Enhancement of Mass Transport for Oxygen Reduction Reaction Using Petal‐Like Porous Fe‐NC Nanosheet

Abstract 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‐N 4 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‐N 4 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.