Determination of the Resistance of Cone-Shaped Solid Electrodes

Henrik Lund Frandsen,Kent Kammer Hansen,Peter Vang Hendriksen,Søren Koch

doi:10.1149/2.0051711jes

Henrik Lund Frandsen, Kent Kammer Hansen + Show 2 more

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https://doi.org/10.1149/2.0051711jes

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Abstract

A cone-shaped electrode pressed into an electrolyte can with advantage be utilized to characterize the electro-catalytic properties of the electrode, because it is less dependent on the electrode microstructure than e.g. thin porous composite electrodes, and reactions with the electrolyte occurring during processing can be avoided. Newman's formula for current constriction in the electrolyte is then used to deduce the active contact area based on the ohmic resistance of the cell, and from this the surface specific electro-catalytic activity. However, for electrode materials with low electrical conductivity (like Ce1-xPrxO2-δ), the resistance of the cell is significantly influenced by the ohmic resistance of the cone electrode, wherefore it must be included. In this work the ohmic resistance of a cone is modelled analytically based on simplified geometries. The two analytical models only differ by a model specific pre-factor, which is consequently determined by a finite element model. The model was applied to measurements on cones of Ce1-xPrxO2-δ characterized on an YSZ electrolyte. Conclusively, the finite element model was used to obtain a formula for the resistance for different cone angles with a small contact area. This reproduces Newman's formula for a cone angle equal to 90°, i.e. a semi-infinite body.

Highlights

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The electrodes in solid-state chemistry are studied by the use of porous planar electrodes deposited on an electrolyte substrate, see e.g.1 This technique suffers the drawbacks that the performance of the electrode material is highly dependent on the electrode microstructure and a reaction between electrolyte and electrodes might occur during processing masking the “true” electrode performance
Another limitation in the use of planar porous electrodes is that electrode materials with a low electronic conductivity are difficult to characterize accurately as it, depending on the geometry, may be difficult to ensure that in-plane resistance and contact losses are negligible

Summary

Introduction

Users may download and print one copy of any publication from the public portal for the purpose of private study or research. The electrodes in solid-state chemistry are studied by the use of porous planar electrodes deposited on an electrolyte substrate, see e.g.1 This technique suffers the drawbacks that the performance of the electrode material is highly dependent on the electrode microstructure and a reaction between electrolyte and electrodes might occur during processing masking the “true” electrode performance Another limitation in the use of planar porous electrodes is that electrode materials with a low electronic conductivity are difficult to characterize accurately as it, depending on the geometry, may be difficult to ensure that in-plane resistance and contact losses are negligible. The purpose of this work is to enable deduction of the area specific electrocatalytic properties of the electrode material from the impedance characteristics, and from an estimate of the circular contact area, A This area can be determined by modeling of the total ohmic resistance by including both the constriction resistance of the electrolyte and the resistance of the cone electrode. The diameter of the circular contact area, d, can be calculated from the measured ohmic resistance with Newman’s formula[4] d= 1

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