Determination methods impedance

Determining the length of the polymer product is of key importance for understanding the polymerization process and received considerable attention ever since the reaction was discovered. On the experimental side direct determination is impeded by the insolubility of most polydiacetylenes — exceptions will be mentioned below — which precludes application of standard methods for measuring the molecular weight. 

The techniques of impedance spectroscopy, widely used in dielectrics (Jonscher, 1983 MacDonald, 1987) have been applied to magnetic materials. In this method, impedance measurements as a function of frequency are modelled by means of an equivalent circuit and its elements are associated with the physical parameters of the material. The complex permeability, p, is determined from the complex impedance, Z, by ... 

The film grown on an electrode surface has a duplex structure with a thin, compact first layer that is directly on the electrode surface and a porous second layer contacting the electrolyte. An equivalent circuit can be used to represent the electrical properties of this film. The components of an equivalent circuit can be determined by impedance spectroscopy. Therefore, this method has become one of the key methods for the characterization of conducting polymers. 

Such a method was used in the literature for the determination of impedances [99-101], and a commercial apparatus [102] applying a current step was described. Taking the FT of the derivative of the potential and current versus time gives the impedance as a function of frequency. However, some authors [100, 101] tried to extrapolate the obtained results to low frequencies beyond the experimental values. If the data are acquired during time T = NAt, the information in the measured signal is obtained for frequencies from l/T up to the Nyquist frequency l/2At, where At is the sampling time. It has been shown [103] that extrapolating impedances to frequencies lower than l/T introduces artifacts. In addition, the measured... 

Based on that knowledge, the impedance of electrode processes in the presence of diffusion in various geometries and adsorption is mathematically developed. This leads to the general method of determining the impedances of complex mechanisms. As an illustration, the impedance of electrocatalytic reactions involving hydrogen adsorption, absorption, and evolution is presented. 

Comparison between state of charge determination methods for lithium-ion batteries based on the measurement of impedance, voltage and coulomb counting... 

Thus, in addition to the aforementioned variable frequency method the variable electrode distance method [2] also can be used. From the slope p of the R — l/S graph, accurate electrical conductivity can be determined. Using this method, impedance due to the electrode polarization can be completely eliminated. 

The most accurate method for the determination of impedance is, again, by the use of a.c. bridges used for the measurement of capacity of the double layer. There is one difference, however. Since impedance measurements are usually made at the equilibrium potential, the need for the d.c. potential... 

Thermal-oxidative degradation of polymer binders was investigated via derivatographic method on MOM device with the heating-up velocity of 3.2°/min. Electroconductive properties of nanocomposite samples (cross-section 0.2 cm, length 1 cm) were determined via impedance measurements (frequency 1000 Hz, amplitude 5 mv) on Electrochemical workstation CHI 660D. 

Electrochemical impedance spectroscopy (EIS) in a sufficiently broad frequency range is a method well suited for the determination of equilibrium and kinetic parameters (faradaic or nonfaradaic) at a given applied potential.268,269 EIS has been used to study polycrystalline Au, Cd, Ag, Bi, Sb, and other electrodes.152249 270-273... 

The electrical double layer of pc-Cd electrodes has been studied in many works,10,220,221,271,637,662 but the picture is still somewhat unclear. The first attempt to determine the electrical double layer parameters at solid Cd, Pb, and T1 electrodes by the impedance method was made by... 

Guidelli, and methods for the determination of, 63 Heusler and Lang, anisotropic surface potential and, 34 and the impedance method, 35 importance, 5... 

Transient measnrements (relaxation measurements) are made before transitory processes have ended, hence the current in the system consists of faradaic and non-faradaic components. Such measurements are made to determine the kinetic parameters of fast electrochemical reactions (by measuring the kinetic currents under conditions when the contribution of concentration polarization still is small) and also to determine the properties of electrode surfaces, in particular the EDL capacitance (by measuring the nonfaradaic current). In 1940, A. N. Frumkin, B. V. Ershler, and P. I. Dolin were the first to use a relaxation method for the study of fast kinetics when they used impedance measurements to study the kinetics of the hydrogen discharge on a platinum electrode. 

The second limitation is concerned with the high time constant Tceii determined by the high capacitance of the CLs and by substantial cell resistance. Tceu for a thick MEA of large geometric area may exceed several minutes, thus strongly limiting the application of transient methods and methods based on the concept of impedance. 

Apart from the necessity of excluding interferences from any diffusion potential, normal potentiometry requires accurate determination of the emf, i.e., without any perceptible drawing off of current from the cell therefore, usually one uses the so-called Poggendorff method for exact compensation measurement the later application of high-resistance glass and other membrane electrodes has led to the modern commercial high-impedance pH and PI meters with high amplification in order to detect the emf null point in the balanced system. 

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