Coupling of metallic Co with atomic Co–N–C as efficient bifunctional oxygen electrocatalyst for rechargeable zinc-air battery

The development of efficient and cost-effective bifunctional oxygen electrocatalysts is critical for advanced rechargeable zinc–air batteries (ZABs). Here, a high-activity hybrid catalyst comprising metallic cobalt nanoparticles coupled with atomically dispersed Co-N_x-C sites embedded in a mesoporous nitrogen-doped carbon matrix (Co@NC-800) is synthesized via controlled pyrolysis of a Co–complex. This unique structure induces electronic modulation that optimizes the adsorption of oxygen intermediates, resulting in exceptional bifunctional activity for both the oxygen reduction reaction (ORR, half-wave potential E_1/2 of 0.91 V) and oxygen evolution reaction (OER, overpotential of 400 mV), with a small reversible oxygen potential gap ΔE of 0.72 V. In addition, electrochemical results and in situ infrared spectroscopy (IR) jointly confirmed that ORR forms water through a more efficient 4-electron ORR process. When applied in ZABs, Co@NC-800 delivers a high peak power density of 244.16 mW∙cm^-2, superior rate capability, and favorable cycling stability over 420 hours with minimal efficiency decay, outperforming Pt/C+IrO₂ (1:1) benchmark. This work highlights the importance of synergistic electronic interactions in non-noble metal hybrid catalysts for ORR/OER bifunction and rechargeable ZABs.