Linker Group Directed High Mass Activity Fe–N–C Cathode in Proton Exchange Membrane Fuel Cells

Atomically dispersed Fe-N-C catalysts are regarded as promising alternatives to platinum-group-metal (PGM) catalysts for proton exchange membrane fuel cells (PEMFCs). However, their further development is hindered by inadequate utilization of active sites in membrane electrode assembly (MEA). Herein, we developed a high mass activity O-FeNC catalyst with high site density and enhanced site utilization. C═O groups function as hard base linkers, promoting the densification of FeN₄ sites through Lewis acid-base interactions. Moreover, they also direct interfacial alignment within triple-phase boundaries, leading to concentrated hydronium ions and accelerated oxygen permeation via regulated ionomer nanophase segregation. As a result, the obtained O-FeNC cathode delivered a current density of 66.45 mA cm^-2 at 0.90 V_iR-free, surpassing the US Department of Energy 2025 target (44 mA cm^-2 at 0.9 V_iR-free), with a mass activity that is 59% higher than commercial Pt/C. The peak power densities reached 1.8 W cm^-2 under H₂-O₂ and 0.93 W cm^-2 under H₂-air, alongside demonstrated industrial scalability through gram-scale synthesis and a 500 W PGM-free cathode stack prototype.