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

The electrochemical CO reduction reaction (CORR) has been widely studied as a promising means to convert anthropogenic CO into valuable chemicals and fuels. In this process, the alkali metal ions present in the electrolyte are known to significantly influence the CORR 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 nanoclusters (NCs). The CORR activity of the synthesized Au(MHA) NCs was compared with that of Au(HT) NCs (HT=1-hexanethiolate). While both NCs selectively produced CO over H, the CO-to-CO conversion activity of the Au(MHA) NCs was significantly higher than that of the Au(HT) NCs when the catholyte pH was higher than the pK of MHA, demonstrating the cation-relaying effect of the anionic terminal group. Mechanistic investigations into the CORR occurring on the Au NCs in the presence of different catholyte cations and concentrations revealed that the CO-to-CO conversion activities of these Au 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.