Synthesis, chemical polymerization and electrochemical properties of low band gap conducting polymers for use in supercapacitors

A set of nine monomers derived from diaryl-cyanovinylene, -carboxyvinylene and -cyanobutadiene were synthesized as were the corresponding polymers resulting from the chemical polymerization of the monomers in the presence of an almost quantitative amount of FeCl3 in chloroform. The aim of this work was to investigate the effect of the chemical structure of the polymers on their charge capacitance and stability upon galvanostatic charge/discharge cycling. The electrochemical performances of composite electrodes based on polymer, acetylene black and PTFE have been investigated in acetonitrile containing 1 M Et4NBF4 using cyclic voltammetry and galvanostatic charge/discharge cycling experiments. The best performances in terms of charge capacitance for both the p- and n-doping processes were demonstrated with poly(7) (2E,4E)-2,5-di-2-thienylpenta-2,4-dienenitrile and poly(9) (2E)-3-(2,2'-bithienyl-5-yl)-2-(2-thienyl)prop-2-enenitrile since values as high as 245 C g(-1) were obtained with poly(7) in its n-doped state and 325 C g(-1) with p-doped poly(9). The energy density (68 Wh kg(-1)) and power density (24 kW kg(-1)) delivered by a poly(9) capacitor are in good agreement with those expected from cyclic voltammetry and galvanostatic charge/discharge experiments performed with single electrodes. Unfortunately, a capacitance loss was observed upon cycling and was ascribed exclusively to the n-doping process occurring at the negative electrode since the capacitance of the positive electrode remained almost unchanged during these experiments.