Nonprecious bifunctional electrocatalysts for oxygen electrode reactions

The two most crucial reactions in energy storage and conversion systems are oxygen reduction reaction (ORR) and oxygen evolution reaction (OER). However, their sluggish kinetics arise the need for commercially feasible bifunctional electrocatalysts to assist the reaction by improving its kinetics at the same time ensuring durability and also taking cost into account. The fundamentals of the oxygen electrodes are discussed followed by various techniques adopted by researchers to tune the electronic structures of carbon- and transition metal-based nanostructures towards enhanced activity in ORR/OER. Emphasis is placed on correlating catalyst structure/composition with electrocatalytic properties, simultaneously highlighting the persistent challenges. Hence, the review provides an overview on the recent advances in the field of non-precious bifunctional electrocatalysts for oxygen electrode reactions, which will serve as a foundation for their application in various fields including metal–air batteries.