Selenium doping modulates FeN4 sites for high-efficiency oxygen reduction reaction in acidic media.

Abstract

Atomically dispersed Fe-N-C single-atom catalysts are regarded as the most competitive substitutes for commercial Pt/C in proton exchange membrane fuel cells. Nevertheless, symmetric planar FeN4 these atomic active centers exhibit sluggish inherent catalytic kinetics together with unsatisfactory cycling stability under acidic operation, severely limiting their practical applications. Herein, we constructed FeSe-NC catalysts with asymmetric Fe-SexN4-x coordination. XPS and in-situ Raman spectroscopy, combined with theoretical calculations, provide multiple lines of complementary evidence supporting the plausible formation of Fe-SexN4-x-like coordination motifs. Relative to Fermi energy, a downward shift can be detected for the Fe d-band center, mitigating the overly strong adsorption of oxygenated intermediate species. Strong Fe 3d-Se 4p orbital coupling tuned the interplay between the process of surface capture and liberation of the OH⁎ intermediate. The optimized FeSe-NC-3:1 delivers an E1/2 of 0.80 V (vs. RHE) in acidic 0.5 M H2SO4 electrolyte, which is close to that of commercial 20 wt% Pt/C (0.81 V). It merely underwent a 13 mV decay after 10,000 accelerated durability test cycles, while retaining 85.7% of its initial current density in a 20,000 s chronoamperometry test. This study clarifies the electronic modulation mechanism of asymmetric Fe-SexN4-x coordination and provides a feasible coordination reconstruction strategy to design high-stability non-precious metal catalysts for acidic oxygen reduction reaction.

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