Electronically conducting polymers impedance

Impedance, for measurement of the potential of zero charge, 35 Impedance blocks, for polypyrrole, 577 Impedance spectroscopy of electronically conducting polymers, 576 Indium... 

There are other factors that also affect the degree of conduction of electronically conducting polymers when they are in the oxidized state one is alignment of the polymer chains. Thus, a rate-determining step in conduction may be the transfer of electrons from one unit in the spine to another here linearity in the chain would help andjunctions out of alignment would impede the continued passage of electrons along the chain. 

The rate of anion diffusion can be measured in various ways. The conventional way is to use classical electrochemical methods, e.g., chronoamperometry or chronocoulome-try. The measurement of electrochemical impedance is also sometimes used. However, the electronically conducting polymers have a special property, potential-dependent absorption spectrum, which can be advantageously used to monitor the oxidation state of the polymer. In addition to the neglect of capacitive current, monitoring of the spectral change gives additional information. For instance, the presence of an isosbestic point shows that most likely... 

Penner, R. M., and Martin, C. R., Electrochemical investigations of electronically conductive polymers. 2. Evaluation of charge-transport rates in polypyrrole using an alternating current impedance method, J. Phys. Chem., 93, 984-989 (1989). 

Complex Impedence Response of Electronically Conducting Polymer Films... 

FIGURE 1.82. Schematic representation of the equivalent circuit ladder network corresponding to Fletcher porous electrode model for electronically conducting polymers (see Refs. 68, 69). The specific equivalent circuit representation of the interfacial impedance element is also illustrated. 

Figure 1.82 shows the model circuit which takes the form of a diagonally connected discrete ladder network or in simple terms, a dual-rail transmission line of finite dimension. The essential problem is to replace the general impedance elements x, y, and z by suitably arranging such passive circuit elements as resistors and capacitors that adequately represent the microscopic physics occurring within an electronically conducting polymer. 

In situ electron transport measurements on conducting polymers are commonly made by using a pair of parallel-band electrodes bridged by the polymer [Fig. 9(A)].141142 Other dual-electrode techniques in which the polymer film is sandwiched between two electrodes [Fig. 9(B)],139,140 rotating-disk voltammetry [Fig. 9(C)],60,143 impedance spectroscopy,144,145 chronoamperometry,146 and chronopotentiometry147 have also been used. 

Impedance spectroscopy is best suited for the measurement of electronic conductivities in the range 10 -7to 10 2S cm 1.145 In principle, it is perhaps the best method for this range, but it is often difficult to interpret impedance data for conducting polymer films. The charge-transfer resistance can make measurements of bulk film resistances inaccurate,145 and it is often difficult to distinguish between the film s ionic and electronic resistances.144 This is even more of a problem with chronoamperometry146 and chronopotentiometry,147 so that these methods are best avoided. 

These examples and the general subjects mentioned above illustrate that ion conduction and the electrochemical properties of solids are particularly relevant in solid state ionics. Hence, the scope of this area considerably overlaps with the field of solid state electrochemistry, and the themes treated, for example, in textbooks on solid state electrochemistry [27-31] and books or journals on solid state ionics [1, 32] are very similar indeed. Regrettably, for many years solid state electrochemistry/solid state ionics on the one hand, and liquid electrochemistry on the other, developed separately. Although developments in the area of polymer electrolytes or the use of experimental techniques such as impedance spectroscopy have provided links between the two fields, researchers in both solid and liquid electrochemistry are frequently not acquainted with the research activities of the sister discipline. Similarities and differences between (inorganic) solid state electrochemistry and liquid electrochemistry are therefore emphasized in this review. In Sec. 2, for example, several aspects (non-stoichiometry, mixed ionic and electronic conduction, internal interfaces) are discussed that lead to an extraordinary complexity of electrolytes in solid state electrochemistry. 

Figure 4.38. Equivalent circuits of conducting polymers with a Randles circuit [12]. (Reprinted from Journal of Electroanalytical Chemistry, 420, Ren X, Pickup PG. An impedance study of electron transport and electron transfer in composite polypyrrole plus polystyrenesulphonate films, 251-7, 1997 with permission from Elsevier and from the authors.)...

Electronic Interactions Chemical Interactions Redox Reactions at the Conducting Polymer Surface Conducting Polymer as an Oxidant Neutral (Undoped) Forms of Conjugated Polymers Role of the Dopant Ion Influence of CPs on Overall Coating Impedance Approaches to Forming Conjugated... 

It is evident that the shape of the impedance spectra varies with the potential since the values of the charge transfer resistance (Ret), the low frequency (redox) capacitance (Cl) and the Warburg coefficient change with the potential more exactly, they depend on the redox state of the polymer. In many cases D is also potential-dependent. The double-layer capacitance (Cdi) usually shows only slight changes with potential. The ohmic resistance (Rq) is the sum of the solution resistance and the film resistance, and the latter may also be a function of potential due to the potential-dependent electron conductivity, the sorption of ions, and the swelling of the film. In Fig. 3.9 three spectra are displayed, which were constructed using the data obtained for a PTCNQ electrode at three different potentials near its equilibrium potential [23]. 

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