Simulation of the diffusional impedance and application to the characterization of electrodes with complex microstructures

Electrochemical impedance spectroscopy (EIS) has been widely employed to probe material properties in energy materials. One important aspect of EIS is the diffusional impedance. To date, the diffusional impedance behavior is understood based on the analytical solutions of the one-dimensional (1D) diffusion equation. However, transport in materials is strongly influenced by the materials' three-dimensional (3D) microstructures that often possess complex geometries that are unlike the simplified ID domains. In this work, we simulate the concentration response driven by oscillating loads by solving the diffusion equation in complex, experimentally determined 3D microstructures obtained from solid oxide fuel cell cathode and lithium-ion battery cathode. The simulation results demonstrate that the diffusional impedance can serve as a new technique for the evaluation of microstructural characteristics of porous media, including the tortuosity, the porosity, and the area of the loading boundary. Our findings open a new array of applications for diffusional impedance measurements. (C) 2020 Elsevier Ltd. All rights reserved.