An equation for the rate of an electrochemical reaction; it describes the current density at an electrode in terms of the overpotential. The Butler-Volmer equation is given by:j = ja – jc = je[exp(1 – α)Fη/RT – exp(– αF/RT)], where ja and jc are the individual cathode and anode currents respectively, and je is the equilibrium current, called the exchange current density. By definition je = jce = jae, where jce is the equilibrium cathode current and jae is the equilibrium anode current. F is the Faraday constant, η is the overpotential, R is the gas constant, T is the thermodynamic temperature, and α is a quantity called the transfer coefficient.
j = ja – jc = je[exp(1 – α)Fη/RT – exp(– αF/RT)]