Highly dispersed Co nanoparticles decorated on a N-doped defective carbon nano-framework for a hybrid Na–air battery

Abstract

Efficient and low-cost bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and the oxygen evolution reaction (OER) are of vital importance in energy conversion. Herein, an excellent highly dispersed Co nanoparticle decorated N-doped defective carbon nano-framework (Co–N–C) derived from a ZnCo bimetal organic framework (bi-MOF) is reported. A high specific surface area originating from zinc evaporation facilitates the adsorption and desorption of oxygen, which promotes the accessibility of catalytic sites. The abundant Co–N–C species act as strong bridging bonds between Co nanoparticles and carbon materials which facilitate interfacial electron transfer. Co–N–C-0.5 (0.5 represents the molar ratio of Zn in the initial ZIF-67) exhibits a low overpotential gap of 0.94 V due to the number of active sites (e.g. N-doped defective carbon and the CoN_x/Co composite) and fast interfacial electron transfer. In addition, a hybrid Na–air battery with the Co–N–C-0.5 material displays a low voltage gap of 0.31 V and a high round-trip efficiency of 90.0% at a current density of 0.1 mA cm⁻². More importantly, the hybrid Na–air battery shows fantastic cyclability for charging and discharging due to its stable structure. Our results confirm Co–N–C materials derived from a bi-MOF as alternatives to high-cost Pt/C catalysts for ORR and OER activities in metal–air batteries.