Non-Ideal Adsorbed Species

The voltammetry of surface-bound species is often found to exhibit non-ideal behaviour, in which the peak width at half peak height is not 90.6/n mV. Even under conditions where the peak position is not influenced by the scan rate, the peak-to-peak separation may still be non-zero. A large number of models have been proposed to explain these experimentally observed non-ideahties (see M.J. Honeychurch and G.A. Rechnitz, Electroanalysis 10 (1998) 285). 

For what value of a will the surface-bound species behave ideally  

We next use the quotient rule to find the derivative dVi jAx, remembering that we are doing a reduction and so E = Ejnit — vf, as in Problem 7.14  

If we assume that 1 then we achieve a simplified expression  

Consequently, there is a drop in potential between the electrode and the redox species as indicated in Fig. 7.19. Here it is assumed that the volume between the electrode and the redox species is not accessible to solvent molecules, and so potential drops approximately linearly across this region. A mathematical model of this effect was first provided by C.P. Smith and H.S. White [Anal. Chem. 64 (1992) 2398]. 

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