Ethanol formation via CO2 electroreduction at low overvoltage over exposed (111) plane of CuO thin film

In this study, we fabricated CuO thin films using the sol-gel spin coating method. The fabricated thin films were utilized for electrocatalytic reduction of CO<inf>2</inf> (CO<inf>2</inf>ER). Fabrication of thin film is vital to provide a large surface area and a more exposed (111) crystal plane for ethanol selectivity. This is verified by comparing it with bulk powder material which does not give such activity. CO<inf>2</inf>ER over thin film electrode specifically forms CO(g) and Ethanol(l), 2 and 12 electron reduction products, and eliminates the possibility of unwanted HER as a side reaction in the CO<inf>2</inf> saturated NaHCO<inf>3</inf> electrolyte. We achieved significant product selectivity and faradaic efficiency, utilizing the very low potential for both CO and ethanol. Specific formation of only CO and ethanol makes the process efficient as the separation of gas and liquid is easy. Results based on density functional theory calculations suggest that CuO (111) and CuO (-111) surfaces promote CO<inf>2</inf> adsorption and subsequent formation of CO. However, a direct CO-dimerization is observed only on the CuO (111) surface that facilitates the formation of ethanol as the C2 product. This comparative study of bulk and thin-film opens new insight and highlights the importance of catalyst fabrication for the specific product formation utilizing significantly less energy.