An Investigation of Active Sites for electrochemical CO2 Reduction Reactions: From In Situ Characterization to Rational Design

The electrochemical carbon dioxide (CO2) reduction reaction (CO2RR) is among the most promising approaches used to transform greenhouse gas into useful fuels and chemicals. However, the reaction suffers from low selectivity, high overpotential, and low reaction rate. Active site identification in the CO2RR is vital for the understanding of the reaction mechanism and the rational development of new electrocatalysts with both high selectivity and stability. Herein, in situ characterization monitoring of active sites during the reaction is summarized and a general understanding of active sites on the various catalysts in the CO2RR, including metal-based catalysts, carbon-based catalysts, and metal-organic frameworks-based electrocatalysts is updated. For each type of electrocatalysts, the reaction pathway and real active sites are proposed based on in situ characterization techniques and theoretical calculations. Finally, the key limitations and challenges observed for the electrochemical fixation of CO2 is presented. It is expected that this review will provide new insights and directions into further scientific development and practical applicability of CO2 electroreduction.