Promoting CO 2 -to-CO Electroreduction via the Active-Site Engineering of Atomically Precise Silver Nanoclusters

Atomically precise metal nanoclusters (NCs) are promising catalysts for the electrochemical CO 2 reduction reaction (CO 2 RR) and are effective model catalysts for the identification of active sites. We report the metal-dependent CO 2 RR activities of Au 25 (SR) 18 and Ag 25 (SR) 18 (SR = thiolate). While both NCs produced CO as a main CO 2 RR product, the Au 25 NC exhibited a significantly higher CO 2 RR activity than the Ag 25 NC. Theoretical and operando studies revealed that the CO 2 RR limiting potential for the Au 25 NC was significantly smaller than that for the Ag 25 NC, while both NCs contained the partially dethiolated metal sites as the active sites. Active-site engineering was performed by replacing the Ag 12 (SR) 18 shell of the Ag 25 (SR) 18 NC with the Au 12 (SR) 18 shell to generate a core–shell AuAg 12 @Au 12 (SR) 18 NC, which exhibited dramatically enhanced CO 2 RR activity compared with the Ag 25 (SR) 18 NC. The AuAg 12 @Au 12 NCs exhibited stable CO 2 -to-CO electroreduction at a commercially relevant current density of 200 mA/cm 2 and a full-cell potential of 2.1 V in a zero-gap CO 2 electrolyzer.