Comparative performance characteristics of electrical double layer capacitors (EDLCs) based on the multiwalled carbon nanotube (MWCNT) electrodes and ionic liquid incorporated poly(ethylene oxide) (PEO) based magnesium and lithium ion conducting polymer electrolytes have been studied. The polymer electrolytes comprise PEO complexed with magnesium and lithium trifluoromethanesulfonate (triflate) with added ionic liquid 1-ethyl-3-methylimidazolium trifluoromethanesulfonate (EMITf). The ionic conductivity of the polymer electrolytes is found to be similar to 10(-4) S cm(-1) at ambient temperature. The electrochemical stability window, as estimated from cyclic voltammetry, is found to be similar to 4 V (from -2 V to + 2 V) for the Li+ ion conducting electrolyte, whereas a slightly higher potential window is observed for the Mg2+ ion conducting electrolyte. The performance of EDLC cells has been studied by impedance spectroscopy, cyclic voltammetry and constant current charge-discharge techniques at room temperature (similar to 25 degrees C). It has been observed that the Mg-based polymer electrolyte exhibits equivalent (rather better) performance as electrolyte of EDLCs over the corresponding Li-based polymer electrolyte. The EDLC cells with the Mg- and Li-based polymer electrolytes show specific capacitance values of 2.6-3.0 and 1.7-2.1 F g(-1) of MWCNTs, respectively. (C) 2011 Elsevier B.V. All rights reserved.