Chronopotentiometric Response of an Electrically Heterogeneous Permselective Surface: 3D Modeling of Transition Time and Experiment

Understanding of the current density distribution over an electrically heterogeneous surface and its effect on ion transport represents an important issue in electrochemistry, composite materials, geophysics, and some other domains. We report an approach for three-dimensional (3D) modeling (with cylindrical symmetry) of transient ion transfer across a surface composed of conductive and nonconductive areas. In the model formulation and solution we use the electrical current stream function. It allows setting the integral boundary condition for electric current at a heterogeneous surface without any restrictions on the local current density distribution. A very good agreement is found between the numerical solution and the experimental transition time determined from chronopotentiograms. The use of a specially designed membrane allows computation without fitted parameters. We show that the application of specific simplifications for the current density distribution over the surface (uniform distribution throughout all the surface or its conductive area, neglect of tangential current density) results in essential deviations from experimental transition time.