Fabrication of copper-based electrodes for the electrosynthesis of valuable products from carbon dioxide

The electrochemical reduction of carbon dioxide (CO2RR) has emerged as a promising approach to mitigate greenhouse gas emissions while simultaneously producing value-added chemicals and fuels. Among the various conversion strategies, electrochemical conversion stands out as inherently advantageous, as it can directly integrate electricity generated from renewable sources while operating under mild reaction conditions. However, the stability of the CO2 molecule requires efficient electrocatalysts to lower its activation barrier and guide the reaction toward selective products. Copper (Cu) has attracted significant interest due to its unique ability to catalyze the formation of hydrocarbons and oxygenates, while silver (Ag) is known for its high selectivity toward carbon monoxide. Combining these two elements in bimetallic systems represents a potential strategy to enhance the activity and selectivity for the CO2RR. In this thesis work, electrodeposition was selected as the synthesis method, to fabricate free standing gas diffusion electrodes (GDEs) by directly depositing the Cu catalyst onto the substrate. Gas diffusion layer (GDL) carbon paper was employed as conductive and porous substrate for the preparation of the electrodes. Galvanic displacement with silver sulfate was carried out to fabricate Cu-Ag bimetallic GDEs starting from the Cu-based ones. The fabricated GDEs were characterized with field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDS) and X-ray diffraction (XRD), to determine their morphology, surface coverage crystalline phases and elemental composition. The results demonstrated that the electrodeposition technique provides good surface coverage and adjustable particle size, while the Ag displacement modifies the surface composition by replacing the outermost Cu atoms. For the electrochemical characterization, the synthesized GDEs were integrated into a membrane electron assembly (MEA) cell setup. Various measurements have been performed, including linear sweep voltammetry (LSV), chronopotentiometry (CP) and electrochemical impedance spectroscopy (EIS). The reaction products were analyzed in both the gas phase, using gas chromatography (GC), and the liquid phase, using high-performance liquid chromatography (HPLC). By estimating the faradaic efficiencies, it was observed that both materials exhibited good selectivity toward ethylene (C2H4) and ethanol (CH3CH2OH), which are high-valuable chemicals, however the bimetallic GDEs did not show significant performance difference compared to their monometallic counterparts. This study underlines the potential of cost-effective preparation methods such as electrodeposition for producing Cu-based GDEs for the CO2RR, while galvanic Ag displacement has hesitated to express its potential and requires further investigations. These findings contribute to the ongoing effort to develop scalable and efficient solutions for the CO2 electrochemical conversion, with the hope of moving toward a sustainable world.