Study on the Fuel Cell with CeO₂-Based Oxide and Materials for the Oxygen Electrode

Abstract

Ceria-based oxides with high ionic conductivity were investigated for the solid oxide fuel cell. The ionic conductivity of the ceria-samarium oxide system was higher than that of yttria stabilized zirconia and was the highest among the ceria-based oxides (Fig.3). The ceria-samarium oxides were used as the electrolytes of oxygen-hydrogen fuel cell. Althou gh the open circuit voltage of the cell for the ceria-samarium oxide system was low er than that for the zirconia-yttria system, the current density for the ceria-samarium oxide system was higher than that for the zirconia-calcia system at low temperatures. The overall overvoltage of the ceria-samarium oxide fuel cell is caused by the resistance and activation overvoltages (Figs.4 and 5). When the fuel cell is operated at 600-700°C, the output current is largely affected by the electrode material as well as the electrolyte. The perovskite-type, oxide, of La_0.6Sr_0.4CoO₃ exhibited a good performance as an oxygen electrode (Fig.6). The current interruption method revealed that the overvoltage at the oxygen electrode was low for La_0.6Sr_0.4CoO₃ at a small current density, but it was high at a high current density in comparison with Pt electrode (Fig.5). To suppress the reduction near the hydrogen electrode, a thin film of stabilized zirconia was coated on the fuel side of a ceria-samarium oxide disk by theion plating method. The resistance of the fuel cell slightly increased by zirconia coating. However, the fuel cell with zirconia-coated ceria-samarium oxide exhibited a high durability of the cell output and stable open circuit voltage.