Chronocoulometric plots

Chronocoulometry — Figure 4. Chronocoulometric plots for double step experiments. Lines 1 and 2 correspond to the case when no adsorption of the reactant or product occurs. Lines 3 and 4 depict the linear responses when the reactant is adsorbed... 

Figure 5.8.3 Linear chronocoulometric plots for data from the trace shown in Figure 5.8.2. For Q t < r) vs. the slope is 9.89 and...

Fig. II.4.3 Chronocoulometric charge vs. (time) plots. Line 1 results if the reactant is not adsorbed line 2 results for adsorbed reactant with the same parameters (cj. Dr). The dotted extensions of lines 1 and 2 indicate that the intercepts of chronocoulometric plots are usually obtained by linear extrapolation from the shortest times at which reliable data are available. The dashed, horizontal line represents the charge response in the absence of reactant...

In cases where the reactant but not the product of electrode reaction is adsorbed, the intercept of the chronocoulometric plot for the reverse step provides a direct measure of Qc in the presence of adsorbed reactant, while the difference between the intercepts is nFAF, i.e., it gives the amount of the adsorbed reactants. This situation is also displayed in Fig. II.4.5 (lines 3 and 4). Under favorable conditions, intercepts of coulometric plots can be measured with a precision of ca. 0.5 p.C cm , which corresponds to an uncertainty in F of ca. 5 x 10 mol cm for a one-electron process. 

Fig. 4 Chronocoulometry (a) typical charge response (b) Anson plot for a double-step chronocoulometric experiment.

Figure 3.2 Chronocoulometric experiment Anson plot of Q versus t1 2.

Figure 5.8.1 Linear plot of chronocoulometric response at a planar platinum disk. System is 0.95 mM 1,4-dicyanobenzene (DCB) in benzonitrile containing 0.1 M tetra-/2-butylammonium fluoborate. Initial potential 0.0 V Pt QRE. Step potential —1.892 V vs-. Pt QRE. T = 25°C,...

Figure 5.8.4 Chronocoulometric response for 10 mM in 1 M Na2S04. The working electrode was a hanging mercury drop with A = 2.30 X 10 cm. The initial potential was —0.470 V v. SCE, and the step potential was —0.620 V. The slope of the plot is 3.52 iC/ms and = 5.1 [From J. H. Christie, G. Lauer, and R. A. Osteryoung, J. Electroanal Chem., 7, 60 (1964), with permission.]...

Hg, and the chronocoulometric responses show equal intercepts of QiV In the presence of SCN , is adsorbed, and the plots of 2f and have significantly dif-... 

Figure 3 Typical plot of charge versus square root of time for chronocoulometric experiment in a CTAB microemulsion system. (From Ref 24.)...

A potential-step chronocoulometric curve that rises to a horizontal Q(t) "plateau" at one temperature displays at a hi er temperature a continuing rise with time on a Q vs. t plot or a quasi-exponential rise at long times on a Q vs. log t plot. The effect is poorly reproducible from cell to cell, increases strongly with... 

A "successful" (i.e., linear) plot of this type is shown in Fig. 12 for the Agl C pressed-powder interface at 75°C (26b). The linearity of the plot for times larger than several RC allows a "fast-charging" capacitance component to be extracted from the data by extrapolation to t = 0. Again, the usefulness of the chronocoulometric method is seen. In the illustrated system, the temperature dependence of the Q vs. t" slope yielded a linear Arrhenius plot, giving evidence that a single diffusing impurity species was involved. 

Finally, an examination of the chronocoulometric data for polypyrrole presented in the literature clearly shows that these data do not conform to simple theory (25). Note, for example, that Diaz et al. show Q vs. plots with negative intercepts furthermore, the slopes of these plots increased as the positive limit of the potential step increased. We have obtained identical data in our laboratory (40). 

Chronoamperometry, Chronocoulometry, and Chronopotentiometry, Fig. 4 Chronocoulometric charge versus (time) plot in the absence (1) and in the presence (2) of adsorption. The dashed, horiztmtal line represents the charge response in the absence of reactant. This representation is sometimes referred to as Anson plot in the literature... 

Chronocoulometry is a technique related to chronoamperometry in which a potential step is applied to the deposited polymer film and the integrated current response i.e., the charge is monitored as a function of time. It is customary to plot charge q versus t, which defines an Anson plot. The chronocoulometric response for a layer of finite thickness L is given by the following expression ... 

---