Directly assembling initial metal–organic framework and covalent organic polymer toward bifunctional oxygen electrocatalysts for Zn-air flow battery

Abstract

Developing highly efficient bifunctional oxygen electrocatalysts is important but still remains a challenge for Zn-air flow battery. Metal-organic frameworks (MOFs) and covalent organic polymers (COPs) materials have emerged as promising alternatives to the benchmark precious metal electrocatalysts due to their designable and controllable structures at the atomic level. However, their catalytic performances are limited by the conductivity and catalytic activity using initial materials. Moreover, these materials are generally developed either as single oxygen reduction reaction (ORR) or oxygen evolution reaction (OER) electrocatalysts. Herein, we utilize the π-π stacking effect to directly assemble initial nanosheet FeNi-MOF and iron phthalocyanine rich COP hybrid materials toward the highly efficient bifunctional electrocatalysts via pyrolysis-free strategy. The carbon black is added to the composite as support to limit the stacking of composites and increase the conductivity. The obtained catalyst, named as NSFeNi@COPFe-C, exhibits superior catalytic performance with an ORR onset potential of 0.99 V (vs. reversible hydrogen electrode: RHE), half-wave potential of 0.9 V (vs. RHE), and the OER potential of 1.65 V at 10 mA cm−2 in alkaline electrolyte. The assembled zinc-air flow battery with NSFeNi@COPFe-C as the bifunctional oxygen electrocatalyst shows a discharge power up to 115 mW cm−2 and a long-term stability.