The development of efficient and selective catalysts for the carbon dioxide reduction reaction (CO2RR) is crucial for sustainable energy and chemical synthesis. In this work, CeO2-y (y = C (cubic) and R (rod)) was incorporated into Cu2O nanocube electrocatalyst as a promoter for ethylene (C2H4) production. The results demonstrate that the catalyst with a loading of 5 wt% crystalline CeO2-C exhibits competitive activity and stability for ethylene production compared to pristine Cu2O. Under optimized reaction conditions of −250 mA cm−2 current density and 1 M KOH electrolyte, the Cu2O–5CeO2-C catalyst achieved a faradaic efficiency (FE) of ∼53% for C2H4 production, while maintaining stability over a period of 120 minutes. In contrast, non-promoted Cu2O exhibited a lower FE for C2H4 (∼38%) and experienced partial deactivation after 45 minutes. The characterization of the catalysts before and after the reaction revealed that the interaction between Cu2O and CeO2-C creates intrinsic sites (Cux–CeO2−x; Cux = Cu2+, Cu+, and Cu0) for the binding of CO2 and H2O molecules. Moreover, the Cu2O–5CeO2-C catalyst outperforms other reported systems in terms of FE and partial current density for C2H4 production. It requires a lower potential (−0.98 V vs. RHE) to operate at the same electrolyte concentration. This finding highlights the promising nature of Cu2O–5CeO2-C as an efficient and cost-effective catalyst for C2H4 production