Hydrogen fuel cells is a promising technology toward net-zero emission by 2050. It is performance is limited the sluggish oxygen reduction reaction (ORR) on cathodes. Although it is known that ORR happen on catalyst surfaces, only specific surface sites have high catalytic activity. Thus, identifying active sites and maximizing their presence lies at the heart of ORR research. For ORR on Pt group metal surfaces, the classic model categorizes active sites based on surface motifs, such as terraces and steps. However, this simplistic approach often leads to orders of magnitude errors in catalyst activity predictions and qualitative uncertainties of active sites, thus limiting opportunities for catalyst design. Using stepped Pt(111) surfaces as examples, I will illustrate that the root cause of larger errors and uncertainties is such a simplified categorization overlooks atomic site-specific reactivity driven by surface stress release. Specifically, I will show how surface stress release at steps introduces inhomogeneous strain fields, resulting in distinct electronic structures and reactivity for terrace atoms with identical local coordination. This phenomenon leads to a cluster of active sites flanking both sides of the step edge. I will demonstrate strategies to enhance ORR activity by leveraging this effect, such as varying terrace widths, adjusting the thickness of 2D nanosheets or controlling external stress. If time permits, I will briefly introduce our recent work regarding how to tune the surface chemistry of inverse catalysts oxide/metal without site-blocking effects.
