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 FeN 4 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 H 2 –O 2 and 0.93 W cm −2 under H 2 –air, alongside demonstrated industrial scalability through gram-scale synthesis and a 500 W PGM-free cathode stack prototype.