K.S. Perera

Investigation of a Pseudo Capacitor with Polyacrylonitrile based Gel Polymer Electrolyte

Pseudo capacitors belong to one group of super capacitors which are consisted with non carbon based electrodes. As such, conducting polymers and metal oxide materials have been employed for pseudo capacitors. Conducting polymer based pseudo capacitors have received a great attention due to their interesting features such as flexibility, low cost and ease of synthesis. Much work has been done using liquid electrolytes for those pseudo capacitors but has undergone various drawbacks. It has now been realized the use of solid polymer electrolytes as an alternative. Among them gel polymer electrolytes (GPEs) are in a key place due to their high ambient temperature conductivities as well as suitable mechanical properties. In this study, composition of a polyacrylonitrile (PAN) based GPE was optimized and it was employed as the electrolyte in a pseudo capacitor having polypyrrole (PPy) electrodes. GPE was prepared using ethylene carbonate (EC), propylene carbonate (PC), sodium thiocyanate (NaSCN) and PAN as starting materials. The maximum room temperature conductivity of the GPE was 1.92 × 10 Scm for the composition 202.5 PAN : 500 EC : 500 PC : 35 NaSCN (by weight). Performance of the pseudo capacitor was investigated using Cyclic Voltammetry technique, Electrochemical Impedance Spectroscopy (EIS) technique and Continuous Charge Discharge (GCD) test. The single electrode specific capacity (Cs) was found out to be 174.31 F/g using Cyclic Voltammetry technique at the scan rate of 10 mV/s and within the potential window -1.2 V to 1.2 V. The same value obtained using EIS was about 84 F/g. The discharge capacity (Cd) was 69.8 F/g. The capacity fade over 1000 cycles was rather a low value of 4%. The results proved the suitability of the pseudo capacitor for improving the performance further.

Effect of polymerisation current density of electrodes on the performance of polypyrrole based redox-capacitor

Use of redox-capacitors is one of the effective and economic solutions to the demand for power sources. Redoxcapacitors replace the role of batteries and conventional capacitors by hundred times of the power density and energy density. Research activities are being continued to fabricate more comprehensive supercapacitors. Among those, fabrication of the symmetric polymer capacitor is dominant because of its simplicity. In this study, the effect of polymerisation current density on the performance of a symmetric polymer redoxcapacitor is reported. Conducting polymer, polypyrrole (PPy) was used as the electrodes, while a gel polymer electrolyte (GPE) based on polyvinylidenefluoride (PVDF) was used as the electrolyte. Fabrication of the redox-capacitors was carried out in the configuration of PPy : GPE : PPy . They were characterised using cyclic voltammetry tests, continuous galvanostatic charge-discharge tests and electrochemical impedance spectroscopy. An average specific capacitance value of 12 Fg-1 could be obtained by cyclic voltammetry measurements. It was about 7 Fg-1 as per the galvanostatic charge-discharge test. The specific capacity remains rather stable upon continuous cycling. An increase was noticed in specific capacity with the increase in polymerisation current density. From the impedance spectroscopy measurements, it was observed that with increasing polymerisation current density, the capacitive nature of the redox-capacitors can be improved.