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.