A Versatile Approach to Boost Oxygen Reduction of Fe‐N4 Sites by Controllably Incorporating Sulfur Functionality

Abstract Although atomically dispersed Fe‐N 4 on carbon materials (Fe‐NC) have enormous potential for the oxygen reduction reaction (ORR), precise control over the electronic structure of Fe to enhance the catalytic performance and a full understanding of the catalytic mechanism remain elusive. Herein, a novel approach is designed to boost the kinetic activity of single Fe‐N 4 centers by controlling S‐doped content and species (namely, thiophene‐like S and oxidized S). Due to confinement and catalysis effects, the innovative strategy of combining a Mg(OH) 2 template with KOH activation preferentially generates oxidized S and simultaneously constructs porous carbon with a high Fe loading (2.93 wt%) and hierarchical pores. Theoretical calculations suggest that neighboring S functionalities can affect the electronic configurations of Fe‐N 4 sites and increase the electron density around Fe atoms, thereby optimizing the adsorption energy of intermediates and substantially accelerating reaction kinetics, following the trend: oxidized S doped > thiophene‐like S doped > pristine Fe‐N 4 . Benefiting from high activity and accessibility of Fe‐N 4 sites, the optimal FeNC‐SN‐2 electrode displays impressive ORR activity with large power density while maintaining outstanding durability in Zn‐air batteries and microbial fuel cells. The work paves the way to prepare stable single‐atom metal‐N x sites with heteroatom‐doping for diverse high‐performance applications.