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 is not the only factor in enhancing the formation of C₂ products. An optimized surface population of edges and steps on the catalyst is also necessary to facilitate the dissociation of CO₂ and the dimerization of the pertinent CH_xO intermediates to ethylene and ethanol.