Designing superior bifunctional electrocatalyst with high-purity pyrrole-type CoN4 and adjacent metallic cobalt sites for rechargeable Zn-air batteries

Abstract

Developing cost-effective and high-efficient bifunctional electrocatalyst for both oxygen evolution reaction (OER) and oxygen reduction reaction (ORR) is essential for rechargeable Zn-air battery application. However, achieving high-active dual sites for bifunctional oxygen electrocatalysis in a single catalyst, as well as determining the decisive active sites for OER and ORR to explore the synergistically catalytic mechanism remain challenges. Herein, we propose a catalyst consisting of high-purity pyrrole nitrogen anchored cobalt single-atom (CoN4) and adjacent metallic cobalt sites (Cop@CoNC) for explicit research of dominated active sites. The obtained Cop@CoNC exhibits superior electrocatalytic activity with a small overpotential difference of 0.68 V between OER potential at 10 mA cm−2 and ORR half-wave potential, outperforming commercial noble-metal based catalysts. Electrochemical measurements and theoretical simulations verify the pyrrole-type CoN4 and adjacent metallic cobalt are separately decisive active sites for ORR and OER activities. Simultaneously, metallic cobalt regulates electron distribution of CoN4 moiety to improve ORR activity. Importantly, the rechargeable liquid and flexible solid-state Zn-air batteries using Cop@CoNC as air electrode catalysts possess high peak power densities of 188.8 and 121.8 mW cm−2, respectively. Our findings provide a feasible strategy to design high-performance multifunctional catalysts for rechargeable Zn-air batteries application.