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

ABSTRACT 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.