Optimization of Conducting Polymer Synthesis for Battery Applications

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T.F. OTERO, C.SANTAMARIA AND J.RODRIGUEZ Laboratory of Electrochemistry, Faculty of Chemistry, University of the Basque Country. P.O.Box 1072, 20080 San Sebastidn. Spain

ABSTRACT The evolution of the capacity to store electrical charges of electrogenerated polypyrrole and polythiophene films, as a function of the parameters of synthesis (electrical potential, solvent, monomer concentration and temperature) was analyzed. The polymer production was followed by "ex situ" ultramicrogravimetry. The stored charge in each film was controlled by voltammetry and chronoamperometry, in the background electrolyte (in absence of monomer). The charge storage ability was calculated from the ratio between stored charge and polymer mass adhered to the electrode. The charge storage ability of an electrogenerated film decreases several times when one of the parameters of synthesis: potential of polymerization, temperature, concentration of monomer or donor number of the solvent, increase. The change on the polymer property when the conditions of synthesis shift, points to a mixed polymerization-degradation process during polymer growth. The knowledge of those variations allows to optimize the conditions of synthesis to generate conducting polymers for specific batteries applications. INTRODUCTION The electrogeneration of conducting polymers is a fast method, through a complex and flexible mechanism, to obtain mixed materials [1]. During the electrogeneration of a polymer film parallel electropolymerization and acid-catalyzed polymerization processes coexist with degradation processes. The acid-catalyzed polymerization and the degradation promote non electroactive lakes in the film. The properties of the polymer depend on the material composition (electroactive part / passive lakes ratio), which is related to the chemical and electrical conditions of synthesis [2,3]. The control of these conditions and hence of the physical properties of polymer, allow us to postulate the production of tailored polymer films for technological applications [4]. In this work the capacity of polypyrrole and polythiophene to store electrical charge, as a function of electrical and chemical variables of synthesis, is analyzed. The evolution of those capacities with synthesis conditions allows us to stablish correlations between this technological property and the models of interfacial reactions [5,6], and opens new possibilities to use the electrochemical synthesis to obtain tailored conducting polymers for specific applications. EXPERIMENTAL PART Monomers (pyrrole and thiophene, Merck AG), were distilled under vacuum. LiC104 was the used salt. It was dehydrated at 80'C before use. Acetonitrile (LabScan, HPLC grade) was distilled in the presence of P2 0 5 . 805 Mat. Res. Soc. Symp. Proc. Vol. 328. @1994 Materials Research Society

A 273 PAR potentiostat-galvanostat was used to perform electrochemical studies. The potential was measured vs. a saturated calomel reference electrode (SCE). As working electrodes Pt sheets of 1 cm 2 were used. Platinum sheets

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