Metal-nitrogen coordination moieties in carbon for effective electrocatalytic reduction of oxygen

Oxygen reduction reaction is a critical process at the cathode of proton-exchange membrane fuel cells and metal-air batteries. Carbon-based single metal atom nanocomposites have emerged as effective alternatives to state-of-the-art platinum catalysts, in which the electrocatalytic activity is attributed largely to the formation of metal-nitrogen coordination moieties (MNx) within the carbon matrix. In this review, we summarize recent progress in the studies of metal and nitrogen codoped carbon as single-atom catalysts toward oxygen reduction reaction within the context of the atomic configuration of the MNx active sites and topologic characteristics of the carbon skeletons and include a perspective of the design and engineering of the nanocomposites for further enhancement of the electrocatalytic activity.