Poly(Cyano-Substituted Diheteroareneethylene) as Active Electrode Material for Electrochemical Supercapacitors

A new class of low band gap thiophene polymers prepared from (E)-α-cyanoethylene thiophene derivatives were electrochemically and physically evaluated as active electrode material for electrochemical supercapacitors. The corresponding polymers were prepared by electrochemical polymerization of these monomers from a nonaqueous solution (acetonitrile) containing tetraethylammonium tetrafluoroborate. The electrochemical properties and the stability under cyclic voltammetry of the polymers were found to be strongly dependent on their electronic configuration, especially in the case where the monomer has two different aromatic heterocycles. The range of stable electroactivity of the polymers in organic media spans about 2 V. Since poor stability was observed by cyclic voltammetry for poly-(E)-α-[(2-thienyl)methylene]-2-(3-methylthiophene)acetonitrile and poly-(E)-α-(2-thienylmethylene)-2-furanacetonitrile, only poly-(E)-α-[(2-thienyl)methylene]-2-thiopheneacetonitrile, poly-(E)-α-[(3-methyl-2-thienyl)methylene]-2-thiopheneacetonitrile, and poly-(E)-α-[(2-furanyl)methylene]-2-thiopheneacetonitrile were evaluated as electrode materials for an electrochemical supercapacitor. Stability tests upon potential cycling between the n- and p-doped states and a potential range of about 2 V have shown a 60% decrease of the voltammetric charge for poly-(E)-α-[(2-thienyl)methylene]-2-thiopheneacetonitrile following 2000 cycles. Preliminary galvanostatic charge−discharge cycling experiments for the best system indicated an energy density of 8.6 W h/kg while it delivered a power density of 1.6 kW/kg for a discharge time of 20 s.