Progress in Electrochemical Impedance Spectroscopy of Conductive Polymer Films

In the application of conductive polymer film research and development, the potential applications of macromolecule polymers in many fields of new villages have been recognized since the preparation of high-stability and possible stability of the preparation process. The application prospects of new materials such as optoelectronic semiconductors, such as magnetism and energy, have attracted people's attention. In recent years, the noisy oxide billets involving their electrical conductivity have become a hot topic in various fields. Zero-resonance 5-foot quartz crystals were used to test the nature of the needles, deflecting the contact muscles, and radiating small trace experiments. Electrochemical impedance spectroscopy 15 is different from and superior to others. The characteristics of transient technology, especially in the study of the effectiveness of the charge transfer process of polymer membranes have been widely rejected This article is intended to combine several newly developed theoretical models on the electrochemical impedance spectroscopy in conductive polymer membranes The recent progress in the study of the nature of the evaluation conducted a review of the characteristics of the 08 method of conductive polymer membranes and the traditional method of electrochemical impedance spectroscopy 6 is superior to other transient technologies. Applying an infinitesimally small sine-wave perturbation to a steady-state system is very important for the study of thin films on electrodes, such as modified electrodes and electrochemical deposition films, because this measurement does not lead to large changes in the membrane structure. The application frequency range of 13 is broad, and the dynamic parameters and mass transfer parameters of the electrode process can be measured at the same time. Through detailed theoretical models or empirical equivalent circuits, Faraday's system can be implemented with ideal components such as resistors and capacitors. The process space charge, as well as the conduction process of electrons and ions, explain the distribution of microscopic properties of non-homogeneous substances. Therefore, 13 has become an effective method for studying electrochemical systems and corrosion systems. Since this 1 was first introduced in 1982, 3 has been introduced into the research field of conductive polymers, many scholars have applied it, and 3 pairs of conductive polymer systems have been extensively researched and charged by Thunder Female, 34 years old, lecturer, master's researcher. Health, engaged in the study of polymer film physical chemistry. Contact Person National Natural Science Foundation of China Department of Education 29873015 Excellent Young Teachers Fund of the Ministry of Education Natural Science Foundation of Guangdong Province 97,33 and Basic Research Projects of Guangzhou City 卟1 General Characteristics of Conductive Polymers 18 Characteristics of Conductive Polymer Film Modified Electrodes 13 Similar to the behavior of the porous electrode or the redox electrode, a typical complex plane impedance is characterized in that a high-frequency area of ​​the temple has a semicircle whose center is generated by the interface charge transfer process under the real axis, which can be combined in parallel with a resistor and a capacitor. In the past, the point of intersection of the semicircle and the real axis is the brother +, where, and, respectively, the impedance of the type, the slope of which is less than 45; 3 the low-frequency region corresponds to the pure electric resistance caused by the saturation of the high-charge dry charge, 1.2. 18 Equivalent circuit method is used to persuade dissociation; the equivalent concept of Tuen road from Chongfa City 1 is used to explain the formulae. In general, the equivalent components of Tuen Lu Mountain are used to simulate the electrode polymer and electrolyte. Resistance behavior; the capacitance is used to simulate the capacitive behavior of the macromolecule electrode polymer interface and the polymer temple solution interface; the transmission line simulates diffusion with the plant, and the phantom soil resistance; 1 constant phase element, 戛The degree of roughness of the electrode surface or polymer surface, the diffusion element 1 is used to describe the presence of an interface in the medium to prevent the diffusion of the species from flowing, and someone also uses a transmission line composed of a resistor and a capacitor to describe the diffusion of ions in the polymer to replace the element 1 Equivalent circuits have obvious advantages in fitting experimental data. Sometimes, in order to obtain an ideal fitting effect, a considerable number of circuit components are needed. However, some components are difficult to find an appropriate and clear physical meaning.

1.3 Theoretical Model of Conductive Polymer 1 Although 13 has been widely used to study the conductive doping and charge storage mechanism of conductive polymers, the impedance response of these materials is still not completely understood, and so far a large number of them have been proposed. Theoretical models have not yet been widely accepted and accepted by people. At present, the more active theories in the study of conductive polymers are the homogenous homogeneous membrane theory of macromolecules developed from the uniform electrode model and the transmission line theory based on the redox macromolecule model. The theory can give equivalent results in most of the five interpretations of high conductivity. However, there is no definitive theory as to which of the interpretative histories is perfect. The above-mentioned theory and model are still adopted and promoted the development of the field in high frequency. 2 The application of the transmission line theory in the research of conductive polymer film and development in the conductive polymer, due to the presence of charge transfer and electronic tweezers mixed conductive The coupling, therefore its 13 is much more complicated than the simple solution system and the redox polymer film system, in order to separate these properties from 13 separately, there are two different models based on the use of increased resistance and capacitance components to correct The equivalent circuit to describe the mixed conductance of electrons and ions, this is the transmission line theory proposed by Xian 17 et al. 151989.

