Behaviour of the current in a membrane-covered disc microelectrode under steady-state conditions

Abstract

The inlaid disc electrode covered with a membrane can be modelled as a system with axial symmetry containing several parallel layers with different permeabilities. A recent solution of the steady state under diffusion limited conditions of an electroactive species in such a system is implemented with Mathematica. Computation of the theoretical current becomes an easy and fast procedure, capable of being implemented on any personal computer or workstation. The effects of the membrane permeability, the thickness of the membrane, the electrode radius and the electrolyte layer thickness on the current are analysed. We define an index of edge-effect contribution of each layer to the overall flux, providing their formulae together with the physical interpretation. For many sets of parameters, the edge-effect is responsible for an important contribution of the radial diffusion within the electrolyte and membrane. More accurate determination of the permeabilities of the different media is now possible experimentally, as the functional dependence of the current on the physical parameters is readily available for fitting procedures.