Capacitance dispersion

Borisova et al. A diffuse-layer minimum was found in the C, E curves, but the capacitance dispersion was appreciable and the value of C at Emib for Cd was higher than that calculated using the C, E curve for Hg 10,220,221 jt was notect10 that one of the reasons for this was the roughness of the pc-Cd surface. Therefore, Cd, Pb, and T1 electrodes were remelted in an inert atmosphere to give solidified drop electrodes. The capacitance dispersion was somewhat lower, but the difference between calculated and experimental capacitance was still substantial.221... 

The BiDER/DMSO + LiC104 interface has been studied by impedance and a very well-developed diffuse layer minimum has been observed, with ,niB independent of cyao/75 The capacitance dispersion was no greater than 2 to 3% in the region -1.5 E< -0.3 V (SCE in H20). Linear Parsons-Zobel plots with/pz very close to unity were obtained, Q was independent of cya0j. 

In recent years it has been demonstrated by many researchers16,172 173 that the frequency dispersion or capacitance dispersion is intimately related to PSD or pore length distribution (PLD). In this case, the frequency dispersion is not called CPE behavior since the phase angle of the impedance spectra did not show a constant value over the whole frequency range. The phase angle of the impedance spectra measured on the porous electrode with broad PSD or PLD is larger than 45° in value at high frequencies and smaller than 90° in value at low frequencies. 

They found that surface roughness of the order found on polycrystalline metals could lead to the CPE behavior only at much higher frequencies than those observed experimentally. They concluded that an increase in the surface roughness of polycrystalline Pt did not change (even slightly increased) the ( ) parameter. However, it was found that the capacitance dispersion increases markedly with the addition of chloride ions. 

Sadkowski, A., On the ideal polarisability of electrode displaying CPE-type capacitance dispersion. Journal of Electroanalytical Chemistry, 2000, 481 pp. 222-226 Sadkowski, A, Response to the Comments on the ideal polarisability of electrodes displaying CPE-type capacitance by G. Ldng, K. E. Heusler. Journal of Electroanalytical Chemistry, 2000, 481 pp. 232-236... 

Lang, G, and K.L, Heusler, Comments on the ideal polarisability of electrodes displaying CPE-type capacitance dispersion. Journal of Electroanalytical Chemistry, 2000. 481 pp. 227-229... 

Impedance behavior, corresponding to anomalous capacitance dispersion requiring representation by a CPE, has been examined with respect to a specific form of irregularity or roughness, namely a surface having fractal, that is self-similar geometry on various scales, and was treated by Mulder el al. [1990] and by Pajkossy [1991]. 

This capacitance dispersion at solid electrodes depends strongly on the state of the electrode s surface, e.g. its roughness and degree of polycrystallinity, and also, importantly, on anion adsorption. The deviations from ideal capacitative behavior can be empirically represented by the so-called constant phase element (CPE) having the following dependence on frequency and containing the double-layer capacitance quantity, T ... 

A second possible explanation (b) is that the capacitance dispersion is entirely of interfacial origin, not involving bulk-solution resistance. This effect is associated with anion adsorption, probably coupled with complexity of anion adsorption kinetics (cf. Frumkin and Melik-Gaykazyan [1951], Pajkossy [1994]), at a roughened surface. This conclusion arises because it is found that at a deliberately roughened... 

Pt surface, as studied by Pajkossy [1994], almost ideally capacitative behavior can, in fact, be observed this is obviously a critical result indicating that it is not inseparable coupling between solution resistance and capacitance at a roughened (Pt) electrode surface (Pajkossy [1994]) that is the origin of dispersion effects. This led (Pajkossy [1994]) to the conclusion that it is ion (anion) adsorption that plays a crucial role in capacitance dispersion, because of frequency-dependent adsorption pseudocapacitance associated with anion chemisorption and associated kinetics of that process (Pajkossy [1994], Pajkossy et al. [1996]). 

Other types of capacitance dispersion measurements, such as a.c. impedance as a function of frequency, generally tend to give a less complete picture because of the relative inconvenience of measurements over a comparable time scale and the possible missing of fine structure" (34) with point-by-point measurements. 

The problem of combining various types of diffusion processes, including diffusion with finite boundaries and homogeneous reactions were addressed earlier [34,36]. One of the studied cases was finite reflecting boimdary diffusion, which also shows a capacitive dispersion [37]. A total expression for diffusion impedance was derived as a rearrangement of Eq. 5-45 for a case where the capacitive dispersion can be described by a constant phase element... 

In this expression the parameter R, Q( ) essentially represents a ratio of diffusion and capacitive dispersion contributions to the overall impedance process. This type of process can be represented by a parallel combination of a CPE and diffusion resistance R. At high frequencies a familiar -45° semiinfinite-diffusion Warburg impedance line is observed as a function of ... 

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