Effects of electrolysis conditions on the morphologies and corrosion resistances of polyaniline films formed on fe by electropolymerization

Polyaniline films were formed on an Fe substrate using the oxidative electropolymerization technique at 288 K in aqueous solutions with pH values ranging from 2 to 10 and containing aniline, p-toluenesulfonic acid and oxalic acid as supporting electrolytes. The effects of the electrolysis conditions on the morphologies and corrosion resistances of the films were subsequently investigated. Although the polyaniline films were partially formed in solutions of pH 2-4, the films completely formed and their surfaces became smooth when deposited in solutions of pH 7-10. Polyaniline films with smooth surfaces and good corrosion resistance were obtained at 8-30 A·m^-2, whereas the films obtained at current densities greater than 50 A·m² exhibited non-uniform surface morphologies and poor corrosion resistance. Films obtained at anode potentials of 0.4 V and 0.8 V vs. NHE were not formed completely, and the films formed at an anode potential of 2.0 V exhibited very rough surfaces. Films formed from a solution containing only p-toluenesulfonic acid as a supporting electrolyte exfoliated from the Fe substrate after being immersed in a 3 mass% NaCl solution for 3 h. Although the films prepared from a solution containing only oxalic acid as a supporting electrolyte exhibited good adhesion to the substrate, they contained numerous defects and pores; consequently, they improved the Fes corrosion resistance less than films deposited from a solution containing p-toluenesulfonic acid. In the case of polyaniline films formed in an electrolyte solution containing both p-toluenesulfonic acid and oxalic acid, the Fe exhibited improved corrosion resistance, and the films exhibited good adhesion to the Fe substrate.