Functionally graded cathodes for honeycomb solid oxide fuel cells

Functionally graded cathodes were fabricated by slurry coating process for honeycomb solid oxide fuel cells with yttria-stabilized zirconia (YSZ) electrolytes. The cathodes are composed of strontium-doped lanthanum manganate (LSM), gadolinia-doped ceria, and La0.6Sr0.4Co0.2Fe0.8O3 (LSCF). The LSM content was gradually decreased, while the LSCF content was gradually increased with the increasing distance away from the electolyte-electrode interface. Scanning electron microscopy investigation and electrochemical impedance spectroscopy measurements revealed that the electrochemical performance of the graded cathodes depends sensitively on the microstructures that were primarily determined by firing temperatures. The cathodes graded in composition show interfacial resistances about 10 times lower than traditional LSM-YSZ cathodes that have similar microstructures and thickness. The graded cathode fired at low temperature has an interfacial resistance as low as 0.47 Omega cm(2) at 750degreesC, which is very encouraging for developing honeycomb fuel cells operated below 800degreesC. (C) 2002 The Electrochemical Society.