Regulating atomic Fe-Rh site distance for efficient oxygen reduction reaction

Exploring the atomic interaction mechanisms of dense single-atom catalysts (SACs) is of great significance for their application in oxygen reduction reaction (ORR). However, the intrinsic mechanism of the site-distance effect on the catalytic performance has been largely ignored. Here, we demonstrate the site-distance effect of Fe-Rh-x@NC catalysts in ORR theoretically and experimentally. Bader charge analysis reveals that the strong interaction between Fe and Rh atoms at a certain atomic distance (d(Fe-Rh)) alters the catalytic electronic structure, facilitating the optimization of catalyst adsorption strength. Motivated by the theoretical calculations, we designed and synthesized the Fe-Rh-x@NC catalysts through a spatial confinement strategy. The characterization results prove that the Fe-Rh-2@NC has the optimal d(Fe-Rh), which improves its intrinsic ORR activity, providing a half wave potential of 0.91 V, higher than that of the commercial Pt/C (0.86 V). This study emphasizes the importance of determining the basic mechanism of the site-distance effect in dissimilar metal atoms catalysts, which is conducive to the design of efficient catalyst systems for practical applications.