Atomistic Mechanism of Pt Extraction at Oxidized Surfaces: Insights from DFT

In this article, we propose a novel mechanism for the atomic-level processes that lead to oxide formation and eventually Pt dissolution at an oxidized Pt(111) surface. The mechanism involves a Pt extraction step followed by the substitution of chemisorbed oxygen to the subsurface. The energy diagrams of these processes have been generated using density functional theory and were analyzed to determine the critical coverages of chemisorbed oxygen for the Pt extraction and O-ads substitution steps. The Pt extraction process depends on two essential conditions: (1) the local coordination of a Pt surface atom by three chemisorbed oxygen atoms at nearest-neighboring fee adsorption sites; (2) the interaction of the buckled Pt atom with surface water molecules. Results are discussed in terms of surface charging effects caused by oxygen coverage, surface strain effects, as well the contribution from electronic interaction effects. The utility of the proposed mechanism for the understanding of Pt stability at bimetallic surfaces will be demonstrated by evaluating the energy diagram of a Cu-ML/Pt(111) near-surface alloy.