Competitive strain modulation of oxygen reduction reaction in monolayer binary alloy surfaces

• Competitive surface strain modulates ORR activity. • Atomic arrangement control is critical to optimizing catalytic performance in alloys. • Long-range compressive strain enhances ORR activity, while short-range tensile strain reduces the activity. • Phase-segregated Au x Pt 1−x /Pt(111) surfaces minimize tensile strain, improving ORR performance. • Random Au x Pt 1−x /Pt(111) surface arrangements increase tensile strain domains, reducing ORR performance. Binary alloys of transition metals show great promise as catalyst materials for the cathodic oxygen−reduction reaction (ORR) in polymer−electrolyte−membrane fuel cells. However, their catalytic application is limited by a lack of understanding of the factors influencing the ORR performance. To improve this understanding, we examine the activity of monolayer Au x Pt 1−x surface alloys supported on Pt(111) using density functional theory. We found that the catalytic activity of Au x Pt 1−x /Pt(111) alloys varies significantly with the surface atomic arrangements, where phase−segregated surfaces show higher activity than those with random atomic arrangements. A key factor is a competitive strain influencing the Pt adsorption site activity. Distant Au atoms induce a long−range compressive strain that enhances Pt site activity, while adjacent Au atoms generate tensile strain that slightly reduces the Pt site activity. These findings suggest that surface alloys of elements with dissimilar lattice constants can generate competitive strain effects that modulate the activity of different adsorption sites. Our findings underscore the importance of understanding and controlling atomic arrangements in alloys to ensure good catalytic performance.