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Butler-Volmer equation

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 – a)Fη/RT- exp(- aF/RT)]

where ja and jc are the individual cathode and anode currents espect­tively, 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 a is a quantity called the transfer coefficient.