Superior oxygen electrocatalysts derived from predesigned covalent organic polymers for zinc-air flow batteries

Covalent organic polymers (COPs) as emerging porous materials with ultrahigh hydrothermal stability and well-defined and adjustable architectures have aroused great interest in the electrochemical field. Here, we reported a rational design approach for the preparation of a bifunctional electrocatalyst with the assistance of a predesigned bimetallic covalent organic polymer. With the predesigned nitrogen position and structural features of COP materials, the obtained CCOPTDP-FeNi-SiO2 catalyst affords a remarkable bifunctional performance with a positive half-wave potential (0.89 V vs. reversible hydrogen electrode: RHE, superior to the benchmark Pt/C) for ORR activity, and a low overpotential (0.31 V better than the benchmark IrO2) at 10 mA cm-2 for OER activity in alkaline solution. The potential gap between E1/2 and Ej=10 reaches 0.650 V, in line with that observed in the current state-of-the-art bifunctional oxygen electrode materials. Moreover, a homemade rechargeable Zn-air flow battery using the CCOPTDP-FeNi-SiO2 catalyst as an air cathode exhibits an almost twofold power density (112.8 vs. 64.8 mW cm-2) and a lower charge-discharge voltage gap, compared with a commercialized noble Pt/C + IrO2/C-driven Zn-air flow battery. More importantly, the CCOPTDP-FeNi-SiO2-driven battery maintains a better cycling stability compared to a noble metal-driven battery without performance decay. Accordingly, this work will open up new ways for fabricating practical oxygen electrodes for, but not limited to, metal air based battery applications.