Impedance Spectra of Mixed Conductors: a 2D Study of Ceria

TL;DR

This paper presents an analytical and finite element framework for analyzing electrochemical impedance of mixed conductors, specifically ceria, capturing 2D effects and matching experimental data with high accuracy.

Contribution

It introduces a first-principles based 2D modeling approach for impedance spectra of mixed conductors, including surface and bulk transport coupling.

Findings

Model agrees with experimental impedance data within 2% error.

2D effects like thickness reduction influence impedance spectra.

Variable diffusivities significantly impact impedance characteristics.

Abstract

In this paper we develop an analytical framework for the study of electrochemical impedance of mixed ionic and electronic conductors (MIEC). The framework is based on first-principles and it features the coupling of electrochemical reactions, surface transport and bulk transport processes. We utilize this work to analyze two dimensional systems relevant for fuel cell science via finite element method (FEM). Alternate current Impedance Spectroscopy (IS) of a ceria symmetric cell is simulated near equilibrium condition (zero bias) for a wide array of working conditions including variations of temperature and $H_2$ partial pressure on a two dimensional fuel cell sample with patterned metal electrodes. The model shows agreement of IS curves with the experimental literature with the relative error on the impedance being consistently below 2%. Important two-dimensional effects such the effects of thickness decrease and the influence of variable electronic and ionic diffusivities on the impedance spectra are also explored.