LINEAR-SWEEP VOLTAMMETRY IN A CYLINDRICAL-PORE ELECTRODE

A comparison is made between the transfer coefficient and standard rate constant for the oxidation of ferrous to ferric ion obtained from linear-sweep voltammetry (LSV) in a cylindrical pore drilled in a glassy-carbon disk with those obtained on a planar electrode of the same material. Extracting quantitative kinetic information from LSV in a cylindrical-pore electrode is more difficult than on planar electrodes since the electrode surface is not uniformly accessible to the bulk supply of reactant or the counter electrode. A previously reported mathematical methodology to account for the effect of ohmic, mass-transfer, and kinetic resistances on the voltammograms obtained for soluble redox couples was applied to determine the transfer coefficient and the standard rate constant for an irreversible reaction in the cylindrical pore. The transfer coefficients agreed to within 3%, but the standard rate constant was about 1 order-of-magnitude larger on the planar electrode than in the pore. This discrepancy is believed due to the difference in the pretreatment of the electrode surface rather than a failure of the model. The strongest evidence that the methodology is valid is that although the voltammogram is a strong function of the initial concentration of ferrous sulfate, the pore length, the electrolyte conductivity and the sweep rate, the kinetic constants extracted from the data were not when the suggested procedure was used.