Tuning the Selectivity of the CO ₂ Reduction Reaction by Means of Synergistic Interactions in the Cu, Ag, Ce System

ABSTRACT Multi‐metal catalysts offer opportunities for high activity and selectivity in CO 2 electroreduction (eCO 2 RR) through multiple active sites and synergistic effects; however, achieving high current densities remains challenging. Cu x Ce y Ag z nanoparticles (NPs) were synthesized via a modified solvothermal method, with Cu 9 Ce 9 Ag 1 identified as the optimal composition. This catalyst sustained activity up to −1 A cm −2 and delivered a partial current density of −707.2 mA cm −2 for C 2+ products at an iR‐corrected potential of −0.68 V. Ag promotes high local CO generation, while Ce modulates Cu oxidation states, optimizing Cu─O surface chemistry and *CO speciation to favor C─C coupling. In situ mass spectrometry indicated competitive proton utilization among H 2 , ethylene, and methane, with *CO dimerization governing ethylene production. Operando Raman spectroscopy revealed enhanced *CO coverage, a higher *CO atop /*CO bridge ratio, stable Cu─O species, and increased local pH on Cu 9 Ce 9 Ag 1 NPs, collectively suppressing the hydrogen evolution reaction and accelerating CO 2 RR kinetics. These findings highlight the possibilities to rationally design multi‐metal catalysts to maximize synergetic effects, enabling high C 2+ selectivity at industrially relevant current densities.