ELECTROCHEMICAL CHARACTERISTICS OF CATHODES IN SOLID OXIDE FUEL-CELLSBASED ON CERIA ELECTROLYTES

The ionic current-overpotential characteristics of cathodes on ceria-b ased electrolytes have been evaluated by galvanostatic current-interru pt measurements. The measurements were carried out on mixed conducting ceria electrolytes under fuel cell operating conditions. The effect o n the oxygen reduction kinetics of the simultaneous transport of elect rons and oxygen was investigated. As model substances for cathodes wer e La0.8Sr0.2MnO3, La0.84Sr0.16CoO3, Pt, Ag, and Au. Cathode reaction m echanisms as a function of the transport properties are discussed for the different cathode materials. Steady-state cathode overpotentials w ere interpreted using a Butler-Volmer-type equation to describe charge -transfer processes and to evaluate exchange current densities. At 700 degrees C the exchange current density of the best cathode La0.84Sr0. 16CoO3 was 180 mA/cm(2) whereas the one for La0.8Sr0.3MnO3 was only 30 mA/cm(2). In both cases we identified charge-transfer on the cathode material as the rate-limiting step.