Sub-5 nm Cu Clusters for Efficient CO₂-to-C₂H₄ Conversion: Synergistic Microstructure and Catalytic Microenvironment

The electrochemical CO₂ reduction reaction (CO₂RR) is one of the most promising pathways to achieving carbon neutrality. However, in acidic electrolytes, the CO₂RR tends to suffer from competitive hydrogen evolution side reactions. Alkaline electrolytes are typically employed to suppress side reactions and promote the formation of valuable multicarbon (C₂₊) products (e.g., ethylene(C₂H₄)). In this study, we fabricated surface-loaded copper cluster catalysts with particle sizes below 5 nm by magnetron sputtering and inert gas condensation in combination with cluster beam deposition. This approach enabled precise control over the catalyst surface structure, allowing for in-depth investigation of the synergistic effects between the catalyst microstructure and its catalytic microenvironment. We demonstrate that the Faradaic efficiency (FE) for CO₂-to-C₂H₄ conversion exceeds 50% across a broad current density range of 50 to 180 mA cm^-2 in a flow cell using 1 M KOH electrolyte. Compared with a pristine Cu/PTFE catalyst, the optimized Cu cluster catalyst not only exhibits a significant enhancement in FE_C2H4 but also expands the effective current density range. Furthermore, finite element simulations combined with in situ Raman spectroscopy reveal synergistic interactions among interfacial species (e.g., *CO, OH^-, and K⁺). Therefore, this study proposes a general strategy to regulate the dynamic evolution of catalytic interfaces through an initial nanostructure design, thereby opening a promising avenue for the selective conversion of CO₂ to ethylene.