Microstructure and polarization resistance of thermally sprayed composite cathodes for solid oxide fuel cell use

Porous composite cathode coatings containing (La(sub 0.8)Sr(sub 0.2))(sub 0.98)MnO(sub 3) (LSM) and ZrO(sub 2)-12%Y(sub 2)O(sub 3) (YSZ) were prepared by vacuum plasma spraying (VPS) and flame spraying (FS) on prefabricated substrate-based planar solid oxide fuel cells (SOFC) with 60 mm in diameter. Microstructural observations reveal the open porosity of the cathode coatings and prove qualitatively the compositional gradient from YSZ-LSM composite to pure LSM. The electrochemical behavior was investigated by impedance spectroscopy. The results of graded cathodes compared with nongradient and bilayered ones are discussed with respect to the cathodic polarization resistance between 750 and 950°C. Bilayered cathodes indicate the lowest cathodic losses followed by the graded ones and the conventional composite. Flame spraying as a rarely used processing tool for SOFC components can provide cathodes of high electrochemical performance.