A Solution-Processable Covalent Organic Polymer for Bifunctional Oxygen Electrocatalysis in Zinc–Air Flow Batteries

Abstract

Rechargeable zinc-air flow batteries (ZAFBs) feature high theoretical energy density, superior safety, and low cost, rendering them promising energy storage devices. However, traditional carbon-based oxygen electrode catalysts struggle to maintain and replicate stable electrode assembly consistency due to thick catalyst layers and an ambiguous M-Nx active site. Herein, a covalent organic polymer bifunctional oxygen catalyst (COP-N-Fe) was rationally designed and synthesized. Upon interaction with hydroxide ions, the stacked COP-N-Fe structure undergoes intercalation and exfoliation, yielding a few-layered COP skeleton. Taking advantage of its distinctive exfoliation behavior in alkaline media, we fabricate an integrated oxygen electrode to replace traditional spray-coated electrodes, which enables efficient bifunctional catalysis toward both the oxygen reduction and oxygen evolution reactions. With peristaltic-pump-driven catalyst circulation, ZAFBs based on integrated COP-N-Fe oxygen electrodes deliver a continuous operation duration of 140 h, outperforming the 100-h stability of state-of-the-art Pt/C and IrO₂ noble metal catalysts. This facile assembly method effectively simplifies electrode fabrication while boosting its operational stability and reproducibility.