Effects of CuO-derived catalysts morphology on carbon dioxide electrochemical reduction in a flow cell

The electrochemical CO2 reduction reaction (e-CO2RR) represents a sustainable approach to convert CO2 into valuable fuels and chemicals using renewable electricity to close the carbon loop and mitigate the climate change. In this scenario, oxide-derived Cu catalysts (i.e., Cu oxides precursor modified by the application of a negative electrochemical bias to perform the CO2 reduction) have emerged as promising materials for the e-CO2RR, demonstrating an enhanced Faradaic Efficiency (FE) toward C-2 products, while significantly suppressing the CH4 formation. In this work, CuO systems were synthesized using different soft-chemistry approaches (i.e., precipitation vs. hydrothermal routes), and characterized through several advanced techniques such as TEM, SEM, XRD, BET analysis, Raman and FT-IR spectroscopies of adsorbed probe molecules. Catalytic performances were determined in terms of FE by monitoring the production of the main CO2 reduction derivatives in a flow cell. By performing a systematic study, it was demonstrated that both starting CuO particles size and morphology represent critical factors determining the C-C coupling reaction, mandatory to obtain C-2 products. In particular, oxide-derived Cu catalysts presenting particles with sheet-like morphology showed superior selectivity for the CO2 conversion into C-2 derivatives (i.e., 50% at 200 mA cm(-2)), with > 40% of C2H4 formation at high production rate (400 mA cm(-2)). Interestingly, both CuO particles size increase and their morphological changes toward either tabular-prismatic or spheroidal shapes determine a substantial drop of the performances accompanied by a rise in the parasite hydrogen evolution reaction (HER).