Alternating current impedance spectroscopy

EIS, also known as alternating current impedance spectroscopy, is a powerful technique for characterizing the electrode, electrolyte, and the dynamic properties of the solid-liquid interface [47]. This section focuses on the applications of the EIS in characterizing the ESs and the electrolyte materials. 

For SAMs with attached redox molecules, k (units of s ) can be measured by cychc voltammetry, chronoamperome-try (CA), alternating current impedance spectroscopy (ACIS), alternating current voltammetry (AGV), AG electroreflectance spectroscopy, and an indirect laser-induced temperature (ILIT) jump method. 

Frequency Response Analysis the response of an electrode to an imposed alternating voltage or current sign of small amplitude, measured as a function of the frequency of the perturbation. Also called Electrochemical Impedance Spectroscopy. 

The IV measurements on molecules and monolayers have been carried out almost exclusively using direct current (DC) frequency-dependent alternating current (AC) impedance measurements have rarely been performed, even though a rich spectroscopy may reveal itself, if the IV measurements were followed as a function of frequency v. 

The two main techniques for measuring electrode losses are current interrupt and impedance spectroscopy. When applied between cathode and anode, these techniques allow one to separate the electrode losses from the electrolyte losses due to the fact that most of the electrode losses are time dependent, while the electrolyte loss is purely ohmic. The instantaneous change in cell potential when the load is removed, measured using current interrupt, can therefore be associated with the electrolyte. Alternatively, the electrolyte resistance is essentially equal to the impedance at high frequency, measured in impedance spectroscopy. Because current-interrupt is simply the pulse analogue to impedance spectroscopy, the two techniques, in theory, provide exactly the same information. However, because it is difficult to make a perfect step change in the load, we have found impedance spectroscopy much easier to use and interpret. 

Impedance spectroscopy is a versatile electrochemical tool, helpful to characterize the intrinsic dielectric properties of various materials. The basis of this technique is the measurement of the impedance (opposition to alternating current) of a system, in response to an exciting signal over a range of frequencies (Bard and Faulkner, 2001). 

Impedance spectroscopy may provide quantitative information about the conductance, the dielectric coefficient, the static properties of a system at the interfaces, and its dynamic changes due to adsorption or charge-transfer phenomena. Since in this technique an alternating current with low amplitude is employed, a noninvasive observation of samples with no or low influence on the electrochemical state is possible. 

What Is Impedance Spectroscopy The words impedance spectroscopy imply the dependence of impedance on a wavelength and therefore on frequency. The frequency here is not that of an incident light beam, but of an alternative current applied to a cell, and then the question is What is impedance ... 

Both alternating and direct current techniques can be used (see also impedance spectroscopy), but the electrode polarization effects should be minimized or taken into account in all cases. For this goal, a four-electrode method where the potential probes are placed between current probes, is often used. 

Immittance — In alternating current (AC) measurements, the term immittance denotes the electric -> impedance and/or the electric admittance of any network of passive and active elements such as the resistors, capacitors, inductors, constant phase elements, transistors, etc. In electrochemical impedance spectroscopy, which utilizes equivalent electrical circuits to simulate the frequency dependence of a given elec-trodic process or electrical double-layer charging, the immittance analysis is applied. 

In order to understand electrochemical impedance spectroscopy (EIS), we first need to learn and understand the principles of electronics. In this chapter, we will introduce the basic electric circuit theories, including the behaviours of circuit elements in direct current (DC) and alternating current (AC) circuits, complex algebra, electrical impedance, as well as network analysis. These electric circuit theories lay a solid foundation for understanding and practising EIS measurements and data analysis. 

Electrochemical Measurements. Cyclic voltammetry and alternating current (ac) impedance spectroscopy were performed using an ac impedance system (EG G Princeton Applied Research model 378) that included a potentiostat-galvanostat (model 273), a two-phase lock-in analyzer (model 5208), and an IBM PS/2 computer. For ac impedance measurements, a 5-mV sine wave was superimposed on an applied voltage bias from the potentiostat. The reference electrodes were saturated calomel electrodes (SCE Fisher) for measurements in aqueous solution and silver electrodes... 

Impedance spectroscopy Impedance spectroscopy describes the response of a circuit to an alternating current or voltage as a function of frequency. In alternative current (a.c.) theory following Ohm s law given in Equation 12.6,... 

Electrochemical corrosion techniques are essential to predict service life in chemical and construction industries. The following direct current (dc) electrochemical methods are used in corrosion engineering practice linear polarization technique, Tafel extrapolation, and open circuit potential vs. time measurements. The alternating current (ac) technique is electrochemical impedance spectroscopy (EIS). This technique uses alternating current to measure frequency-dependent processes in corrosion and estimates the change of polarization resistance as a function of time. 

B.B. Katemann, A. Schulte, E.J. Calvo, M. Koudelka-Hep, W. Schuhmann, Localized electrochemical impedance spectroscopy with high lateral resolution by means of alternating current scanning electrochemical microscopy, Electrochem. Commun. 4 (2002) 134-138. 

Electrochemical impedance spectroscopy An alternating current technique that measures the impedance of an electrochemical system. The resulting spectra can be used to estimate the various components of an equivalent circuit that represent an electrochemical cell. 

For the investigation of the properties of BLMs, electrical methods have been applied at the very beginning. In addition to the CV technique, other methods such as electrical impedance spectroscopy (EIS) have been applied. Shortly after the discovery of the BLM system, Hanai and Hay don reported the thickness measurement of a planar lipid bilayer using the impedance technique [1 - 3]. Their results are in accord with the value obtained on RBC, estimated by Fricke (see Eq. 1). The impedance technique, nowadays also known as EIS, has subsequently used by many others. The basis of the technique is that a small alternating current (AC) of known frequency and amplitude is applied to the system (e.g. a BLM). The resulting amplitude and phase difference that develop across the BLM are monitored. For a BLM of cross-sectional area (A), and thickness the ability of the BLM to conduct and to store electrical charges are described by the following ... 

Impedance Spectroscopy. Impedance spectroscopy has been carried out on devices with WO3 as the cathodic electrochromic layer, counter electrodes of iridium oxide, polyaniline or Prussian blue, and polymers as electrolytes (Katsube et al [1986], Friestad et al [1997]). The equivalent circuit for a whole device becomes very complicated. In the works quoted above simplified, Randles-type circuits were used for the two electrochromic layers, while the ion conductor was modeled by a pure resistance, or neglected. Extraction of device parameters from the data fitting was reported. However, it is clear that in many cases it will be difficult to distinguish the contributions from the different layers in a device, in particular if the migration impedances, ion diffusion impedances, etc. are of the same order of magnitude. When it comes to characterizing electrochromic devices, impedance spectroscopy is a very time-consuming process, since a spectrum down to low frequencies should be taken at a number of equilibrium potentials. Thus we believe that transient current measurements in many cases offer a faster alternative that sometimes allows a simple determination of diffusion coefficients. 

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