ALD-Engineered Cu x O Overlayers Transform ZnO Nanorods for Selective Production of CO in Electrochemical CO 2 Reduction.

The electrochemical CO 2 reduction reaction (CO 2 RR) holds tremendous promise as a strategy for lowering atmospheric CO 2 levels and creating new clean energy sources. The conversion of CO 2 RR to CO, in particular, has garnered significant scientific interest due to its industrial feasibility. Within this context, the CuZn-based electrocatalyst presents an attractive alternative to conventional CO-selective electrocatalysts, which are often costly and scarce. Nevertheless, the wide-range utilization of CuZn electrocatalysts requires a more comprehensive understanding of their performance and characteristics. In this study, we synthesized ZnO nanorods through electrodeposition and subsequently coated them with Cu x O overlayers prepared by atomic layer deposition (ALD). Cu x O significantly enhanced CO selectivity, and 88% CO selectivity at a relatively low potential of -0.8 V was obtained on an optimized Cu x O overlayer thickness (Cu x O-250/ZnO). The addition of Cu x O on ZnO was found to dramatically increase the electrochemical surface area (ESCA), lower the charge-transfer resistance ( R ct ), and introduce new active sites in the ε-CuZn 4 phase. Furthermore, electrochemical Raman spectroscopy results showed that the Cu x O-250/ALD electrode developed a ZnO layer on the surface during the CO 2 RR, while the bare ZnO electrode showed no evidence of ZnO during the reaction. These results suggest that the addition of Cu x O by ALD played a crucial role in stabilizing ZnO on the surface. The initial amount of Cu x O was shown to further affect the redeposition of the ZnO layer and hence affect the final composition of the surface. We attribute the improvement in CO selectivity to the introduction of both ε-CuZn 4 and ZnO that developed during the CO 2 RR. Overall, our study provides new insights into the dynamic behavior and surface composition of CuZn electrocatalysts during CO 2 RR.