Recent advances in carbon-supported iron group electrocatalysts for the oxygen reduction reaction

Metal-air batteries are emerging energy devices that have received worldwide attention. The oxygen reduction reaction (ORR) is the key electrochemical process of metal-air batteries. The sluggish nature of ORR kinetics and the high cost of Pt-based ORR catalysts have severely hindered their large-scale application. As earth-abundant elements, the iron group elements have a variety of hybrid orbitals, and their incorporation into the carbon skeleton achieves good ORR catalytic activity, giving them great potential for substituting for Pt-based catalysts. Here, their uses for ORR and the function of each active site in the ORR process are summarized. The relationship between the microstructure and performance of these catalysts may help us fully understand the role of iron group elements in ORR and provide basic insight into the design of cheap catalysts with outstanding ORR catalytic performance in the future.