General theory of steady-state voltammetry

Abstract

Modelled on a hemispherical microelectrode, to which transport is by diffusion and migration, a comprehensive theory is developed that predicts the height, position and shape of a steady-state voltammetric wave. The treatment applies to an oxidation or a reduction involving any number of electrons and to an electroreactant of any charge number. Any degree of electrolyte support is covered by the theory, from the virtual absence of supporting electrolyte to overwhelming excess. Ohmic, concentration and activation polarization are incorporated into the theory, which therefore applies for all degrees of reversibility of the electrode reaction. Among the assumptions made are: electroneutrality; the equality of diffusivities of the two electroactive species; all ions obey the Nernst-Einstein relationship; the univalence of supporting ions; the electrode reaction proceeds in a single step without homogeneous complications. This study reveals a great diversity in the response of voltammetric behaviour to support level. It also provides definitive answers to several important questions including: how little supporting electrolyte need be present in order that the support is effectively total? How much electrolyte may be present as impurity without its effect being significant? The answers to these questions depend critically on the charge numbers of the reactant and product.