DEPOSITION AND ELECTRICAL-PROPERTIES OF THIN POROUS CERAMIC ELECTRODE LAYERS FOR SOLID OXIDE FUEL-CELL APPLICATION

The influence of the microstructure on the electrical properties and polarization behavior of thin porous ceramic electrode layers used in solid oxide fuel cells has been investigated. Thin layers (2-10-mu-m) of the cathode material Sr0.15La0.85MnO3 (15SLM) were film coated on YSZ substrates from classified suspensions. Narrow particle-size distributions in the suspension resulted in close-packed layers with a very homogeneous porosity and pore-size distribution. The specific conductivity of the layers decreased significantly with increasing porosity and mean pore size. A specific conductivity of 109 S . cm-1 was obtained at 1000-degrees-C for a 2.9-mu-m thick layer from a suspension with particles in the range 0.10-0.25-mu-m. The current-overvoltage behavior of the film-coated layers presented in this study did not, however, show any significant dependence on the thickness and the microstructure of the porous layers. Overvoltages (eta) at a current density of 0.1 A/cm2 at 898-degrees-C were quite low, i.e., in the range 60-70 mV. In comparison with other studies it is shown that film coating improves the microstructure of the ceramic electrode layers, which in turn lowers the cathodic overvoltages for the oxygen reduction reaction.