Co5.47N loaded N-doped carbon as an efficient bifunctional oxygen electrocatalyst for a Zn–air battery

Abstract

Highly active bifunctional electrocatalysts for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) play a pivotal role in Zn–air batteries. The high cost, scarcity and instability of precious-metal-based electrocatalysts for the ORR and OER dramatically hamper their practical application in such clean-energy set-ups. Here, we report highly active Co_5.47N-loaded N-doped carbon (CoNMC), prepared via the direct NH₃ annealing of a millet–CoCl₂ mixture, which is a cheap and mass-producible form of biomass. The optimized product shows superior ORR activity (a half-wave potential of 0.81 V vs. RHE) and electrochemical stability (a 16.5 mV negative shift of the half-wave potential after 2000 cycles) in alkaline media. Also, it shows appealing OER activity (an operating potential at 10 mA cm⁻² of 1.62 V vs. RHE). This excellent electrochemical performance can be attributed to the formation of active Co_5.47N nanoparticles, the large specific surface area, the abundance of nitrogen active sites, and the high graphitization degree. When assembled into a Zn–air battery, the CoNMC-based cell shows comparable performance to a Pt/C-RuO₂ one.