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

Abstract

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 H₂ SO₄ 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).