Performance of Anode-Supported SOFC Cells Using Thin Electrolyte of Scandia-Doped Zirconia at Intermediate Temperatures

Our recent study on intermediate temperature-operating solid oxide fuel cells (IT-SOFC) are mainly focused on higher performance of single cell at lower operating temperature. We have started the project to develop a 1 kW-class SOFC system for Residential Power Generation (RPG) application. For a 1 kW-class SOFC stack that can be operated at intermediate temperatures, we have developed anode-supported, planar type SOFC to have advantages for commercialization of SOFCs considering mass production and using cost-effective interconnects such as ferritic stainless steels. Single cells with thin electrolyte layer of YSZ and ScSZ, respectively, were fabricated by slurry coating and their performances were investigated. Mixtures of NiO and 8YSZ powders were pressed into rectangular plates of about 13 × 13 cm², which were presintered at 1400°C for 1h. Then the 8YSZ (8mol% Y₂O₃ + ZrO₂) or 10ScSZ (10mol% Sc₂O₃+1mol%CeO₂+ZrO₂) electrolytes dispersed in distilled water were coated on the upper side of anode substrate and co-fired at 1550 or 1500°C for 1h. Thereafter cathode pastes of La_0.78Sr_0.22MnO₃ or (La_0.6Sr_0.4)(Co_1-xFe_x)O₃ were screen-printed on thin electrolytes and heat-treated at 1100°C for 2 h. The size of anode-supported single cells finally sintered was about 10 × 10 cm², and the thickness of the electrolyte and the cathode layer was about 20μm and 30μm respectively. The I-V and AC impedance characteristics of these single cells were evaluated at intermediate temperature (650 ∼ 800°C) by using hydrogen gas as a fuel. The maximum power density of anode-supported cells was 0.5 ∼ 2.0 W/cm² at 750°C and 0.18 ∼ 0.75 W/cm² at 650°C depending on the composition and microstructure of electrolyte/electrodes.