Modulating the Electrode–Electrolyte Interface with Cationic Surfactants in Carbon Dioxide Reduction

Copper is among the most studied electrocatalyst for CO2 conversion due to its remarkable ability to form high-order carbon products. However, controlling factors that lead to high carbon product selectivity remains a major hurdle to fundamental scientific understanding. In this work, we investigate the utility of cationic surfactants to modify the selectivity of Cu foil in electrocatalytic CO2 reduction (CO2RR). We demonstrate that cetyltrimethylammonium bromide (CTAB) significantly suppresses the hydrogen evolution reaction (HER), a competitive parallel reaction to CO2RR. In addition, high surfactant concentrations and long alkyl chain lengths enhance the selectivity for CO2RR in NaHCO3 solutions. Importantly, electrochemical impedance spectroscopy is used to monitor the evolution of the electrode–electrolyte interface in the presence of CTAB under varying experimental conditions. On the basis of our extensive electrochemical characterization, we propose that cationic surfactants accumulate in the electrochemical double layer and effectively lower the available proton sources for HER. Our approach provides a facile strategy to modify the surface reactivity of metal electrodes with broad implications for electrocatalysis.