Low-coordination M-N active sites with high accessibility and efficiency for electrocatalytic O and CO reduction

This review summarizes the methods to construct an efficient M-N 3 site-enriched porous structure with enhancement of the electrochemical accessibility. Compared with intact M-N 4 , the low-coordination M-N 3 with defect-regulated geometry and high-density electronic structure is elaborated based on the recent progress of various electron beam-based techniques. The catalytic mechanism and the underlying structure-activity relationship of atomically dispersed M-N 3 reactive centers for the electrocatalytic oxygen reduction reaction and carbon dioxide reduction are well summarized. Finally, by highlighting the prospects and challenges for the development of defect-based single-atom catalysis, we hope to provide valuable insights for fabricating cost-effective SACs towards energy conversion. The review summarizes developments of low-coordination M-N 3 reactive centers for electrocatalytic CO 2 reduction and O 2 reduction, as well as the underlying structure-activity relationships and catalytic mechanisms.