Physically-based Modelling to Unveil the Complex Interplay between Electrode Microstructure and Impedance Response

Solid oxide fuel cells (SOFCs) are promising systems which produce heat and power from the direct electrochemical conversion of a fuel, such as hydrogen, at high temperature. The cell performance and durability, which are typically assessed by using electrochemical impedance spectroscopy (EIS), are known to depend strongly on the microstructure of the porous electrodes. However, the complex interplay between electrode microstructure and EIS response is not well understood: very often spectra interpretation relies on phenomenological equivalent circuits and on empirical evaluations, thus making spectra deconvolution and the assessment of microstructure-performance correlation quite inaccurate. In this work, we describe how the use of physically-based models, based on the mechanistic description of electrochemical phenomena occurring within the electrode microstructure, provide an effective strategy to quantitatively assess the interplay between electrode microstructure and EIS response. Taking advantage of tomographic techniques, which allow for the three-dimensional reconstruction of the electrode microstructure, we show how the microstructure-performance correlation can be accurately described and predicted in a wide range of conditions [1,2]. Then, we show how modelling and EIS can be integrated to infer kinetic information [3] and to elucidate the degradation mechanisms which undermine the stability of SOFC electrodes [4], revealing that paradigms commonly accepted for charge-transfer phenomena in porous electrodes should be revisited [5]. Finally, we report how inhomogeneous microstructural properties may affect the EIS response of a porous electrode, providing ad-hoc modelling tools [6] to help researchers deconvolve real impedance spectra with more awareness.