Electrochemically deposited polypyrrole films and their characterization J. Tietje-Girault a,1 , C. Ponce de León b, ⁎ , F.C. Walsh b a Department of Pure and Applied Chemistry, University of Strathclyde, 295 Cathedral Street Glasgow, G1 1XL Scotland, UK b Electrochemical Engineering Group, School of Engineering Sciences, University of Southampton, Highfield, Southampton SO17 1BJ, UK Received 1 July 2006; accepted in revised form 12 November 2006 Available online 16 January 2007 Abstract Ionically conductive polypyrrole films have been deposited at 295 K from anhydrous acetonitrile, acetonitrile/H 2 O and NaBF 4 aqueous solutions onto platinum, mild steel and stainless steel discs, using cyclic voltammetry, potentiostatic and galvanostatic techniques. Cyclic voltammetry of the polymer films has been studied as a function of water content of the acetonitrile solvent, polypyrrole concentration and potential sweep rate. Potentiostatic growth of thicker (b 30 micron) films on stainless steel allowed free-standing polypyrrole membranes to be produced. Well adherent and conductive films were deposited at constant potential in stirred solutions from acetonitrile electrolytes containing 1% (v/v) of water. The membrane resistivity of the reduced films in 0.5 mol dm - 3 KCl (aq) at 295 K was ≈ 1×10 6 Ω cm, while the resistivity of the oxidised membrane was 2700 Ω cm. © 2006 Elsevier B.V. All rights reserved. Keywords: Conductive polymers; Polymer membrane; Polypyrrole formation; Pyrrole oxidation 1. Introduction Over the past two decades, much interest has been shown in electrochemically synthesized, conductive polymers such as polypyrrole [1,2]. The applications of these materials include: elastic textile composites of high electrical conductivity [3], supercapacitors for energy storage and secondary batteries [4] and enhancement of shear strength and toughness of graphite fibres [5]. The ability of polypyrrole to switch between oxidised and reduced states leading to conducting or insulating polymer films has also generated great interest [6,7]. Polypyrrole films have been applied to the protection of metals [8,9]; Garcia et al., [10] studied films containing Fe 3 O 4 and Fe 2 O 3 particles to protect iron surfaces immersed in 3% NaCl (aq) solution. The authors suggested that the strong oxidative power of the iron oxide particles significantly improved the corrosion resistance of the polypyrrole covered metal and maintained the polypyrrole film in its passive, oxidised state, keeping the metallic iron in its reduced form. Polypyrrole films can be used as ion exchange membranes that respond to external stimulations [11,12]. Free-standing films based on polypyrrole and polyaniline are produced with a variety of counterions and co-polymers for applications such as mineral recovery, protein separation and salt rejection [13]. Polypyrrole has been used to fabricate patterned arrays of nanoparticles on substrates by electrodepositing it on the interstitial spaces of polystyrene spheres assembled on a gold substrate. When the polystyrene spheres are dissolved, a template of interconnected, circular chambers of polypyrrole is formed in which metal could be deposited forming a polypyrrole/metal nanodot composite. Removing the polypyr- role leaves an array of nanodots with potential applications in photonic crystals, data storage media or biosensors [14]. A large number of papers and books focusing on sensors and biosensors have been published [15]. A specific example is a cholesterol biosensor where the electrochemical polymerization of poly- pyrrole onto a Prussian-blue film formed on a platinum electrode is used to detect the hydrogen peroxide formed during the reaction between cholesterol and the cholesterol oxidase enzyme [16]. Surface & Coatings Technology 201 (2007) 6025 – 6034 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. E-mail address: capla@soton.ac.uk (C. Ponce de León). 1 Present address:1088 Ropraz, Lucerne, Switzerland. 0257-8972/$ - see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2006.11.009