Research progress of Fe-N-C catalysts for the electrocatalytic oxygen reduction reaction

The oxygen reduction reaction (ORR) is an important half-reaction for various energy devices, such as fuel cells and metal-air batteries. The sluggish kinetics of the four-electron ORR needs the development of electrocatalysts with high efficiency and activity to replace precious metal platinum. Alternatively, metal-nitrogen-carbon catalysts, particularly Fe-N-C, are considered the most promising candidates because their rich active sites can reduce the energy barrier of oxygenic intermediates. In this review, the recent research breakthroughs of Fe-N-C catalysts in theoretical and experimental studies are summarized in detail. First, the mechanistic understanding of the electrocatalytic ORR based on Fe-N-C catalysts is outlined. Then, the design strategies of Fe-N-C catalysts and classifications of active sites are expounded, after which the connection between the active site and catalytic performance is discussed. Subsequently, the application status of Fe-N-C catalysts in polymer membrane fuel cells and zinc-air batteries is described. Finally, the challenges and opportunities of Fe-N-C catalysts regarding controllable synthesis, mechanism, and applications in energy devices are further proposed.