Hierarchically Ordered Porous Carbon with Atomically Dispersed FeN4 for Ultraefficient Oxygen Reduction Reaction in Proton‐Exchange Membrane Fuel Cells

The low catalytic activity and poor mass transport capacity of platinum group metal free (PGM‐free) catalysts seriously restrict the application of proton‐exchange membrane fuel cells (PEMFCs). Catalysts derived from Fe‐doped ZIF‐8 could in theory be as active as Pt/C thanks to the high intrinsic activity of FeN4; however, the micropores fail to meet rapid mass transfer. Herein, an ordered hierarchical porous structure is introduced into Fe‐doped ZIF‐8 single crystals, which were subsequently carbonized to obtain an FeN4‐doped hierarchical ordered porous carbon (FeN4/HOPC) skeleton. The optimal catalyst FeN4/HOPC‐c‐1000 shows excellent performance with a half‐wave potential of 0.80 V in 0.5 m H2SO4 solution, only 20 mV lower than that of commercial Pt/C (0.82 V). In a real PEMFC, FeN4/HOPC‐c‐1000 exhibits significantly enhanced current density and power density relative to FeN4/C, which does not have an optimized pore structure, implying an efficient utilization of the active sites and enhanced mass transfer to promote the oxygen reduction reaction (ORR). Smart doping: When Fe‐doped ZIF‐8 single crystals were pyrolyzed, catalytically active FeN4 centers were atomically dispersed in a 3D hierarchical ordered porous carbon matrix. The interconnected carbon skeleton sufficiently meets the mass transfer requirement, thus boosting the catalytic efficiency for the oxygen reduction reaction (ORR).