Controlled-current techniques preceding reaction

In the preceding three sections reaction mechanisms in which the homogeneous chemical reaction was coupled with the electrode process were discussed. This coupling enables exceptionally fast chemical reactions to be investigated and their rate constants determined. Nevertheless, voltammetric methods can also be exploited for kinetic studies on chemical reactions occurring independently of the electrode process in the bulk of the solution. For this purpose all voltammetric techniques can be used for which the dependence of voltammetric response on the concentration of one or more reactants is defined in a simple way. Various amperometric sensors are mostly applied, working at the potentials of limiting current. The response need not be a diffusion-controlled current. Kinetic currents within the diffusion-controlled zone can also be taken into account. 

In a variation of the preceding technique, a voltage (potential) step is applied to the electrolysis cell and the potential is held constant for a predetermined period. Such a waveform is shown in Fig. A3. For this technique one also needs a poten-tiostat and a signal generator to apply the waveform. The height of the potential step is chosen to exceed slightly the potential of the maximal rate of reaction (the CV peak). Because the current flow in this case is controlled by diffusion, to derive an expression for the current as a function of time one needs to write Pick s law. 

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