Browsing by Author "Selvakumar, M."

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Activated carbon-polyethylenedioxythiophene composite electrodes for symmetrical supercapacitors
(2008) Selvakumar, M.; Bhat, D.K.
A symmetrical (p/p) supercapacitor has been fabricated by making use of activated carbon (AC)-poly-ethylenedioxythiophene (PEDPT)-composite electrodes for the first time. The composite electrodes have been prepared via electrochemical deposition of ?-napthalenesulphonate doped PEDPT onto AC electrodes. The characteristics of the electrodes and the fabricated supercapacitor have been investigated using cyclic voltammetry (CV) and AC impedance spectroscopy. The electrodes show a maximum specific capacitance of 158 Fg-1 at a scan rate of 10 mV s_1. This indicates that the in situ electro-polymerization of ethylenedioxythiophene (EDPT) onto AC could improve the performance of carbon electrodes for use in supercapacitors. 2007 Wiley Periodicals, Inc.
Biopolymer Electrolytes
(2018) Sudhakar, Y.N.; Bhat, D. Krishna; Selvakumar, M.
Characterization of composites based on biodegradable poly(vinyl alcohol) and nanostructured fly ash with an emphasis on polymer-filler interaction
(2016) Patil, A.G.; Selvakumar, M.; Anandhan, S.
A thermal power station fly ash (FA) was mechanochemically activated by high-energy ball milling that yielded nanostructured FA. This nanostructured FA was incorporated into biodegradable poly(vinyl alcohol) (PVA) matrix by solution mixing and ultrasonication. Transmission electron micrographs revealed that the smooth spherical particles of FA were changed into irregular and rough ones; in addition, the particle size of FA was reduced to a few hundred nanometers, and its specific surface area value increased after the high-energy milling process. All these factors, in turn, led to a thermodynamically favorable interaction between the mechanochemically activated FA and PVA as evidenced by Fourier transform infrared spectroscopy. The incorporation of a very small amount of the nanostructured FA led to an increase in crystallinity of the polymer matrix. The glass transition temperature of the PVA matrix increased by about 18 C when 5 wt% of the nanostructured FA was used as the reinforcement. The Author(s) 2014.
Ductility and Flame Retardancy Enhancement of PVC by Nanostructured Fly Ash
(2019) Patil, A.G.; Mahendran, A.; Selvakumar, M.; Anandhan, S.
Fly ash (FA) obtained from a coal-fired local thermal power station was converted into a nanostructured material by mechano-chemical activation using a high energy planetary ball mill. Contact angle measurements and FTIR spectroscopy confirmed the surface modification of mechano-chemically activated FA (MCA-FA). Subsequently, a solution casting method was used to prepare poly(vinyl chloride) (PVC) matrix composites with varying amounts of fresh FA and MCA-FA. Mechanical testing results of the composites revealed that incorporation of fresh FA in PVC resulted in a higher tensile strength with brittle failure; addition of MCA-FA to PVC resulted in higher elongation at break values while retaining the ductility of the PVC. We have proposed a plausible mechanism explaining the influence of fresh FA and MCA-FA on the mechanical behavior of these composites. As fresh FA and MCA-FA contain basic oxide materials, they tend to improve the fire retardancy of PVC even at a very small loading. Overall, the nanostructured MCA-FA could find application as a filler in PVC-based products. 2016, Springer Science+Business Media Dordrecht.
Effect of acid dopants in biodegradable gel polymer electrolyte and the performance in an electrochemical double layer capacitor
(2015) Sudhakar, Y.N.; Selvakumar, M.; Bhat, D.K.
