In this study, for the first time, aniline was oxidized by ammonium persulfate (APS) at higher temperatures without any protic acid, and APS acted as an oxidizing agent and a protonating agent. During the oxidation of aniline by APS, sulfuric acid formation occurred, and the sulfuric acid was incorporated into polyaniline (PANI) as a dopant. PANI-sulfate samples were characterized by IR spectroscopy, X-ray diffraction, and scanning electron microscopy techniques. In this methodology, a highly ordered PANI-sulfate salt (H2SO4) with a nanofiber morphology was synthesized. Interestingly, a PANI base was also obtained with a highly ordered structure with an agglomerated netlike nanofiber morphology. PANI-H2SO4 was used as an electrode material in a symmetric supercapacitor cell. Electrochemical characterization, including cyclic voltammetry (CV), charge-discharge (CD), and impedance analysis, was carried out on the supercapacitor cells. In this study, the maximum specific capacitance obtained was found to be 273 F/g at 1 mV/s. Scan rate from cyclic voltammetry and 103 F/g at 1 mA discharge current from CD measurement. Impedance measurement was carried out at 0.6 V, and it showed a specific capacitance of 73.2 F/g. The value of the specific capacitance and energy and power densities for the PANI-H2SO4 system were calculated from CD studies at a 5-mA discharge rate and were found to be 43 F/g, 9.3 W h/kg, and 500 W/kg, respectively, with 98-100% coulombic efficiency. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 780-788, 2011