A pH universal ORR catalyst with core-shell ZIF-derived binary cobalt/iron sites for Zn-air batteries

Developing high-efficiency non-precious metal catalysts is essential for the oxygen reduction reaction (ORR). Herein, Co, Fe bimetallic nitrogen-doped carbon core–shell catalyst Co@Fe-NC-4 is prepared by double-layer ZIF strategy. The Co@Fe-NC-4 catalyst displays outstanding ORR activity across a broad pH range, particularly under neutral conditions, where it reaches a half-wave potential of 0.756 V. This value exceeds the performance of most previously studied non-precious metal catalysts as well as traditional Pt/C catalysts. Its catalytic efficiency is comparable to that of Pt/C under both alkaline and acidic conditions. This remarkable efficiency under different pH conditions is likely due to the cooperative effect between the metal ions in the catalyst, the core–shell structure that minimizes the aggregation of metal atoms, and excellent electron/proton transport capacity due to its abundance of defects and hierarchical porous features. Co@Fe-NC-4 has a direct four-electron transfer pathway and good stability in alkaline, neutral, and acidic media. Alkaline zinc-air batteries utilizing Co@Fe-NC-4 as the cathode achieve outstanding performance, with open-circuit voltages up to 1.50 V and peak power outputs of 126.9 mW cm⁻². Moreover, neutral liquid zinc-air batteries also exhibit excellent performance.