Abstract: The Pt/YSZ(yttria stabilized zirconia) solid electrolyte systems both in three and two electrode configurations have been studied by AC impedance technique at 700～950 ℃. At open circuit potential, only one semicircular arc in the complex impedance plot was found, correspoding to the electrochemical activation step of the oxygen transfer reaction at the Pt/YSZ. The apparent electrochemical activation energy was measured to be 171.5kJ/mol and the interface capacitance was found to be about 300 μF/cm², which is exceptionally large and can not be explained by the classic double layer theory. When the Pt/YSZ system was anodically polarized, the electrochemical resistance was profoundly reduced, but an increase in the electrochemical resistance and the concentration limitation in the impedance diagram were observed when the system was cathodically polarized.

Key words: Pt electrode, solid electrolyte, yttria stabilized zirconia, AC impedance