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 cathode side of ZrO₂-based solid oxide fuel cells have been studied for the intermediate temperature operation range between 700 and 900°C. Starting powder characteristics, powder calcination temperature, and sintering temperature strongly influence the final microstructure of cathodes. Electrochemical performance depends on these processing parameters as well as on the cathode thickness and the contact spacing of current collectors. A decrease in effective electrode area occurs both on the microscopic level with coarse and inhomogeneous cathode microstructure and on the macroscopic level with a wide contact spacing of 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 cathodic polarization. These losses are evaluated using La_0.35Sr_0.15MnO₃ cathodes with different microstructures and on the ZrO₂-8 mole percent Y₂O₃ electrolyte. The influence of current path constrictions on the ohmic and nonohmic losses is demonstrated using Pt current collectors of different geometric spacings.