Confined Covalent Organic Framework Anchored Fe Sites Derived Ultra-Uniform Electrocatalysts for Rechargeable Zn-Air Batteries

Abstract

Exploiting clean, highly efficient energy storage and conversion device like Zn-air battery is of significance for alleviation the energy and environmental crises of this society. Metal organic frameworks have been regarded as the ideal templates to synthesis non-noble metal catalysts for a long time. However, the high density of metal nodes always leads to the aggregation of metal nanoparticles during thermolysis transformation process, which greatly hinders the maximizing of electrochemical performances. To improve the dispersity of metal active sites and avoid the heavy aggregation during high temperature pyrolysis, herein, we propose to employ covalent organic framework (COF) to anchor the Fe ions (COF-Fe) and then confine the COF-Fe into the pore of porous g-C3N4. After calcination, the metal nanoparticles highly dispersed Fe-CFN catalysts can be obtained. The optimal Fe-CFN-800 catalysts exhibit excellent ORR and OER performances with the potential difference between ORR and OER of merely 0.723 V. Moreover, experimental way and DFT theoretical calculations were also employed to disclose the reaction mechanism. Finally, the all-solid-state and aqueous Zn-air batteries assembled with the optimized Fe-CFN-800 as cathode present excellent performances with high peak power density (82.85 mW·cm-2; 199.23 mW·cm-2), flexible rate performance, strong discharge stability and long-term charge-discharge cycling performance

Keywords: Covalent organic frameworks, Fe-based composites, Oxygen reduction reaction, oxygen evolution reaction, all-solid-state Zn-air battery, aqueous Zn-air battery