EIS spectra

Figure 19. EIS spectra for zinc-coated steel with polyurethane topcoat exposed to natural seawater for 1, 7, and 13 months.

PB-MS appears to have high potential as an identification method for residues of some antibiotics in foods, since it generates library-searchable EI spectra and CI solvent-independent spectra. Limitations of the PB-MS interface. 

Equivalent circuit analysis is well suited for analysis of EIS measurements of conversion coatings and is the primary method for interpreting EIS spectra from conversion coated metal surfaces. A widely accepted generalized equivalent circuit model for the EIS response of pitted conversion coatings is shown in Fig. 22a (66,67). Several related models discussed below are also shown. In the gener-... 

For the EIS evaluation, samples were exposed to an aerated 0.5 M NaCl solution for 24 h under free corrosion conditions. During this time, some amount of corrosion damage occurred that normally manifested itself as pitting. Replicate EIS spectra were collected from each sample between 10 kHz and 10 mHz using a 10 mV sinusoidal voltage perturbation. During the 24 h exposure period, sam-... 

Figure 28 EIS spectra of the porous film formed at 360 s in 20% sulfuric acid at a current density of 400 A/m2, and a barrier film formed in 3% ammonium tartarate at a current density of 88 A/m2. (From J. DeLaet. H. Terryn, J. Vereecken. Electrochim. Acta 41, 1155 (1996).)...

Breakdown of anodic films is yet another phenomenon for which EIS is well suited. Equivalent circuit analysis has been used to analyze EIS spectra from corroding anodized surfaces. While changes in anodic films due to sealing are detected at higher frequencies, pitting is detected at lower frequencies. Film breakdown leads to substrate dissolution, and equivalent circuit models must be amended to account for the faradaic processes associated with localized corrosion. 

EIS can also detect defects arising from lack of adhesion at adhesively bonded surfaces (111). The presence of such defects produces pronounced changes in the character of the data presented either in complex plane plots or in Bode plots. Figure 38 illustrates the measurement configuration and provides examples of EIS data for defective and defect-free samples. Studies have shown that the presence of defects is readily revealed and that the geometry of the defects and their spatial extent can be inferred from a detailed analysis of EIS spectra. 

Figure 5.42 shows an example of the effect of humidity on the EIS spectra. It can be seen that the cut-off for anode humidification does not affect the spectra too much compared with the cut-off for cathode humidification. As we know, the fuel cell EIS primarily represents the cathode behaviour. Therefore, cathode humidification can greatly affect the whole impedance spectra. The humidification cut-off at the cathode causes a large difference in both the membrane resistance and the kinetic resistance. Dehydration of the anode also brings about a substantial increase in cathode impedance because a dry anode pulls water away from the cathode and across the membrane, which makes it hard to keep the cathode well hydrated [18],... 

EIS has played an important role in fuel cell technology development, as one of the most important research tools for fuel cell diagnosis. EIS can help to identify the contributions from different components or processes to the total impedance of a PEM fuel cell. Such information is very helpful for understanding the fundamental processes within the fuel cell, the performance-structure relationships, and the contributions of various components to performance loss, as well as the associated failure modes and mechanisms EIS thus assists with fuel cell design optimization and selection of the most appropriate fuel cell operating conditions. In this chapter, we will present some typical examples of the applications of EIS in PEM fuel cell research, and an overview of EIS spectra analysis. 

The ion traps generate low-resolution mass spectra but can have very good sensitivity. Some problems have been reported regarding the similarity between the spectra generated by ion traps and other types of mass spectrometers when the concentration of a certain compound is high. For high concentration, some ion traps do not generate typical EI+ spectra. 

It should be mentioned, however, that surface inhomogeneities of different dimensionality (cf. Section 2.1) significantly influence the kinetics of metal electrodeposition and the time-dependent surface morphology. Therefore, an exact analysis of corresponding EIS spectra is rather difficult. The necessary presumptions of stationarity and linearity for EIS measurements and quantitative interpretation of EIS data are often violated. The lack of direct local information on surface dynamics strongly hinders a quantitative analysis of the impedance behavior of time-dependent systems. Such considerations have been mainly disregarded in previous EIS data interpretations. In future, a combination of EIS measurements with in situ local probe... 

Figure 19 shows the LAMMA 1000 positive spectra of Irganox 1010 (Clba Geigy a high molecular weight (1176), multifunctional anti-oxidant and thermal stabilizer. The LAMMA matches the EI spectra well, with the LAMMA giving additional information the t-butyl, phenyl and benzyl ions suggest an aromatic compound. 

Eu " emission bands overlap with Sm bands as well as bands from other REE. Hence assignment of Eu " features requires careful comparison with doped standards, and use of time-resolution measurement techniques if available. Piriou et al. (2001) obtained high resolution spectra of Eu " in a synthetic sodium lead apatite, and confirmed that Ei spectra can be used to determine individual site occupations due to symmetry, splitting and lifetime effects. Eu " doped into synthetic Ca hydroxyapatite was also investigated by Ternane et al. (1999) with time-resolved techniques (see below). 

The EIS spectra for coated metal-electrolyte systems are characterised by two time constants, two semicircles in Nyquist plots, two negative slopes in Bode magnitude plots and two negative inflections in Bode phase plots [114, 115]. Figs. 1.6, 1.7, 1.8, 1.9 show coated metal solution interface (two time constant system) and C i is double-layer capacitance. 

Fig. 1.3 EIS spectra for single time Constant of bode magnitude plot...

Fig. 1.7 EIS spectra for two time constant of Bode magnitude plot...

EIS was carried out on unexposed coated panels using potentiostats viz. Gamry and CH Instmment, USA (model 600C, Reference electrode Ag/AgCl2(199 mV), Auxiliary electrode Platinum). EIS spectra were acquired through suitable model fit and AC 10 mV (rms) with varying frequencies 1-100 kHz were applied. The test plan of EIS on coated panels is given in Table 2.16. 

Figure 1. Combined EIS-EQCM measurements used to study non-stationary interfaces. At each of the steps of the staircase scan, EIS spectra are taken while EQCM measurements run continuously in parallel.

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