AC impedance analysis

The accuracy of the AC-impedance analysis far exceeds the previous studies based on cyclic voltammetry. However, the limited frequency range available for liquid-liquid interfaces imposes severe restrictions for the deconvolution of the various responses associated with the elements in Fig. 7. An alternative approach was introduced by Ding et al. 

Hie main experimental techniques used to study oxygen migration in doped cerias are based on the AC impedance analysis of the measured electrical conductivity. It is found that the oxygen ion conductivity of ccria-bascd oxides depends strongly upon the dopant size and concentration. Both these factors are related to defect association between oxygen vacancies (the charge carriers) and other defects (mainly dopant substitutionals) which were discussed in section 8.3.2,. 

We now use an equivalent circuit shown in Fig. 2.21. As opposed to Fig. 2.18, the faradaic impedance Zf and double-layer non-faradaic impedance Zcapacitance elements. That is, it is unnecessary to specify each of the elements involved in these two partial impedance units. We assume that we have a data set of Zt including the frequencies at the high limit from which we can determine the value of (this frequency is usually called the high frequency Umif in the ac impedance analysis protocol). Then, the ac potential difference across Zf,... 

A disadvantage common to both classes of spectrum analyzer discussed so far is that they do not measure absolute amplitudes accurately, and they do not measure phase at all. Although this last limitation can be circumvented by the use of KK transformations (see Section 3.1.2.9), these instruments generally are poor choices for linear circuit (ac impedance) analysis. 

In this chapter, we are concerned with machine implementation of transform techniqnes, either software or hardware, to obtain data in a form convenient for ac impedance analysis. In recent years, the advent of hard-wired (dedicated) Fourier transform nnits (Reticon [1977]) and the fast Fourier transform algorithm, or FFT (Cooley and Tnkey [1965], Hartwell [1971]), have concentrated practical interest almost exclnsively on the Fourier transform. 

Thomas, M.G.S.R.,P.G. Bruce, andJ.B. Goodenough(1985). AC Impedance Analysis of Polycrystalline Insertion Electrodes Application to LiCoO. Journal of the Electrochemical Society 132, 1521. 

Arai H, Muller S, Haas O (2000) AC impedance analysis of bifunctional air electrode for metal air batteries. J Electrochem Soc 146 3584... 

Rate constants obtained by ac impedance analysis are much higher than those obtained by techniques based on the passage of a direct current through the interface. 

Polymer film conductivities were measured by complex AC impedance analysis, as described previously for MgCl electrolytes. Among the lead bromide electrolytes, PbBr2.(PEQ) has tne-.highest conductivity between 60 C and 200°C. It is about 10 ohm-cm) at 180°C. The variation of conductivity with temperature cycling reveals complex hystereses that surely are the result of the various dissolution and crystallization processes which occur as the temperature is changed. The lead iodide electrolytes are generally lower in conductivity compared to the bromides. 

Samples for AC impedance analysis were pressed into pellets inside air-tight conductivity cells. Pt or Li (ribbon, Foote Mineral Co.) electrodes were used in these measurements. The frequency dependent impedance of the samples was measured on a HP 4192A impedance analyzer (13 MHz-5 Hz) or a Solartron 1250 Frequency Response Analyzer/1286 potentiostat system (65.5 KHz-10 Hz). 

To achieve the performance level of liquid electrolyte-based systems which can be discharged at current densities of up to several mA/cm, the polymer electrolyte should possess ion conductivities approaching or beyond 10 S/ cm at ambient temperature. As the polymer electrolyte can be processed into a self-standing membrane, the ion conductivity is usually measured via AC impedance analysis with an electrochemical cell consisting of the polymer electrolyte film sandwiched between two blocks of stainless steel. 

The measurement of the electrode impedance has also been ealled Faradaie impedanee method. Since measurements are possible by applying either an electrode potential modulated by an AC voltage of discrete frequeney (which is varied subsequently) or by applying a mix of frequencies (pink noise, white noise) followed by Fourier transform analysis, the former method is sometimes called AC impedance method. The optimization of this method for the use with ultramicroelectrodes has been described [91Barl]. (Data obtained with these methods are labelled IP.)... 

Measurements of electrochemical noise and AC impedance of coated metal substrates are under development (indeed have been used for quite some time). These measurements relate to the corrosion protection afforded by the coating and can, in principle, be made continuously. The complexity of the electrochemical reactions require sophisticated data analysis for extraction of useful information and relationships. 

A consistent picture for dynamics of heterogeneous ET has been emerging in the last 5 years with the development of new experimental approaches. Techniques such as AC impedance, modulated and time-resolved spectroscopy, SECM, and photoelectrochemical methods have extended our knowledge of charge-transfer kinetics to a wide range of time scales. This can be exemplified by comparing impedance analysis, which is limited to k of... 

This circuit is usually referred to as the Randles circuit and its analysis has been a major feature of AC impedance studies in the last fifty years. In principle, we can measure the impedance of our cell as a function of frequency and then obtain the best values of the parameters Rct,<7,C4i and Rso by a least squares algorithm. The advent of fast micro-computers makes this the normal method nowadays but it is often extremely helpful to represent the AC data graphically since the suitability of a simple model, such as the Randles model, can usually be immediately assessed. The most common graphical representation is the impedance plot in which the real part of the measured impedance (i.e. that in phase with the impressed cell voltage) is plotted against the 90° out-of-phase quadrature or imaginary part of the impedance. 

In addition, from the analysis of the ac impedance spectra obtained from the previously pitted surfaces under open circuit conditions at room temperature in 0.5 M Na2S04 solution51 and from the in-situ pitted surfaces in Cl ion-containing thiosulfate solution at various applied potentials and solution temperatures,52 they verified that dr>ss is inversely proportional to the CPE exponent for capacitive charging process (Eq. 30)51 and the depression parameter for charge transfer process.52... 

Xiong, S. Wei, J. Jia, P. Yang, L. Ma, ]. Lu, X., Water-processable polyaniline with covalently bonded single-walled carbon nanotubes Enhanced electrochromic properties and impedance analysis. Acs. Appl. Mater. Interfaces 2011, 3, 782-788. 

As is well known in the field of electrochemistry in general, electrode kinetics may be conveniently examined by cyclic voltammetry (CV) and by frequency response analysis (ac impedance). The kinetics of the various polymer electrodes considered so far in this chapter will be discussed in terms of results obtained by these two experimental techniques. 

Simplicity and reliability of operation make AC impedance measurements attractive as a technique in the evaluation of coating integrity. As opposed to classical salt spray test, analysis times are shorter with the AC impedance technique and quantitative data are obtained permitting relevant mechanistic Information to be derived. Impedance test methods are likely to find many applications in the resolution of unsolved practical problems ( .) ... 

AC Impedance system 368 (EG G PARC, Princeton, NJ) with Fast Fourier Transform analysis was used along with a potentlostat EG G model 273. The potentlostat was coupled to an Apple 11+ computer through an IEEE-488 Interface. A frequency range of 0.01 Hz to 10 Hz was used for many of the experiments. The electrolyte used was a 3 weight percent sodium chloride solution and was prepared using ACS certified chemicals and deionized water. 

This circuit is usually referred to as the Randles circuit and its analysis has been a major Feature of AC impedance studies in the last fifty years. In principle, we can measure the impedance of our cell as a Function of Frequency and then obtain the best values of the parameters and by a... 

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