Experimental evidence of distinct sites for CO2-to-CO and CO conversion on Cu in the electrochemical CO2 reduction reaction

The electrochemical CO2 reduction reaction on Cu is widely believed to occur via two consecutive and orthogonal reaction steps, that is, CO2-to-CO and CO-to-C2+, on the same sites. Here we provide compelling experimental evidence that challenges these long-held assumptions. We show that the presence of CO2 promotes the electrochemical CO reduction reaction, and there are at least two distinct types of Cu sites, with one (Cu-CO2) more active in the CO2-to-CO conversion and the other (Cu-CO) favouring the further reduction of CO to C2+ products. CO adsorbed on Cu-CO is at least six times more active towards the formation of C2+ products than that on Cu-CO2. Isotopic labelling experiments on Cu(111) and Cu(100) surfaces indicate that Cu-CO2 and Cu-CO probably correspond to Cu(111)-like and defect sites, respectively. These insights highlight the possibility of selectivity control in the CO2 reduction reaction.

Automated summary

The electrochemical CO2 reduction reaction on Cu is believed to occur via two consecutive and orthogonal reaction steps, but we provide experimental evidence challenging this assumption. We show that CO2 promotes the electrochemical CO reduction reaction and there are at least two types of Cu sites, with one being more active in CO2-to-CO conversion and the other favoring further reduction to C2+. CO adsorbed on Cu-CO is more active towards C2+ formation compared to Cu-CO2. Isotopic labelling experiments suggest Cu-CO2 and Cu-CO correspond to Cu(111)-like and defect sites, respectively. These insights suggest the possibility of controlling selectivity in the CO2 reduction reaction.