INTERMEDIATE TEMPERATURE SOLID OXIDE FUEL-CELLS USING A NEW LAGAO3 BASED OXIDE-ION CONDUCTOR - I - DOPED SMCOO3 AS A NEW CATHODE MATERIAL

LaGaO3-based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of oxygen partial pressure. In this st udy, the stability of LaGaO3-based oxide was investigated. The LaGaO3- based oxide was found to be very stable in reducing, oxidizing, and CO 2 atmospheres. Solid oxide fuel cells (SOFCs) using LaGaO3-based perov skite-type oxide as the electrolyte were studied for use in intermedia te-temperature SOFCs. The power-generation characteristics of cells we re strongly affected by the electrodes. Both Ni and LnCoO(3)(Ln:rare e arth) were suitable for use as anode and cathode, respectively. Rare-e arth cations in the Ln site of the Go-based perovskite cathode also ha d a significant effect on the power-generation characteristics. In par ticular, a high power density could be attained in the temperature ran ge 973-1273 K by using a doped SmCoO3 for the cathode. Among the exami ned alkaline earth cations, Sr-doped SmCoO, exhibits the smallest cath odic overpotential resulting in the highest power density. The electri cal conductivity of SmCoO, increased with increasing Sr doped into the Sm site and attained a maximum at Sm0.5Sr0.5CoO1. The cathodic overpo tential and internal resistance of the cell exhibited almost the oppos ite dependence on the amount of doped Sr. Consequently, the power dens ity of the cell was a maximum when Sm0.5Sr0.5CoO3 was used as the cath ode. For this cell, the maximum power density was as high as 0.58 W/cm (2) at 1073 K, even though a 0.5 mm thick electrolyte was used. This s tudy revealed that a LaGaO3-based oxide for electrolyte and a SmCoO3-b ased oxide for the cathode are promising components for SOFCs operatin g at intermediate temperature.