Mixed electronic-oxide ionic conductor of BaCoO3 doped with La for cathode of intermediate-temperature-operating solid oxide fuel cell

Mixed electronic-oxide ionic conductivity and the cathodic property of BaCoO3 doped with La was investigated in this study for a solid oxide fuel cell (SOFC) operating at intermediate temperature. The electrical conductivity of BaCoO3 increases systematically with increasing amounts of La doped for Ba site. Cathodic overpotential at 1073 K decreased with increasing La content and attained a minimum at X=0.3–0.4 in Ba1−XLaXCoO3. Since the cathodic overpotential of Ba0.6La0.4CoO3 was small at decreased temperature, Ba0.6La0.4CoO3 is the optimum composition for a cathode of intermediate-temperature fuel cells among BaCoO3-based oxides. Mixed conductivity and surface activity for oxygen dissociation was investigated with 18O–16O exchange reaction. It was found that BaCoO3 doped with La exhibits a large oxide ion conductivity and surface activity. When La0.8Sr0.2Ga0.8Mg0.115Co0.05O3 (0.4 mm in thickness) was used as electrolyte, the power density of a cell using Ba0.6La0.4CoO3 for the cathode at 873 K attained a value of 120 mW/cm2, which is slightly larger than that using a conventional Sm0.5Sr0.5CoO3 oxide for the cathode.