| Budget Amount *help |
¥1,600,000 (Direct Cost: ¥1,600,000)
Fiscal Year 1991: ¥300,000 (Direct Cost: ¥300,000)
Fiscal Year 1990: ¥1,300,000 (Direct Cost: ¥1,300,000)
|
|---|
| Research Abstract |
The feasibility of electrochemical reduction of carbon dioxide by use of a gas-phase electrochemical system with oxyaen-conducting solid oxide electrolyte/electrode interface has been demonstrated.
The electrolyte/electrode interface behavior for the reduction of CO_2 was investigated by means of d. c. and a. c. measurements in solid oxide electrolyte cells possessing the general configurations
CO_2, CO_2-H_2O or CO_2-H_2, Metal (Pt, Ag, and Ni) /Y_2O_3 stabilized ZrO_2 (YSZ) /Pt, O_2 (air), and CO_2, CO_2-H_2O, La_<0.5>MO_3 (M : Ni, Co, and Mn) /Y_2O_3 stabilized ZrO_2 (YSZ) /Pt, O_<> (air).
The electrode process and the product distribution are dictated primarily by the nature of electrode interface and the gas atmosphere. The reduction of CO_2 involves both an intrinsic and an electrochemical catalytic reaction. The La_<0.5>Sr_<0.5>MO_3 electrode prepared by the thermal decomposition method employing the ultrasonic technique improved the current and the efficiency of reaction products as compared to the elemental electrode of Pt and Ag. The principal product was CO whose current efficiency reached above 90% in the CO_2 atmosphere. In the CO_2-H_<>0 gas atmosphere, formation of CH_4 in addition to CO was observed on all electrodes examined, although the efficiency was mainly very low. The stability of cells was discussed in terms of the breakdown potentials due to a rapid decrease of electrolyte resistance induced by partial electronic conduction. The La_<0.5>Sr_<0.5>MO_3/YSZ system in the CO_2-H_2O gas atmosphere showed the higher stability than that of the other-electrode/YSZ systems. The effects of electrode/electrolyte interface on the electrode process have been investigated by electrochemical impedance spectroscopy. The principal polarization processes are observed in the complex impedance plots for the interfaces ; kinetic control, transport impedances by the influence of surface inhomogeneties or roughness, and electrolyte resistance.
|
