This thesis focuses on optimizing the catalytic layer for CO2 electroreduction in an acidic medium, integrated into a proton-exchange membrane (PEM) electrolyzer. The aim is to upgrade CO2 by converting it into valuable chemicals, such as carbon monoxide. The acidic environment inherent to PEM electrolyzers helps limit carbonate formation, improving CO2 conversion efficiency. However, CO2 reduction in acidic media competes with the hydrogen evolution reaction, which reduces the selectivity of electroreduction products. This work seeks to develop noble-metal-free catalysts inspired by those used for oxygen reduction in fuel cells, improve the properties of carbon supports, and optimize the design of the catalytic layer, in particular thickness, porosity and hydrophobicity, to maximize CO2 conversion into target molecules. Finally, the active layer will be integrated into a 16 cm² PEM electrolyzer to assess overall performance and gain insights into the mechanisms involved through electrochemical characterization.