In situ encapsulation of Co-based nanoparticles into nitrogen-doped carbon nanotubes-modified reduced graphene oxide as an air cathode for high-performance Zn–air batteries

Abstract

Exploring highly efficient catalysts for the oxygen reduction/evolution reaction (ORR/OER) is very important in rechargeable Zn–air batteries. N-doped carbon coupled with transition metal-based species are among the most promising cathode catalysts for Zn–air batteries. However, the aggregation of metal-based sites during the synthetic/cycling process is a serious drawback of these catalysts. Herein, in situ encapsulation of ultra-small Co/Co₄N nanoparticles into N-doping carbon nanotubes (N-CNTs) anchored on reduced GO (Co/Co₄N@N-CNTs/rGO) has been achieved through pyrolyzing a core–shell-structured ZIF-8@ZIF-67-modified GO (ZIF-8@ZIF-67/GO) precursor; the nanoparticles have been further applied as a bifunctional catalyst in Zn–air batteries. Benefitting from its uniform dispersion of Co-based particles, close contact of Co/Co₄N species and N-CNTs, and high N content, Co/Co₄N@N-CNTs/rGO shows outstanding catalytic activity/stability towards ORR and OER. Moreover, Zn volatilization and rGO introduction in Co/Co₄N@N-CNTs/rGO can effectively promote the reactions of Zn–air cells. Hence, the Co/Co₄N@N-CNTs/rGO-based conventional Zn–air battery exhibits a fantastic specific capacity of 783 mA h g_Zn⁻¹, a continuous discharge platform over 6 days, a high-power density of ∼200 mW cm⁻² and an ultra-long cycling life of 440 h with a small overpotential of ∼0.8 V. Moreover, a flexible Co/Co₄N@N-CNTs/rGO-based Zn–air cell was also designed and revealed outstanding mechanical flexibility and good electrochemical performance, which suggests its potential application prospects in wearable electronic devices.