Proximity-engineered Ru single-atom sites modulate Fe-N4 spatial distortion for enhanced acidic oxygen reduction reaction

Fe-N-C catalysts are promising substitutes for precious-metal platinum in acidic oxygen reduction reactions (ORR), yet their moderate intrinsic activity and susceptibility to reactive oxygen species (ROS)-induced degradation hinder practical implementation. Herein, we fabricate a Ru-Fe dual-site catalyst (RuFe-N-C) through a two-step pyrolysis strategy. Structural characterization reveals atomic-scale proximity between Ru single atoms and Fe-N 4 moieties, exhibiting a projected distance of ~1.7 Å. This configuration induces Fe–N bond elongation accompanied by 2.5% lattice distortion. The optimized RuFe-N-C catalyst exhibits high ORR performance, with a half-wave potential ( E 1/2 ) of 0.840 V and peak power density ( P max ) of 938 mW cm –2 under 150 kPa absolute H 2 -O 2 . These metrics signify substantial enhancements relative to conventional Fe-N-C benchmarks (+21 mV in E 1/2 and +42% in P max ). Moreover, the catalyst maintains outstanding stability, showing merely 17 mV E 1/2 decay after 10000 accelerated durability test (ADT) cycles. Experimental analyses reveal a bifunctional mechanism: (1) Adjacent Ru sites substantially enhance the intrinsic ORR activity of Fe-N 4 moieties, delivering a notable turnover frequency (TOF = 17.86 e site –1 s –1 at 0.85 V vs. RHE) that exceeds state-of-the-art Fe-N-C benchmarks by 1–2 orders of magnitude (< 1 e site –1 s –1 ); (2) Ru centers function as electron relays that facilitate ROS scavenging, thus suppressing degradation. This work establishes a paradigm for engineering bimetallic single-atom catalysts through synergistic electronic modulation to concurrently enhance activity and stability.