Recent progress in electrochemical reduction of carbon dioxide on metal single-atom catalysts

Electrochemical reduction reaction of CO2 (CO2RR) is a promising technology for alleviating the global warming caused by the emission of CO2. This technology, however, is still in the stage of finding efficient catalysts. The catalysts must be able to convert CO2 to other carbon-based products with high activity and selectivity to valuable chemicals. In this review, previous development of heteroatom-doped metal-free carbon materials (H-CMs) is briefly summarized. Recent progress of CO2RR promoted by metal single-atom catalysts (M-SACs) is then discussed with emphasis on the synthesis of M-SACs, the catalytic performance, and reaction mechanisms. The high temperature pyrolysis method and electrodeposition are attracting attentions recently to prepare M-SACs with high metal loading on N-doped carbon materials, a very active M-SACs system for the CO2RR. Theoretical calculations of free energy change on active sites, the Operando X-ray absorption near edge structure (XANES), and Bader charge analysis reveal a significant role of metal oxidation state and charge transfer between metal atoms and absorbed CO. The challenges and perspectives for the extensive applications of M-SACs in CO2RR are also discussed in this review.