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

Abstract

Journal ofThe Electrochemical Society, 162 (6) F537-F546 (2015) A Precise, Reduced-Parameter Model of Thin Film Electrolyte Impedance Benjamin E. McNealy,a,z Jun Jiang,b and Joshua L. Hertza,b,∗ aDepartment ofMechanical Engineering, University ofDelaware, Newark, Delaware 19716, USA bDepartment ofMaterials Science and Engineering, University ofDelaware, Newark, Delaware 19716, USA The extreme shape factors inherent in characterizing thin film electrolytes can present a challenge to quantitative interpretation of impedance spectra. Here, the impedance of a thin film ceramic electrolyte with surface microelectrodes is modeled via direct numerical solution of current conservation. Faradaic and non-faradaic currents at the electrode-electrolyte interface are modeled phe- nomenologically using a formulation based on the Butler-Volmer equation. The model is able to reproduce complex, experimentally obtained impedance spectra for Pt/YSZ and Pt/GDC cells using only four adjustable, physically intuitive parameters: electrolyte conductivity, permittivity, exchange current density, and double layer capacitance. Equivalent circuit models typically used to fit these spectra instead require six or more adjustable parameters with ambiguous physical meaning. Notably, the model described here is able to capture a heretofore unexplained intermediate frequency arc seen in the experimental results. A parametric study enables the mechanism of the intermediate frequency feature to be identified as a spreading resistance in the electrolyte that vanishes at high frequencies 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