Magnetron-Sputtered Bimetallic Cu–Zn Layers on Gas Diffusion Electrodes for Electrochemical CO₂ Conversion

Electrochemical CO₂ reduction is attracting growing interest as a promising method for converting excess carbon dioxide into useful chemical compounds. Copper catalysts are among the few materials capable of producing hydrocarbons and multicarbon products. However, their selectivity is often unstable and strongly dependent on surface structure. The addition of zinc modifies the catalytic properties of copper and, in many cases, improves the distribution of carbon products. In this study, thin Cu-Zn layers prepared by magnetron sputtering were investigated as catalytic coatings for CO₂ electroreduction on gas diffusion electrodes. Composition was determined using XRF. Electrochemical experiments were carried out in a flow reactor using a 1 M KHCO₃ electrolyte with continuous CO₂ supply at current densities from -140 to -200 mA · cm^-2. Gaseous products were analyzed via gas chromatography, while surface morphology and structural changes before and after electrolysis were examined using SEM and XRD. Different Cu/Zn ratios caused noticeable changes in product selectivity, although the trends were not fully linear. Significant amounts of carbon monoxide were observed for all samples. Methane and ethylene formation depended more strongly on catalyst composition and applied current density. The results suggest that zinc alters the local reaction environment near the catalytic surface, affecting the adsorption of intermediate species during CO₂ reduction. Hydrogen evolution remained a major competing reaction. SEM images revealed surface reconstruction after electrochemical operation, consistent with XRD analysis. The study demonstrates that magnetron sputtering provides good control over Cu-Zn catalytic layers for CO₂ electroreduction. Even moderate changes in Zn content influenced gaseous product distribution, indicating that composition tuning in sputtered bimetallic systems may improve hydrocarbon selectivity.