Carbon nanofibers were prepared using electrospinning and thermal treatment of a new precursor, poly(acrylonitrile-co-vinylimidazole). Raman spectroscopy confirmed carbonization. Steam activation resulted in high surface area of 1120 m(2)/g. Coin cells were assembled using ethylmethylimidazolium bis(trifluoromethylsulfonyl) imide (EMITFSI) as the electrolyte. Cyclic voltammetry showed classic box-like behavior of electrochemical double layer capacitors with specific capacitances ranging between 122 F/g (10 mV/s) and 86 F/g (300 mV/s). From Ragone plots, the maximum energy and power densities were 47.4 Wh/kg (0.5 A/g) and 7.2 kW/kg (5 A/g), respectively. (C) 2012 Elsevier B.V. All rights reserved.