Self-Assembled Monolayers on Copper Promote Electrochemical Carbon Dioxide Reduction to Methane

In this study, we demonstrate CO2 electroreduction using self-assembled monolayers (SAMs) of thiols on Cu electrodes, where cooperative catalysis between thiolated and exposed electrode sites drives the reaction. This synergistic catalytic behavior enables methane production with remarkably high Faradaic efficiency, achieving up to 93% using Cu electrodes modified with a SAM of 3-mercapto-1-propanesulfonate. To understand the origin of the high selectivity, we investigated the impact of the sulfonate group in the SAM tail by comparing it with previous studies using Nafion-modified Cu electrodes. Our findings suggest that the hydrophilicity of the SAM significantly affects catalytic selectivity. Hence, we systematically explored various tail functional groups and applied voltages to assess their influence on catalyst performance. Additionally, the SAM linkage remains active under CO2 reduction conditions, maintaining excellent selectivity for methane production after 12 h of continuous operation. Collectively, these insights highlight a straightforward design strategy for developing highly selective CO2 reduction electrocatalysts using SAM-based electrodes.