Electrical and electrochemical properties of reduced, oxidized, and overoxidized poly[2,5-di(-2-thienyl)-pyrrole] films in water/acetonitrile mixture

Poly[2.5-di(-2-thicnyl)-pyrrole] [poly(SNS)] films up to 1.29 mum thick wer e anodically synthesized from a 5 mM monomer and 0.1 M LiClO4 + acetonitril e solution at 0.50 mA cm(-2). These deposits with a large proportion of ele ctroactive polarons compensated with ClO4- dissolve upon reduction in this medium. Insoluble reduced films were synthesized in a water; acetonitrile ( 3:2 v/v) mixture with 0.1 M LiClO4 at - 200 mV. having a small proportion o f electroinactive charges trapped in polymer. Their cyclic voltammograms di splay an initial redox pair related to the reversible doping/undoping proce ss with electroactive polarons, which can be continuously cycled from -200 to 340 mV. A further oxidation peak involves generation of bipolarons, whil e two subsequent overoxidation processes lead to polymer reticulation, with out charge accumulation. Reduced films are then progressively oxidized from ca. 150 to ca. 600 mV and overoxidized between 660 and 1400 mV. The electr ical conductivity rises upon oxidation, remaining almost constant during ov eroxidation. The impedance of reduced and oxidized forms decays with increa sing film thickness and potential, although upon overoxidation; it increase s as potential is shifted in the positive direction. All impedance measurem ents can be adequately simulated by a simple equivalent circuit. The calcul ated film capacitance for reduced and overoxidized forms is very low, and i ncreasing values are found only as the polymer is gradually oxidized from c a. 150 to 500 mV. The high capacitances found for oxidized poly(SNS) indica te that it is adequate for charge-storage devices, although its use should be limited to potentials only involving its reversible doping/undoping cycl ing. (C) 2000 The Electrochemical Society. S00 13-4651 (00)05-01 9-7. All r ights reserved.