Capacitance-potential curve

Fig. 20.9 Experimental capacitance-potential curve for O-OOI m KCl and calculated curve using the Gouy-Chapman model. The experimental curve and the theoretical curve agree at potentials (us R.H.E.) near the p.z.c. Note the constant capacitance of 17 x 10 F m at negative potentials (after Bockris and Drazic )...

Bagotskaya and the integration of capacitance-potential curves for the determination of surface charges, 45 Bai and Conway, discussion of bubbles, 529 Band... 

Fig. 4. Differential capacitance-potential curves for various concentrations of aniline in 1-0 M aqueous potassium chloride and at a mercury electrode-frequency 400 Hz.

Fig. 9. Capacitance-potential curves for a number of common electrochemical solvents containing O lM potassium hexafluorophosphate, a relatively non-adsorbing electrolyte. (From Payne 1967, 1970.)...

Hiratsuka et al102 used water-soluble tetrasulfonated Co and Ni phthalocyanines (M-TSP) as homogeneous catalysts for C02 reduction to formic acid at an amalgamated platinum electrode. The current-potential and capacitance-potential curves showed that the reduction potential of C02 was reduced by ca. 0.2 to 0.4 V at 1 mA/cm2 in Clark-Lubs buffer solutions in the presence of catalysts compared to catalyst-free solutions. The authors suggested that a two-step mechanism for C02 reduction in which a C02-M-TSP complex was formed at ca. —0.8 V versus SCE, the first reduction wave of M-TSP, and then the reduction of C02-M-TSP took place at ca. -1.2 V versus SCE, the second reduction wave. Recently, metal phthalocyanines deposited on carbon electrodes have been used127 for electroreduction of C02 in aqueous solutions. The catalytic activity of the catalysts depended on the central metal ions and the relative order Co2+ > Ni2+ Fe2+ = Cu2+ > Cr3+, Sn2+ was obtained. On electrolysis at a potential between -1.2 and -1.4V (versus SCE), formic acid was the product with a current efficiency of ca. 60% in solutions of pH greater than 5, while at lower pH... 

The presence of the diffuse layer determines the shape of the capacitance-potential curves. For a majority of systems, models describing the double-layer structure are oversimplified because of taking into account only the charge of ions and neglecting their specific nature. Recently, these problems have been analyzed using new theories such as the modified Poisson-Boltzmann equation, later developed by Lamper-ski. The double-layer capacitanties calculated from these equations are... 

Anastopoulos et al. [47] have analyzed interfacial rearrangements of triphenyl-bismuth and triphenylantimony at mercury electrode in nonaqueous solvents of high dielectric constant. These phenomena were detected as the peaks in the capacitance-potential curves at intermediate negative potentials for triphenyl-bismuth and triphenylantimony in N-methylformamide, A,A-dimethylforma-mide, dimethyl sulfoxide, propylene carbonate, and methanol solutions. 

However, even taking all these facts into account, this theory is not able to reproduce the capacitance-potential curves in the regions beyond the pzc proximity. The model seems, in fact, to be in sharp disagreement with the experimental behavior. The Gouy-Chapman theory might best be described as a brilliant failure. However, as will be seen, it represents an important contribution to a truer description of the double layer it also finds use in the understanding of the stability of colloids and, hence, of the stability of living systems (see Section 6.10.2.2). 

The capacitance-potential curves have parabolic shapes with a minimum at Eq = 0 (i.e., at the potential of zero charge). 

The capacitance—potential curves of the basal plane of highly ordered pyrolytic graphite (HOPG) (Fig. 19.3) show an anomalous low capacitance... 

Figure 19.3 Capacitance-potential curves for HOPG in NaF solutions of pH of about 6 at 25°C a.c. measurements at 20 Hz. (Reproduced from Ref. [26] with permission from Elsevier.)...

The surface state capacitance for t i CdTe-electrolyte interface is plotted as a function of electrode potential in Fig. 16 (the minimum was taken as the value at 0.2V NHE). The surface state capacitance decreases in the cathodic direction in the region -0.56 to -2.26V (NHE). Capacitance measurements at cathodic potentials less negative than -0.56V could not be carried out because of the onset of a C02 independent anodic dark current. Assuming (in consistence with other examples of pseudo capacitance behavior) that the capacitance-potential curve is symmetrical with respect to a maximum at -0.66V, the number of surface states was calculaed using the above equation. The number of surface states as a function of electrode potential, on the basis of this assumption, is shown in Fig. 17. Geometric area of the electrode was used to calculate the surface state density. Real surface area may be larger. 

