Heteroatom doped M–N–C single-atom catalysts for high-efficiency oxygen reduction reaction: regulation of coordination configurations

Abstract

The oxygen reduction reaction (ORR) is the core reaction at the cathode of fuel cells and metal–air batteries. However, the sluggish ORR kinetics leads to insufficient output performance of these energy devices. In recent years, transition metal–nitrogen–carbon single-atom catalysts (M–N–C SACs) have been widely considered as one of the most promising alternatives to Pt-based catalysts. However, the strongly electronegative N and symmetric electron distribution in the common M−N₄ site of M–N–C SACs result in unsatisfactory performance. Recently, heteroatomic doping has been proposed to optimize the electron structure of M–N–C SACs, and has been demonstrated to be an appealing way to enhance the ORR activity by regulation of coordination configurations. Herein, recent advances of heteroatom-doped M–N–C SACs are systematically summarized. Particularly, the regulation of active coordination configurations in heteroatom-doped M–N–C SACs using single dopants (S, B, P, halogen) and dual dopants is discussed in detail with an aim to clarify the structure–property correlations. Finally, the future challenges and research directions of heteroatom-doped M–N–C SACs for the ORR are proposed.