Atomically precise M-N-C electrocatalysts for oxygen reduction: Effects of inter-site distance, metal–metal interaction, coordination environment, and spin states

Inspired by molecular catalysts, researchers developed atomically precise nitrogen-coordinated single or dual metal sites imbedded in graphitized carbon (M-N-C) to fully utilize metallic sites for O₂ activation. These catalysts performed remarkably well in the electrocatalytic oxygen reduction reaction (ORR) due to their distinct coordination and electrical structures. Nonetheless, their maximum efficacy in practical applications has yet to be achieved. This agenda identifies tailoring the coordination environment, spin states, intersite distance, and metal–metal interaction as innovative approaches to regulate the ORR performance of these catalysts. However, it is necessary to undertake a precise assessment of these methodologies and the knowledge obtained to be implemented in the design of future M-N-C catalysts for ORR. Therefore, this review aims to analyze recent progress in M-N-C ORR catalysts, emphasizing their innovative engineering with aspects such as alteration in intersite distance, metal–metal interaction, coordination environment, and spin states. Additionally, we critically discuss how to logically monitor the atomic structure, local coordination, spin, and electronic states of M-N-C catalysts to modulate their ORR activity. We have also highlighted the challenges associated with M-N-C catalysts and proposed suggestions for their future design and fabrication.