Low-coordination M-N₃ active sites with high accessibility and efficiency for electrocatalytic O₂ and CO₂ 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.