Polypyrrole (PPy) grown from organic media and polymeric material produced by coelectropolymerization of pyrrole and aniline in organic acidic media were investigated by cyclic voltammetry, electrochemical impedance spectroscopy (EIS), differential scanning calorimetry (DSC), infrared spectroscopy (FTIR), scanning electron microscopy (SEM), and X-ray photoelectron spectroscopy (XPS). The cyclic voltammogram of the polypyrrole grown from non aqueous media containing an organic acid (CF3COOH) is not significantly affected up to a 0.5 M CF3COOH concentration in the deposition solution. Al higher CF3COOH concentration a shift of the redox waves to more positive potential is observed but the voltammetric charge of the cyclic voltammogram of the polymer and the stabilization potential during the galvanostatic growth of the polymer are barely affected. The coelectropolymerization of pyrrole and aniline was carried out: in acetonitrile in the presence of an organic acid (CF3COOH) and an appropriate supporting electrolyte (tetraethylammonium tetrafluoroborate or tetramethylammonium trifluoromethanesulfonate). The resulting polymer, named thereafter PANIPY, is electroactive over a potential range of ca. 1.5 V. The thermal properties of the films were studied by DSC, and the thermograms suggest the presence of a mixture of polypyrrole, polyaniline, and a random polyaniline-polypyrrole copolymer. This is also confirmed by the FTIR spectra of the polymer grown from a mixture of aniline and pyrrole which are not the sum of the spectra of each individual polymers. SEM photomicrographs of the PANIPY polymer deposited onto carbon paper electrode show a smooth and even surface. Low-frequency capacitance (C-LF) as high as 100 mF/cm(2) (60 F/g) is evaluated from the EIS data. Galvanostatic charge-discharge cycling between a cell voltage of 0 and 1.5 V shows energy and power densities of 5 Wh/kg and 1.5 kW/kg of composite polymer, respectively, for a discharge time of about 13 s.