OHMIC DISTORTION OF MASS-TRANSPORT AND OF CURRENT-VOLTAGE CURVES AT ACHANNEL ELECTRODE

The distortion caused by the ohmic resistance of the solution in a cha nnel electrode experiment has been calculated by combining a three-dim ensional finite element approach based on a resistor network, solved b y the SPICE program, in an iterative procedure with the backward-impli cit 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 potentia l distribution imposed by the electrolyte resistance but also the alte ration to mass transport induced by the potential distribution. The po tential-dependent variation in Tafel slope introduced by the ohmic dis tortion is calculated and is shown to be in close agreement with exper imental data obtained from the reversible one-electron reduction of p- chloranil, allowing the practical current range for experimental measu rements to be assessed and if necessary extended. The three-dimensiona l SPICE simulation has also been applied to study the effect of reduci ng the electrode width to a small fraction of the channel width when s ignificant current flow to the sides of the electrode will occur.