The aperiodic current, and its semiintegral, in reversible a.c. voltammetry: Theory and experiment

•The aperiodic component of the current from a.c. voltammetry is predicted by several routes.•It shares features with the Randles–Ševčik current but is a strong function of the amplitude of the a.c.•Its semiintegral has a characteristic sigmoidal shape.•Experiments with hexammoniaruthenium(III) confirm the predictions.

There is difficulty in attaching a precise meaning to the term “aperiodic component” in the context of a.c. voltammetry. Once this difficulty is circumvented, it becomes possible to use a filter or Fourier processing to model the dependence of the aperiodic component of the reversible current, and its semiintegral, on the various electrical parameters: d.c. potential, d.c. scan rate, a.c. frequency, and a.c. amplitude. No particular utility has been ascribed to the aperiodic current, but its semiintegral can provide information similar to that of d.c. linear-scan voltammetry. Experiments with the hexammoniaruthenium(III) cation provide confirmation of the theory and allow determination of the ion’s diffusivity and the halfwave potential of its reduction.