Co-doped Sr2FeNbO6 as cathode materials for intermediate-temperature solid oxide fuel cells

Sr2Fe1−xCoxNbO6 (0.1 ≤ x ≤ 0.9) (SFCN) oxides with perovskite structure have been developed as the cathode materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs). These materials are synthesized via solid-state reaction and characterized by XRD, SEM, electrical conductivity, AC impedance spectroscopy and DC polarization measurements. The reactivity tests show that the Sr2Fe1−xCoxNbO6 electrodes are chemically compatible with the Zr0.85Y0.15O1.925 (YSZ) and Ce1.9Gd0.1O1.95 (CGO) electrolytes at 1200 °C, and the electrode forms a good contact with the electrolyte after sintering at 1200 °C for 12 h. The total electrical conductivity that has a considerable effect on the electrode properties is determined in a temperature range from 200 °C to 800 °C. The highest conductivity of 5.7 S cm−1 is found for Sr2Fe0.1Co0.9NbO6 at 800 °C in air. The electrochemical performances of these cathode materials are studied using impedance spectroscopy at various temperatures and oxygen partial pressures. Two different kinds of reaction rate-limiting steps exist on the Sr2Fe0.1Co0.9NbO6 electrode, depending on the temperature. The Sr2Fe0.1Co0.9NbO6 electrode on CGO electrolyte exhibits a polarization resistance of 0.74 Ω cm2 at 750 °C in air, which indicates that the Sr2Fe0.1Co0.9NbO6 electrode is a promising cathode material for IT-SOFCs.