Impedance spectra of mixed conductors: a 2D study of ceria

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 non-equilibrium thermodynamics 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 the finite element method (FEM). Alternate current impedance spectroscopy (AC-IS or IS) of a ceria symmetric cell is simulated near equilibrium conditions (zero bias) for a wide array of working conditions including variations of temperature and H₂ partial pressure on a two-dimensional doped ceria sample with patterned metal electrodes. The model shows agreement between computed IS curves and the experimental literature where the relative error on the impedance is consistently below 2%. Important two-dimensional effects such as the impact of thickness decrease and the influence of variable electronic and ionic diffusivities on the impedance spectra are also explored.