Progress on Bifunctional Carbon-Based Electrocatalysts for Rechargeable Zinc-Air Batteries Based on Voltage Difference Performance

Zinc-air batteries (ZABs) hold potential as clean, cost-effective, and sustainable energy storage system for the next generation. However, the application of ZABs remains challenging because of their poor rechargeability and low efficiency . The design of efficient bifunctional catalysts toward oxygen reduction reaction (ORR) during discharging and the oxygen evolution reaction (OER) during charging is essential to developing rechargeable ZABs. Transition metal (TM)-doped carbon (TM-C) materials stand out from all the available bifunctional catalysts due to the excellent specific surface area, diverse morphological structures , and the multiple metal active sites formed after TM doping. This paper, therefore, focuses on the synthesis, electrochemical properties, and potential mechanism of TM-C catalysts. To make a novelty and logical statement, the voltage difference (Delta E = E-i = 10 - E-1/2) between the ORR/OER catalytic process is employed to categorize different TM-C catalysts reported in recent years, which are divided into two groups: I (Delta E = 0.7 - 0.9 V) and II (Delta E = 0.5 - 0.7 V). The catalytic mechanisms of bifunctional catalysts are clarified. More ways and ideas for synthesizing high-performance bifunctional TM-C catalysts are also provided. Finally, the current problem and prospects of this group materials are presented.