Recent progress in heteroatom doping to modulate the coordination environment of M–N–C catalysts for the oxygen reduction reaction

Abstract

The development of highly catalytic performance, low-cost, and durable electrocatalysis for the oxygen reduction reaction (ORR) is important to facilitate the commercial applications of fuel cells and metal–air batteries. In recent years, single-atom catalysts, especially non-precious metal–nitrogen–carbon (M–N–C) catalysts, have exhibited great potential in ORR due to their unique coordination structures, abundant raw material sources, and high atomic utilization. However, the N atom adjacent to the central metal atom in the plane M–N₄ molecule exhibited a strong electronegativity, leading to a limitation of the intrinsic activity of the M–N–C catalysts. To address the insufficient intrinsic activity of M–N–C catalysts, many studies have pointed out that the improved ORR catalytic activity can be achieved by adjusting the coordination environment and electronic structure of the central metal atom through heteroatom (O, N, B, P, and S) doping. In this review, a series of representative recent research results on the role of heteroatoms in modulating the coordination configuration and electronic structure of M–N–C catalysts are presented. Combining advanced characterization technologies and density functional theory calculations, the effects of heteroatom doping on the microstructure and catalytic activity of M–N–C catalysts are systematically elucidated from three aspects: coordinated atoms, environmental atoms and axial coordinated atoms. Furthermore, the applications of heteroatom-doped M–N–C catalysts in fuel cells and Zn–air batteries are briefly reviewed. Finally, the challenges and prospects for the future development of heteroatom-doped M–N–C catalysts for ORR are discussed.