Progress in Organic Coatings 65 (2009) 281–287 Contents lists available at ScienceDirect Progress in Organic Coatings journal homepage: www.elsevier.com/locate/porgcoat Electrochemical impedance spectroscopy of poly[carbazole-co-N-p-tolylsulfonyl pyrrole] on carbon fiber microelectrodes, equivalent circuits for modelling Murat Ates a,b , A. Sezai Sarac a,∗ a Department of Chemistry & Polymer Science and Technology, Istanbul Technical University, Maslak, 34469, Istanbul, Turkey b Department of Chemistry, Namık Kemal University, Namık Kemal Street, Number: 14, 59100, Tekirdag, Turkey article info Article history: Received 5 May 2008 Received in revised form 6 August 2008 Accepted 16 December 2008 Keywords: Poly(carbazole-co-p-tolylsulfonyl pyrrole) Microelectrodes Electrochemical impedance spectroscopy abstract Polycarbazole (PCz) and copolymerization of carbazole (Cz) and N-p-tolylsulfonyl pyrrole (pTsp), P(Cz- co-pTsp), thin films have been cyclovoltammetrically coated onto carbon fiber electrodes as an active functionalized microelectrode in sodium perchlorate (NaClO 4 )/acetonitrile (ACN) medium. The result- ing thin films of homopolymer and copolymer were characterised by using Fourier transform infrared reflectance spectroscopy (ATR-FTIR), energy dispersive X-ray (EDX) point analysis, scanning electron microscopy (SEM) and atomic force microscopy (AFM). An electrical impedance study on the pre- pared electrodes is reported in the present paper under different feed ratios of [pTsp] 0 /[Cz] 0 during electrochemical impedance spectroscopic (EIS) measurements. Specific capacitance (C sp ) were cal- culated, P(Cz-co-pTsp) in feed ratio of [pTsp] 0 /[Cz] 0 = 200 has preserved more capacitive behavior especially at lower frequency (C sp = ∼156 mF g -1 ) than polycarbazole (C sp = ∼2.1 mF g -1 . The electrochem- ical impedance data fitted to three different equivalent models were used to find out numerical values of the proposed components. © 2008 Elsevier B.V. All rights reserved. 1. Introduction During the last years a great interest has been focused on the application of carbon as electrode materials because of their accessibility, easy processibility, and relatively low cost. They are chemically stable in different solutions (from strongly acidic to basic) and able for performance in a wide range of temperatures. Well-established chemical and physical methods of activation allow producing materials with a developed surface area and a controlled distribution of pores that determine the electrode/electrolyte interface for electrochemical applications [1]. The synthesis and modification of carbazole-based polymers have been reviewed to obtain polymers exhibiting better thermal, electrical, photo- electrical, ion exchange and other physicochemical properties [2]. However, PCz has poor processing properties [3], which need to be improved to suit practical applications. There have been quite number of studies concerning the syn- thesis, characterization, and some on electrochemical impedance spectroscopic and sensor applications of conductive polymers. For example, copolymerization of carbazole derivatives with methylpyrrole (MPy) has been studied by chemical and elec- trochemical methods [4]. Due to expected additional combined ∗ Corresponding author. Tel.: +90 212 2853153; fax: +90 212 2856386. E-mail address: sarac@itu.edu.tr (A.S. Sarac). URL: http://atlas.cc.itu.edu.tr/ sarac/ (A.S. Sarac). properties of alkyl substituted pyrrole and carbazole monomers, MPy has been copolymerized with ethylcarbazole (ECz) [5] and methylcarbazole [6] on CFMEs and their characterization were comparatively studied. Results showed that there was an improve- ment in the electrochemical properties of copolymer with the incorporation of methylpyrrole into the structure. Electrochemical impedance spectroscopic measurements and morphological analy- sis of electrocoated thin films of pyrrole derivatives [7], poly(N-vinyl carbazole) [8], polyaniline [9] and poly (N-methyl pyrrole) [10,11], were studied previously. Self-doped (pTsp) [12] was used as a new type of monomer, which contains sulfonyl groups. It was used as a base for high performance polymers used in electro techniques, aero spatial, chemical, drug and food industries, due to their resis- tance to high temperature, impact, fire and X and  radiations, as well as to their mechanical and electrical properties [13,14]. Modified polysulfones were used in coatings, membranes, selec- tively permeable films, ion-exchange fibers, and resins [15]. The modified copolymer electrode was obtained by electrochemically [16]. Electrochemical technique was used as an efficient method for improving copolymer properties. The modified thin films were also tested as sensor electrodes against different dopamine concentra- tions. The influence of the presence of ascorbic acid together with dopamine signal was analyzed by differential pulse voltammetry (DPV) [17]. Taking into account all the mentioned characteristics, carbon as a material for the storage of energy in electrochemical capacitors seems to be extremely attractive. EIS has been proven as a powerful 0300-9440/$ – see front matter © 2008 Elsevier B.V. All rights reserved. doi:10.1016/j.porgcoat.2008.12.007