Electropolymerization of Polypyrrole and Polypyrrole-ZnO Nanocomposites on Mild Steel and Its Corrosion Protection Performance M. G. Hosseini, 1 R. Bagheri, 1 R. Najjar 2 1 Department of Physical Chemistry, Electrochemistry Research Laboratory University of Tabriz, Tabriz, Iran 2 Department of Organic Chemistry, Polymer Research Laboratory, University of Tabriz, Tabriz, Iran Received 10 March 2010; accepted 27 November 2010 DOI 10.1002/app.33952 Published online 6 April 2011 in Wiley Online Library (wileyonlinelibrary.com). ABSTRACT: Polypyrrole (PPy) and Polypyrrole-ZnO (PPy-ZnO) nanocomposites were electrodeposited on mild steel and its corrosion protection ability was studied by Tafel and Impedance techniques in 3.5% NaCl solution. Pure Polypyrrole film was not found to protect the mild steel perfectly but the coating with nano-sized ZnO (PPy- ZnO) has dramatically increased the corrosion resistance of mild steel. Electrochemical Impedance Spectroscopy (EIS) measurements indicated that the coating resistance (R coat ) and corrosion resistance (R corr ) values for the PPy- ZnO nanocomposite coating was much higher than that of pure PPy coated electrode. V C 2011 Wiley Periodicals, Inc. J Appl Polym Sci 121: 3159–3166, 2011 Key words: conducting polymers; nanocomposites; electrochemistry; corrosion; polypyrrole INTRODUCTION Conducting polymers due to their nontoxic, envi- ronmentally friendly, high stability and ease of syn- thesis, are the most promising coatings for corro- sion protection of industrial metals. Among various conducting polymers, polypyrrole has been exten- sively investigated because of its attractive proper- ties from the practical point of view, e.g., the rela- tively good environmental stability, the high conductivity, and the ease of preparation either by chemical or by electrochemical polymerization. 1–8 A new method for the synthesis of conducting poly- pyrroles (PPy), based on chemical and combined electrochemical-chemical oxidation of pyrrole mono- mers. 9 Simultaneous formation and deposition of electrically conductive polymers are possible by electrochemical polymerization technique. Using this technique, controlling the thickness and uni- formity of coatings is possible and practical. In addition, nontoxic and nonvolatile chemicals for polymer coating, allows this method an environ- mental friendly process. 10 Application of PPy coatings for corrosion protec- tion of metals and alloys is however subjected to some limitations. The first, charges stored in the polymer layer can be irreversibly consumed during the system’s redox reactions. Consequently, quality of the protection with polymer coatings may be lost with time. Also, porosity and ion exchanges of PPy coatings might be disadvantageous, particularly when it comes to localized corrosion caused by small and aggressive anions. Therefore, interests have been focused on the use of conducting polymers as copolymers, 9–13 composites, 14–16 nanocomposites 17–20 or bilayers. 21,22 In this reasearch, following our previ- ous investigations, 23–26 first, the possibility of electro- chemical synthesis of PPy-ZnO nanocomposite films on mild steel electrode was studied using Fourier Transform Infrared (FT-IR) spectroscopy and Scan- ning Electron Microscopy (SEM) techniques then, its protective performance against corrosion in 3.5% NaCl solution was evaluated using Electrochemical Impedance Spectroscopy (EIS). EXPERIMENTAL Materials Pyrrole and oxalic acid were purchased from Merck. Dodecylbenzene sulfonic acid (DBSA) as acid dopant was supplied by Fluka. Pyrrole was purified by dis- tillation under vacuum just before use and all the aqueous solutions were prepared with distilled water. ZnO nanorods were prepared according to Correspondence to: M. G. Hosseini (mg-hosseini@tabrizu. ac.ir). Contract grant sponsor: Vice Chancellor in Charge of Research of Tabriz University and Research of Iranian Nanotechnology Society. Journal of Applied Polymer Science, Vol. 121, 3159–3166 (2011) V C 2011 Wiley Periodicals, Inc.