Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper(I) Oxide Catalysts

The selective electroreduction of carbon dioxide to C2 compounds (ethylene and ethanol) on copper(I) oxide films has been investigated at various electrochemical potentials. Aqueous 0.1 M KHCO3 was used as electrolyte. A remarkable finding is that the faradic yields of ethylene and ethanol can be systematically tuned by changing the thickness of the deposited overlayers. Films 1.7–3.6 μm thick exhibited the best selectivity for these C2 compounds at −0.99 V vs RHE, with faradic efficiencies (FE) of 34–39% for ethylene and 9–16% for ethanol. Less than 1% methane was formed. A high C2H4/CH4 products’ ratio of up to ∼100 could be achieved. Scanning electron microscopy, X-ray diffraction, and in situ Raman spectroscopy revealed that the Cu2O films reduced rapidly and remained as metallic Cu0 particles during the CO2 reduction. The selectivity trends exhibited by the catalysts during CO2 reduction in phosphate buffer, and KHCO3 electrolytes suggest that an increase in local pH at the surface of the electrode i...