Journal Articles

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    LiClO4-doped plasticized chitosan as biodegradable polymer gel electrolyte for supercapacitors
    (2009) Muthu, M.S.; Bhat, D.K.
    Studies on redox supercapacitors using electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In this study, electrochemical properties of a chitosan-based biodegradable polymer gel electrolyte (PGE) and a p/p polypyrrole supercapacitor fabricated using this electrolyte have been investigated. The variation of conductivity and dielectric properties of the electrolyte film with temperature has also been measured. The PGE film chosen for the study exhibited a specific conductivity of 5.5 × 10-3 S cm~. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The fabricated supercapacitor showed a fairly good specific capacitance of 120 F g-1 and a time constant of 1 s. © 2009 Wiley Periodicals, Inc.
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    Nano ZnO-activated carbon composite electrodes for supercapacitors
    (2010) Muthu, M.S.; Bhat, D.K.; Aggarwal, A.; Prahladh Iyer, S.; Sravani, G.
    A symmetrical (p/p) supercapacitor has been fabricated by making use of nanostructured zinc oxide (ZnO)-activated carbon (AC) composite electrodes for the first time. The composites have been characterized by field emission scanning electron microscopy (FESEM) and X-ray diffraction analysis (XRD). Electrochemical properties of the prepared nanocomposite electrodes and the supercapacitor have been studied using cyclic voltammetry (CV) and AC impedance spectroscopy in 0.1 M Na2SO4 as electrolyte. The ZnO-AC nanocomposite electrode showed a specific capacitance of 160 F/g for 1:1 composition. The specific capacitance of the electrodes decreased with increase in zinc oxide content. Galvanostatic charge-discharge measurements have been done at various current densities, namely 2, 4, 6 and 7 mA/cm2. It has been found that the cells have excellent electrochemical reversibility and capacitive characteristics in 0.1 M Na2SO4 electrolyte. It has also been observed that the specific capacitance is constant up to 500 cycles at all current densities. © 2010 Elsevier B.V. All rights reserved.
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    Effect of surfactant on high capacitance of galvanostatically deposited MnO2
    (Elsevier B.V., 2012) Suhasini; Hegde, A.
    Manganese dioxide has been galvanostatically deposited on stainless-steel substrate from an aqueous acidic solution of manganese sulphate (1 M) in presence of a surface active agent (surfactant), namely, sodium lauryl sulphate (SLS), for supercapacitor applications. The deposits have been developed under different conditions of SLS and their specific capacitance is measured by cyclic voltammetry (CV) and also by galvanostatic charge/discharge cycle. The oxide film (?0.1 mg cm-2) anodized from the manganese solution at 2.0 mA cm-2 has shown the highest specific capacitance of 255.8 F g -1, at scan rate of 10 mV s-1. It is observed that the capacitance increased by about 40% compared to the oxide prepared in the absence of SLS. Improved specific capacitance is due to the effect of the surfactant molecules in the deposit, causing high surface area of the deposit. The deposit is found to display good cycleability, even up to 1500 cycles. The structure and surface morphology of the deposits have been studied by means of X-ray diffraction (XRD) analysis and Scanning Electron Microscopy (SEM). XRD study reveals that crystallinity of the deposit with SLS remains unchanged, both are amorphous in nature. The surface area of the deposit is found to increase considerably due to the effect of SLS, as evident by SEM study.© 2012 Elsevier B.V. All rights reserved.
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    Effect of deposition method and the surfactant on high capacitance of electrochemically deposited MnO2 on stainless steel substrate
    (Elsevier B.V., 2013) Suhasini
    Manganese dioxide has been considered as a promising material for electrochemical supercapacitors. In order to obtain a high specific capacitance, MnO2 has been electrodeposited from an aqueous acidic solution of MnSO4 consisting of an ionic surfactant, namely, sodium lauryl sulphate (SLS) on stainless steel. The electrodeposited films of MnO2 in the presence of the surfactant possess greater porosity and hence greater surface area in relation to the films prepared in the absence of the surfactant. Cyclic voltammetry and galvanostatic charge-discharge cycling experiments reveal that specific capacitance is higher by about 22% due to the effect of SLS. © 2012 Published by Elsevier B.V.
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    LiClO4-doped plasticized chitosan and poly(ethylene glycol) blend as biodegradable polymer electrolyte for supercapacitors
    (Institute for Ionics, 2013) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.
    Biodegradable polymer electrolyte comprising the blend of chitosan (CS) and poly(ethylene glycol) (PEG) plasticized with ethylene carbonate and propylene carbonate, as host polymer, and lithium perchlorate (LiClO4), as a dopant, was prepared by solution casting technique. The ionic conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. The variation of conductivity and dielectric properties has been investigated as a function of polymer blend ratio, plasticizer content and LiClO4 concentration at temperature range of 298-343 K. The DSC thermograms show two broad peaks for CS/PEG blend and increased with increase in the LiClO4 content. The maximum conductivity has been found to be 1. 1 × 10-4 S cm-1 at room temperature for 70:30 (CS/PEG) concentration. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The activation energy of all samples was calculated using the Arrhenius plot, and it has been found to be 0. 12 to 0. 38 eV. A carbon-carbon supercapacitor has been fabricated using this electrolyte, and its electrochemical characteristics and performance have been studied. The supercapacitor showed a fairly good specific capacitance of 47 F g-1. © 2012 Springer-Verlag.
