Promoting CO₂-to-CO Electroreduction via the Active-Site Engineering of Atomically Precise Silver Nanoclusters

Atomically precise metal nanoclusters (NCs) are promising catalysts for the electrochemical CO2 reduction reaction (CO2RR) and are effective model catalysts for the identification of active sites. We report the metal-dependent CO2RR activities of Au25(SR)18 and Ag25(SR)18 (SR = thiolate). While both NCs produced CO as a main CO2RR product, the Au25 NC exhibited a significantly higher CO2RR activity than the Ag25 NC. Theoretical and operando studies revealed that the CO2RR limiting potential for the Au25 NC was significantly smaller than that for the Ag25 NC, while both NCs contained the partially dethiolated metal sites as the active sites. Active-site engineering was performed by replacing the Ag12(SR)18 shell of the Ag25(SR)18 NC with the Au12(SR)18 shell to generate a core–shell AuAg12@Au12(SR)18 NC, which exhibited dramatically enhanced CO2RR activity compared with the Ag25(SR)18 NC. The AuAg12@Au12 NCs exhibited stable CO2-to-CO electroreduction at a commercially relevant current density of 200 mA/cm2 and a full-cell potential of 2.1 V in a zero-gap CO2 electrolyzer.