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Primary and secondary distributions after a small-amplitude potential step at disk electrode coated with conducting film

Electrochimica Acta
Publication Date
DOI: 10.1016/j.electacta.2011.07.004
  • Primary Current Distribution
  • Film Resistance
  • Specific Conductivity
  • Secondary Current Distribution
  • Interfacial Resistances


Abstract The set of equations and boundary conditions for the “primary potential/current distribution” after a small-amplitude potential step has been analyzed for a film-coated disk electrode in contact with an electrolyte. The solution of these equations provides the overall short-time resistance of this system, R tot, which is determined by the short-time resistance of the electrolyte solution in contact with the bare disk electrode, R s, and the short-time film resistance to the current passage in the normal direction, R f = L f / κ f π r o 2 ( r o, disk radius; L f, film thickness; κ f, its specific conductivity). The deviation of R tot from the sum of these resistances, R s + R f, originates from a three-dimensional potential/current distribution in solution. Procedures to calculate the film resistance and its specific conductivity on the basis of the measured values of R tot and R s have been proposed. Similar analysis has also been carried out for the “secondary potential/current distribution” in the same system. The overall resistance for this regime is related to the short-time solution resistance, R s, and to the total resistance of the electrode, equal to the sum of the resistance, R f, and two interfacial resistances, R m/f and R f/s. A method to determine the bulk-film parameters, R f and κ f, from data for the secondary distribution is discussed. Advantages and restrictions of the proposed route to transport parameters of a film at the electrode surface are analyzed, in comparison with existing methods of their determination.

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