AC impedance spectroscopy

EIS was also carried out on the exposed coated MS and WS panels using Gamry potentiostat and the overall plan of conducting EIS is given in Table 2.9. 

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AC impedance spectroscopy is widely employed for the investigation of both solid- and liquid-phase phenomena. In particular, it has developed into a powerfiil tool m corrosion teclmology and in the study of porous electrodes for batteries [, and ]. Its usage has grown to include applications ranging from... 

A.D. Frantzis, S. Bebelis, and C.G. Vayenas, Electrochemical promotion (NEMCA) of CH4 and C2H4 oxidation on Pd/YSZ and investigation of the origin of NEMCA via AC impedance spectroscopy, Solid State Ionics 136-137, 863 (2000). 

This does not imply that this double layer is at its point of zero charge (pzc). On the contrary, as with every other double layer in electrochemistry, there exists for every metal/solid electrolyte combination one and only one UWr value for which this metal/gas double layer is at its point of zero charge. These critical Uwr values can be determined by measuring the dependency onUWR of the double layer capacitance, Cd, of the effective double layer at the metal/gas interface via AC Impedance Spectroscopy as discussed in Chapter 5.7. 

The technique of AC Impedance Spectroscopy is one of the most commonly used techniques in electrochemistry, both aqueous and solid.49 A small amplitude AC voltage of frequency f is applied between the working and reference electrode, superimposed to the catalyst potential Uwr, and both the real (ZRe) and imaginary (Zim) part of the impedance Z (=dUwR/dI=ZRc+iZim)9 10 are obtained as a function of f (Bode plot, Fig. 5.29a). Upon crossplotting Z m vs ZRe, a Nyquist plot is obtained (Fig. 5.29b). One can also obtain Nyquist plots for various imposed Uwr values as shown in subsequent figures. 

For the experiments shown in Fig. 5.30 the ratio Cdi2/Cdi] is on the average 2500, very close to the ratio NG/Ntpb ( 3570)54 where N0 is the gas-exposed electrode surface area and Ntpb is the surface area of the three phase boundaries. These quantities were measured via surface titration and via SEM and the techniques described in section 5.7.2, respectively. Thus once N0 has been measured, AC Impedance spectroscopy allows for an estimation of the three-phase-boundary (tpb) length via ... 

Similar are the conclusions from the work of Kek, Pejonic and Mogensen55 who were first to use AC Impedance spectroscopy for the detailed investigation of Pt, Au and Ni films deposited in YSZ and exposed... 

In summary AC impedance spectroscopy provides concrete evidence for the formation of an effective electrochemical double layer over the entire gas-exposed electrode surface. The capacitance of this metal/gas double layer is of the order of 100-300 pF/cm2, comparable to that corresponding to the metal/solid electrolyte double layer. Furthermore it permits estimation of the three-phase-boundary length via Eq. 5.62 once the gas exposed electrode surface area NG is known. 

Thus, due to the lack of sufficient Ds data for most metals, other than Pt, the most reliable method for measuring Kpb and N,Pb,n is based on AC Impedance spectroscopy as outlined in the previous section and using equation (5.62), i.e. 

Thus the difference jJ02-(S) Po2 (M) is the thermodynamic driving force for O2 backspillover from the support onto the catalyst surface as already discussed in Chapter 3 and as proven by AC Impedance spectroscopy, STM, TPD and XPS as reviewed in Chapter 5. It should be noted in equations (11.4) and (11.5) that the Fermi level of the metal is also the Fermi level of the support. 

AC Impedance spectroscopy, 237 Auger electron spectroscopy, AES, 254 High resolution electron energy loss spectroscopy, HREELS, 43, 69 Infrared spectroscopy, IRS, 39, 69 Surface enhanced Raman spectroscopy, SERS, 256... 

Z. G. Shao, 1. M. Hsing, H. Zhang, and B. Yi. Influence of anode diffusion layer on the performance of a liquid feed direct methanol fuel cell by AC impedance spectroscopy. International Journal of Energy Research 30 (2006) 1216-1227. 

The ion conductivities of a range of TPEOCELL complexes with LiCFsSOs were examined by AC impedance spectroscopy from 293-373 K, so that all the complexes remained in the liquid-crystalline state during the measurements [235]. The inorganic salt concentration, indicated by the molar ratio of lithium ions to oxygens in the polymer chain, [Li]/[0], ranged from 0.038 to 0.125. The bulk conductivities were 10-6 Son-1 at ambient temperatures... 

In this respect, this review provides a comprehensive survey of synthetic methods and physicochemical properties of the porous carbon materials. Furthermore, as electrochemical applications of the porous carbons to electrode materials for supercapacitor, the effects of geometric heterogeneity and surface inhomogeneity on ion penetration into the pores during double-layer charging/ discharging are discussed in detail by using ac-impedance spectroscopy, current transient technique, and cyclic voltammetry. 

V. ELECTROCHEMICAL CHARACTERISTICS OF CARBON-BASED POROUS ELECTRODES FOR SUPERCAPACITOR THE USES OF AC-IMPEDANCE SPECTROSCOPY, CURRENT TRANSIENT AND CYCLIC VOLTAMMETRY... 

To evaluate the kinetics of fast reactions, transient techniques are being used, such as voltammetry, potential step amperometry and ac impedance spectroscopy. 

The technique that measures the AC impedance of a circuit element or an electric circuit is called AC impedance spectroscopy. As described in Section 2.4, the impedances of a resistor (X, ). a capacitor (Zc), and an inductor (ZL) for a sinusoidal system can be expressed, respectively, as follows ... 

If AC impedance spectroscopy is used in an electrochemical system, this technique is generally called electrochemical impedance spectroscopy, known as EIS. The impedance of an electrochemical system can also be expressed typically in Cartesian coordinates ... 

Springer TE, Zawodzinski TA, Wilson MS, Gottesfeld S (1996) Characterization of polymer electrolyte fuel cells using AC impedance spectroscopy. J Electrochem Soc 143(2) 587-99... 

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