## 1 Introduction  
Impedance Spectroscopy (IS) plays a fundamental role in many research and development (R&D) areas, particularly in Materials Science and Electrochemistry, where it is an essential analytical technique for studying the performance of functional materials [1, 2]. It is a methodology that allows for the characterization of the electrical behavior of systems for which differently coupled processes contribute to their overall response. With advances in electronics, such as high-quality impedance bridges and large-frequency-band integrated circuits (such as multipliers, integrators, demodulators, etc. ), impedance measuring equipment has become cheaper and popular, and consequently more engineers and researchers are using them [3]. The history of IS dates back to the 19 th Century, during which linear systems theory found significant advances. Near the end of the same century, [PERSON] carried out its efforts and enlarged IS application to electrochemical systems [4]. During the second half of the 20 th century, the world witnessed the development of solid-state batteries, a revolution in high-temperature electrochemical sensors, among other fields (by the time the potentiostat was invented, followed by the arrival of frequency response analyzers) [3; 5; 6]. The major advance during that period was the application of IS to solid systems, instead of their usage mainly for the characterization of aqueous systems, which allowed for the conduction mechanisms present on solid-solid and solid-liquid interfaces (where it is quite common to observe ionic nature phenomena) to be revealed [1; 3]. Near the interfaces, crystallographic, mechanical, compositional, and electrical properties induce changes in the charge distribution, governing the overall electrical conductivity of a system [7]. When an electrical potential differential is applied to the diverse interfaces composing a system, they will become polarized in unique ways. The rate at which the polarization of each region changes with the reversion of applied electric potential is characteristic of each interface; for instance, it is slow near the triple structure composed of electrode, electrolyte, and surrounding environment but considerably faster in the grain boundaries of the electrolyte [8]. So, phenomena analysis shifted from time/concentration to frequency-related dependencies evaluation; therefore, electric double layers are now characterized by a distribution of relaxation times. In summary, the electrical response of heterogeneous systems varies and depends on the charge species available, the microstructure, the electrodes' shape, placement, and type, and IS can be used to assess how charges are bounded or transferred along the bulk or along the existing interfaces (solid-solid, solid-liquid, etc.) in almost every solid and liquid; consequently, semiconductors, ionic, electronic, and mixed-type materials, among others, can all be evaluated [9]. Characterizing electrolytes' electrical behavior by IS implies using electrodes to perform the measurements [10; 11]. The technique consists of applying an electrical stimulus through the electrodes (a known and defined current or voltage) and analyzing the system response, assuming that the system's electrical properties are time-invariant [10]. If so, several contributions to the overall electrical response can occur: electrons transport along the electrolyte, electrons transfer along the interface composed by the electrode and electrolyte, or ions flow through the electrolyte structural defects [10; 11; 12]. Therefore, the flow rate of the charged particles and, consequently, of the current, depends on the ohmic resistance of the electrodes and electrolyte, and on the reaction rates at the existing interfaces (it should not be forgotten that band structure anomalies or structural defects can further impede charge flow). Three different types of electrical stimuli can be used when applying IS [13].