Influence of Copper Sites with Different Coordination on the Adsorption and Electroreduction of CO<sub>2</sub> and CO
Futian You, Shibo Xi, Jelynn Jie Ying Ho, Federico Calle‐Vallejo, Boon Siang Yeo
Abstract
Mechanistic studies on CO 2 and CO electroreduction (CO 2 R and COR, respectively) usually focus on detecting reaction intermediates and elucidating the first C–C coupling step. Interestingly, the structural sensitivity of the adsorption of CO 2 or CO has been largely overlooked, although their adsorption is the first step of the electrolysis and thus directly impacts their activities and selectivities. Herein, we first show, through density functional theory calculations and microkinetic considerations, that CO 2 adsorption on copper (Cu) is largely enhanced by sites with low coordination numbers (cn), while the adsorption strength of CO is fairly constant across surfaces with different cn. This implies that the yields of CO 2 R products would be more enhanced on highly undercoordinated sites, while the yields of COR products would be similar even on sites with different coordination. To test this prediction, we prepared two Cu catalysts with different overall roughness/cn and performed CO 2 R and COR on them from −0.60 to −0.85 V vs reversible hydrogen electrode. On the more undercoordinated Cu catalyst, CO 2 reduced with an average Faradaic efficiency (FE) that is 13 percentage points higher compared to that of the more coordinated Cu. In contrast, CO reduced with similar FEs on both catalysts (average difference of 2 percentage points). Our complementing experimental and computational observations challenge the general view that CO is always a better feedstock than CO 2 for producing multi-carbon products and illustrate the importance of combining suitable feedstocks and Cu sites to optimize the production of high-value chemicals.