Boosting the Electroreduction of CO 2 to CO by Ligand Engineering of Gold Nanoclusters.

The electrochemical CO 2 reduction reaction (CO 2 RR) has been widely studied as a promising means to convert anthropogenic CO 2 into valuable chemicals and fuels. In this process, the alkali metal ions present in the electrolyte are known to significantly influence the CO 2 RR activity and selectivity. In this study, we report a strategy for preparing efficient electrocatalysts by introducing a cation-relaying ligand, namely 6-mercaptohexanoic acid (MHA), into atom-precise Au 25 nanoclusters (NCs). The CO 2 RR activity of the synthesized Au 25 (MHA) 18 NCs was compared with that of Au 25 (HT) 18 NCs (HT=1-hexanethiolate). While both NCs selectively produced CO over H 2 , the CO 2 -to-CO conversion activity of the Au 25 (MHA) 18 NCs was significantly higher than that of the Au 25 (HT) 18 NCs when the catholyte pH was higher than the pK a of MHA, demonstrating the cation-relaying effect of the anionic terminal group. Mechanistic investigations into the CO 2 RR occurring on the Au 25 NCs in the presence of different catholyte cations and concentrations revealed that the CO 2 -to-CO conversion activities of these Au 25 NCs increased in the order Li + <Na + <K + <Cs + , and are gated by the cation-coupled electron transfer step. These results were confirmed by the Nernstian shifts of the polarization curves at different cation concentrations.