Investigations of Redox Reactions by Linear Sweep Voltametry

Investigations of Redox Reactions by Linear Sweep Voltametry 

In the case of a diffusion-controlled reaction, a current-potential curve can be evaluated quantitatively. The diffusion equation has to be solved again by using time-dependent boundary conditions. The mathematics, however, is very complicated and cannot be shown here. They end up with an integral equation which has to be solved numerically [11]. The peak current, j, for a diffusion-controlled process (reversible reaction) is found to be 

The factors 0.446 in Eq. (7.35) and 1.11 in Eq. (7.36) originate from an approximation used for solving the rather complex Eq. (7.29). The positive sign is valid for the anodic and the minus sign is valid for the cathodic peak. According to this equation, the shift amounts to 28.5 mV and the separation of the two peaks to 57 mV in a cyclic scan. The easiest way of getting nd is given by f/i/2 = 1 f2(Up u + f/p c). It should be emphasized that the peak current increases with the square root of the scan rate its position on the potential scale, however, is independent of the scan rate, provided that the electron transfer is diffusion controlled. 

In the case of a kinetically controlled reaction (irreversible process), the situation is different. Here current peaks also occur because the current finally becomes diffusion limited at large polarization. However, the position of the current peak is shifted to higher potentials when the scan rate is increased. 

7 Charge Transfer Processes at the Semiconductor-Liquid Interface 

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