Continuous-Flow Microfluidic Synthesis Enhances C2+Selectivity for Cu2 O Catalysts

The electrochemical reduction of CO2 to multicarbon (C2+ ) products offers a promising pathway to replace fossil fuels in thechemical and transportation sectors. However, achieving high C2+ selectivity requires precisely engineered structures, which,in turn, necessitate advanced synthetic strategies and in situ characterization. Herein, we leverage microfluidic technologies torationally design and synthesize Cu 2 O nanoparticles with tunable features under laminar flow conditions, thereby providing apreviously inaccessible level of control over catalyst structure. By tuning flow parameters within the microfluidic platform, weprecisely regulate the reaction-diffusion interface, enabling fine control over nanoparticle size, morphology, and defect density.The resulting Cu 2 O nanoparticles exhibit a high defect density and intrinsic nanoporosity, two properties known to enhanceC2+ selectivity during CO2 electroreduction. In contrast, Cu 2 O nanoparticles synthesized via conventional batch methods underidentical stoichiometric conditions exhibit larger pore sizes, lower defect densities, and lower C 2+ selectivity. Using in situ liquid-phase transmission electron microscopy and operando X-ray absorption spectroscopy, we further elucidate the evolution of bothcatalyst systems. Finally, we demonstrate that surface modification with polyaromatic films further promotes C 2+ formation. Thiswork highlights microfluidic synthesis as a powerful platform for designing advanced electrocatalysts with tunable structuralfeatures and enhanced CO2 conversion performance to C2+ products.