Enhancement in CO Selectivity by Modification of ZnO with Cu_xO for Electrochemical Reduction of CO₂

The electrochemical reduction reaction of carbon dioxide (CO 2 RR) 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 Cu x O 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 Cu x O amount. Electrochemical surface area and electrochemical impedance spectroscopy measurements suggest that the addition of Cu x O 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 CuZn 4 alloy during the reduction reaction. Furthermore, X‐ray photoelectron spectroscopy depth profile analysis shows that after CO 2 RR 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.