Analysis of the impedance frequency spectrum of a passive iron electrode by combined impedance and photoadmittance measurements

The Frequency spectra of electrochemical impedance Z, photocurrent Deltai, and photopotential DeltaE are obtained for a passive Fe electrode in 0.2 M KOH in a frequency range 1.3 to 8300 Hz. The validity of relationship Delta E/Deltai = -Z is proved experimentally. The oxide film impedance Z(F) is ca lculated from the Frequency spectrum of DeltaE with expression Z(F) = -Delt aE/Deltag. The generation current Deltag is found from the photocurrent fre quency spectrum. The frequency impedance spectrum Z(F/S) of the oxide/solut ion interface is determined with equation Z(F/S) = Z - Z(F) - R-el, where R -el is the solution resistance.