Electrochemical Reduction of CO_2 using Copper Oxide Nanoparticles supported on Glassy Carbon Electrodes

摘要

We have studied the electrochemical reduction of CO_2 using Cu_2O nanoparticles deposited on planar electrodes. Nanoparticles are prepared in aqueous solution by chemical reduction of CuCl_2 using ascorbic acid with polyethylene glycol surfactant. The particles are then re-suspended in ethanol with added Nafion binder and brush-coated onto glassy carbon substrates. The CO_2 electroreduction activity is measured in KHCO_3 electrolyte under flowing CO_2 using a two-compartment electrochemical cell. Product formation rates are determined using gas chromatography; major gas phase products include CO, H_2, C_2H_4, and CH_4, while liquid phase products include C_2H_5OH and 1-C_3H_5OH. The observed product distribution agrees with results obtained previously using similar Cu_2O particles deposited on carbon fiber paper supports, as well as Cu_2O catalysts prepared by electrodeposition or thermal oxidation. In particular, the catalysts produce a much higher ratio of C_2H_4 to CH_4 than observed using poly-crystalline Cu foil. The potential dependence of the formation rates for hydrocarbon and alcohol products is roughly two times greater than for H_2 and CO formation. Both XRD and SEM measurements confirm the Cu_2O nanoparticles undergo at least partial reduction to Cu metal under CO_2 reduction conditions, accompanied by significant surface morphological changes. Thus the kinetic results are consistent with current models that the increased C_2H_4/CH_4 ratio is due to the presence of a more open atomic structure on the freshly reduced Cu surfaces.