Dissecting Critical Factors for Electrochemical CO 2 Reduction on Atomically Precise Au Nanoclusters.

This work investigates the critical factors impacting electrochemical CO reduction reaction (CO RR) using atomically precise Au nanoclusters (NCs) as electrocatalysts. First, the influence of size on CO RR is studied by precisely controlling NC size in the 1-2.5 nm regime. We find that the electrocatalytic CO partial current density increases for smaller NCs, but the CO Faradaic efficiency (FE) is not directly associated with the NC size. This indicates that the surface-to-volume ratio, i.e. the population of active sites, is the dominant factor for determining the catalytic activity, but the selectivity is not directly impacted by size. Second, we compare the CO RR performance of Au isomers (Au Q and Au T) to reveal that structural rearrangement of identical size NCs can lead to significant changes in both CO RR activity and selectivity. Au Q shows higher activity and selectivity towards CO than Au T, and density functional theory (DFT) calculations reveal that the average formation energy of the key *COOH intermediate on the proposed active sites is significantly lower on Au Q than Au T. These results demonstrate how the structural isomerism can impact stabilization of reaction intermediates as well as the overall CO RR performance of identical size Au NCs. Overall, this work provides important structure-property relationships for tailoring the NCs for CO RR.