Developing Catalysts for the Selective Electrochemical Reduction of Carbon Dioxide to C2 and C3 Products

The electrochemical reduction of carbon dioxide (CO₂) to hydrocarbons and alcohols using copper catalysts is a promising way to produce valuable carbon fuels and chemical feedstocks. However, the selectivity for this process is still rather poor. Here, we present our recent efforts to develop Cu-based catalysts for the electroreduction of CO₂ to target molecules such as ethylene, ethanol, and propanol. In the case of CO₂ reduction to ethylene and ethanol, we found that their faradaic yields can be systematically tuned by changing the thickness of the deposited Cu₂O overlayers. 1.7-3.6 μm thick films exhibited the best selectivity for these C₂ compounds at -0.99 V vs. RHE, with faradaic efficiencies 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. We also demonstrate in this presentation the importance of defects in the formation of propanol from CO₂ reduction.

Reference: Ren D, Deng Y, Handoko AD, Chen CS, Malkhandi S and Yeo BS. Selective Electrochemical Reduction of Carbon Dioxide to Ethylene and Ethanol on Copper (I) Oxide Catalysts. ACS Catal. 2015, 5, 2814-2821