Review on the use of impedance spectroscopy for IPMC-like devices: application, models, and a new approach to data treatment

Abstract

Although efforts to model the electrochemical behavior of ionomeric polymer-metal composite (IPMC) devices through electrochemical impedance spectroscopy (EIS) have been made, there is no equivalent circuit that provides either good data fit or understanding of the electrochemical phenomena when external factors, such as type of counterion and relative humidity, are considered. Most models have either a Warburg element or an ideal capacitor, which results in poor fitting at high frequencies, where the charge motion within the polymer membrane is observed. For the actual application of these devices, a consistent model must be used to comprehend their behavior while working. Furthermore, the models in the literature have limitations as they do not cover the environment and counterion influences. In this manuscript, we review the articles that applied EIS to characterize IPMC devices for different purposes, pointing out the technique's usefulness. At the same time, we use EIS in different relative humidities and counterions to propose a new model based on transmission lines, in which the data obtained have a better adjustment at high frequencies, lower statistical residue value e can also grant robustness regarding the external factors when compared with other five models found in the literature.