Nernst Diffusion Layer(2)

Nernst Diffusion Layer

Within this layer, diffusion alone controls the ionic transfer to the electrode. This occurs down a concentration gradient. *

Outside this layer, diffusion is negligible and the concentration of the considered species is maintained at a value of CO by convective transfer.

If we look at the concentration gradient in the diffusion layer, we note that it is both linear and constant. We can represent the concentration gradient mathematically as:

Because the concentration of chemical species considered at the electrode surface is zero, this equation can be simplified to give:

By considering the flux J to the electrode surface, we can define the limiting current iL for the stirred solution as:

When the chemical species being reacted at a surface participates in the conducting current through migration a generic form of the layer has to be used. When only one cation is involved in plating, for example, the limiting current at the cathode could be written as follows for the specific plating of nickel ions in Watts solution rich in conducting ions: