电化学阻抗谱的应用及其解析方法（Applications and analytical methods of electrochemical impedance spectroscopy）Documents from the network, I collected, finishing, and if there are omissions, errors, but also please correct me!Applications and analytical methods of electrochemical impedance spectroscopyA very important method in electrochemical measurement of AC impedance is an important means to study the dynamics and surface phenomena of electrode processesEspecially in recent years, due to the rapid development of frequency response analyzerThe test precision is more and more high impedance, ultra low frequency signal impedance spectrum also has good reproducibility, coupled with the development of computer technology, the higher the impedance spectra of the increasing degree of automation, so that we can better understand the electrode surface electric double layer structure, activation passivation film conversion, desorption process the pitting induction, development and termination and active substances1. basic components in impedance spectraThe analysis of AC impedance spectrum is usually carried out by equivalent circuit, in which the basic components include pure resistance R, pure capacitance C, impedance value 1/j, Omega C, pure inductance L, and its impedance value is j Omega LIn actual measurement, a perturbation frequency of sine wave signal is applied to the Omega cell, which is the double layer as a capacitor, the resulting electrode itself, solution and electrode reaction resistance are regarded as resistance, then the equivalent circuit shown in Figure 1Fig. 1. equivalent circuit of electrolytic cell with large area inert electrode as auxiliary electrodeThe AB in the figure represents the electrode of the electrolytic cell and the ends of the auxiliary electrode, respectively, RaRb represent the resistance of the electrode material itself, Cab said on the capacitance between the electrode and auxiliary electrode, Cd and Cdelectric double layer capacitor electrode and auxiliary electrode, Zf and Zf said the AC impedance of electrode and auxiliary electrodeUsually referred to as an electrolytic impedance or a Faraday impedance, the numerical value is determined by the electrode dynamics and the frequency of the measured signal, and Rl represents the solution resistance between the auxiliary electrode and the working electrodeIn general, the parallel connection of the double layer capacitor Cd and the Faraday impedance is called the interface impedance ZIn actual measurement, the internal resistance of the electrode is very small, and the distance between the auxiliary electrode and the working electrode is larger. Therefore, the capacitance Cab is generally far smaller than the double-layer capacitor CdIf the auxiliary electrode is the electrochemical reflect that Zfis particularly large, and the auxiliary electrode area is far greater than on the electrode area (for example, platinum black electrode large), Cd, the capacitance Xcdthan other elements in the series circuit is much smallerTherefore, the interfacial impedance of the auxiliary electrode can be neglectedThus, Fig. 1 can be simplified into Fig. 2, which is also a common equivalent circuitFig. 2. simplified circuit of electrolytic cell with large area inert electrode as auxiliary electrode2. special components in impedance spectrumThe equivalent circuit mentioned above is only a basic circuit, in fact, due to the dispersion effect of the electrode surface, double layer capacitance measured is not a constant, but varies with the frequency and amplitude of AC signal change, generally speaking, the dispersion effect is mainly related to the electrode surface current distribution in corrosion the potential near the electrode surface of cathode and anode current coexist, when the inhibitor exists in the medium, the electrode surface will be covered, as the corrosion inhibitor layer at the same time, iron ion can only penetrate the inhibitor layer forming the anode current in the local region, this caused extreme non-uniform current distribution, dispersion coefficient is lowPerformance of variable capacitance arc flat, as shown in Figure 3In addition, the roughness of the electrode surface can also affect the dispersion effect coefficient. The coarser the electrode surface is, the lower the dispersion effect coefficient is2.1 constant phase angle elements (Constant, Phase, Angle, Element, CPE)When characterizing dispersion effectsRecently, a new electrochemical element, CPE, has been proposedThe equivalent circuit of CPE is analytic:The impedance of CPE is defined by two parameters, that is, CPE-T, CPE-P, we know,Therefore, the impedance Z CPE element can be expressed as the equivalent element argument for =-p PI /2, because it is a function of the numerical impedance frequency, regardless of its frequency and amplitude,It is called t