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    Nano CeO2/activated carbon based composite electrodes for high performance supercapacitor
    (2013) Aravinda, L.S.; Bhat, K.; Badekai Ramachandra, B.
    Cerium oxide (CeO2)/Activated carbon (AC) based composite were prepared by simple mechanical mixing method with high degree of scalability. The samples were characterized using X-ray diffraction (XRD), Field emission scanning electron microscope (FESEM) and Transmission electron microscope (TEM). The composite mixture with 10 wt% (weight %) CeO2 exhibits a specific capacitance of 162 F g-1 in two electrode configuration. The test cell retains 86% specific capacitance even at high current density with excellent cycle stability. The composite electrode exhibits a power density of 3500 W kg-1 at a high current density, suggesting a good electrode material for supercapacitor. © 2013 Elsevier B.V. All rights reserved.
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    Binder free MoO3/multiwalled carbon nanotube thin film electrode for high energy density supercapacitors
    (2013) Aravinda, L.S.; Bhat, K.; Badekai Ramachandra, B.
    MoO3/multiwalled carbon nanotube (MWCNT) composites were prepared by Magnetron sputtering in Ar/O2 atmosphere. This will provide a greener alternative for the fabrication of binder free composite electrode for supercapacitor applications. MWCNT provides good support for the growth of MoO3 thin films. This integrated composite electrode exhibited specific capacitance of 93 F g-1 and a corresponding energy density of 7.28 Wh kg-1 in non-aqueous electrolyte, which is almost fourfold increase compared to the bare MWCNT. Also the electrode maintains high power density of 4930 W kg-1 at high current rates, suggesting a potential energy storage material for portable and consumer electronics. © 2013 Elsevier Ltd. All rights reserved.
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    Porous MnO2 nano whiskers bunch/activated carbon based composite electrodes for high energy density supercapacitor
    (2013) Aravinda, L.S.; Bhat, K.; Badekai Ramachandra, B.
    A simple room temperature method was used to synthesize Porous ?-MnO2 nano whiskers bunch. The porous ?-MnO2 /Activated carbon (AC) composites were prepared by very simple mechanical mixing method with varying amount of MnO2. A symmetric supercapacitor stack was fabricated using the prepared composite electrode material. The composite with 30% MnO2 exhibit a maximum specific capacitance of 107 Fg-1 at 1 mAcm-2 in non-aqueous electrolyte. The corresponding energy density was found to be 8.35 Whkg-1. The electrode also exhibits excellent cyclic stability. © 2013 The Electrochemical Society.
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    Reduced graphene oxide derived from used cell graphite and its green fabrication as an eco-friendly supercapacitor
    (Royal Society of Chemistry, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.; Senthil Kumar, S.
    Graphite extracted from a used primary cell was converted into reduced graphene oxide (rGO) using calcium carbonate together with rapid and local Joule heating by microwave irradiation. Electrodes were prepared by ultrasonically dispersing rGO in biodegradable poly(vinylpyrrolidone) (PVP) binder and coating this on recyclable poly(ethyleneterephthalate) (PET) sheet using a low cost screen printing technique. The use of the same polymer (PVP) as a binder, in addition to as the solid polymer electrolyte (SPE), enhances the compatibility and ionic conductivity of the hydrophobic rGO electrode in the supercapacitor system. Further, the phosphoric acid (H3PO4)-doped biodegradable SPE was screen printed for the first time on the rGO electrodes. Ionic conductivity and dielectric studies of the SPE were carried out at different temperatures and different dopant acid concentrations. The morphology, composition and structure of the graphene electrode components were characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. Transmission electron microscopy (TEM) images showed a single layer or a few layers of rGO sheets and selected area electron diffraction showed the presence of slight defects. The fabricated environmentally friendly, industrially favorable and green supercapacitor showed a specific capacitance of 201 F g-1 and cyclic stability with 97% retention of the initial capacitance over 2000 cycles. Furthermore, the performance of this green supercapacitor is comparable to that of those fabricated using rGO synthesized from commercial graphite and in other literature reports. © 2014 The Royal Society of Chemistry.
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    Novel eco-friendly synthesis of graphene directly from graphite using 2,2,6,6-tetramethylpiperidine 1-oxyl and study of its electrochemical properties
    (Elsevier B.V., 2015) Subramanya, B.; Bhat, D.K.
    Herein we report a simple, low cost, highly efficient and environment friendly one-pot method for the high throughput synthesis of graphene directly from graphite using 2,2,6,6-tetramethylpiperidine 1-oxyl (TEMPO) and H2O2 under microwave irradiation. The formation mechanism of graphene nanosheets (GNS) as investigated by Raman spectroscopy and electron microscopy techniques reveal surface defect generation, intercalation and exfoliation as the main steps. The rapid and local Joule heating of graphite by microwave radiation results in simultaneous deoxygenation and exfoliation forming GNS. The as-synthesized GNS are a few layer thick with a high surface area of 937.6 m2 g-1 and a high C/O ratio of 9.2. These results open the perspective of replacing toxic oxidizing and reducing agents by environment friendly chemicals of similar efficacy, thus facilitating the large-scale production of GNS by a greener method. Furthermore, GNS exhibits good electrochemical performance with a large specific capacitance (197 F g-1), excellent rate capability and a long cycle life (1000 cycles) in neat 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte. It also has a high energy density of 76.03 W h kg-1 while simultaneously possessing a high power density of 1.12 kW kg-1. © 2014 Elsevier B.V.