Electroreduction of CO2 to C1 and C2 products on dual active sites

• CuS/ZnS nanocomposites with varying compositions enhance CO₂ reduction. • CuS/ZnS (2:1) shows 60 % Faradaic efficiency for C₁ and 20 % for C₂ products. • Achieved −280 mA·cm⁻² current density in flow-cell systems. • CuS-rich composites improve selectivity for multicarbon products. • Provides insights for designing efficient CO₂ conversion catalysts. 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 C 2 products (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 (∼1 Ω·cm²). 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.