Randles- Sevdk equation

Ngamchuea K, Eloul S, TschuKk K, Compton RG (2014) Planar diffusion to macro disc electrodes - what electrode size is required for the Cottrell and Randles-Sevdk equations to apply quantitatively J Solid State Electrochem 18 3251-3257... 

The Randles-Sevdk equations are derived from the assumption that the concentration of the species at the electrode surface at the beginning of the linear voltammetric scan is equal to that in bulk. This is correct for a forward scan, but is not correct for the two cases outlined above because electron transfer has aheady taken place. In this case, a diffusion layer has aheady been developed and so the system is perturbed. 

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