Investigation of polyaniline films doped with Ni2+ as the electrode material for electrochemical supercapacitors

► The PANI/Ni2+ films was synthesized by CV on stainless steel substrates. ► The growth rate of PANI/Ni2+ films was greatly increased. ► The PANI/Ni2+ films show a larger specific capacitance and lower resistance. Polyaniline (PANI) films doped with Ni2+ (PANI/Ni2+) were synthesized by cyclic voltammetry (CV) on stainless steel (SS) substrates in 0.2mol/L aniline (An) and 0.5mol/L sulfuric acid (H2SO4) electrolyte with various concentration of nickel sulfate (NiSO4). The structure and morphology of PANI/Ni2+ films were characterized by Fourier transform infrared (FTIR), 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/Ni2+ films were investigated by cyclic voltammetry, galvanostatic charge–discharge test and electrochemical impedance spectroscopy (EIS) in 0.5mol/L H2SO4 electrolyte in three-electrode system. The results suggest that the growth rate of PANI was greatly increased, which may arise from the interactions between PANI chain and Ni2+. The PANI/Ni2+ films show a larger specific capacitance of 658.3F/g at a current density of 5mA/cm2 and lower resistance compared with the pure PANI film. The results indicate that the PANI/Ni2+ films are promising material for supercapacitors.