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 > thiophenelike 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 highperformance applications.

Nitrogen‐coordinated single‐atom catalysts (SACs) have emerged as a new frontier for accelerating oxygen reduction reaction (ORR) owing to the optimal atom efficiency and fascinating properties. However, augmenting the full exposure of active sites is a crucial challenge in terms of simultaneously pursuing high metal loading of SACs. Here, petal‐like porous carbon nanosheets with densely accessible Fe‐N4 moieties (FeNC‐D) are constructed by combining the space‐confinement of silica and the coordination of diethylenetriaminepentaacetic acid. The resulted FeNC‐D catalyst possesses an enhanced mesoporosity and a balanced hydrophobicity/hydrophilicity, which can facilitate mass transport and advance the exposure of inaccessible Fe‐N4 sites, resulting in efficient utilization of active sites. By virtue of the petal‐like porous architecture with maximized active site density, FeNC‐D demonstrates superior ORR performance in a broad pH range. Remarkably, when utilized as the air cathode in Zn‐air battery (ZAB) and microbial fuel cell (MFC), the FeNC‐D‐based device displays a large power density (356 mW cm−2 for ZAB and 1041.3 mW m−2 for MFC) and possesses remarkable stability, substantially outperforming the commercial Pt/C catalyst.

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