|Budget Amount *help
¥3,400,000 (Direct Cost : ¥3,400,000)
Fiscal Year 1998 : ¥500,000 (Direct Cost : ¥500,000)
Fiscal Year 1997 : ¥2,900,000 (Direct Cost : ¥2,900,000)
First of all, we have compared the steady state conventional potentiostatic method with pulsed method in the electrochemical reduction of CO_2. It was found that the faradaic efficiencies for the pulsed electroreduction ofCO_2 to methane and ethylene using copper electrode are higher than those for the potentiostatic reduction and more stable in a long-term electrolysis. In the next study, we have made various electrolysis from copper-based alloys and examined the faradaic efficiencies for methane and ethylene production from CO_2 reduction using pulsed electrolysis in CO_2 saturated 0.1 M KHCO_3 solution at room temperature. Amorphous Cu-Zr and Cu-Tialloy electrodes were prepared using a single-roller melt-spinning method. The sputtering method was applied to prepare Cu-Ag alloys. The amorphous Cu-(30, 40, 60)Zr and Cu-30Ti alloys showed considerably low faradaic efficiencies for methane and ethylene production and both efficiencies were less than 3 %. The sputter-deposited crystalline Cu-Ag alloy electrodes, when the alloys contain small amount of Ag (5-7at%), have a higher faradaic efficiency of methane in comparison with pure Cu electrode. However, excess amount of Ag was detrimental. Although methane and ethylene were not detected on pure Ag electrode, the efficiency of methane increased with the addition of a small amount of Cu but the efficiency was lower than that on pure Cu electrode. Next, gas-diffusion electrodes have been employed as the cathode. The gas-diffusion electrodes have been prepared from sputter-deposited Cu-Ag alloyed powder, carbon black powder and polytetrafluoroethylene dispersion. Thegas-diffusion electrode only made up of carbon black powder produced exclusively hydrogen gas. However, the Cu-Ag alloy powder-loaded gas-diffusion electrodes produced methane and ethylene and the total reduction current density was remarkably high, but their faradaic efficiencies were lower than those on the plate-type alloyelectrodes.