Concentration Optimization of Localized Cu(0) and Cu(+) on Cu-Based Electrodes for Improving Electrochemical Generation of Ethanol from Carbon Dioxide

Copper-based electrodes can catalyze electroreduction of CO(2) to two-carbon products. However, obtaining a specific product with high efficiency depends on the oxidation state of Cu for the Cu-based materials. In this study, Cu-based electrodes were prepared on fluorinated tin oxide (FTO) using the one-step electrodeposition method. These electrodes were used as efficient electrocatalysts for CO(2) reduction to ethanol. The concentration ratio of Cu(0) and Cu(+) on the electrodes was precisely modulated by adding monoethanolamine (MEA). The results of spectroscopic characterization showed that the concentration ratio of localized Cu(+) and Cu(0) (Cu(+)/Cu(0)) on the Cu-based electrodes was controlled from 1.24/1 to 1.54/1 by regulating the amount of MEA. It was found that the electrode exhibited the best electrochemical efficiency and ethanol production in the CO(2) reduction reaction at the optimal concentration ratio Cu(+)/Cu(0) of 1.42/1. The maximum faradaic efficiencies of ethanol and C(2) were 48% and 77%, respectively, at the potential of −0.6 V vs. a reversible hydrogen electrode (RHE). Furthermore, the optimal concentration ratio of Cu(+)/Cu(0) achieved the balance between Cu(+) and Cu(0) with the most favorable free energy for the formation of *CO intermediate. The stable existence of the *CO intermediate significantly contributed to the formation of the C–C bond for ethanol production.