Performance of Anode-Supported SOFC Single Cells Using Thin Electrolyte of YSZ and ScSZ at Intermediate Temperatures

Present results on intermediate temperature-operating solid oxide fuel cells (IT-SOFC) are mainly focused to obtain higher performance of single cell at lower operating temperature, especially with planar type. In order to develop a 1 kW-class SOFC system for Residential Power Generation (RPG) application that can be operated at intermediate temperatures, we have developed an anode-supported and planar type SOFC stack using cost-effective interconnects such as ferritic stainless steels. To improve electrical performance of the anode-supported SOFC, cells with alternative electrode or 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, which were pre-sintered at 1400°C for 1 h. Then the 8YSZ (8mol%Y₂O₃+ZrO₂) or 10ScSZ (10mol%Sc₂O₃+1 mol%CeO₂+ZrO₂) electrolytes were coated by slurry coating method on the upper side of anode substrate and cofired at 1550 or 1500°C for an hour. Thereafter, composite cathode pastes of LSM (La_0.7Sr_0.2MnO₃) or LSCF ((La_0.6Sr_0.4)(Co_0.2Fe_0.8)O₃ ) were screen-printed on thin electrolytes and heat-treated at 1100°C for 2 h. The final size of anode-supported single cell sintered was about 5 × 5 cm², and the thickness of the electrolyte and the cathode layer was about 20 μm and 30 μm, respectively. The I-V and AC impedance characteristics of these single cells were evaluated at intermediate temperature (650 ∼ 750°C) using hydrogen gas as a fuel. The maximum power density of anode-supported cell was 0.4 ∼ 1.7 W/cm² at 750°C and 0.12 ∼ 0.55 W/cm² at 650°C depending on the composition and microstructure of electrolyte/electrodes.