Insights into selectivity modulation of electrochemical CO 2 reduction reactions over Cu-based catalysts in terms of the key intermediates

Electrochemical CO2 reduction reaction (CO2RR) is an appealing strategy to alleviate the energy and environment issues caused by CO2 emission, and Cu-based electrodes show great potential in CO2 conversion. The wide product distribution makes Cu fail to be a high-efficiency catalyst for a specific product, and the competition with hydrogen evolution reaction is another critical issue. Various intermediates are involved in the CO2RR processes and some of them act as selective-dependent species, resulting in different products. Identifying the favorable pathways among those furcated from the key intermediates is crucial to target specific products. Herein, the key intermediates and competitive pathways furcated from them are discussed in detail. The *COOH and *OCHO can be formed upon CO2 activation, leading, respectively, to CO and HCOO− production. The *CO intermediate can competitively undergo hydrogenation and C-C coupling to, respectively, form *CHO/*COH and *OCCO. Aldehydes can lead to the formation of alcohols or hydrocarbons. The approaches to modulate the reaction tendency of these key intermediates are reviewed based on the characteristics of each possible pathway. The challenges and perspectives for the mechanism understanding are also discussed.