Competitive Strain Modulation of Oxygen Reduction Reaction in Monolayer Binary Alloy Surfaces

Binary alloys of transition metals are promising catalytic materials for the cathodic oxygen-reduction reaction (ORR) of polymer-electrolyte-membrane fuel cells (PEMFCs). However, a lack of understanding of the factors that affect the ORR's catalytic performance hampers the catalytic applications of binary alloys. To obtain further knowledge of binary alloys for efficient ORR, we investigate the activity of monolayer AuxPt1-x alloy surfaces supported on Pt(111), considering from random distribution until phase-segregated surface atoms. Using the *OH adsorption energy as a descriptor, we found that the activity of monolayer binary alloy surfaces depends on the distribution of the surface atoms within surfaces with segregated Pt and Au domains showing higher activity. The adsorption energy of *OH increases with the fraction n of Au near the adsorption site and decreases with the fraction p of Au outside the heptamer. The energy increase due to n is related to a tensile strain, while the decrease with the increase of p is due to a long-range surface strain effect on the Pt-Pt and Pt-Au bonds, improving the activity of the available Pt adsorption sites. Due to the weak *OH adsorption energy on Au sites, an Au overall percentage considerably above the Pt percentage starts to reduce surface activity because of the reduction of the number of very active Pt sites.