Figure 12,1 Potential pulse waveforms used in chronocoulometry.
coulometry can be obtained from integration of the models for chrono-amperometry ,
Chronocoulometry has certain distinct advantages over chronoampero-metry. The large initial charging current at the electrode upon stepping the potential in chronoamperometry can often be treated as a constant charge in chronoamperometry. Since the current is integrated to obtain the charge, the signal to noise ratio is better in chronocoulometry because of averaging of the random noise in the current. For these reasons, chronocoulometry is generally the preferred approach for parameter estimation by nonlinear regression. We deal with only this variant of the potential step experiment.
We assume that chronocoulometry will be used for the estimation of accurate and precise values of parameters of an electrochemical system that has been investigated at least qualitatively by other methods. It would be unusual to employ chronocoulometry to a completely unknown electrode reaction without having used other techniques to investigate the system first. Candidate systems would typically be examined first by cyclic or square wave voltammetry. Chronocoulometry might then be used to obtain the diffusion coefficient of an electrochemical reactant, the surface concentration of an adsorbed electroactive species, or a rate constant for a step in the electrode reaction pathway. The following sections deal with these topics in turn.
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