In order to improve energy density of a capacitor, an operative potential limit extension is a simple way. Based on this concept, we have studied 2-electrode symmetric electrical double layer capacitor (EDLC) of PICACIFF-activated carbon electrodes in 4 mol dm(-3) of sodium nitrate using ethylene glycol (EG)-aqueous solution as an electrolyte media. Infrared spectroscopy was used to characterize the interactions of the electrolyte components. The electrochemical performance of the capacitor was experimented using cyclic voltammetry, galvanostatic charge-discharge cycling and impedance spectroscopy techniques at 0 degrees C, 25 degrees C and 60 degrees C through the aqueous and EG-aqueous electrolytes. The electrochemical performances of the aqueous cells were significantly enhanced by the EG addition. In such cases, a 1.5-2.0 V potential window and a range of 12-16 Wh kg(-1) energy density were obtainable. This energy density value is two times higher than a usual aqueous cell. Moreover, a little percentile of aqueous to EG electrolyte changes the conductivity and its power density drastically. We conclude that this kind of electrolyte might be a suitable solution in between the aqueous and organic electrolytes. Also, it can achieve much higher energy density than the aqueous just a partial substitution of an organic medium. (c) 2013 Elsevier B.V. All rights reserved.