Electrodeposited Cu-Sn Alloy for Electrochemical CO2 Reduction to CO/HCOO-

Cu-Sn alloy electrodes were prepared by simple electrodeposition method for the electrochemical reduction of CO2 into CO and HCOO-. The alloy electrode surfaces provided good selectivity and efficiency in electrochemical CO2 conversion because they provided appropriate binding energies between the metal and the reactive species obtained through CO2 reduction. Therefore, product selectivity can be modulated by altering the Cu-Sn crystal structure of the electrode. Using the Cu-Sn alloy electrodes, electrochemical reduction was performed at applied potentials ranging from - 0.69 to - 1.09 V vs. reversible hydrogen electrode (RHE). During electrochemical CO2 reduction, all the prepared Cu-Sn alloy electrodes showed prominent suppression of hydrogen evolution. In contrast, Cu87Sn13 has high selectivity for CO formation at all the applied potentials, with maximum faradaic efficiency (FE) of 60% for CO at - 0.99 V vs. RHE. On the other hand, Cu55Sn45 obtained a similar selectivity for electrodeposition of Sn, with FE of 90% at - 1.09 V vs. RHE. Surface characterization results showed that the crystal structure of Cu87Sn13 comprised solid solutions that play an important role in increasing the selectivity for CO formation. Additionally, it suggests that the selectivity for HCOO- formation is affected by the surface oxidation state of Sn rather than by crystal structures like intermetallic compounds.