Chronocoulometric responses

Chronocoulometry — Figure 1. Waveform of a potential step experiment (a) and the respective chronocoulometric response (b). Dashed curves in b displayed for the illustration of the capacitive charge effect... 

Chronocoulometric responses may be governed wholly or partially by the -> charge transfer kinetics. In some cases, the diffusion-limited situation cannot be reached, e.g., due to the insufficient power of the po-tentiostat and the inherent properties of the system, especially at the beginning of the potential step. If the heterogeneous - rate constants, k x, or kreare small the following expression can be derived, e.g., for the... 

It means that the product 0+ is reduced again during the second step from 2 to 1. If the magnitude of the reversal step is also large enough to ensure diffusion control, the chronocoulometric response for t > r - where r is the duration of the first step - is given by the following equation ... 

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,...

Chronocoulometric response for a double-step experiment performed on the system of Figure 5.8.1. The reversal step was made to 0.0 V V5. QRE. [Data courtesy of R. S. Glass.]... 

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-... 

Fig. II.4.2 Typical waveform of (a) a potential step experiment and the respective (b) chronoam-perometric and (c) chronocoulometric responses. E and E2 are as given in Fig. IL4.1. Dashed curves for the capacitive current (b) and capacitive charge (c) obtained when the experimental was repeated in pure supporting electrolyte...

It follows that, in the presence of a thick L > 100 nm, F > 10 molcm" ), electrochemically active surface layer, a superposition of Gdiff + Gads can only be measured in the time window from milliseconds to some seconds. If the chronocoulometric response of the electroactive film is measured alone - in contact with inert supporting electrolyte - Cottrell-type response can be obtained usually for thick films only, because, at short times (t < 0.1 -1 ms), the potential of the electrode is not established while, at longer times (t > 1-10 ms), the finite diffusion conditions will prevail and I will exponentially decrease with time. 

The chronocoulometric responses can be derived from the current transients by integration from t = 0. In the case of Eq. (II.4.14), the integration gives the following expression ... 

Fig. 82. Chronocoulometric response of a double potential step, t time of the potential reversal, Qf charge consumption in the forward potential step, charge in the backward step, Qr charge removed in the reverse step up to the time t>tr-...

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 ... 

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