The influence of addition (5 wt%) of 1-ethyl-3-methylimidazolium iodide (EMImI) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMEmBF(4)) on the melting point, bulk conductivity and electrochemical properties of the room temperature ionic liquid (RTIL) mixture as an electrolyte in electrical double layer capacitor (EDLC) has been studied using cyclic voltammetry, electrochemical impedance spectroscopy, constant current charge-discharge and constant power discharge methods. Electrodes were prepared of the D-glucose derived activated carbon powder, which was prepared by hydrothermal carbonization method followed by additional pyrolysis and carbon dioxide activation steps. The specific conductivity reduced from 13.6 mS cm(-1) to 12.8 mS cm(-1) and the melting point increased from 17 degrees C to 19.5 degrees C by adding 5 wt% of EMImI into EMImBF(4). However, noticeable increase in specific capacitance (245 F g(-1) at 1.0 V), specific energy (36.7 Wh kg(-1)) and specific power and minor increase in characteristic relaxation time constant (from 1.45 s to 1.48 s) values has been established for EDLCs using the mixture of RIM as an electrolyte. The EDLC based on EMImBF(4) + 5,wt% EMInd demonstrated nearly 50% higher stored charge values than EDLCs without EMImI addition. (C) 2013 The Electrochemical Society. All rights reserved.