Characterization of YSr 2Fe 3O 8 − δ as electrode materials for SOFC

Abstract

YSr 2Fe 3O 8 − δ was prepared by traditional solid state reaction method and characterized by X-ray diffraction, ac impedance, dc conductivity, dilatometry and thermogravimetric analysis for possible use in solid oxide fuel cells (SOFCs). YSr 2Fe 3O 8 − δ crystallizes with tetragonal symmetry in the space group P4/mmm and found to be stable at high temperatures under H 2 and air. Four probe dc electrical conductivity measurements show that the conductivity increases up to 745 K and then decreases with temperature; the highest conductivity σ 745K = 43.5 S cm − 1 . The n-type conductivity at low oxygen partial pressure (pO 2) changes to p-type at high pO 2. Polarization behavior was investigated measuring the ac impedance response in symmetrical cell arrangements in air with YSZ and GDC electrolytes. Cathodic area specific resistance (ASR) varies with firing temperature. The lowest area specific resistance was observed with a GDC electrolyte fired at 1000 °C. In case of YSZ, ASR increases and in case of GDC, ASR decreases in air when electrode firing temperature decreases. At 800 °C ASRs are 0.20 Ω cm 2 and 0.65 Ω cm 2 with GDC and YSZ electrolytes, respectively, in air. Fuel cell measurements with symmetrical electrodes were performed using a thin YSZ electrolyte under H 2 at anode and air at cathode, show that the power density is about 0.035 W/cm 2 at 900 °C.