Preparation and evaluation of Ca _3-xBi _xCo ₄O _9-δ (0< x ≤ 0.5) as novel cathodes for intermediate temperature-solid oxide fuel cells

The misfit compounds Ca _3-xBi _xCo ₄O _9-δ (x = 0.1-0.5) were successfully synthesized via conventional solid state reaction and evaluated as cathode materials for intermediate temperature-solid oxide fuel cells. The powders were characterized by X-ray diffraction, scanning emission microscopy, X-ray photoelectron spectroscopy, thermogravimetry analysis and oxygen-temperature programmed desorption. The monoclinic Ca _3-xBi _xCo ₄O _9-δ powders exhibit good thermal stability and chemical compatibility with Ce _0.8Sm _0.2O _2-γ electrolyte. Among the investigated single-phase samples, Ca _2.9Bi _0.1Co ₄O _9-δ shows the maximal conductivity of 655.9 S cm ^-1 and higher catalytic activity compared with other Ca _3-xBi _xCo ₄O _9-δ compositions. Ca _2.9Bi _0.1Co ₄O _9-δ also shows the best cathodic performance and its cathode polarization resistance can be further decreased by incorporating 30 wt.% Ce _0.8Sm _0.2O _2-γ. The maximal power densities of the NiO/Ce _0.8Sm _0.2O _2-γ anode-supported button cells fabricated with the Ce _0.8Sm _0.2O _2-γ electrolyte and Ca _2.9Bi _0.1Co ₄O _9-δ + 30 wt.% Ce _0.8Sm _0.2O _2-γ cathode reach 430 and 320 mW cm ^-2 at 700 and 650°C respectively.