Cyclic voltammetry for reversible redox-electrode reactions in thin-layer cells with closely separated working and auxiliary electrodes of the same size

Abstract

The characteristics of a thin-layer cell with a planar auxiliary electrode placed opposite a planar working electrode are quite similar to those of a thin-layer cell with dual working electrodes, i.e. regeneration of the redox species takes place and a steady-state current is established. Theoretical equations are derived for cyclic voltammetry for a reversible redox system at this thin-layer configuration. The shape of the voltammograms depends on a single dimensionless parameter, p = nFvδ 2/ RTD, where δ is the distance between the working and the auxiliary electrodes, v is the potential sweep rate and D is the diffusion coefficient. When p is less than 2, no peak appears on the forward sweep of the voltammogram. At the other limit, when p is greater than 15 the peak current and peak potential values are the same as those for semi-infinite diffusion. Good agreement between the theoretical and experimental results has been obtained for the hexacyanoferrate(II/III) system. Using voltammetry, both the inter-electrode distance δ and the diffusion coefficient of the substrate may be found simultaneously.