18 transmission line model analysis method The basic idea of ​​this method is to first conduct an AC impedance test on a system, get the system with frequency changes in the real muscle resistance 77 and local resistance, then; for the relationship between 2 and the Court transmission line model into the analysis, seeking The ionic resistance of the system 4 electronic resistance and Faraday capacitor 0 equal value, and then through the relationship between 0 and the frequency of electrical power to analyze the nature of the system and its analytical mode can be used 1 1 叩 聚 1 坫 3 咯 1 slightly more than 1 red station Pyridinium salts with electron-conducting anion-exchange polymers with good reproducibility and elimination of tunne chemistry confirm the feasibility of this model in 15 analysis! In the transmission line model, the porous electrode solvated polymer is seen as two overlapping phase phases that are the polymer transport electrons, and the other phase is the electrolyte transport separation. And assume that the structure of electrode 1 is good enough to stick electronically. , AC impedance measurement transmission line analysis model analysis ruler where 0 and the potential frequency of the relationship between the nature of the system to obtain private. The characteristics of this model are that, first of all, the conductivity of the host ions and electrons of the conductive polymer is easily obtained from the impedance data; secondly, these conductivities vary with experimental parameters such as the concentration of the solvent electrolyte and the degree of oxidation of the electrode potential. This helps to understand the interpretation of the conduction mechanism of the film 2.2 transmission line theory. The transmission line model is used to explain the conductive mechanism of the ion-conducting electron-conducting ions and electrons in the polypyrrole film, and the large-scale experimental work on the polyconductor has been carried out. Most conductive polymers, when they are in the conductive state, the transmission speed of this sub-element is much greater than that of ion transport. For example, poly 3 mercaptopyrrole 4, the electron conductivity of acid is about 1023, which is 1000 times greater than its ion conductivity. Therefore, ion transport is a speed control step. For the ion transport of polypyrrole, the model assumes that the membrane is selective, only the anion contributes to the ion transmission, etc. On the basis of the transmission line theory for poly 3 aryl pyrrole 4, the acid ion conductivity of the acid varies with the concentration of the solvent electrolyte. A comprehensive analysis of the changes in the potential of the electrode was conducted. It is believed that although polypyrrole 4 carboxylic acid is generally considered to be negligible in the electroconductive polymer for electron resistance, Human 745 et al. reported that the resistance of ions and electrons in polypyrrole was similar. It is believed that this result is due to the coupling of the positive charges in the polymer chain with the movement of the ions in the pore solution. These measurements measured the impedance of poly-1-methylpyrrolidine 1 perchlorate perchlorate, which varies with the electrode potential under various solvents. It was found that the ratio of the ion and electron conductivity can be changed by changing the solvent and electrode potential. This provides an effective way to fully discuss the polymer double-resistance transmission line model. The experimental results are consistent with the model predictions, and through the analysis of experimental data by the model, reasonable and accurate electron and ion conductivity can be obtained but in the oxidation state. At the time, the abnormal dependence of the ion conductivity on the electrode potential was observed, which is considered to be related to the numerical values ​​of the electron and ion conductivity of the polymer, and pointed out that there is indeed a coupling transport of ions and electrons in the polypyrrole film. The ion transport can be controlled by doping polyanions. The larger polyanions are easily entangled with the polypyrrole and trapped in the polypyrrole matrix. This not only improves the stability and mechanical strength of the polypyrrole film, but also changes the polymerization. Compensating the charge on the pyrrole backbone When polypyrrole is doped with small anions, the ionic conductivity is mainly derived from anions; when doped with polyanions Mainly from the cationic polypyrrole perchlorate, rare, 4 and polypyrrole, styrene sulfonate complexes, 33 In addition, the scale, etc., were prepared, 0, and 33 simultaneously doped polypyrrole film, which 13 The ion transport behaviors of both 4 and 33 are simultaneously present. The fully oxidized form contains 0. As the main ion-flowing species, the ionic conductivity decreases as the electrode potential decreases; the reduced form contains, as the main flow species, increases. The electrode potential leads to a decrease in the ionic conductivity of the membrane; in the intermediate oxidation state, both flowing anions and cations contribute to the ionic conductivity of the membrane. Its complex impedance complex capacitance and cyclic voltammetry showed two separate charging processes. The polymer, 33, and 04 doping regions were separately transmitted and transmitted by Yangsangzi. However, at low frequencies, the experimental and simulated complex planes do not deviate from the ideal capacitive response of a simple transmission line! Since the electron transport process is too fast and has no effect on the electrochemical response of the polymer, when it becomes slow, such as a reduced conductive polymer, the ion transmission also becomes slow, so it is difficult to clearly interpret the experimental data.

