The Butler–Volmer equation is:
or in a more compact form:
where:
* : electrode current density, A/m (defined as j = I/S)
*: exchange current density, A/m
* : electrode potential, V
* : equilibrium potential, V
* : absolute temperature, K
* : number of electrons involved in the electrode reaction
* : Faraday constant
* : universal gas constant
*: so-called cathodic charge transfer coefficient, dimensionless
*: so-called anodic charge transfer coefficient, dimensionless
* : activation overpotential (defined as ).
The right hand figure shows plots valid for .