ZIF-derived N-doped carbon nanorods supporting bimetallic CoFe single-atoms/nanoclusters as bifunctional oxygen electrocatalysts for stable Zn-air batteries

High-performance bifunctional oxygen electrocatalysts that simultaneously boost the sluggish oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) need to be developed for advanced rechargeable Zn-air battery applications. In this work, a zeolitic imidazolate framework (ZIF)-phase conversion associated with a subsequent thermal fixing strategy was developed to fabricate bimetallic CoFe single atoms/clusters embedded in N-doped carbon (denoted as CoFe–N–C) nanorods, which can serve as efficient bifunctional ORR/OER electrocatalysts. Microstructural observation and X-ray absorption spectroscopy analysis confirm the co-existence of highly active Co/Fe–N_x dual sites and CoFe alloy nanoclusters. X-ray photoelectron spectroscopy (XPS) results prove that implanting secondary Fe atoms into Co–N–C matrix nanorods can induce electronic redistribution of atomic Co/Fe active sites and generate synergistic effects, which would optimize the adsorption energy of the reaction intermediates and thus enhance the bifunctional ORR/OER activity. The bimetallic CoFe–N–C nanorods exhibit significantly enhanced bifunctional ORR/OER activity and stability than the monometallic Co/Fe–N–C nanorods in alkaline electrolytes in terms of a very positive half-wave potential of 0.90 V (vs. reversible hydrogen electrode (RHE)) for ORR, and an overpotential of 440 mV to reach current density of 10 mA·cm⁻² for OER, yielding a small overpotential gap of 0.77 V. Furthermore, the rechargeable Zn-air batteries using bimetallic CoFe–N–C nanorods as air–cathode catalyst demonstrates peak power density of 200.7 mW·cm⁻² and robust cycling stability of up to 200 h, corresponding to 1200 discharge–charge cycles. Graphical abstract: (Figure presented.).