Warburg coefficient
The Warburg coefficient is the diffusion coefficient of ions in solution, associated to the Warburg element,. The Warburg coefficient has units of
The value of can be obtained by the gradient of the Warburg plot, a linear plot of the real impedance against the reciprocal of the square root of the angular frequency. This relation should always yield a straight line, as it is unique for a Warburg.
Alternatively, the value of can be found by:
where
- is the ideal gas constant;
- is the thermodynamic temperature;
- is the Faraday constant;
- is the valency;
- is the diffusion coefficient of the species, where subscripts and stand for the oxidized and reduced species respectively;
- is the concentration of the and species in the bulk;
- is the concentration of the electrolyte;
- denotes the surface area;
- denotes the fraction of the and species present.