Planar diffusion to macro disc electrodes-what electrode size is required for the Cottrell and Randles-Sevcik equations to apply quantitatively?

Simulations and experiments are reported which investigate the size of a macro disc electrode necessary to quantitatively show the chronoamperometric or voltammetric behaviour predicted by the Cottrell equation or the Randles-Sevcik equation on the basis of exclusive one-dimensional diffusional mass transport. For experimental time scales of several seconds, the contribution of radial diffusion is seen to be measurable even for electrodes of millimetres in radius. Recommendations on the size of macro electrodes for quantitative study are given and should exceed 4 mm radius in aqueous solution.