Cop/CoFe-NC@MWCNTs as a bifunctional electrocatalyst for rechargeable zinc-air batteries.

Designing low-cost, high-performance bifunctional electrocatalysts for the oxygen reduction and evolution reactions (ORR/OER) is critical for advancing rechargeable zinc-air batteries (ZABs); however, simultaneously optimizing both reactions within a single material system remains a significant challenge. Herein, a Cop/CoFe-NC@MWCNT catalyst is constructed by integrating multi-metal active sites into a conductive multi-walled carbon nanotube (MWCNT) network. Outperforming the commercial Pt/C and RuO2 benchmarks, the Cop/CoFe-NC@MWCNT catalyst delivers an ORR half-wave potential of 0.855 V and an OER overpotential of 310 mV at 10 mA cm-2 under alkaline conditions. The evolution of the active sites during both reactions is tracked by in situ Raman spectroscopy, providing mechanistic insights into the ORR and OER pathways. When assembled into ZABs, the Cop/CoFe-NC@MWCNT catalyst achieves peak power densities of 164.1 and 77.15 mW cm-2 in liquid and flexible configurations, respectively, with the liquid cell delivering a specific capacity of 688.37 mAh g-1 and the flexible device retaining exceptional stability over 48 h. At a current density of 5 mA cm-2, the Cop/CoFe-NC@MWCNT electrodes achieved a round-trip efficiency of 42.6%, higher than the 38.7% recorded for the benchmark Pt/C + RuO2. This work establishes an effective strategy for developing highly active bifunctional electrocatalysts using non-noble bifunctional electrocatalysts.