Using Faraday’s law for an electrode reaction, m, at the interface between the electron and ion conducting phase this corresponds to
where ΔHm is the enthalpy change of the reaction, and
ΔGm is the Gibbs free energy of the reaction,
ΔGm, defined as
where ΔSm is the net entropy change.
Equation 4-5 may now be rearranged into
In Equation 4-5 we have used the total overpotential,
ηm,tot (including potential effects from film resistances and similar), defined as
The total heat source due to the electrochemical reactions, QEC, for an electrode surface is the sum of all individual heat sources of the electrode reactions according to