Electrochemical impedance of thin rust film fabricated artificially

This chapter presents a study to investigate the electrochemical nature of rust film and the effect of MoO₄^2- adsorption on the film resistance. In this study, thin rust films were fabricated by the oxide precipitation on the cellulose membrane set at the interface between NaOH and Fe(NO₃)₃ solutions. The rust film was identified by X-ray diffraction, which mainly composed of α-FeOOH. The rust film showed anion selective permeability when it was immersed in NaCl solution. The electrochemical impedance of the thin rust film membrane was measured by using a four-electrode method, which showed a capacitive loop on the complex plane. The film resistance increased with the decrease of NaCl concentration and the increase of film thickness, as the migration of ions incorporated in the rust film with water controlled the film resistance. The immersion of the rust film in Na₂MoO₄ solution changed the ion-selective permeability and increased the film resistance.