Chemical synthesis and characterization of

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Chemical synthesis and characterization of fluorinated polyphenylthiophenes for ... [4] J.Roncali, Chemical Reviews 97 (1997) 173. [5] A.Laforgue, P.Simon, ...
Chemical synthesis and characterization of fluorinated polyphenylthiophenes for supercapacitors application

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A. Laforgue, P. Simon and J. F. Fauvarque Laboratoire d’Electrochimie Industrielle du CNAM 2, rue Conté 75003 PARIS - FRANCE [email protected]

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Y = F : Poly-4-FPT X,Y = F : Poly-3,4-DFPT X,Z = F : Poly-3,5-DFPT X,Y,Z = F : Poly-3,4,5-TFPT

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Figure 1 : Description of the different polymers synthesized and characterized.

80 Poly-4-FPT Poly-3,5-DFPT Poly-3,4-DFPT Poly-3,4,5-TFPT

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Figure 2 : Cyclic voltammetry showing the doping processes of the different conductive polymers synthetized, in an electrolyte NEt4CF3SO3 1M in acetonitrile. Sweeping rate is 20 mV/s.

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Nowadays, the electronically conductive polymers (ECPs) are the subject of many studies, due to their capability to go quickly and reversibly from an insulating state (also called undoped state) to a conductive state (or doped state), which corresponds also in many cases to an optical change [1-3]. The polythiophene and its derivatives possess two different doped states (positive and negative). In the negative doping, the conduction is realized by the electrons delocalisation on the polymer chains while on the positive doping, the conduction is assured by "positive holes" delocalisation. The grafting of the thiophene ring stabilises the polymer chain and allows better doping/dedoping cyclabilities. By choosing different substituents, the electrochemical characteristics of the polymer can be modified and adjusted to the needs [4]. The polythiophene negative doping appears at very negative potentials where electrolyte reduction occurs, but when grafted with electron acceptor groups (as fluorophenyl ones), the polymer negative doping potential is shifted to more positive potentials (cf. figure 2). In this way several fluorinated polyphenylthiophene were synthezised and characterised. It was decided to synthezise the polymers chemically to obtain powders which are easier to manipulate than electrochemical films to produce large and double-faced electrodes. The monomers were synthezised by a coupling reaction of 3-bromothiophene and the different fluorophenylmagnesium bromides in THF with NiCl2(diphenylphosphino propane) as catalyst. The reaction yields varied from 41 wt% to more than 90 wt%. The monomers were polymerized by a direct oxidation with FeCl3 in chloroform [5]. The polymers were then washed several times with methanol to remove the residual FeCl2 and chlorid ions. The yield was always more than 80 wt%. The polymers appear as red to brown powders. Characterization was performed by cyclic voltammetry and galvanostatic cycling in different organic electrolytes (cf. Fig. 2). The polymers exhibited good electrochemical properties. For the positive doping, 35 mAh/g were reached, associated to 260 F/g. For the negative doping, 12 mAh/g associated to 130 F/g were obtained. Impedance spectroscopy showed almost theoretical Nyquist plots with a small diffusion and a total capacity at relatively high frequency (5 Hz) (cf. Fig.3). Results concerning the cyclability of such polymers will also be presented and discussed.

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References : [1]

A.Rudge, I.Raistrick, S.Gottesfeld, J.P.Ferraris, Electrochimica Acta 39 (1994) 273-287. [2] J.P. Ferraris, M.M. Eissa, I.D.Brotherson, D.C.Loveday, A.A.Moxey, J. Electroanal. Chem. 459 (1998) 57-69. [3] H.Sarker, Y.Gofer, J.G.Killian, T.O.Poehler, P.C.Searson, Synthetic Metals 97 (1998) 1-6. [4] J.Roncali, Chemical Reviews 97 (1997) 173. [5] A.Laforgue, P.Simon, C.Sarrazin, J.F.Fauvarque, J. Power Sources 80 (1999) 142-148.

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Figure 3 : Nyquist plot of Poly-3,5-DPFPT.between 65 kHz and 40 mHz.