Corrosion Protection of Mild Steel by Formation of Iron Oxide Polybithiophene Composite Films

Polybithiophene (PBT) was freshly electrodeposited on platinum (Pt) and steel electrodes using cyclic voltammetry from 2,2′-bithiophene (BT), electrolyte and acetonitrile (AC). The electrolytes used were LiBF4, LiClO4, LiCF3SO3, Bu4NBF4, Bu4NClO4, or Bu4NCF3SO3. Black to red colored PBT films with metallic lustre were electropolymerized on Pt and steel electrodes with good adherence. The electrochemical properties and the surface morphology of the deposited PBT film depend on the type of ions used during the electropolymerization. It was found that the steel surface was covered with FexOy–PBT composite. The results are discussed on the basis of the structural and the electrochemical properties of the electrolyte ions. The presence of PBT–iron oxide composite on the steel surface causes a shift of the pitting potential (Epit) in the positive direction, indicating the inhibitive effect of PBT–FexOy composite on the chloride pitting corrosion.