Electrochemical Reduction of CO2 at Functionalized Au Electrodes

Electrochemical reduction of CO2 provides an opportunity to store renewable energy as fuels with much greater energy densities than batteries. Product selectivity of the reduction reaction is known to be a function of the electrolyte and electrode; however, electrodes modified with functional ligands may offer new methods to control selectivity. Here, we report the electrochemical reduction of CO2 at functionalized Au surfaces with three thioltethered ligands: 2-mercaptopropionic acid, 4-pyridinylethanemercaptan, and cysteamine. Remarkably, Au electrodes modified with 4-pyridinylethanemercaptan show a 2-fold increase in Faradaic efficiency and 3-fold increase in formate production relative to Au foil. Conversely, electrodes with 2mercaptopropionic acid ligands show nearly 100% Faradaic efficiency toward the hydrogen evolution reaction, while cysteminemodified electrodes show 2-fold increases in both CO and H-2 production. We propose a proton-induced desorption mechanism associated with pKa of the functionalized ligand as responsible for the dramatic selectivity changes.