Abstract: Electrochemical CO2 reduction (eCO2RR) is a promising method for transforming CO2 emissions into useful multicarbon products. This study involved the synthesis and evaluation of CuS/ZnS nanocomposites with varying compositions (CuS: ZnS = 1:1, 2:1, and 1:2) in both H-type and flow-cell electrolyzers. The catalyst with a 2:1 CuS/ZnS ratio (S2) exhibited excellent performance, with a Faradaic efficiency (FE) of 60 % for C1 products and approximately 20 % for C2products (C2H4) at a current density of -280 mA·cm-2 in the flow-cell configuration. The flow-cell arrangement significantly enhanced catalytic activity, suppressed hydrogen evolution, and increased selectivity for CH4 and C2H4 at greater negative potentials. Augmented ethylene production was ascribed to Cu-rich active sites promoting efficient C-C coupling and increased CO2 accessibility at gas diffusion electrodes (GDEs), corroborated by low charge-transfer resistance. This work emphasizes the pivotal importance of catalyst composition and reactor design, showcasing the 2:1 CuS/ZnS catalyst in a flow-cell format as a scalable and effective method for sustainable CO2 conversion to multicarbon fuels. Density functional theory (DFT) calculations further validated the experimental results by revealing favorable adsorption energies and interactions between the CuS/ZnS catalyst and key intermediates in the CO2 conversion process.

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