Electrode redox properties of Ba1−xLaxFeO3−δ as cobalt free cathode materials for intermediate-temperature SOFCs

• Cobalt-free Ba1−xLaxFeO3−δ (BLF) was evaluated as candidate cathode for IT-SOFCs.
• The polarization resistance of Ba0.9La0.1FeO3−δ was as low as 0.079 Ω cm2 at 800 °C.
• The thermal expansion coefficients of BLF decreased gradually with La content.

Cobalt-free perovskite oxides Ba1−xLaxFeO3−δ (x = 0.1–0.4) were synthesized by glycine-nitrate combustion method and investigated as a candidate cathode material for intermediate temperature solid oxide fuel cells (IT-SOFCs). Cubic perovskite structure was obtained when 10–20 mol% La was substituted at Ba-site in Ba1−xLaxFeO3−δ, and the crystal structure was transformed from cubic structure into orthorhombic one at x ≥ 0.2 with an addition of lanthanum doping. The thermal expansion coefficients of Ba1−xLaxFeO3−δ oxides decreased gradually with La content due to increasing electrostatic attraction forces. A gradual increase existed in electrical conductivity tendency with La content due to disproportionation of Fe3+ and the larger extent of electron clouds. The electrode redox performance was investigated by electrochemical impedance spectroscopy. Among Ba1−xLaxFeO3−δ series oxides, Ba0.9La0.1FeO3−δ exhibited the best electrochemical performance. The area specific resistance (ASR) of Ba0.9La0.1FeO3−δ was 0.079 Ω cm2, 0.37 Ω cm2, and 2.15 Ω cm2 at 800, 700 and 600 °C under open circuit potential. To investigate electrochemical performances after cathodic polarization, bias potentials were employed on Ba1−xLaxFeO3−δ cathode at 650–800 °C. The results demonstrated the potential applications for Ba0.9La0.1FeO3−δ as cathode materials for IT-SOFCs as a tradeoff between electrochemical and thermal expansion performance.