Polyaniline film was electropolymerized in organic acidic media (CF3COOH) and then investigated by cyclic voltammetry, AC impedance, and galvanostatic charging and discharging tests in ionic liquid-1-methyl-3-butylimidazolium hexafluorophosphate (BMIPF6) and the mixture electrolytes of BMIPF6 and acetonitrile (ACN) with different ratios. The results showed that the polymer in mixture of BMIPF6 and ACN have lower solution resistance, higher cycle life, and higher electrochemical capacitance. The relationship of the peak current to the scan rates provides some insight into the nature of the polyaniline film switching reaction in different electrolytes. (c) 2005 Elsevier Inc. All rights reserved.