Normalized potential sweep voltammetry: Part II. Application to heterogeneous charge transfer kinetics

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/I p) on the Z-coordinate revealed that projections on to the X−Y plane resulted in: ( E− E p/2) quasi= m( E− E p/2) Nern where the slopes m are directly related to the normalized heterogeneous rate constant Λ (Λ= k s( 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 k s. For the experimental evaluation of k s, values of m−1 are obtained as a function of the voltage sweep rate, ν, which allows both k s and α to be obtained from the working curves. The method is applicable to processes with k s<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.