Only 6. And rot. 1 in 2 found that +38 at low potential, can be used to study the phenomenon of electron transport At this time, the impedance of +33 in the frequency band appears semicircle, which is due to the electron transfer resistance of the polymer on the interface of the electrode, its impedance behavior The equivalent circuit and transmission line theory of 2 gas can be used to describe; as the potential rises gradually, the resistance electron resistance of Yunhe decreases exponentially until it is ignored, and then the impedance behavior of the polymer is still described by a simple circuit given by 2.

2.3 Transmission Line Theory Interpretation of the Microstructure of the Membrane 61 The microstructure of the polypyrrole film was first investigated. It is believed that Ding Wei is similar to the porous electrode. Then, the Hexane et al. The two-phase model has a selective permeability of macromolecules and electrolyte-filled pores and channels. Hckup et al. 13 measured the ion conductivity of the complex of 33 and 33, and found that the ionic conductivity has a strong dependence on the electrode potential and the electrolyte concentration, thus the porous electrode and the homogeneous phase selective transmission ionic conductivity. The influence of ionic ions is very large and the impact of common ions is very small. It is speculated that these materials are composed of selective permeability polymer aggregates, which contain pores filled with electrolytes, and the inter-well interconnectivity is low. The transmission line model explained the conductivity mechanism of the polypyrrole film more successfully, indicating that the polypyrrole and the like conductive polymer can be treated with the redox polymer model, which is reasonable at least when the low oxidation degree is 1 , which indicates that in a broad sense In the equivalent circuit of the transmission line, it is appropriate to use the homogeneous redox polymer model to fit polypyrrole, as proposed by Renhe et al.1, but the transmission line model still cannot explain the situation when the electronic resistance and the ionic resistance are equal. The research progress of the homogeneous membrane model considers the polymer membrane as a homogeneous phase, and the electrons and ions as carriers move in the single phase in the form of diffusion migration. The transmission of different types of metal membranes is also known as modified electrode electrolyte membrane electrolytes and metal membrane metals. Most of the reports in the past focused on the study of asymmetrically arranged modified electrodes, due to the existence of two different systems. At the interface, at least two kinds of carriers contribute to the current. Therefore, the charge transfer mechanism is very complicated. In order to more completely and clearly distinguish the electron and ion conduction in the film, in recent years, the high conductivity that was proposed in this field in the 1980s has also begun. Symmetrical disposition of the molecular membranes, namely electrolyte membrane dissociation and metal membranes, is studied by 13 recent studies. 1 and 7 et al. 4 propose a new model that considers the diffusion of electrons and ions in the membrane.撄 撄 撄 撄 传输 传输 传输 性质 性质 性质 ; ; ; 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104 104. State information; metal film metal only provides steady state information for electron conduction, which gives a separate study of ion conduction and electrons in conducting polymer films. The guide provided a convenient route to Jiashan et al.'s modified kinetic model of the electrolyte membrane rejection at the base of the Modified Tunji Model. By comparing the AC impedance of the membrane and the modified electrode, it clearly defined each The role of the interface, and the experimental data of polyaniline and polypyrrole in the two configurations were fitted with the model at the same time, but the theoretical value and the experimental value in the low frequency area does not match. Subsequently, 681.16 used this model to study the polypyrrole in the film and modified electrode configuration. Through the analysis and comparison, the transmission coefficient diffusion coefficient of the polypyrrole film and the concentration and interface of the ion and electron exchange sites were calculated. Parameter charge transfer resistance and electric double layer capacitance, the research found that its transmission properties depend on the anions and cations contained in the electrolyte, but not with the thickness of the film. In addition, some limitations of the model have also been found in the study. It remains to be determined. Modifications for Progress 4 Influence of the Porosity of the Conductive Polymer Film on Its 18 In the 13 explanation, the conventional equivalent circuit has only a reasonable result for an extremely thin polymer layer because there is no macroscopic distribution element. Thus, or capacitive capacitance transmission lines are often used to describe the porosity of materials, but the physical meaning of the former is not clear enough, or only roughly explained as related to the microscopic properties of porous materials; while in the transmission line model, the charge transfer resistance often does not contain On the transmission line, it is considered that the charge transfer resistor is a macroscopic non-distributive circuit element, but this is inconsistent with the facts! Contrary to the above, the theory of 171 is also hypothesized to persuade phase 1 transfer to occur at the boundary of the high-dimension boundary. Electrons transfer at the interface of the metal polymer, and ions enter at the interface of the polymer melt, while at the polymer layer. The neutrons and pairs of anions are transported by a diffusion-transfer mechanism.

