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

Benjamin E Mcnealy,Jun Jiang,Joshua L Hertz

doi:10.1149/2.0281506jes

Benjamin E Mcnealy, Jun Jiang + Show 1 more

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https://doi.org/10.1149/2.0281506jes

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Abstract

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 phenomenologically 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.

Highlights

Electrochemical impedance spectroscopy (EIS) is a commonly used experimental technique that can deconvolute the contributions of multiple physical processes to the overall electrical impedance of a sample.[1]
The high frequency arc I is typically attributed to the bulk electrolyte, while the low frequency arc III is attributed to the electrode reaction
The work described in this paper suggests instead that the mechanism for the intermediate frequency impedance is the spreading of current in the electrolyte at low frequencies

Summary

Introduction

Electrochemical impedance spectroscopy (EIS) is a commonly used experimental technique that can deconvolute the contributions of multiple physical processes to the overall electrical impedance of a sample.[1]. In impedance studies of such cells, an anomalous intermediate frequency feature[18,19] is sometimes observed A thin film electrolyte considered alone has negligible spreading resistance.[20] Zhang et al have shown that contact between two phases with different conductivities can result in a much larger spreading resistance.[21] A result similar to Zhang’s could be expected if there is substantial resistance to current flow at the electrode-electrolyte interface. The possibility of a diffusion-related feature in the impedance spectrum was discounted

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