Electrochemical polymerization of aniline from an oxalic acid medium

Cyclic voltammetric (CV) studies on steel were done to study the effects of oxalic acid on the polymerization of aniline. Steel is first passivated forming an iron(II)-iron(III) oxalate layer at potentials more negative than those used to polymerize aniline. The formation of this oxalate passivation layer is dependent upon the scan rate and only forms at <25 mV/s. With continued anodic polarization, the Fe(II)-Fe(III) oxalate coating forms an Fe(III) oxide layer followed by aniline polymerization at potentials greater than about +1.3 V vs. Ag/AgCl. Poor adhesion of polyaniline (PANT) is observed if the steel is not properly passivated. After PANT deposition, the Fe(III) layer is reduced to Fe(H) on the reverse scan but the adhesion of the PANT coating is excellent. (C) 2002 Elsevier Science B.V. All rights reserved.