Chronopotentiometry is used to study mechanism and kinetics of chemical reactions. In this technique, the instrument operates in galvanostatic mode to control current and measure voltage. The applied current can consist of either a single or double step. It is generally performed in a quiet (unstirred) solution.
This technique can be used to investigate the mechanism of a redox process. For systems where only one redox species is present, we expect an S-shape response. The potential of the electrode changes from open-circuit potential to an approximately constant value, until the concentration of the redox species at the electrode is depleted. When this species is depleted at the electrode surface, the potential rapidly shifts to a potential able to sustain the applied current. This sudden shift is called the transition time (tau, τ, in the equations, below). If only one redox species is present, the potential shifts to a value that causes either the supporting electrolyte or solvent to be reduced/oxidized.
If the redox process is reversible, the potential response during the plateau of the sigmoidal curve is controlled by the concentration of the oxidized and reduced forms of the redox couple at the electrode surface. Therefore you can use the Nernst equation to evaluate the formal potential (E0')for the reduction process, as long as the diffusion coefficients of the oxidized (DO) and reduced (DR) form of the redox couple are known (Bard and Faulkner).
The chronopotentiometry technique can also be used as a general-purpose galvanostatic technique for applications such as plating, or measuring battery charge/discharge curves.