Recent progress in cobalt-based carbon materials as oxygen electrocatalysts for zinc-air battery applications

Zinc-air batteries (ZABs) have the advantages of low price, environmental friendliness, and high energy density that enables great potential for the application of energy storage devices. Unfortunately, the main limitation of ZABs is the low kinetics of air cathode, including oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), making it necessary to develop catalysts with excellent performance to speed up the reaction rates and improve their efficiency. For these purposes, cobalt-based carbon has the advantages of low cost, high activity, and stability, which are suitable for oxygen electrocatalysts. In this review, the basic mechanisms of ORR and OER electrocatalysis are introduced and analyzed, and the development of cobalt-based carbon materials used as electrocatalysts in ZABs in recent years is reviewed, including cobalt oxide–based carbon, cobalt-nitrogen–doped carbon (Co–N–C), and cobalt bimetallic–based carbon. In addition, we review the use of in situ/in operando characterization techniques applied to trace the catalytic reactions. Finally, we provide an account of the current challenges and future perspectives for the design of new types of high efficiency and bifunctional electrocatalysts.