electrochemical 
 capacitors ( ecs ) are electrical energy storage devices that have the 
 potential to be very useful in a wide range of applications , especially 
 where there is a large disparity between peak and average power demands 
 . 
 the use of ionic liquids ( ils ) as electrolytes in ecs can increase 
 the energy density of devices ; however , the viscosity and conductivity 
 of ils adversely influence the power density of the device . 
 we present 
 experimental results where several ils containing different cations 
 have been employed as the electrolyte in cells containing mesoporous 
 carbon electrodes . 
 specifically , the behavior of ils containing an 
 ether bond in an alkyl side chain are compared with those of a similar 
 structure and size but containing purely alkyl side chains . using 
 electrochemical impedance spectroscopy and constant current cycling , 
 we show that the presence of the ether bond can dramatically increase 
 the specific capacitance and reduce device resistance . 
 these results 
 have the important implication that such ils can be used to tailor 
 the physical properties and electrochemical performance of il - based 
 electrolytes .