An electrochemical device for the reduction of CO2 back to liquid fuels is here presented. The key of this novel electrocatalytic approach is the design and development of the gas diffusion membrane (GDM), which is obtained by assembling (i) a proton selective membrane (Nafion), (ii) a nanocomposite electrocatalyst based on metal-doped conjugated microporous polymer (CMP) and (iii) a C-based support working as the gas diffusion layer. CMP is a very attractive material able to adsorb CO2 selectively with respect to other gases (such as H2, O2, N2, etc.), also in mild conditions (r.t. and atmospheric pressure). Particularly, tetrakis-phenylethene conjugated microporous polymer (TPE-CMP) was synthesized through Yamamoto homo-coupling reaction. TPE-CMP was modified by depositing noble (Pt) and non-noble (Fe) metal nanoparticles to create the active catalytic sites for the process of CO2 reduction directly on the polymer surface where CO2 is adsorbed. The metal-doped TPE-CMP electrocatalysts were fully characterized by infrared spectroscopy (IR), thermo-gravimetric analysis (TGA) and transmission electron microscopy (TEM). Then, the as-assembled GDM was tested in our homemade semi-continuous three-electrode electrochemical cell working in gas phase at 60 °C, coupled with a cold trap for the accumulation of the liquid products. Results showed the better performances of the metal-doped TPE-CMP in terms of total productivity (C1-C8 oxygenates) with respect to other kinds of materials that do not show high CO2 adsorption capacity.