Functionally graded cathodes fabricated by sol-gel/slurry coating for honeycomb SOFCs

Functionally graded cathodes for honeycomb solid oxide fuel cells are prepared using sol-gel/slurry coating techniques. The compositions of the cathodes are gradually changed from a material that is active for oxygen reduction and more compatible with the electrolyte (e.g., LSM for YSZ) to another material that is more conductive for current collection. The microstructure and electrochemical properties of the electrodes are systematically characterized using electron microscopy and electrochemical impedance spectroscopy. The cathodic interfacial polarization resistances for a graded cathode fired at 900 °C are 0.21 and 0.10 Ω cm2 at 700 and 800 °C, respectively. The impedance spectra indicate that at least two separate processes contribute to the overall polarization resistances. The effects of cathode fabrication temperature and oxygen partial pressure on the high- and low-frequency impedance responses are studied in detail.