We present in this work a study of the electrochemical behaviour of terthiophene and its corresponding polymer, which is obtained electrochemically as a film by cyclic voltammetry (CV) on platinum electrode. The analysis focuses essentially on the effect of two solvents acetonitrile and dichloromethane on the electrochemical behaviour of the obtained polymer. The electrochemical behavior of this material was investigated by cyclic voltammetry and electrochemical impedance spectroscopy (EIS). The voltammograms show that the film of polyterthiophene can oxide and reduce in two solutions; in acetonitrile, the oxidation current intensity is more important than in dichloromethane. The impedance plots show the semicircle which is characteristic of charge-transfer resistance at the electrode/polymer interface at high frequency and the diffusion process at low frequency. 1. Introduction As other conjugated conducting polymers, polythiophene and its oligomers can be polymerized from their monomers in solutions by electrochemical methods. The electrochemical synthesis is advantageous method: polymers are formed in the doped state; films generally possess interesting electrochemical and good semiconductor properties  and relatively good stability in air for both the neutral and oxidised states [2–7]. The mechanism of the electropolymerisation of conducting polymers and polyheterocycles occurred by the coupling via α-α bonding of monomer radical cation after its oxidation at the electrode, and the protons are removed from dihydrodication leading to neutral species [8–10]. As the dimer is more easily oxidized than the monomer, it is immediately oxidized. The chain elongation occurs by the addition of new monomer radical cation leading to polymerization and forms the insoluble polymeric species, which subsequently deposits onto the electrode . Conducting polymer-modified electrodes have been widely investigated because of their potential application in areas such as electrocatalysis [12, 13], sensors [14, 15], corrosion [16–18], batteries [19, 20], electronic displays, and devices [21–24]. In our previous work , we have studied the role of P3T in corrosion of stainless steel; the results were important and show effectively that the film of P3T will decrease the corrosion rate. In this paper, we are interested in performing an electrochemical characterisation of P3T films electrochemically synthesized, in two organic solvents: acetonitrile (CH3CN) and dichloromethane (CH2Cl2), at platinum substrates. We want to show how the medium of the analysis is
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