CO2 electrochemical reduction at thiolate-modified bulk Au electrodes

Abstract

Electrochemical reduction provides an opportunity to convert atmospheric CO₂ to fuels or chemicals using renewable energy. In this work, we demonstrate unexpected influence on the catalytic activity and selectivity of the electrochemical CO₂ reduction reaction (CO₂RR) through the functionalization of Au with thiols. 2-Phenylethanethiol modified Au electrodes (2-PET-Au) show up to a 2-fold enhancement in both Faradaic efficiency and current density for CO evolution, between −0.6 and −0.9 V vs. the reversible hydrogen electrode. Functionalization with 2-mercaptopropionic acid, which has a readily ionized carboxylate group, leads to hydrogen evolution with up to 100% Faradaic efficiency at the expense of CO evolution. Remarkably, the adsorption of certain thiols on Au does not have a negative impact on the total current density compared to blank Au. We present evidence that it is due to ligand-induced reconstruction of Au surfaces resulting in the creation of structurally and chemically modified local reaction environments. Thus a thiol species such as 2-PET, which does not contain any nitrogen-based heterocycle with a charge transfer center, can induce the formation of active sites on Au that are electrochemically active toward CO₂RR within the range of electrode potential that most of the ligand concentration remains stable on Au. Our findings suggest a simple, effective, and tunable way to modify the activity and selectivity of Au electrodes.