Is the mixture of 1-ethyl-3-methylimidazolium tetrafluoroborate and 1-butyl-3-methylimidazolium tetrafluoroborate applicable as electrolyte in electrical double layer capacitors?

The influence of small addition (from 0.005 to 1 M) of 1-butyl-3-methylimidazolium tetrafluoroborate (BMImBF(4)) in 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF(4)) on the melting point, bulk conductivity and electro-chemical properties of ionic liquid mixtures as electrolytes in electrical double layer capacitors (EDLCs) has been studied using cyclic voltammetry and electrochemical impedance spectroscopy methods. The melting point of EMImBF(4) can be reduced from 135 degrees C to 5.6 degrees C by adding small amount of BMImBF(4) (0.5 M) without noticeable decrease in capacitance (135 F g(-1) at 32 V), energy (49 Wh kg(-1)) and power (38 kW kg(-1)) densities and minor increase in characteristic relaxation time (similar to 16 s) for EDLCs studied. However, the EDLCs based on EMImBF(4) with 1 M addition of BMImBF4 (melting point of mixture -6 degrees C) demonstrated noticeable decrease in capacitance (similar to 122 F g(-1) at 32 V), energy (43 Wh kg(-1)) and power (30 kW kg(-1)) densities and increase in characteristic relaxation time to 25 s. (C) 2012 Elsevier B.V. All rights reserved.