The basic principles of electrochemical impedance spectroscopy (EIS). For any electrical circuit, consisting of various passive elements (i.e. resistors, capacitors and inductors), the behavior of the entire circuit with respect to an applied alternating current voltage, depends both on the behavior of the individual elements, and also on their arrangement in the circuit the one compared to the other. If a continuous direct voltage is applied to the elements that make up the equivalent circuit, the resulting current can be measured using Ohm's law. In the case where a low amplitude sine wave Eac, of a particular frequency, is applied through a passive element, then :E ac = E0 sin(ω t) (1)Where:Eac = potential at time t;E0 = maximum voltage amplitude; ω = is the angular frequency, ω = 2πf; t = is the time. Under these conditions, the resulting current response of a sine wave Iac will be given by: I ac = Eac /X …. (2)Where:Iac = current at time t;X = the reactance of the particular passive element in the electrical circuit.When the applied signal is a sinusoidal voltage wave and the resulting signal is a sinusoidal current wave, then called Z impedance; vice versa, when the applied signal is a sinusoidal current wave, the resulting signal is a sinusoidal voltage wave, X which is called admittance Y. The value of the reactance of a capacitor or an inductor can be expressed as a quantity complex by the complex formula operator j, j = −1 [11], and using this notation the reactance of the elements is given by [12]:For a resistor: XR = RFor a capacitor: 1/-jωCFor an inductor: XL = jωL … ……… (3-4) For the impedance, Z(ω), as mentioned above...... middle of the paper ...... looking at the answer of real world systems. In some systems, the Nyquist plot was expected to be a semicircle with the center on the x-axis. However, the observed graph was actually the arc of a circle, but with the center some distance below the x-axis . “These depressed semicircles have been variously explained by a series of phenomena depending on the nature of the system investigated. However, the common thread of these explanations is that some properties of the system are not homogeneous or that there is a certain distribution (dispersion) of the value of some physical properties of the system. The CPE is usually represented by two parameters, Q° and n”. “It is tempting to simply associate the value of Q° for a CPE with the value of capacitance, C, for an equivalent capacitor. The range of values ​​of n is 0 to 1. When n = 0, Q° = R. When n = 1, Q = C.”