Proton-conducting biodegradable gellan gum gel polymer electrolytes (GPEs) have been prepared using three different dopants, namely ortho-phosphoric (o-H3PO4), sulfuric (H2SO4) and hydrochloric acids (HCl). The GPEs were cross-linked using borax. The polymeric gels were characterized by spectroscopic, thermal, ionic conductivities and dielectric measurements. Proton conductivity was in the range of 5.1 10-3 to 3.7 10-4 s cm-1 and activation energies were between 0.14 meV and 0.19 meV, at different temperatures. Among the doped acids, the H3PO4 doped GPE exhibited thermal stability at varying temperature. Electrochemical double layer capacitors (EDLCs) were fabricated using activated carbon as electrode material and GPEs. The EDLCs were tested using cyclic voltammetry, ac impedance spectroscopic and galvanostatic charge-discharge techniques. The maximum specific capacitance value was 146 F g-1 at a scan rate of 2 mV s-1. Quite stable values were obtained at a constant current density up to 1000 cycles. 2015 The Royal Swedish Academy of Sciences.
h-MoO 3 /Activated carbon nanocomposites for electrochemical applications
(2019) Sangeetha, D.N.; Krishna, Bhat, D.; Selvakumar, M.
MoO 3 nanorods were synthesized through the microwave method and the nanocomposites of MoO 3 /activated carbon were prepared for supercapacitor and hydrogen evolution reaction (HER). The XRD pattern revealed that the prepared MoO 3 has a hexagonal phase (h-MoO 3 ). The as-prepared h-MoO 3 was composited with activated carbon (AC) and tested for supercapacitor studies. The fabricated supercapacitor exhibited an appreciable specific capacitance, power density, and energy densities. Further, dedoping of nitrogen in the doped AC creates defects on AC (DAC). These DAC/MoO 3 nanocomposites were prepared and tested for its electrocatalytic activity towards hydrogen evolution reactions. DAC/MoO 3 nanocomposite showed much higher electrocatalytic activity than the neat MoO 3 . [Figure not available: see fulltext.]. 2018, Springer-Verlag GmbH Germany, part of Springer Nature.
Hemocompatibility of Sulfuric Acid-Treated Metallocene Polyethylene and its Application in Reducing the Quantity of Medical Plastic Waste
(2017) Jaganathan, S.K.; Balaji, A.; Mohandas, H.; Sivakumar, G.; Kasi, P.; Selvakumar, M.; Kadiman, S.B.; Srinivasan, A.; Mohd, Faudzi, A.A.B.; Supriyanto, E.; Mandal, M.
The hazards of dumping medical plastics have created a huge demand to reduce the quantity of plastic usage without compromising its quality. The metallocene synthesized polyethylene is one such advent, however, its clinical usage is limited by the problem of hemocompatibility. This study investigates the effect of sulfuric acid-induced changes in metallocene polyethylene. Fourier transform infrared spectroscopy analysis illustrated the addition of OH and sulfonic acid group, which subsequently increased the wettability. An improvement in micro as well as nanosurface roughness was observed. Ultimately, the treated surfaces depicted delayed clotting time, adsorption of specific plasma proteins, reduced hemolysis, and resistance against platelet adhesion. 2017 Taylor & Francis.
High power density and improved H2 evolution reaction on MoO3/Activated carbon composite
(2019) Sangeetha, D.N.; Holla, R.S.; Ramachandra, Bhat, B.; Selvakumar, M.
The formation of hexagonal MoO3 (h- MoO3) microrods was favoured at lower pH in the hydrothermal synthesis method. Symmetric and Hybrid supercapacitors were fabricated using h-MoO3/plastic bottle derived activated carbon (PAC) composite in 1 M Na2SO4 aqueous electrolyte. The operating voltage for the aqueous electrolyte was maximized to 1.6 V with this combination. The wide operating voltage led to a maximum specific capacitance of 211 Fg-1, power density of 287 W kg?1 and 79% efficiency even at 5000 charge-discharge cycles for the hybrid supercapacitor combination. The combined effect of PAC micropores along with the 1-D rod-shaped h-MoO3, helped in faster charge-transfer, hence increasing the efficiency of supercapacitors. Further, the composites of defective PAC (PDAC) together with the h-MoO3 when tested for hydrogen evolution reactions (HER), provided lesser onset potential and Tafel slope values of ?0.23 mV and ?93 mVdec?1. There was a change in the structural environment of carbon due to the heteroatom doping and dedoping producing defects in PAC, termed as PDAC. These defects together with the hexagonal microrods of MoO3 provided fast electron transfer towards hydrogen adsorption/desorption hence effectively producing H2. 2019 Hydrogen Energy Publications LLC
Improving hydrogen evolution reaction and capacitive properties on CoS/MoS2 decorated carbon fibers
(2019) Sangeetha, D.N.; Krishna, Bhat, D.; Senthil, Kumar, S.; Selvakumar, M.
