ABSTRACTElectrochemical Double Layer Capacitors, EDLC, using Cobalt sulfide- Graphene (CoSG) composite electrodes, were fabricated and the storage process was studied. CoSG composite was prepared by a simple chemical route. X-ray diffraction (XRD), Fourier Transform Infrared Spectroscopy (FTIR), Thermogravimetric Analysis (TGA) and Field Emission Scanning Electron microscopy (FESEM) were used to characterized the as prepared composites which indicated formation of Co S phase. Solutions of perfluorosulfonic acid and Polyvinylidene Fluoride (PVDF) were used as electrode binding material. The storage capacitance of the composites were studied in 1M KCl and 6M KOH electrolytes using standard electrochemical techniques like cyclic voltammetry, CV, electrochemical impedance spectroscopy, EIS, and discharge profiles. The capacitance was estimated for various binder concentrations for both the electrolytes. The concentration of perflurosulfonic acid binder of 0.8 wt% and PVDF of 0.04 wt% showed optimized specific capacitances of 657.8 F/gm and 1418.8 F/g, respectively. Some of the problems in storage density in activated carbon, like varying micro or meso pores, poor ion mobility due to varying pore distribution, low electrical conductivity, can be overcome by using Graphene and composites of Graphene. Graphene in various structural nomenclatures have been used by different groups for charge storage. Optimization of the electrode structure in terms of blend percentage, binder content and interface character in the frequency and time domain provides insights to the double layer interface structure.

Nirmala Grace A

Centre for Nanotechnology Research

Vellore Campus

Ramachandran R

Grace N.A

Chittur S.K.

Vellore Institute of Technology (VIT) is a private university located in&nbsp;Tamil Nadu, India. Founded in 1984, as Vellore Engineering College, the institution offers 20 undergraduate, 34 postgraduate, four integrated and four research programs. It has campuses in Vellore, Amravati, Bhopal and Chennai.

VIT is one of the top ranked private universities in India according to NIRF, THE and QS Rankings.&nbsp;Govt. of India has recognized&nbsp;VIT, Vellore as an&nbsp;Institution of Eminence. This has allowed VIT to take independent quality initiatives and move up in world ranking.

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VIT University

MRS Proceedings

Graphene platelets were synthesized from graphene oxide by chemical and electrochemical route. Under the chemical method, sodium borohydride and hydrazine chloride were used as reductants to produce graphene. In this paper, a novel and cost effective electrochemical method, which can simplify the process of reduction on a larger scale, is demonstrated. The electrochemical method proposed in this paper produces graphene in powder form with good yield. The atomic force microscopic images confirmed that the graphene samples prepared by all the routes have multilayers of graphene. The electrochemical process provided a new route to make relatively larger area graphene sheets, which will have interest for further patterning applications. Attempt was made to quantify the quantum of reduction using cyclic voltammetry and choronopotentiometry techniques on reduced graphene samples. As a measure in reading the specific capacitance values, a maximum specific capacitance value of 265.3 F/g was obtained in sodium borohydride reduced graphene oxide. © 2013 Elsevier Ltd. All rights reserved.

Materials Research Bulletin

Synthesis of graphene platelets by chemical and electrochemical route

An alternate energy storage device for high power applications are supercapacitors. They store energy either by pure electrostatic charge accumulation in the electrochemical double layer or as pseudo capacitance from fast reversible oxidation reduction process. However, they have low energy density. The electrodes in the Electrochemical Double Layer Capacitors (EDLC) are made of high surface area carbon. The carbon that can be used range from activated carbon to Graphene, with varying particle size, surface area, pore size and pore distribution. The main emphasis in the development of EDLCs is fabrication of electrodes having high surface area which would enhance the storage density of the EDLC. The EDLCs are assembled with different electrolytes which determine the operational voltage. Solid electrolytes can also be used as electrolyte and have an advantage in that we can avoid electrolyte leaks and are easy to handle. This would improve the reliability. They can also be shaped and sized to suit the application. The perflurosulfonic acid polymer as electrolyte has been used by various groups for EDLC application. The perflurosulfonic acid polymer possesses high ionic conductivity, good thermal stability, adequate mechanical strength and excellent chemical stability. The EDLCs, which are based on high-surface area carbon materials, utilize the capacitance arising from a purely non-Faradaic charge separation at an electrode/electrolyte interface. Carbon is widely used for many practical applications, especially for the adsorption of ions and molecules, as catalyst supports and electrode materials. The chemical characteristics of carbon determine the performance in all these applications. It is now possible to synthesize one-, two-, or three-dimensional (1-, 2-, or 3-D) carbons. Thus, carbon materials are very suitable candidates for super capacitor electrodes. We can overcome some of the problems in activated carbon like varying micro or meso pores, poor ion mobility due to varying pore distribution, low electrical conductivity, by using Graphene. Many forms of Graphene have been used by various groups. Graphene nanoplates (GNP), with narrow mesopore distribution have been effectively used to enhance charge storage performance. It has been found that graphene shows smaller decrease in storage capacity with increasing scan rate. © 2012 Bentham Science Publishers.

Micro and Nanosystemse

Double Layer Energy Storage in Graphene - a Study

We present the electrochemical performance of solid-state EDLCs constructed using composites of perfluorosulfonic acid polymer (Nafion) with micro porous polytetrafluoroethylene (PTFE) membrane and with cellulose acetate (CA), as electrolyte with carbon as electrodes (surface area: 260 m2 g -1). The performance is compared with EDLCs constructed with perfluorosulfonic acid polymer as electrolyte. Scanning electron microscopy is used to study the morphology of the composite electrolyte while micro-Raman and IR measurements determine the integrity of the composite. The performance of the EDLC with perfluorosulfonic acid and PTFE composite electrolyte is good and comparable with the performance of the EDLC with pure perfluorosulfonic acid polymer electrolyte. A specific capacitance of 16 F g-1 is obtained for this EDLC with a maximum working potential of 2.0 V. There is an increase in the equivalent series resistance value from 0.08 Ω for the Nafion EDLC to 4.1 Ω for the Nafion/PTFE composite EDLC. However, the performance of the EDLC with the composite of Nafion/CA is poor due to substantial increase in ESR. The probable reasons are discussed. © 2010 Springer Science+Business Media B.V.

Journal of Applied Electrochemistry

Performance of EDLCs using Nafion and Nafion composites as electrolyte

Various carbon-carbon EDLCs were assembled with ionic polymers of perfluorosulphonic acid polymer in the H+, Na+ and K + forms, composites of polytetrafluoro ethylene (PTFE) and perfluorosulphonic acid, PVA-KOH, sulphonated PEEK and PVdF. The surface area of the carbon used in these EDLCs is 260 m2/gm. CV, EIS and discharge profiles were used for characterization. The working voltage of these EDLCs was 2V. The specific capacitance was found to be 20 F/g, 40 F/g and 55 F/g for the perflurosulphonic acid electrolyte in H+, Na+ and K +, respectively. A specific capacitance of 16 F/g was obtained for the EDLC with the composite of PTFE/perluorosulphonic acid and 7.5 F/g and 1.0 F/g for PVA-KOH and sulphonated PEEK electrolyte, respectively. Modules of 5F (2.0V) were developed using carbon electrodes and composites of PTFE/perflurosulphonic as electrolyte. The maximum energy stored in these modules, was of the order of 7.5 Watth/kg. ©The Electrochemical Society.

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ISSN	0272-9172
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