Influence of Copper Sites with Different Coordination on the Adsorption and Electroreduction of CO2 and CO

Mechanistic studies on CO2 and CO electroreduction(CO2R and COR, respectively) usually focus on detectingreactionintermediates and elucidating the first C-C coupling step.Interestingly, the structural sensitivity of the adsorption of CO2 or CO has been largely overlooked, although their adsorptionis the first step of the electrolysis and thus directly impacts theiractivities and selectivities. Herein, we first show, through densityfunctional theory calculations and microkinetic considerations, thatCO(2) adsorption on copper (Cu) is largely enhanced by siteswith low coordination numbers (cn), while the adsorption strengthof CO is fairly constant across surfaces with different cn. This impliesthat the yields of CO2R products would be more enhancedon highly undercoordinated sites, while the yields of COR productswould be similar even on sites with different coordination. To testthis prediction, we prepared two Cu catalysts with different overallroughness/cn and performed CO2R and COR on them from -0.60to -0.85 V vs reversible hydrogen electrode. On the more undercoordinatedCu catalyst, CO2 reduced with an average Faradaic efficiency(FE) that is 13 percentage points higher compared to that of the morecoordinated Cu. In contrast, CO reduced with similar FEs on both catalysts(average difference of 2 percentage points). Our complementing experimentaland computational observations challenge the general view that COis always a better feedstock than CO2 for producing multi-carbonproducts and illustrate the importance of combining suitable feedstocksand Cu sites to optimize the production of high-value chemicals.