Abstract

Plotting theoretical voltammetric electrode potential data for Nernstian charge transfer on the X-coordinate, that for quasi-reversible charge transfer on the Y-coordinate and normalized current (I/Ip) on the Z-coordinate revealed that projections on to the X−Y plane resulted in:(E−Ep/2)quasi=m(E−Ep/2)Nern where the slopes m are directly related to the normalized heterogeneous rate constant Λ (Λ=ks(DnF/RT)−1/2ν−1/2). Working curves, m−1 vs. 1/Λ, dependent upon the value of the transfer coefficient, α, were calcualted for the determination of ks. For the experimental evaluation of ks, values of m−1 are obtained as a function of the voltage sweep rate, ν, which allows both ks and α to be obtained from the working curves. The method is applicable to processes with ks<1 cm s−1 and is most suitable for processes having rate constants ranging from 10−3 to 10−1 cm s−1. After obtaining the rate constant and transfer coefficient from the working curves, the appropriate theoretical current-voltage curve can be calculated and used in the three-dimensional analysis of the experimental data. An experimental verification of the method is presented.

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