Axial Sulfur-Coordination Engineering Boosting Fe-N-C Catalysts for High-Performance Proton Exchange Membrane Fuel Cells

Fe-N-C catalysts have long suffered from kinetically sluggish oxygen reduction reaction (ORR) due to excessive adsorption strength toward oxygen intermediates and low site utilization. Heteroatom doping effectively accelerates ORR reaction kinetics through electronic structure modulation of metal sites for optimal intermediate adsorption, while chemical vapor deposition (CVD) enhances the turnover frequency (TOF) of active sites. Herein, we developed an FeSNC catalyst featuring abundant FeS₁N₄ sites via a dual-precursor CVD strategy. Experimental and theoretical analyses revealed that S incorporation disrupts the symmetric coordination of active sites, which optimizes OH* adsorption energies from 0.212 eV to 1.194 eV. Moreover, the TOF increased from 1.98 e^–1·site^–1·s^–1 to 6.32 e^–1·site^–1·s^–1, significantly enhancing the intrinsic activity of the catalyst. More notably, the hydrophilic character of S-containing species substantially improved hydrophilicity in the S-doped catalyst, thereby promoting mass transport of oxygen and proton delivery. As a result, the FeSNC catalyst exhibited an extremely high half-wave potential of 0.863 V in 0.1 mol·L^–1 HClO₄ and achieved a peak power density of 1.2 W·cm^–2 in H₂-O₂ PEMFCs. This work highlights the critical role of coordination engineering.