Morphology Evolution of CuO Supported on CeO₂ and Its Role in Electrochemical CO₂ Reduction

Ceria (CeO₂) is one of the most widely used metal oxides of rare earth metals. Crucially, ceria has synergistic effects with various active metals via strong metal-support interactions. Therefore, it is attracting attention as a catalyst material for the electrochemical CO₂ reduction reaction (eCO₂RR). Cu–ceria composites are known to involve close interactions such as charge transfer between adjacent Cu and Ce atoms, but in-depth studies are needed to utilize the properties at the catalyst interface. In this study, Cu–ceria nanocubes (NCs) are synthesized, and the Cu–ceria NC interface is characterized at each step of the synthetic process. In addition, analysis of ceria nanorods (NRs) is used for comparison to identify how the CuO morphologies at the Cu/ceria interface differ, and the formation mechanism of CuO on ceria at each synthesis step is discussed in detail. Finally, analyses of valence states and interactions through charge transfer at the Cu/ceria interface reveal that Cu in a mixed oxidation state conducive to C₂₊ production is stabilized at the Cu/ceria interface. In the eCO₂RR using Cu–ceria NC, the C₂₊ partial current density is about 32 times higher than that of the corresponding Cu–carbon catalyst.