Electrode kinetic behaviour of (U0.4Pr0.6)O2±x/YSZ/(U0.4Pr0.6)O2±x cells

Abstract

Results of kinetic studies on (U_0.4Pr_0.6)O_2±x/stabilised zirconia/(U_0.4Pr_0.6)O_2±x cells as a function of oxygen partial pressure (1–10^–4atm), temperature (500–900 °C) and electrode heat treatment have been described. Impedance spectroscopy was used for kinetic studies. At all temperatures and in various oxygen partial pressures a single arc, skewed on the high-frequency end of the impedance spectrum, was observed. The data were deconvoluted into two electrode processes with relaxation times differing by about an order of magnitude. The electrode process relaxing in the lower frequency range had an activation energy of 165 ± 10 kJ mol^–1, a small angle of depression for the impedance arc, [p(O₂)]^–0.5 dependence for the time constant and has been attributed to an adsorption/dissociation of oxygen at the gas/electrode interface. The activation energy associated with the high-frequency arc was lower by ca. 35 kJ mol^–1 than that for the low-frequency arc and this arc appears to be associated with the charge-transfer reaction.