Electrochemical Reduction of Carbon Dioxide to Ethane Using Nanostructured Cu2O-Derived Copper Catalyst and Palladium(II) Chloride

A method to facilitate the electrochemical reduction of carbon dioxide (CO2) to ethane (C2H6) was developed. The electrolyte used was aqueous 0.1 M KHCO3. Chronoamperometry, scanning electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, online gas chromatography, and nuclear magnetic resonance spectroscopy were used to characterize the electrochemical system and products formed. Carbon dioxide reduction using a Cu2O-derived copper working electrode gave ethylene (C2H4) and ethanol as main C-2 products, with optimized faradic efficiencies (FE) of 32.1 and 16.4% at -1.0 V vs RHE. The active catalysts were similar to 500 nm-sized crystalline Cu-0 particles, which were formed via the reduction of the Cu2O precursor during the initial phase of the CO, reduction reaction. When palladium(II) chloride was added to the electrolyte, C2H6 formation could be achieved with a significant FE of 30.1% at the said potential. The production of C2H4 was, on the other hand, suppressed to a FE of 3.4%. The alternate use of Pd-0, PdO, or Pd-Al2O3 dopants did not afford the same conversion efficiency. Extensive mechanistic studies demonstrate that C2H4 was first produced from CO, reduction at the Cu-0 sites, followed by hydrogenation to C2H6 with the assistance of adsorbed PdClx. Interestingly, we discover that both Cu and PdClx sites are necessary for the efficient reduction of C2H4 to C2H6. The PdCl2 was "consumed" during the reaction, and a hypothesis for how it contributes to the reduction of CO, to ethane is proposed.