Characterization of YSr2Fe3O8 − δ as electrode materials for SOFC

YSr2Fe3O8 − 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). YSr2Fe3O8 − δ crystallizes with tetragonal symmetry in the space group P4/mmm and found to be stable at high temperatures under H2 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 σ745K = 43.5 S cm− 1. The n-type conductivity at low oxygen partial pressure (pO2) changes to p-type at high pO2. 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 cm2 and 0.65 Ω cm2 with GDC and YSZ electrolytes, respectively, in air. Fuel cell measurements with symmetrical electrodes were performed using a thin YSZ electrolyte under H2 at anode and air at cathode, show that the power density is about 0.035 W/cm2 at 900 °C.

Research Highlights
► YSr2Fe3O8-δ has high electronic conduction even at 900 °C.
► Thermal expansion coefficient is very close to the state-of-the art YSZ electrolyte.
► Stable in both oxidizing and reducing atmosphere.
► Suitable to use as symmetrical SOFC electrode materials.