Stabilization of oxidized Cu species via CeO <i>x</i> nano-islands for enhanced CO2 reduction to C2+ products

The presence of oxidized copper species (CuO <i>_x</i> ) on metallic Cu surfaces is widely acknowledged as a critical factor for promoting C-C coupling during the CO₂ reduction reactions (CO₂RR). However, the inherent instability of CuO <i>_x</i> under negative potentials, where it is prone to reduction to metallic Cu, remains a formidable challenge. In this study, we developed a CeO <i>_x</i> -modified CuO catalyst for the CO₂RR, featuring CeO <i>_x</i> uniformly distributed as isolated nano-islands on CuO nanoparticles. Upon reduction of the CuO matrix to metallic Cu, the CeO <i>_x</i> layer effectively stabilizes the interfacial CuO <i>_x</i> , preventing its further reduction. <i>Operando</i> characterization verified the sustained presence of Cu²⁺ and Cu⁺ species at highly reductive potentials, underscoring the role of CeO <i>_x</i> in preserving CuO <i>_x</i> stability. Theoretical calculations revealed that Ce³⁺ enhances the formation energy of oxygen vacancies, stabilizing the CuO <i>_x</i> interface and *OC-CO intermediates, which are crucial for C-C coupling. With this surface modification strategy, the catalyst achieved a remarkable C₂₊ faradaic efficiency of 78% at -700 mA cm^-2, while demonstrating persistent performance with a faradaic efficiency exceeding 70% for C₂₊ products at -100 mA cm^-2 for over 110 h. These findings present an effective strategy for stabilizing metal oxides and advancing durable CO₂RR catalysts.