Synthetic Metals 160 (2010) 2180–2185 Contents lists available at ScienceDirect Synthetic Metals journal homepage: www.elsevier.com/locate/synmet Effect of various parameters on the conductivity of free standing electrosynthesized polypyrrole films Tilia Patois a , Boris Lakard a,∗ , Nicolas Martin b , Patrick Fievet a a Institut UTINAM, University of Franche-Comté, 16 route de Gray, 25030 Besanc ¸ on Cedex, France b Institut FEMTO-ST, UMR 6174, CNRS UFC ENSMM UTBM, 32 avenue de l’Observatoire, 25044 Besanc ¸ on Cedex, France article info Article history: Received 1 July 2010 Received in revised form 2 August 2010 Accepted 4 August 2010 Available online 25 August 2010 Keywords: Conductivity Van der Pauw method Conducting polymer Polypyrrole Electrochemistry abstract Electrical characteristics of polypyrrole films electrodeposited in different aqueous electrolyte solutions including p-toluenesulfonate, naphtalenesulfonate, nitrate, tetrafluoroborate, and perchlorate anions were investigated using the Van der Pauw procedure. The polymer films were synthesized by electro- chemical oxidation at a fixed potential. Experimental parameters including the pyrrole concentration, electrolyte, applied potential and substrate were shown to affect the electrical conductivity  of polypyrrole films. Since the substrate contributes significantly to the overall conductivity of polypyrrole- coated electrodes, the results obtained with free standing polymer films appeared more reliable. The results indicated that the p-toluenesulfonate doped PPy film showed the highest average conductivity ( 293 K = 4.5 × 10 5 Sm -1 ) whereas the perchlorate doped one produced the lowest of all the films prepared ( 293 K =2 × 10 4 Sm -1 ). © 2010 Elsevier B.V. All rights reserved. 1. Introduction Over the last few decades, conducting -conjugated poly- mers such as polythiophene, polyaniline, and polypyrrole (PPy) have intensely been investigated. It was shown that they exhibit many excellent properties such as electrochemical reversibility, relative environmental stability, high conductivity, good mechan- ical performance and an easy preparation through chemical and electrochemical methods. Thanks to these attractive behaviours, conducting polymers can be used for a wide range of applica- tions including field effect transistors [1,2], light-emitting diodes [3–5], solar cells [6–8] and quantum dots [9] for photovoltaics, elec- trochromic devices [10–12], corrosion [13–15], catalysis [16–18], liquid sensors [19–27] or gas sensors [28,29]. Most of the - conjugated polymers are straightforwardly prepared by chemical and/or electrochemical methods and their electronic properties can be reversibly changed between insulating and conducting states by chemical and/or electrochemical doping reactions [30–32]. The high electrical conductivity (low resistivity) of conducting poly- mer films belongs undoubtedly to one of their most important properties [33–37]. In the case of electrochemically oxidized con- ducting polymers, the conductivity is usually measured in liquids using electrochemical impedance spectroscopy (EIS) [38,39]. In the case of chemically oxidized conducting polymers, the conductivity is usually measured using Van der Pauw technique (VDP), which ∗ Corresponding author. Tel.: +33 3 81 66 62 95. E-mail address: boris.lakard@univ-fcomte.fr (B. Lakard). eliminates voltage drop on current leads. Moreover, the Van der Pauw technique [40–42] is frequently used, because it does not need defined sample geometry. The detailed shape and position of contacts are not important, but the sample area must be singly con- nected. Even if VDP technique has many advantages, it is generally not used for studying electrodeposited films since it is difficult to discriminate between the contribution of the conducting substrate and the one of the electrodeposited film. Consequently, the only solution to obtain the conductivity of the polymer films consists in the fabrication of free standing polymer films. The aim of the present study is the determination of a protocol allowing the determination of the conductivity of electrosyn- thesized polypyrrole films using the Van der Pauw technique. Polypyrrole has been chosen for its ease of preparation, high electronic conductivity and good stability. Moreover, since it has already been proved that polymerization parameters, such as solvent [43–47], temperature [48], potential or current density [49,50], concentration of monomer [51], pH [50,52], supporting electrolyte [50,52,53] and nature of working electrode [54], have strong effects on the polymerization processes of pyrrole, the present study will try to determine the effects of many of these parameters on the conductivity of the electrodeposited PPy films. 2. Materials and methods 2.1. Electrochemistry All cyclic voltammetry experiments were carried out and recorded with a PGZ 301 potentiostat (Tacussel-Radiometer Ana- 0379-6779/$ – see front matter © 2010 Elsevier B.V. All rights reserved. doi:10.1016/j.synthmet.2010.08.005