PROPERTIES OF THE PASSIVE FILM ON IRON ELECTRODES BY CAPACITY AND PHOTOCURRENT MEASUREMENTS.

Passive iron electrodes were investigated in 1M HClO//4, 1M NaClO//4-pH 8 and 1M NaOH covering a pH range of almost 14 units. Capacity measurements were carried out in the frequency range ca. 3 Hz-3 kHz. Applying a Schottky-Mott analysis to the results yields donor concentrations on the order of 1020cm** minus 3. At higher potentials, however, a frequency dependent capacity encountered is probably due to OH minus adsorption. Photocurrent spectra measured in all electrolytes yielded a similar shape of the spectrum. The onset of the photocurrent was between 2. 0 and 2. 5 eV photon energy depending on the electrolyte the passive film was formed in. Photocurrents have a pronounced transient like behaviour in neutral and basic solutions. The potential dependence of the photocurrent shows an exponential increase with additional peaks at low potentials in neutral and basic solutions after prolonged polarization of the electrode. (Edited author abstract. )