Local Single Co Sites at the Second Shell of Fe-N₄ Active Sites to Boost Oxygen Reduction Reaction

Fe single-atom catalysts (SACs) are a promising catalyst for oxygen reduction reaction (ORR) in both Zn–air batteries (ZABs) but have a certain distance to compete with Pt-based catalysts. Rational modulation of the coordination environment in the second coordination shell of SACs offers an opportunity to improve the intrinsic ORR activity, yet a challenge. Here, a novel strategy is reported to construct a dual-metal catalyst by introducing a single Co atom in the second coordination shell of the Fe center. The dual-metal N₃─Fe─N─Co site with a certain Fe─Co distance of 0.312 nm is constructed. It allows for manipulation of the positive shift of the Fe center charge state, driving the d-band center up-shift by 0.63 eV, thereby offering the optimal adsorption of intermediates. Benefiting from this structure, the as-prepared Fe(Co_2nd)-NC enables an excellent ORR activity with a half-wave potential of 0.948 V in 0.1 M KOH. As a cathode in ZABs, it delivered an outstanding peak power density of 218 mW cm⁻² and a specific capacity of 915 mAh g_Zn⁻¹ at 5 mA cm⁻², respectively, with superior long-term durability over 680 h. The second shell layer alignment regulation strategy shows great potential for energy storage applications.