Figure 1.15 Capacitance-potential curves for n-pentanol in 0,1 U KCl at a Hg drop electrode.

Figure 11.13. Simulations of the capacitance-potential curves employing Equations (11.17)-(11.19) taking = —38 kJ mol , = 10 molm and various...

Figure 11.14. Capacitance-potential curves for various concentrations of ZnTPPC (a) and Cu-chlorophyllin (b) at the water/DCE interface. The changes in the potential dependence of the capacitance, as well as the shift of the potential of minimum capacitance reflect the specific adsorption of the water-soluble porphyrin derivatives. Figure (a) reprinted with permission from ref.[95]. Copyright (2003) American Chemical Society. Figure (b) reproduced from ref.[87] by permission of the Royal Society of Chemistry.

Figure 4.5 Capacitance-potential curves for the basal plane of stress-annealed graphite for a range of concentrations (0.9, 10-, 10-2,, 0-3, 0-4 10-5M from...

Islam MM, Alam MT, Okajima T, Ohsaka T (2009) Electrical double layer structure in ionic liquids an understanding of the unusual capacitance—potential curve at a nonmetallic electrode. J Phys Chem C 113 3386-3389... 

The foregoing observations have proved a durable guide to interfacial properties over a number of years. However, in the light of more recent studies, including those of electrode processes in melts, it may be necessary to revise certain detailed aspects, particularly concerning the higher-temperature behavior of the two branches of the capacitance-potential curves. 

Graves and Inman surmised that the capacitance-potential curves comprised two regions quasi-ideally reversible behavior, on the one hand, and quasi-ideally polarizable behavior on the other. In the former case, the predicted log AC-potential relationship is experimentally observed, where AC represents the enhanced interfacial capacitance for the quasi-ideally reversible region. 

An attractive proposition is that the change in shape of the capacitance-potential curves with increasing temperature arises from a decrease in the range of potentials over which quasi-ideally polarizable behavior prevails. Thus, the sharply rising extremities of these curves become compressed at higher temperatures. Graves and Inman were able subsequently to quantify this hypothesis. ... 

A typical capacitance-potential curve of aqueous solution of nucleic acid bases resemble at low solute concentrations the capacitance-potential curve of several other surfactants solutions (Fig. la). The potential Uq of the capacitance minimum is the potential at which the solute molecules are maximally adsorbed. The peak on the capacitance-potential curve at the potential is denoted as desorption or tensammetric peak (see Section 2.1). At this potential the desorption rate (the change of the concentration of adsorbed molecules with the largest electrode potential) is largest, Eq. (16). 

Potential of adsorption maximum and of capacitance pits The pit appears on capacitance-potential curves near the potential at which the molecules are maximally adsorbed. The potential of the maximum adsorption and thus the potential of the pit depends on the mutual competition between the electrostatic and non-electrostatic adsorption forces and the forces which repulse the adsorbed molecules from the electrode surface [37-40]. 

Retter [43] has found that on the capacitance-potential curves of cytosine solutions in a Mcllvaine buffer, pH 7, (total ionic strength of the solution was 0.7 M) at T = O C, besides the pit around —1.2 V, still another very narrow pit around —0.05 V (related to the SCE at 25"Q... 

To some extent the influence of double layer charging currents may be reduced by subtracting from the I-E curve for the test solution, the l-E curve for the electrolyte solution in the absence of the electroactive species. This technique assumes that the double layer capacitance/potential curve is unchanged by the presence of electroactive species. A better approach may be to use a microelectrode. With solid electrodes, changes in oxidation state of the surface lead to similar distortions of the I-E response and then the problem is even more difficult as the surface film may effect the rate of other electron transfer processes. 

Islam, M. M. Alam, M. T. Okajima, T. Oshaka, T. (2009). Electrical double layer structure in ionic liquids an understanding of the xmusual capacitance-potential curve at a nonmetallic electrode. /. Phys. Chem. C, Vol. 113,3386-3389 Johnson, M. Nordholm, S. (1981). Generalized van der Waals theory. VI. Application to adsorption. /. Chem. Phys., Vbl. 75,1953-1957... 

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