How the microenvironment dominated by the distance effect to regulate the FeN₄ site ORR activity and selectivity?

The distance effect of the doped heteroatoms away from the catalytic centers has rarely been reported. In this work, we conducted density functional theory calculations to thoroughly investigate the influence of heteroatom (N, P, B, and S atoms) doping distance on the oxygen reduction reaction (ORR) activity of graphene-based FeN₄ sites. We uncovered a Sabatier-like relationship between heteroatom doping distance and ORR activity of FeN₄ sites. The nearest doping does not significantly improve and even block the ORR activity of FeN₄ sites. Optimal ORR activity is achieved when the heteroatoms are 4–5 Å (N, P, and S atoms) or 6–7 Å (B atoms) away from the Fe atoms. Analysis of electronic structure indicates that distance effect can modulate the local chemical environment of Fe atoms, thereby account for the changes in ORR activity along with the doping distance and doping atoms. This study provides insights into the influence of heteroatom doping on the chemical environment of reaction active centers, and provides the theoretical guidance for controlling the doping distance of heteroatoms to achieve optimal catalytic activity and selectivity.