Boosting the bifunctional electrocatalytic oxygen activities of CoOx nanoarrays with a porous N-doped carbon coating and their application in Zn-air batteries

The rational structure and composition manipulation for the efficient, affordable bifunctional electrocatalysts of the oxygen evolution reaction (OER) and the oxygen reduction reaction (ORR) is critical for renewable-energy technologies including fuel cells and metal-air batteries. Metal oxide nanoarray electrodes are considered to be alternative options for this issue, although they always suffer from poor conductivity and limited ORR performance in terms of onset potential and diffusion current. In this study, we develop an alternative strategy to prepare a novel bifunctional catalyst by coating threedimensional CoOx nanoarrays with a porous nitrogen-doped carbon layer (NC). The porous NC not only provides a conductive coating to benefit the charge transfer and retains the channels for electrolyte diffusion, but also greatly enhances the electrochemical surface area, which endows the electrode with higher activity for both the OER and ORR in terms of onset potential and diffusion current. When employed as an air cathode in rechargeable zinc-air batteries over 100 cycles, the electrode exhibits durable performance superior to those of Pt/C and IrO2/C. The results fully demonstrate the great potential of the strategy in electrode construction.