Analytical low-current and numerical high–current models for the impedance of a hydrogen–fed anode of an anode–supported button SOFC are developed. The models use the full dusty gas transport model for the binary H2–H2O mixture. We show that neglecting the pressure gradient may lead to a severe underestimation of the effective hydrogen diffusivity in the support layer. A least-squares fitting of the analytical model to a literature spectrum of a button cell is demonstrated. The analytical impedance allows to indicate pitfalls when using equivalent circuits with the Warburg finite-length element for fitting experimental spectra. The model parameters include the Knudsen hydrogen diffusivity, hydraulic permeability, porosity/tortuosity ratio of the support layer and the ionic conductivity, double layer capacitance, and HOR Tafel slope of the active layer. All of the above parameters can be obtained by fitting the models to experimental spectra.
Andrei Kulikovsky (Wed,) studied this question.