Influence of activating and supporting oxygen in M–N–C electrocatalysts for oxygen reduction.

It has been identified that the oxygen reduction reaction (ORR) is an extremely vital process for sustainable energy supply and sufficient chemical productions. In order to explore noble metal-free catalysts, instead of noble Pt, for ORR to overcome sluggish kinetics, much amazing and interesting research progress has been made in the past decades. Recently, owing to the intrinsic merits of tunable single-atom coordination structures, biomimetic active sites and comparable catalytic activity with Pt, transition metal-nitrogen-carbon (M–N–C) materials have been considered as one of the most promising catalysts toward ORR. Herein, regarding the critical role of activating and supporting oxygen (ASO) in the M–N–C materials toward ORR performances, a comprehensive review of the most recent significant research breakthroughs, remaining challenges and perspectives is timely presented in this work. Firstly, mechanism pathways of ORR catalyzed by M–N–C materials are displayed. Also, for boosting the intrinsic 4 e− /2 e− ORR activity and selectivity, influence of manipulating the microenvironments in the M–N–C catalysts is overviewed at length. Subsequently, the role of ASO in the M–N–C catalysts is systematically summarized. Then, the methods of oxygen identification and introduction are addressed in detail to achieve the M–N–C materials with outstanding electrochemical catalytic performances. Last but not the least, opinions/points of view for remaining challenges of the M–N–C catalysts are given. In closing, future directions of the M–N–C catalysts for ORR and other analogous reactions are proposed. [ABSTRACT FROM AUTHOR]