Intermediate temperature solid oxide fuel cells using a new LaGaO₃ based oxide ion conductor

LaGaO₃-based perovskite oxides doped with Sr and Mg exhibit high ionic conductivity over a wide range of oxygen partial pressure. In this study, the stability of LaGaO₃-based oxide was investigated. The LaGaO₃-based oxide was found to be very stable in reducing, oxidizing, and CO₂ atmospheres. Solid oxide fuel cells (SOFCs) using LaGaO₃-based perovskite-type oxide as the electrolyte were studied for use in intermediate-temperature SOFCs. The power-generation characteristics of cells were strongly affected by the electrodes. Both Ni and LnCoO₃ (Ln:rare earth) were suitable for use as anode and cathode, respectively. Rare-earth cations in the Ln site of the Co-based perovskite cathode also had a significant effect on the power-generation characteristics. In particular, a high power density could be attained in the temperature range 973-1273 K by using a doped SmCoO₃ for the cathode. Among the examined alkaline earth cations, Sr-doped SmCoO₃ exhibits the smallest cathodic overpotential resulting in the highest power density. The electrical conductivity of SmCoO₃ increased with increasing Sr doped into the Sm site and attained a maximum at Sm_0.5Sr_0.5CoO₃. The cathodic overpotential and internal resistance of the cell exhibited almost the opposite dependence on the amount of doped Sr. Consequently, the power density of the cell was a maximum when Sm_0.5Sr_0.5CoO₃ was used as the cathode. For this cell, the maximum power density was as high as 0.58 W/cm² at 1073 K, even though a 0.5 mm thick electrolyte was used. This study revealed that a LaGaO₃-based oxide for electrolyte and a SmCoO₃-based oxide for the cathode are promising components for SOFCs operating at intermediate temperature.