Electrochemical synthesis of poly(indole-co-thiophene) on low-nickel stainless steel and its anticorrosive performance in 0.5 mol L-1 H2SO4

The electrochemical synthesis of poly(indole-co-thiophene) copolymer coatings was achieved on low-nickel stainless steel (LN SS) with the cyclic voltammetry technique using indole and thiophene monomers in acetonitrile medium containing lithium perchlorate. The optimization of synthesis parameters such as monomer feed ratio and various scan rates was studied and also their influence on the morphology of the copolymer coatings on LN SS. For the first time, a possible radical cationic electro-copolymerization mechanism is also proposed in order to understand the electrochemical synthesis. The bonding and structure of the as-synthesized coatings were characterized using Fourier transform infrared and H-1 NMR spectroscopies. The surface morphology and composition of the coatings were also assessed using scanning electron microscopy and energy-dispersive X-ray analysis. It was observed that changes in morphology occurred which had a marked and significant effect on the electrochemical behaviour of the coated LN SS confirmed using electrochemical techniques of potentiodynamic polarization and electrochemical impedance spectroscopy in aqueous 0.5molL(-1) H2SO4 solution. The obtained results revealed that the copolymer coatings on LN SS provided significant corrosion protection in the acid medium. It was also found that a 1:1 ratio of indole to thiophene yielded the most stable and corrosion-protective copolymer coating. (c) 2013 Society of Chemical Industry