H+ and Fe3+ ions co-doped polyaniline were synthesized by cyclic voltammetry onto the stainless steel mesh with various concentration of ferric chloride (FeCl3 center dot 6H2O) in electrolyte. The structure and morphology of PANI and PANI/Fe3+ films were characterized by Fourier transform infrared (FT-IR), X-ray diffraction (XRD), Scanning electron microscopy (SEM), Energy dispersive X-ray spectroscopy (EDS) and X-ray photoelectron spectroscopy (XPS) techniques. The electrochemical properties of PANI and PANI/Fe3+ films were investigated by cyclic voltammetry, galvanostatic charge-discharge test and electrochemical impedance spectroscopy (EIS) in 0.5 mol L-1 H2SO4 electrolyte in three-electrode system. The PANI/0.2 M Fe3+ film shows a larger specific capacitance of 602 F g(-1) at a current density of 3 mA/cm(2) and lower resistance compared with the pure PANI film. The relationship between electrochemical properties of a serious of transition metal ions doped PANI/Mn+ (Mn+ = Mn2+, Co2+, Ni2+, Cu2+, Zn2+ and Fe3+) films and the ratio of electronic affinity and ionic radius (Ea/r) has also been researched. (C) 2015 Elsevier Ltd. All rights reserved.