Butler-Volmer equation ($j=j_0(e^{{\alpha }_{a}nF\eta /(RT)}-e^{-{\alpha }_{c}nF\eta /(RT)})$)

A kinetic model for the net electrode current near and away from equilibrium. For a single effective reaction with consistent activities and ${\alpha }_a+{\alpha }_c=1$, $j=j_0[\exp ({\alpha }_{a}nF\eta /RT)-\exp (-{\alpha }_{c}nF\eta /RT)]$. Near equilibrium it gives $j\simeq j_{0}nF\eta /(RT)$; at sufficiently large overpotential one exponential gives the Tafel equation. Multistep reactions can require a different kinetic interpretation.