Stack Performance of Intermediate Temperature-Operating Solid Oxide Fuel Cells Using Stainless Steel Interconnects and Anode-Supported Single Cells

We are continuing a national project to develop 1 kW-class SOFC system for Residential Power Generation (RPG) application supported by Korean Government. For intermediate temperature operation, we chose anode-supported, planar type SOFC design to have advantages for commercialization of SOFCs considering mass production and using cost-effective interconnects such as ferritic stainless steels. Anode-supported single cells with thin electrolyte layer of YSZ or ScSZ, respectively, were fabricated and their small stacks were built and evaluated. The size of anode-supported single cells finally sintered was about 10 × 10 cm2, and the thickness of electrolyte and the cathode layer was about 20μm and 30μm, respectively. The I-V and AC impedance characteristics of these single cells and small stacks were evaluated at intermediate temperature (650 ∼ 800°C) by using hydrogen gas as a fuel. We have already carried out long-term performance test for YSZ thin electrolyte single cell for above 33,000 h (3.8 years) at 750°C, applying 0.76 V with power density of 200 mW/cm₂. Using these YSZ thin electrolyte 10 × 10 cm₂ cells and Inconel interconnect plates coated by silver paste, the 15-cell and 60-cell short stack were prepared. The initial stack voltage at 150 mW/cm² was 12.5 V in hydrogen as fuel of 120 sccm/cell at 750°C and decreased to about 10.9 V at 500 h operation time. It was then stabilized until 4,000 h with a degradation rate of 10 mV/(1000h, 1 cell). AC impedance of this small stack and microstructure of cell components were analyzed during and after the operation. Furthermore ScSZ thin electrolyte 10 × 10 cm² cells and ferritic stainless steel interconnects were built into a 5-cell stack and the small stack was operated at 650°C for cost-effective planar SOFC RPG system. I-V and AC impedance characteristics of the small stack were evaluated at 650°C by using hydrogen gas or methane gas as fuel.