Author's personal copy Electrochimica Acta 54 (2009) 3618–3622 Contents lists available at ScienceDirect Electrochimica Acta journal homepage: www.elsevier.com/locate/electacta Barrier films to control loss of 9,10-anthraquinone-2-sulphonate dopant from PEDOT films during electrochemical transitions S. Harish, D. Sridharan, S. Senthil Kumar, James Joseph ∗ , K.L.N. Phani Electrodics and Electrocatalysis Division, Central Electrochemical Research Institute, Karaikudi 630 006, India article info Article history: Received 12 September 2008 Received in revised form 6 January 2009 Accepted 12 January 2009 Available online 20 January 2009 Keywords: PEDOT Anthraquinone sulphonate Nafion Polystyrene sulphonate Barrier film Stability abstract We describe a simple approach for the synthesis of stable electroactive poly[3,4-ethylene dioxythiophene] (PEDOT) in an acid medium, by incorporating a redox active dopant like 9,10-anthraquinone-2-sodium sulphonate (AQS) on a glassy carbon (GC) electrode. The modified electrode is responsive up to a pH of 7. The stability of the modified electrode during continuous electrochemical cycling is poor, due to leaching of the dopant from the PEDOT film. Efforts are made to improve the stability of the modified electrode by forming an anionic barrier film on the PEDOT-AQS interface either physically or electrochemically. The modified electrodes were monitored by cyclic voltammetry and Fourier transform-infrared (FT-IR) spectroscopy for the presence of AQS in the film. © 2009 Elsevier Ltd. All rights reserved. 1. Introduction Conducting polymers are essential components in electrochem- ical devices because of their electronic conductivity and doping properties. The latter characteristic allows chemists to individ- ually tune the properties of conducting polymers [1]. Various redox-active dopants, like viologens, quinones, tetrathiafulvalene, ferrocenes and polyoxometallates are used as dopants in the con- ducting polymer matrix to improve the interfacial properties of electrocatalysis, ion sensing and electrochromism [2–6]. The con- ducting polymers of polyaniline, polypyrrole, and polythiophene derivatives are used as electrode modifiers or as matrices for trap- ping redox species [5–7]. Among the conducting polymers, PEDOT has received special attention for various applications, including use as a matrix for entrapping enzymes in biosensors, use in elec- trochromic displays, and use as a hole conductor in solid state devices [8]. There is intense interest in this polymer because of its high-electronic conductivity (ca. 300 S cm -1 ), regio-regular struc- ture and good chemical stability. The electrocatalytic properties of the modified electrodes can be altered by modification of interfaces with thin films of redox species. Electrochemical modification of glassy carbon/ITO electrodes with redox electron transfer media- tors is common practice in electrochemistry [9]. Electrodeposition ∗ Corresponding author. E-mail address: jameskavalam@yahoo.com (J. Joseph). provides an easy way to fabricate thin films of conducting polymer matrices with entrapped redox mediators. There have been attempts to incorporate polyoxometallate electroactive species in conducting polymer thin films. These compounds are multi-centered redox anionic species. The electro- catalytic mediating properties of silicotungstic acid doped PEDOT, for the reduction of molecular oxygen, was reported recently by Kulesza et al. [10]. One advantage of using PEDOT as a matrix for entrapping redox-active species is that, unlike polyaniline, it remains electroinactive in highly acid medium. In other words, the electroactivity of the PEDOT film does not interfere with the redox chemistry of the doped electroactive species. Doping of PEDOT with high-molecular weight anionic polymeric species such as PSS - (polysyrene sulphonate anion) has been well established [11]. Once incorporated, it is difficult to remove this bulky dopant because it is polymeric. This feature is also responsible for the pseudo-n-doping behavior of electronic conducting polymers [12,13]. However, if the dopant is not big enough (for example, aryl sulphonates), it is likely that, during potential cycling, the dopant will leach out into the solution, which contains smaller anions such as perchlorate. In this work, we report electropolymerization of EDOT in an acid medium containing AQS. The sulphonate group is highly anionic in nature. Therefore, it can easily be incorporated into the PEDOT film during electropolymerization. The incorporation of an anthraquinone moiety yields a highly reversible symmetric voltam- metric peak due to the redox reactions. PEDOT-like films can be used to incorporate anionic redox mediators through counterion 0013-4686/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2009.01.032