Enhancement in CO selectivity by modification of ZnO with CuxO for electrochemical reduction of CO2

Abstract

The electrochemical reduction reaction of carbon dioxide (CO2RR) has garnered significant attention due to its potential for the formation of carbon monoxide, which has industrial relevance. Herein, an oxide-derived Cu-Zn electrocatalyst with an optimized CuxO layer that shows high selectivity toward CO with a faradic efficiency of 75% at a low overpotential (-0.8 V vs reversible hydrogen electrode) is reported. Various structural characterizations and activity tests are conducted to understand the origin of this improvement depending on the CuxO amount. Electrochemical surface area and electrochemical impedance spectroscopy measurements suggest that the addition of CuxO increases double-layer capacitance and decreases charge transfer resistance. Scanning electron microscopy images indicate that the electrodes undergo a severe reconstruction process, which is further confirmed by X-ray diffraction that shows the formation of CuZn4 alloy during the reduction reaction. Furthermore, X-ray photoelectron spectroscopy depth profile analysis shows that after CO2RR at -0.8 V, the Cu/Zn ratio is higher than that after -1.2 V, which suggests that applied potential plays a significant role in the reconstruction process and hence the difference in selectivity. The presence of copper in the surface layer has a significant impact on the improvement of selectivity toward CO.