Electrochimica Acta 57 (2011) 91–97 Contents lists available at ScienceDirect Electrochimica Acta jou rn al hom epa ge: www.elsevier.com/locate/electacta Preparation and characterization of magnesium ion gel polymer electrolytes for application in electrical double layer capacitors S.N. Asmara, M.Z. Kufian, S.R. Majid, A.K. Arof ∗ Centre for Ionics, University of Malaya, Physics Department, Faculty of Science, 50603 Kuala Lumpur, Malaysia a r t i c l e i n f o Article history: Received 30 November 2010 Received in revised form 12 June 2011 Accepted 13 June 2011 Available online 21 June 2011 Keywords: Magnesium triflate PMMA Cyclic voltammetry EDLC Gel electrolyte a b s t r a c t This work describes the preparation and characterization of poly (methyl methacrylate) (PMMA) based gel polymer electrolytes with magnesium triflate (Mg(CF 3 SO 3 ) 2 ) as the ion providing salt. Liquid elec- trolytes containing 0.4 M Mg(CF 3 SO 3 ) 2 in solvents comprising different ratios of ethylene carbonate (EC) and diethyl carbonate (DEC) have been prepared at room temperature. The highest conducting electrolyte contains EC and DEC in the weight ratio of 2:1. To the highest conducting liquid electrolyte, 25–50 wt.% PMMA has been added and the mixtures were heated at 80 ◦ C for 2 min to form gel polymer electrolytes. The gel electrolyte with composition 40 wt.% PMMA and 60 wt.% of 0.4 M Mg(CF 3 SO 3 ) 2 in EC:DEC (2:1, w/w) has the highest conductivity of 5.58 × 10 -5 S cm -1 and activation energy 0.11 eV. The gel polymer electrolyte with highest conductivity at room temperature has Mg 2+ ion transference number of 0.37 and electrochemical stability window 2.42 V. The highest conducting gel polymer electrolyte has been used to fabricate an electric double layer capacitor (EDLC) which exhibits a nearly rectangular voltammogram even after the 50th discharge cycle. The capacitance of the EDLC is about 27 F g -1 after the 1st cycle and 23 F g -1 after the 50th cycles. © 2011 Elsevier Ltd. All rights reserved. 1. Introduction The development of polymer electrolytes has drawn the atten- tion of researchers from all over the globe. This is due to the many potential applications of polymer electrolytes in electrochemical devices such as lithium ion batteries, electrochromic devices and electric double layer capacitor (EDLC). Ion conducting polymer electrolytes have many advantages compared to liquid electrolytes. These advantages include being leak proof and non-bulky [1]. For applications in an all solid-state electrochemical device, ion con- ducting polymer electrolytes should possess sufficient electrical conductivity, good mechanical strength and thermal stability and have appreciable cationic transference number [2–5]. They should also be compatible with the electrodes used. To date, three classes of polymer electrolytes have been estab- lished. They are dry solid-state, gel plasticized and composite polymer electrolytes. Gel polymer electrolytes (GPEs) can be pro- duced when the polymer swells up in an organic solvent. GPEs can provide better contact with the electrode surface compared to dry solid electrolytes [6,7]. Low molecular weight organic solvents such as dimethyl sulphoxide (DMSO), dimethyl carbonate (DMC), diethyl carbonate (DEC), ethylene carbonate (EC) and propylene carbonate (PC) can be used to improve the electrolyte conductivity. The last ∗ Corresponding author. Tel.: +60 3 79674085; fax: +60 3 79674146. E-mail address: akarof@um.edu.my (A.K. Arof). two solvents are the most frequently used to prepare gel polymer electrolytes due to their high dielectric constant and low viscos- ity, respectively [8–10]. Although many gel polymer electrolytes have been reported, most research focus on Li + ion conducting elec- trolytes [11–13]. The ionic radius of Li + and Mg 2+ is about the same, i.e. 68 and 65 pm, respectively; hence it is possible to replace Li + ions with Mg 2+ ions as the charge carrier in gel polymer electrolytes. Magnesium metal is more stable compared to lithium metal. It is easier to handle magnesium metal in oxygen or humid atmo- sphere compared to lithium metal. To handle lithium metal argon or helium atmosphere is required. Magnesium metal is more abun- dant in nature compared to that of lithium and magnesium metal is much cheaper than lithium. Studies on polymer electrolytes using Mg 2+ ions as the charge carriers are being intensively undertaken [14–19]. In this work, gel polymer electrolytes were prepared by adding poly (methyl methacrylate) (PMMA) to liquid electrolytes comprising magnesium triflate Mg(CF 3 SO 3 ) 2 in binary solvent mixtures containing different ratios of ethylene carbonate (EC) and diethyl carbonate (DEC). The GPEs were then characterized using Fourier transform infrared (FTIR) spectroscopy, differen- tial scanning calorimetry (DSC) and electrochemical impedance spectroscopy (EIS). The electrolyte decomposition voltage was determined using linear sweep voltammetry (LSV). The highest conducting magnesium ion gel polymer electrolyte was employed in EDLC fabrication. Cyclic voltammetry (CV) was performed in the voltage range between 0 and 0.85 V at a constant current of 1 mA 0013-4686/$ – see front matter © 2011 Elsevier Ltd. All rights reserved. doi:10.1016/j.electacta.2011.06.045