Mechanistic modeling of the dielectric impedance of layered membrane architectures

Electrochemical impedance spectroscopy (EIS) is frequently used to investigate properties of layered membrane systems in aqueous electrolyte solutions. However, attributing features of the underlying plots to chemical or structural characteristics of the system is difficult, as it usually requires the assumption of structural elements of an analogous equivalent electrical circuit. Furthermore, some parameters are not easily accessible in experimental studies, making the analysis of EIS subject to interpretation rather than rigorous understanding. We address these difficulties by conducting direct numerical simulations of layered structures composed of electrolyte solutions, ion exchange membranes and membrane modification layers, using our EnPEn framework. By changing the parameters of the model, it is possible to isolate features of impedance spectra as they relate to chemical and structural properties of different layers and interfaces. For the first time, we show the general influence of the thickness and charge density of surface modification layers on the complex impedance of such layered membrane architectures in multi-ionic mixtures. The results can be used to characterize and understand impedance spectra gained by experiments. This is important in increasingly complex systems with multiple layers and complex multi-ionic electrolyte solutions. Understanding the influence of design parameters on the performance of a membrane is important for a wide range of applications, such as ion selective electrodes, desalination and deionization. The dynamic EnPEn framework closes the gap between experimental EIS and the uncertainty introduced by assuming equivalent circuits.