To achieve carbon neutrality, there is a growing need to effectively utilize carbon dioxide (CO₂), which has become a major societal challenge. Electrochemical CO₂ reduction offers the potential to produce CO₂-free chemicals at room temperature and atmospheric pressure by utilizing surplus renewable electricity. However, while the generation of carbon monoxide (CO), a two-electron reduction product, is straightforward, there are challenges in the selective production of methane (CH₄), an eight-electron reduction product. Therefore, we investigated methods to improve the yield of CH₄ using an Ag-Cu composite electrode. Specifically, we used lithography, a semiconductor fabrication technique, to form a slit-shaped Ag layer on a Cu electrode and investigated the electrochemical CO₂ reduction characteristics in a 0.1 M KHCO₃ solution. The results showed that while only CO was produced on the Ag electrode alone, the Ag-Cu composite electrode exhibited almost no CO production, and the proportion of CH₄ produced was higher than that of the Cu electrode alone. These results suggest a CO spillover phenomenon on the composite electrode. Moving forward, we plan to detect intermediates using in-situ Attenuated Total Reflection (ATR) – Surface-Enhanced Infrared Absorption Spectroscopy (SEIRAS) to identify the reaction pathway.