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 C2 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 C2 products. In particular, oxide-derived Cu catalysts presenting particles with sheet-like morphology showed superior selectivity for the CO2 conversion into C2 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).