Computational Study of Chronoamperometry at Rectangular Microelectrodes

Three (space) dimensional diffusion to a rectangular microelectrode of length l and width w, embedded in an infinite coplanar insulator is simulated with boundary conditions for a chronoamperometric experiment. An alternating direction implicit finite difference method (Douglas‐Gunn algorithm) utilizing a problem adapted grid is used to solve the diffusion equation. Current transients are computed for different values of the dimensionless length parameter L=l/w, starting with L=1, i.e., a square electrode. Edge effects at the four sides of the rectangular electrode as well as the vertex effect contribute to the total current. With increasing L the transients approach the behavior of a microband electrode transient, where diffusion is essentially two dimensional. The breakdown of the two dimensional diffusion approach with decreasing values of L is analyzed and quantified. This serves as a guideline for analyzing transients measured with electrodes where the condition l » w is not fulfilled.