In addition, 3 spit, etc. proposed the theory of impedance of macroscopically uniform porous electrodes. 18 taste description of porous electrode materials such as electrochemical synthesis of small lengths of the inside of the diffusion or swell process and may compensate the load caused by transfer reactions. (1) Theoretical analysis of the impedance spectrum of polyaniline, calculation of special ohmic resistance and charge transfer resistance, changes in the structure of macromolecules during the redox and protonation processes, and their electrode potentials and their dependence Zhai Ming has been able to correctly understand the high frequency limit of the impedance under the assumption that the polymer's porosity, the conductive polymer in the presence of parallel conduction channels of ions and electrons. The 6 explained that the homogeneous charge transfer between Qiandengtun and Fudaotun1.

5Comparative study of homogeneous membrane model and heterogeneous porous model Since both the homogeneous model and the heterogeneous porous model 15 and 8 can fit the same experimental results, the model is appropriate and perfect for interpretation of the system and experimental results. Sexuality is increasingly attracting the attention of researchers in order to compare homogeneity of homogeneity and transmission line theory. The impedance response of the complexes in different experimental configurations was determined by the solution of the metallocene solution and the metal solution. And applying the theory of co-diffusion and non-shifting of hole and cation production explained the low-frequency capacitance of the charge-transfer film and the variation of the width of the stomach and the width of the eight-zone region with the degree of oxidation and the thickness of the polymer. People's satisfaction with the reduction of macromolecules also increases, which is consistent with the increase of the electron resistance of the membrane and the decrease of the ion resistance, although the diffusion coefficient of the pore is larger than that of the cation, but at the low oxidation level, The number of shifts in holes is much smaller than the number of cations migrated. The experimental results show that the homogeneous homogeneous model can describe the charge transport behavior of the composite film well.

Since the interpretation of the parameters obtained from the impedance analysis depends on the model used, Fu, 21 studied the effect of ionic strength and film thickness on the transport properties of poly(o-aminophenol) film electrodes, and explained it using the transmission line theory and the electronic jump model22. The characteristic impedance alarms, prepared 1 words, 4 private words, speech numbers, and effective diffusion coefficients derived from the electronic jump model, have a dependence on the ionic strength and film thickness, and are not. It is close, which proves that the charge transport in the polymer is mainly determined by electron conduction. The porous model and the homogeneous model were also used to analyze the influence of the electrolyte concentration temperature of the membrane 7 and the electrode potential polythiol thiophene membrane electrode. As a result, the low-frequency part of the impedance spectrum can be fitted with a simple porous model to the 618 conductivity. Polymerization mechanism and conductive behavior study of polymer 13 combined with other technologies to explore the polymerization mechanism of conductive polymers, etc. The process of depositing conductive polymers on the electrode by electrochemical polymerization is quite complicated, involving monomer-to-electrode The diffusion has the subsequent reverse diffusion of the electro-oxidation oligomers of the intermediate primary ions and the precipitation on the electrode. For its deposition mechanism, there is a dispute of dimensionality 3, growth and growth of the dimension 20 .

Conductive macromolecules are a multidisciplinary research field. The demand for practical application of this technology in turn requires a deeper understanding of its conductive mechanism. This poses new opportunities and challenges for the development of electrochemical impedance spectroscopy. From the results of the above-mentioned recent research, it can be seen that although a lot of encouraging work has been carried out, it is still necessary to make a thorough study of the 15 behaviors of conductive polymers in theory and experiments.