Impedance of a hydrogen--fed SOFC anode: Analytical and numerical models based on the dusty gas transport model

TL;DR

This paper develops analytical and numerical models for the impedance of hydrogen-fed SOFC anodes using dusty gas transport, highlighting the importance of pressure gradients and enabling parameter extraction from spectra.

Contribution

It introduces combined analytical and numerical impedance models for SOFC anodes based on dusty gas transport, including pressure gradient effects and fitting procedures.

Findings

Neglecting pressure gradients underestimates hydrogen diffusivity.

Analytical impedance model fits experimental spectra effectively.

Model parameters can be extracted from impedance spectra.

Abstract

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 dusty gas transport model for the binary H$_2$--H$_2$O 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 traps 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.