Electrodeposition of Cu-Cu2O composite films of adjustable band structure for photoelectrochemical conversion of carbon dioxide to hydrocarbons

The electrodeposited Cu-Cu₂O composite films were investigated in terms of their selectivity, efficiency, and stability in the electrochemical and photoelectrochemical conversion of CO₂ to hydrocarbons. Composite films were deposited at various potentials from an alkaline copper(II) lactate solution. The influence of electrode potential on the structure, morphology, and location of the valence and conduction bands was investigated. Finally, the catalytic activity of the materials was investigated in the dark and under illumination at various potentials in a CO₂-saturated KHCO₃ solution. Gas chromatography analysis indicated that maximum concentrations of CH₄ and C₂H₄ were observed under illumination and amounted to 13.37 and 8.99%, respectively. The highest Faradaic efficiencies for ethylene formation were observed at −0.893 V vs. RHE, while for methane at −0.893 V or 0.993 V, depending on the applied deposition potential. Performed studies indicated that at even relatively low conversion potentials, Cu₂O may not be fully reduced to metallic copper and therefore affects the mechanism and kinetics of electrode reactions. Moreover, reported results indicated possibilities for controlling the selectivity toward the formation of hydrocarbons through proper selection of the composite synthesis conditions and conversion parameters as well.