A Precise, Reduced-Parameter Model of Thin Film Electrolyte Impedance

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The Electrochemical Society
he extreme shape factors inherent in characterizing thin film electrolytes can present a challenge to quantitative interpretation f impedance spectra. Here, the impedance of a thin film ceramic electrolyte with surface microelectrodes is modeled via direct umerical solution of current conservation. Faradaic and non-faradaic currents at the electrode-electrolyte interface are modeled phe- omenologically using a formulation based on the Butler-Volmer equation. The model is able to reproduce complex, experimentally btained impedance spectra for Pt/YSZ and Pt/GDC cells using only four adjustable, physically intuitive parameters: electrolyte onductivity, permittivity, exchange current density, and double layer capacitance. Equivalent circuit models typically used to fit hese spectra instead require six or more adjustable parameters with ambiguous physical meaning. Notably, the model described here s able to capture a heretofore unexplained intermediate frequency arc seen in the experimental results. A parametric study enables he mechanism of the intermediate frequency feature to be identified as a spreading resistance in the electrolyte that vanishes at high requencies due to low-impedance dielectric transport of current across the electrode-electrolyte interface. The fitting results are validated by comparison of the parameter values with literature reports.
Publisher's PDF.
J. Electrochem. Soc. 2015 volume 162, issue 6, F537-F546