diffusion layer thickness

Defined by the equation:

$δ = D k d = n F D c A l i$

where $D$ is the diffusion coefficient, $k d$ is the heterogeneous diffusion rate constant, $F$ is the Faraday constant, $c$ is the concentration, $A$ is the geometric area of the electrode, $l i$ is the limiting current and $n$ is the charge number of the cell reaction.

Source:

PAC, 1974, 37, 499 (Electrochemical nomenclature) on page 513