MICROSTRUCTURE-PROPERTY RELATIONS OF SOLID OXIDE FUEL-CELL CATHODES AND CURRENT COLLECTORS - CATHODIC POLARIZATION AND OHMIC RESISTANCE

Microstructure, cathodic polarization, and ohmic resistance on the cat hode side of ZrO2-based solid oxide fuel cells have been studied for t he intermediate temperature operation range between 700 and 900 degree s C. Starting powder characteristics, powder calcination temperature, and sintering temperature strongly influence the final microstructure of cathodes. Electrochemical performance depends on these processing p arameters as well as on the cathode thickness and the contact spacing of current collectors. A decrease in effective electrode area occurs b oth on the microscopic level with coarse and inhomogeneous cathode mic rostructure and on the macroscopic level with a wide contact spacing o f the current collectors. The smaller effective electrode area causes inhomogeneous current density distribution and results consequently in higher ohmic losses originating from the electrolyte and higher catho dic polarization. These losses are evaluated using La0.85Sr0.15MnO3 ca thodes with different microstructures and on the ZrO2-8 mole percent Y 2O3 electrolyte. The influence of current path constrictions on the oh mic and nonohmic losses is demonstrated using Pt current collectors of different geometric spacings.