Review—Non-Noble Metal-Based Single-Atom Catalysts for Efficient Electrochemical CO ₂ Reduction Reaction

Single-atom catalysts (SACs), as the name suggests, indicate that only one element participates in the catalytic reaction. The characteristic feature of SACs is that it has immobilized active sites with specific properties, such as unexpected catalytic activity, high product selectivity, and reduced energy barrier. SACs for electrochemical CO ₂ reduction reactions (CO ₂ RR) should have isolated metal atoms acting as active sites to maximize the efficiency of metal use. Conventional metal catalysts with nano-sized metal particles, however, contain a variety of inactive sites showing inferior efficiency of metal use. Therefore, systematic synthesis and analysis of high-efficiency SACs have been an interesting challenge in the CO ₂ RR. To address these issues, many researchers have attempted to synthesize SACs through various methods and employed numerous characterization techniques to identify single atoms and their electrochemical properties. In this review, we discuss recent trends in the synthesis strategies and analyzing techniques of SACs and explain the influence of SACs on electrochemical CO ₂ RR mechanisms of various C1 and C2 products.