Importance of Ag-Cu Biphasic Boundaries for Selective Electrochemical Reduction of CO2 to Ethanol

In recent years, electrochemical reduction of carbon dioxide (CO2) has received a great deal of attention due to the potential that this process can mitigate the atmospheric CO2 concentration and produce valuable organic compounds. In particular, Cu and Cu-based catalysts have exhibited the capability of converting CO2 into multicarbon fuels and chemicals in significant quantities. Here, we report a facile and cheap fabrication method for the development of an Ag-incorporated cuprous oxide (Ag-Cu2O) electrode enabling selective synthesis of ethanol via electrochemical CO2 reduction and reveal the key factor improving the ethanol (C2H5OH) selectivity. The incorporation of Ag into Cu2O leads to the suppression of hydrogen (H-2) evolution, and furthermore, by varying the elemental arrangement (phase-separated and phase-blended) of Ag and Cu, we observe that C2H5OH selectivity can be controlled. Consequently, the Faradaic efficiency for C2H5OH on phase-blended Ag-Cu2O (Ag-Cu2OPB) is 3 times higher than that of the Cu2O without Ag dopant. We propose that the electrochemical reaction behavior is not solely associated with a role of Ag dopant, carbon monoxide (CO) leading to an ethanol formation pathway over ethylene, but also the doping pattern related population of Ag-Cu biphasic boundaries relatively suppresses the H-2 evolution reaction and encourages the reaction of mobile CO generated on Ag to a residual intermediate on a Cu site.