Transition metal-based single-atom catalysts(TM-SACs);rising materials for electrochemical CO2 reduction

The continuous increase of global atmospheric COconcentrations brutally damages our environment. A series of methods have been developed to convert COto valuable fuels and value-added chemicals to maintain the equilibrium of carbon cycles. The electrochemical COreduction reaction(CORR) is one of the promising methods to produce fuels and chemicals, and it could offer sustainable paths to decrease carbon intensity and support renewable energy. Thus, significant research efforts and highly efficient catalysts are essential for converting COinto other valuable chemicals and fuels. Transition metal-based single atoms catalysts(TM-SACs) have recently received much attention and offer outstanding electrochemical applications with high activity and selectivity opportunities. By taking advantage of both heterogeneous and homogeneous catalysts, TM-SACs are the new rising star for electrochemical conversion of COto the value-added product with high selectivity. In recent years, enormous research effort has been made to synthesize different TM-SACs with different M–Nxsites and study the electrochemical conversion of COto CO. This review has discussed the development and characterization of different TMSACs with various catalytic sites, fundamental understanding of the electrochemical process in CORR,intrinsic catalytic activity, and molecular strategics of SACs responsible for CORR. Furthermore, we extensively review previous studies on 1 st-row transition metals TM-SACs(Ni, Co, Fe, Cu, Zn, Sn) and dual-atom catalysts(DACs) utilized for electrochemical COconversions and highlight the opportunities and challenges.