DRT analysis and transmission line modeling of ceria based electrodes for solid oxide cells

Abstract

For the analysis of performance limiting processes in various electrochemical systems like lithium ion batteries, polymer electrolyte membrane fuel cells or solid oxide cells, impedance spectroscopy is a powerful tool. The distribution of relaxation times (DRT) enables the deconvolution of the polarization processes in the spectrum. The simple approach, to correlate each peak in the DRT with a single polarization process fails for multiphase electrodes as the complex coupling of electronic, ionic and transport of different species by spatially distributed charge transfer reactions leads to a number of correlated peaks in the DRT.In this contribution such coupling of transport and reaction is analyzed for ceria based fuel electrodes applied in solid oxide cells. A physicochemically meaningful two-channel transmission line model is developed. Due to the ambiguity of impedance spectra and DRT, the straightforward approach of fitting this model to measured spectra does not allow an unambiguous model parameterization. Additional methods as conductivity measurements and focused ion beam-tomography are indispensable to obtain physicochemically meaningful parameters to be applied in the fitting procedure. With this parameterization approach DRT based modeling becomes feasible and ionic/electronic transport resistances and area specific charge transfer resistance of the ceria surface can be quantified.