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

Abstract

The selective electroreduction of\ncarbon dioxide to C₂ compounds (ethylene and ethanol) on\ncopper­(I) oxide films has been\ninvestigated at various electrochemical potentials. Aqueous 0.1 M\nKHCO₃ was used as electrolyte. A remarkable finding is\nthat the faradic yields of ethylene and ethanol can be systematically\ntuned by changing\nthe thickness of the deposited overlayers. Films 1.7–3.6 μm\nthick exhibited the best selectivity for these C₂ compounds\nat −0.99 V vs RHE, with faradic efficiencies (FE) of 34–39%\nfor ethylene and 9–16% for ethanol. Less than 1% methane was\nformed. A high C₂H₄/CH₄ products’\nratio of up to ∼100 could be achieved. Scanning electron microscopy,\nX-ray diffraction, and in situ Raman spectroscopy revealed that the\nCu₂O films reduced rapidly and remained as metallic Cu⁰ particles during the CO₂ reduction. The selectivity\ntrends exhibited by the catalysts during CO₂ reduction\nin phosphate buffer, and KHCO₃ electrolytes suggest that\nan increase in local pH at the surface of the electrode is not the\nonly factor in enhancing the formation of C₂ products.\nAn optimized surface population of edges and steps on the catalyst\nis also necessary to facilitate the dissociation of CO₂ and the dimerization of the pertinent CH_<i>x</i>O intermediates to ethylene and ethanol.