An analytical, 1-dimensional impedance model for a composite solid oxide fuel cell cathode is derived. It includes geometrical parameters of the cathode, e.g., the internal surface area and the electrode thickness, and also material parameters, e.g., the surface reaction rate and the vacancy diffusion coefficient. The model is successfully applied to a total of 42 impedance spectra, obtained in the temperature range 555°C–852°C and in the oxygen partial pressure range 0.028 atm–1.00 atm for a cathode consisting of a 50/50 wt% mixture of (La0.6Sr0.4)0.99CoO3 − δ and Ce0.9Gd0.1O1.95 − δ. The surface exchange coefficient in oxygen for T = 802°C and [Formula] is found to be kEx = 1.42 × 10− 4 m s− 1 and with an activation energy of Ea = 107 kJ mol− 1, in fair agreement with literature. A parameter variation and a steady state analysis is performed, verifying the soundness of the model and providing both qualitative and quantitative information on the evolution of the impedance spectra of cathodes with changing parameters.
Journal of the Electrochemical Society, 2014, Vol 161, Issue 3