(641a) Characterization of a Prismatic SOFC Stack by AC Impedance Spectroscopy

Impedance spectra of a prismatic solid oxide fuel cell (SOFC) stack, consisting of five (61 cm²) single planar SOFC cells, were obtained at 800°C and varying operating conditions. The contributions of chemical and physical processes occurring on the electrodes and in the electrolyte of the stack to the output cell impedance were determined by equivalent circuit (EC) diagram modeling. The EC diagram was proposed based on our previous investigations on small sized button cells (2 cm²), brushed with reference electrodes. The EC elements were attributed to certain cell processes; its validity was verified by changing stack load current (in the range between OCV and 150 mA/cm²) and anode fuel gas compositions. Combined with previous button cell investigation, our work provides useful information for SOFC scaling up, stack diagnostics and designing process controls.