Parallel disks edge effects

The conditions for planar diffusion are theoretically fulfilled only if the electrode surface is very large. In case of finite disk electrodes, edge effects arise and linear diffusion is no longer linear overall the electrode surface (Fig. 15.3). Diffusion also develops parallel to the electrode surface in the radial direction. However, if the radius of the disk electrode is large enough with respect to the diffusion layer thickness (as is the case of common employed disk electrode of millimeter size), edge effects can be neglected and Cottrell equation accurately accounts for the current profile at the electrode surface. These electrodes are nowadays called either conventional or macroelectrodes. ... 

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