Impedance spectroscopy observing effects

Finally, it can be seen from Fig. 9.9a that the real impedance does not remain constant at low frequencies for the textile electrode, and this effect is more pronounced at higher electrolyte concentrations. Probably, Zr is influenced by other effects only occurring in the low-frequency range. This effect is frequently observed and described in the literature and is caused by non-uniformity of surfaces at the micro-scale, which in fact is the case for the textile electrodes. It is also not possible to explain this effect by a pure resistor or a pure capacitor in the electrical equivalent circuit. For this purpose, constant-phase elements are implemented as described in the theoretical discussion of electrochemical impedance spectroscopy (presented in Chapter 2, section 2.4). 

Impedance spectroscopy is discussed in depth in the monograph edited by J.Ross Macdonald [17]. It has its origins in the classical work of K.S. Cole and R.H. Cole, published more than 60 years ago, concerned with methods of plotting the response of a dielectric material to applied voltages as a function of frequency. The method assists in identifying observed relaxation effects with processes at the atomic and microstructural levels. For a system having a single well-defined... 

The similar breakdown of the surface state was also observed with parylene C film. Parylene C is a semicrystalline polymer and one of the most effective barriers for gases and vapors according to permeability values. It was thought that such an excellent barrier film would provide superior corrosion protection of a metal when it was deposited on the metal surface. Contrary to the expectation, parylene C film didn t provide good corrosion protection due to the surface state breakdown described above. This conclusion was ascertained by studies using electrochemical impedance spectroscopy (EIS), which is described in Chapter 28. 

As already mentioned, the formal transition to the frequency domain does not offer problems, yet in most cases the experimental application of impedance spectroscopy for evaluating the stoichiometric polarization is not of great worth as the frequencies used in the impedance experiments (as shown in Figure 44) are too high to observe the diffusion. Nonetheless, in such cases a combination of dc and ac methods is helpful, as the impedance branches which include bulk and boundary effects of Zr02 can be used to correct the steady-state value of the dc experiment (steady state initial value Onfy in cases of very... 

Electrochemical impedance spectroscopy (EIS) technique has been used for the experimental assessment of CO tolerance on different Pt-alloy catalysts and at different temperatures [187]. Hsing et al. [187] proposed that the critical potential at which pseudo-inductive behavior occurs could be used as a criterion for the evaluation of CO tolerance. A mathematical impedance model based on two state-variables (Pt-H and Pt-CO) was also developed to elucidate the reaction kinetics and mechanism of the H2/CO oxidation on a Pt/C catalyst [188]. In fact, this study has given better insight into explicitly understanding the impedance patterns and the quantitative assessment of the effect of applied potentials upon the oxidation reaction kinetics in a broad range of applied potentials. Nevertheless, with the consideration of only two adsorbed species, Pt-H and Pt-CO, the impedance model based on two state-variables was not able to explain the experimental observation... 

Because of the high cost of microgravity research, it is important to develop techniques that can continuously monitor the polymerization process in space. Impedance spectroscopy is one technique, which is being developed to complement other techniques used to study polymerization reactions. Impedance spectroscopy has been used successfully to study the photopolymerization of diacetylene both in solution and at the surface. There are distinct differences between the measurements of the solution and surface polymerization processes. In addition, the effect of convection on the polymerization process was observed using this technique. Impedance spectroscopy can potentially become a useful tool for monitoring polymerization processes in microgravity. 

Self-assembled mmiolayers (SAMs) of these compounds formed on Au bead electrode surfaces were used to incorporate Ceo onto the Au surfaces as judged by observation of its first two reduction potentials. Only the SAM of p-tcrt-butylcalix [8]arene thioctic ester 13 was found to be reasonably effective at immobilizing Cgo on the surfaces (Fig. 33.14). Cyclic voltammetiy with Ru(NH3)6 as a redox probe, together with impedance spectroscopy and reductive desorption, indicated that SAMs of 13 had a higher coverage than those of 11 and 12 [21]. 

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