Chronopotentiometry

Electroanalytical techniques essentially involve three quantities (or a function derived from them, e.g. electrochemical impedance): current i, potential E and time t. Etymologically, chronopotentiometry is a measurement of potential E as a function of time t. However, according to IUPAC (International Union of Pure and Applied Chemistry) recommendations, it is limited to techniques for which :

• on the one hand, the excitation signal i is constant or variable with time t (at least during a first pulse in the case of pulse trains) and non-zero (which implies at least one electrochemical reaction);

• on the one hand, and diffusion alone, on the other.

This excludes potentiometry and potentiometric titration techniques at zero current, and at constant current in the case of forced diffusion (solution agitation).

In the case under consideration, i.e. that of the existence of an electrochemical reaction in the pure diffusion regime, the resulting transient modification of the electro-active species leads to a temporal variation in the response to any electrical excitation applied to the indicator electrode.

It is possible – as previously shown by Reinmuth [4] – to visualize this aspect in three dimensions. Figure 1 shows the relationship between the three fundamental quantities: current i, voltage E and time t (this diagram was drawn for the general case of a fast electrochemical system corresponding to the reduction of a soluble oxidizing species – Ox – to another soluble species). It provides a link between the various electrochemical techniques involving a monotonic excitation signal....