Electronic Modulation of Cobalt Single‐Atom Catalysts via In‐Plane and Axial Coordination Engineering for Enhanced H ₂ O ₂ Electrosynthesis

ABSTRACT Cobalt‐based single‐atom catalysts (Co SACs) have emerged as attractive candidates for promoting the two‐electron oxygen reduction reaction (2e ⁻ ORR) toward efficient H ₂ O ₂ generation. Yet universal strategies to regulate their electronic structure remain limited. Here, we demonstrate that in‐plane and out‐of‐plane heteroatom coordination modulates the Co electronic states, thereby governing 2e ⁻ ORR activity and selectivity. By correlating atom‐induced charge redistribution with H ₂ O ₂ production efficiency, we establish a general design strategy for SACs with tunable performance. Incorporating electron‐withdrawing O or electron‐donating N creates asymmetric Co–N _x O _y –O–C sites, among which Co–N ₅ –O–C is most effective. Its electron‐rich Co center in a distorted pentacoordinate geometry promotes 2e ⁻ ORR, achieving 90% H ₂ O ₂ selectivity and 89.5 A g ⁻¹ in mass activity under 0.65 V versus RHE conditions, outperforming symmetric Co–N ₄ –O–C and electron‐deficient Co–N ₂ O ₂ –O–C. Density functional theory reveals that electron‐donating N in Co–N ₅ broadens the Co dz ² orbital near the Fermi level, weakening *OOH binding, whereas in‐plane O in Co–N ₂ O ₂ withdraws electrons, increasing empty d ‐states and strengthening *OOH adsorption. Under flow‐cell conditions, Co–N ₅ –O–C delivered 15.88 mol g _cat ⁻¹ h ⁻¹ H ₂ O ₂ (300 mA cm ⁻² ) with >88% Faradaic efficiency over 50 h and enabled complete degradation of 50 ppm pollutants within 10 min, demonstrating practical potential for wastewater treatment.