Axial sulfur-coordination engineering boosting Fe–N–C catalysts for high-performance proton exchange membrane fuel cells

The slow kinetics of the oxygen reduction reaction (ORR) at the cathode remains a major bottleneck for the widespread adoption of proton exchange membrane fuel cells (PEMFCs). While Fe–N–C catalysts are promising non-precious metal alternatives to platinum, they typically suffer from excessive adsorption of OH* species and low active site utilization.

A research team led by Prof. Junjie Ge from the University of Science and Technology of China (USTC) recently reported a breakthrough in catalyst design. By employing a dual-precursor chemical vapor deposition (CVD) strategy, they successfully incorporated sulfur (S) as an axial ligand to the iron center, forming Fe-S₁N₄ sites.

The study reveals that the axial sulfur atom disrupts the symmetric electronic structure of the Fe-N₄ plane. According to Density Functional Theory (DFT) calculations, this modulation optimizes the OH* adsorption energy, effectively mitigating “site blocking” effects and accelerating reaction kinetics. Furthermore, experimental results using nitrite stripping showed that the FeSNC catalyst achieved a 3.2-fold increase in turnover frequency (TOF) compared to traditional FeNC catalysts.

Beyond atomic-level optimization, the introduction of sulfur also improved the macro-scale performance of the membrane electrode assembly (MEA). The sulfur-doped catalyst layer exhibited enhanced hydrophilicity, which significantly reduced proton and oxygen transport resistance. Consequently, the FeSNC-based fuel cell achieved a peak power density of 1.2 W·cm^-2 in H₂-O₂ and 0.52 W·cm^-2 in H₂-Air conditions.

This research provides a synergistic strategy to enhance Fe–N–C catalysts from both the intrinsic activity of active sites and the mass transport within the electrode, paving the way for low-cost and high-efficiency fuel cell technologies. The work entitled “Axial Sulfur-Coordination Engineering Boosting Fe–N–C Catalysts for High-Performance Proton Exchange Membrane Fuel Cells” was published on Journal of Electrochemistry (published on Mar. 28, 2026).