THE ELECTRODE SYSTEM O2/PT//ZRO2-8Y2O3 INVESTIGATED BY IMPEDANCE SPECTROSCOPY

Impendance spectra have been recorded for the system O2/Pt//ZrO2:8Y2O3 in the temperature range 650-850-degrees-C and oxygen partial pressure range 10(-4)-1 atm. The measured impedance spectra have been deconvoluted by means of an NLLS program and are well described with a Randles-type equivalent circuit, in which the electrode resistance is the sum of a charge transfer resistance and a diffusional resistance. The charge transfer process had an apparent activation energy of 199 kJ/mol and conformed with the Langmuir adsorption isotherm with a P(O2)-1/4 dependency. This indicates that the cathodic reaction is limiting. The diffusional impedance is suggested to consist of two different processes, one dominant at higher temperatures and lower partial pressures of oxygen and a second dominating at lower temperatures and higher partial pressures of oxygen. It is suggested that the latter is related to the formation of a PtOx compound.