Potential Link between Cu Surface and Selective CO2 Electroreduction: Perspective on Future Electrocatalyst Designs.

Electrochemical reduction of carbon dioxide (CO2 RR) product distribution has been identified to be dependent on various surface factors, including the Cu facet, morphology, chemical states, doping, etc., which can alter the binding strength of key intermediates such as *CO and *OCCO during reduction. Therefore, in-depth knowledge of the Cu catalyst surface and identification of the active species under reaction conditions aid in designing efficient Cu-based electrocatalysts. This progress report categorizes various Cu-based electrocatalysts into four main groups, namely metallic Cu, Cu alloys, Cu compounds (Cu + non-metal), and supported Cu-based catalysts (Cu supported by carbon, metal oxides, or polymers). The detailed mechanisms for the selective CO2 RR are presented, followed by recent relevant developments on the synthetic procedures for preparing Cu and Cu-based nanoparticles. Herein, the potential link between the Cu surface and CO2 RR performance is highlighted, especially in terms of the chemical states, but other significant factors such as defective sites and roughened morphology of catalysts are equally considered during the discussion of current studies of CO2 RR with Cu-based electrocatalysts to fully understand the origin of the significant enhancement toward C2 formation. This report concludes by providing suggestions for future designs of highly selective and stable Cu-based electrocatalysts for CO2 RR.