Asymmetric N/O coordination of bimetallic Fe and Co single-atom pairs to enhance bifunctional efficiency in rechargeable Zn-air batteries

The oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) are fundamental processes in rechargeable metal-air batteries. Fe-N-C and Co-N-C-based catalysts dispersed on carbon supports have demonstrated efficient performance in oxygen electrocatalysis for ORR and OER. However, precise regulation of the coordination environment of metals to enhance the catalytic activity of single-atom catalysts (SACs) remains a significant challenge. Herein, this work reports a bifunctional catalyst featuring an asymmetric N/O-coordinated Fe-Co bimetallic single-atom sites anchored on a high-surface-area, micron-sized carbon sphere (MCC) support. Benefiting from optimized intermediate adsorption energies induced by N/O coordination, as well as large interparticle channels formed by dense packing of microspheres, the prepared FeCo-N₄O₂-C exhibits efficient bifunctional activity and stability for both ORR (E_1/2 = 0.897 V) and OER (E_j=10 = 1.535 V). Moreover, using the FeCo-N₄O₂-C catalyst, the Zn-air battery achieves peak power densities of up to 309.3 mW cm⁻². Advanced characterizations and theoretical studies confirm that FeCo-N₄O₂-C, Fe-N/O-C, and Co-N/O-C can simultaneously serve as key active sites. The fine structure of asymmetric N/O coordination environment induces charge redistribution around the metal centers, thus optimizing the adsorption free energy of intermediates. This work provides a novel and effective strategy for regulating the coordination environment of single-atom catalysts.