Ohmic distortion of mass transport and of current-voltage curves at a channel electrode

The distortion caused by the ohmic resistance of the solution in a channel electrode experiment has been calculated by combining a three-dimensional finite element approach based on a resistor network, solved by the SPICE program, in an iterative procedure with the backward-implicit finite difference method, for the case of a reversible 1-electron reduction. By this means, the current distribution over the electrode may be calculated taking into account not only the nonuniform potential distribution imposed by the electrolyte resistance but also the alteration to mass transport induced by the potential distribution. The potential-dependent variation in Tafel slope introduced by the ohmic distortion is calculated and is shown to be in close agreement with experimental data obtained from the reversible one-electron reduction of p-chloranil, allowing the practical current range for experimental measurements to be assessed and if necessary extended. The three-dimensional SPICE simulation has also been applied to study the effect of reducing the electrode width to a small fraction of the channel width when significant current flow to the sides of the electrode will occur.