Effects Due to Capacitance and Resistance

Cyclic voltammetric data, even when using a three-electrode potentiostat form of instrumentation, can be affected by the presence of uncompensated resistance in the solution phase between the reference and the working electrode and of the working electrode itself, and by the capacity of the working electrode. A simple electrochemical cell may be described by an equivalent circuit, in which electronic 

In Fig. II. 1.12, cyclic voltammograms incorporating both IR drop and capacitance effects are shown. Effects for the ideal case of a potential independent working electrode capacitance give rise to an additional non-Faradaic current (Fig. II. 1.12b) that has the effect of adding a current, /capacitance = Cw x v, to both the forward and backward Faradaic current responses. Tbe capacitance, Cw, is composed of several components, e.g. double layer, diffuse layer, and stray capacitance, with the latter becoming relatively more important for small electrodes [61]. On the other hand, the presence of uncompensated resistance causes a deviation of the applied potential from the ideal value by the term R x /, where R denotes the uncompensated resistance and I the current. In Fig. II. 1.12, the shift of the peak potential, and indeed the entire curve due to the resistance, can clearly be seen. If the value of Ru is known (or can be estimated from the shape of the electrochemically reversible 

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