Where Rfilm (SI unit: ohm·m
2) is a generalized film resistance and
itot the sum of all currents over the interface. The activation overpotentials,
ηm, for all occurring electrode reactions on the electrode with the film receive an extra potential contribution due to the film resistance according to:
where s0 is the reference/initial film thickness,
Δs the electrode thickness change, and
σfilm the conductivity (SI unit: S/m) of the film.