Photoelectrochemical study on the passive film on Fe

Abstract Electronic properties of the passive film formed on Fe in pH 8.5 buffer solution were examined by the photoelectrochemical spectroscopy. Photocurrent responses for the passive film on Fe with film formation potential are explained by the modified band structure model developed on the basis of that for crystalline spinel (γ-Fe2O3) involving two types of electronic excitation processes. i.e., the p–d and the d–d transition. The photocurrent spectra for the passive film on Fe measured in a wide range of photon energy could be resolved into two components of photocurrent spectrum reflecting effects of each electronic transition on the photocurrent spectra. The band gap energy of each electronic transition process was determined from the resolved photocurrent spectrum; 2.87 eV for the d–d transition, and 3.67 eV for the p–d transition. A small photocurrent peak at 2.7 eV appeared at film formation potentials higher than 400 mV was associated with the formation of γ-FeOOH layer on γ-Fe2O3 film.