formation is inhibited while promoting the formation of Au oxide. These findings are essential to understand the compositional changes in the bimetallic surface alloy, which could potentially lead to modifying the catalytic properties of PtAu up to catalyst deactivation. Our results offer a strategy to control Pt surface coverage on Au(111), a quantity that is of paramount relevance given the applications of PtAu alloys as catalysts in reactions such as the oxygen reduction reaction or the oxidation of methanol and carbon monoxide. Additionally, our findings indicate a method for controlling the composition and properties of the surface of PtAu catalysts through adjustments made during the formation of the PtAu alloy.