Numerical Simulation of Potential Step Chronoamperometry at Low Concentrations of Supporting Electrolyte

Electrochemical systems are considered for which the concentration of ions in solution is low, and therefore there is an electric field which extends deep into solution away from the electrode surface. Finite difference methods are used to model a potential step chronoamperometry experiment at a microhemisphere electrode. Concentration profiles, potential profiles, and current-time curves are presented for a range of electrochemical systems and physical parameters. The model uses the Nernst-Planck-Poisson system of equations to model mass transport and includes a description of the electrical double layer at the working electrode surface. Two approximations are then considered as a means of greatly simplifying the model while retaining accuracy under certain conditions. These are the approximation of a negligibly small electrical double layer and the approximation of electroneutrality. It is concluded that the former approximation is both more appropriate than the latter approximation and more conveniently implemented in terms of CPU simulation times.