S.A. Hashmi

Experimental studies on poly methyl methacrylate based gel polymer electrolytes for application in electrical double layer capacitors

Studies have been carried out on gel polymer electrolytes comprising poly methyl methacrylate (PMMA)-ethylene carbonate (EC)–propylene carbonate (PC)–salts, LiClO4, NaClO4 and (C2H5)4NClO4 (TEAClO4) with a view to using them as electrolytes in electrical double layer capacitors (EDLCs) based on activated charcoal powder electrodes. The optimum composition of gel electrolytes, PMMA (20 wt%)–EC : PC (1 : 1 v/v)–1.0 M salts exhibit high ionic conductivity of the order of ~10−3 S cm−1 at room temperature with good mechanical/dimensional stability, suitable for their application in EDLCs. The EDLCs have been characterized using linear sweep cyclic voltammetry, galvanostatic charge–discharge tests and ac impedance spectroscopy. The values of capacitance of 68–151 mF cm−2 (equivalent to single electrode specific capacitance of 38–78 Fg−1 of activated charcoal powder) have been observed. These values correspond to a specific energy of 5.3–10.8 Wh kg−1 and a power density of 0.19–0.22 kW kg−1. The capacitance values have been observed to be stable up to 5000 voltammetric cycles or even more. A comparison of studies shows the predominant role of anions of the gel electrolytes in the capacitive behaviour of EDLCs.

Experimental investigations on a proton conducting nanocomposite polymer electrolyte

A new proton conducting nanocomposite polymer electrolyte (NCPE) comprising polyethylene oxide (PEO)-NH4HSO4 salt complex dispersed with nanosized SiO2 particles has been investigated. The NCPE films have been formed following the usual solution cast method. The results of various studies based on scanning electron microscopy, x-ray diffraction, differential scanning calorimetry, Fourier transform infra-red spectroscopy as well as some basic ionic transport parameters, namely conductivity, and ionic transference number, are presented and discussed. SiO2 concentration dependent conductivity measurements have been carried out on the NCPE films at room temperature. This study revealed the existence of two conductivity maxima at SiO2 concentrations ~3 and 12 wt% which have been attributed to two percolation thresholds in the composite polymer electrolyte phase. An optimum value of conductivity (σ ~ 6.2 × 10−5 S cm−1 at 27 °C) was achieved for the NCPE film with 3 wt% SiO2 dispersion. This has been referred to as optimum conducting composition. The temperature dependence of conductivity exhibited an Arrhenius-type thermally activated behaviour both below and above the semicrystalline–amorphous phase transition temperature of PEO.