Effect of ionic conductivity of zirconia electrolytes on the polarization behavior of various cathodes in solid oxide fuel cells

The polarization behaviors of porous platinum and La(Sr)MnO3 (LSM) cathodes coupled with zirconia electrolytes with various ionic conductivities (sigma(ion)) were investigated. The exchange current density, j(0), on Pt cathode was not influenced by the sigma(ion) at 900 and 1000 degrees C, whereas j(0) increased proportionally to sigma(ion) at a lower temperature of 800 degrees C. However, the j(0) on LSM cathodes increased in proportion to the sigma(ion) in the temperature region between 800 and 1000 degrees C. The dispersion of nanometer-sized Pt catalysts on LSM particles greatly enhanced the performance, the magnitude of which depended on the temperature, the sigma(ion) and the microstructure of LSM. The observations are well explained kinetically, i.e., the cathode performance is controlled by the transport rate of O2- at the interface when the surface reaction rate is sufficiently high. Consequently, the use of high-performance electrodes in combination with the solid electrolyte having high sigma(ion) is very important for achieving the high performance of solid oxide fuel cells. (C) 1999 The Electrochemical Society. S0013-4651(98)03-090-0. All rights reserved.