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

The selective electroreduction of carbon dioxide to C-2 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 mu m thick exhibited the best selectivity for these C-2 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 similar 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 Cu-0 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 C-2 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 CHxO intermediates to ethylene and ethanol.