We report a facile method to transform abundantly dumped banana stem fibers into carbon fibers (CFs) useful for energy applications. The CFs surface area is increased by varying the quantity of KOH activation to 488 m2g-1. The solvothermal method is used to synthesize CoS, CoS/MoS2 and also grown on the activated carbon fibers (ACFs). Nano nodules of CoS arranged into sheets and layers of MoS2 stacked together were found in FESEM analysis. The morphology of the CoS/MoS2 differs when grown on ACFs. The growth of CoS/MoS2 along the ACFs length prevents any stacking of the pseudocapacitance materials. The ternary composite ACFs/CoS/MoS2 exhibits superior supercapacitor behavior as well as hydrogen evolution reaction (HER) due to the synergetic effect of the conducting ACF surface and redox active CoS/MoS2. A maximum specific capacitance of 733 Fg-1, energy and power density of 33 WhKg?1 and 999 WKg-1 respectively are obtained. A low Tafel slope value of 61 mVdec?1 is obtained for the ACFs/CoS/MoS2 ternary composite electrode. The present work therefore offers a fresh insight into the effective conversion of waste materials into electrode material for energy storage and conversion applications. 2019 Hydrogen Energy Publications LLC
Ionic conductivity and dielectric studies of acid doped cellulose acetate propionate solid electrolyte for supercapacitor
(2016) Sudhakar, Y.N.; Krishna, Bhat, D.; Selvakumar, M.
Phosphoric acid doped cellulose acetate propionate (CAP) consisting of poly(ethylene glycol) (PEG) as plasticizer was investigated. Ionic conductivities and dielectric studies were carried at different temperature with varying concentration of H3PO4 using AC impedance method. The highest conductivity was 8.1 10-4 S cm-1 at 343 K and a long tail was featured in dielectric studies indicating good capacitance nature of the electrolyte. Interactions between added constituents were observed in FTIR and differential scanning calorimetry studies. Thin and compact fabricated supercapacitor demonstrated specific capacitance of 64 F g-1 using cyclic voltammetry. Furthermore, the supercapacitor properties like AC impedance and charge-discharge were studied. Stability was up to 96% at 1000th cycle. POLYM. ENG. SCI., 56:196-203, 2016. 2015 Society of Plastics Engineers.
LiClO4 doped cellulose acetate as biodegradable polymer electrolyte for supercapacitors
(2008) Selvakumar, M.; Krishna, Bhat, D.
The possibility of producing a biodegradable polymer electrolyte based on cellulose acetate (CA) with varied concentration of LiClO4 for use in supercapacitors has been investigated. The successful doping of the CA films has been analyzed by FTIR and DSC measurements of the LiClO4 doped CA films. The ionic conductivity of the films increased with increase in salt content and the maximum ionic conductivity obtained for the solid polymer electrolyte at room temperature was 4.9 10-3 ?-1for CA with 16% LiClO4. The biodegradation of the solid polymer electrolyte films have been tested by soil burial, degradation in activated sludge, and degradation in buffer medium methods. The extent of biodegradation in the films has been measured by AC Impedance spectroscopy and weight loss calculations. The study indicated sufficient biodegradability of the materials. A p/p poly-pyrrole supercapacitor has been fabricated and its electro-chemical characteristics and performance have been studied. The supercapacitor showed a fairly good specific capacitance of 90 F g-1 and a time constant of 1 s. 2008 Wiley Periodicals, Inc.
LiClO4-doped plasticized chitosan and poly(ethylene glycol) blend as biodegradable polymer electrolyte for supercapacitors
(2013) Sudhakar, Y.N.; Selvakumar, 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.
Lithium salts doped biodegradable gel polymer electrolytes for supercapacitor application
(2015) Sudhakar, Y.N.; Selvakumar, M.; Krishna, Bhat, D.
A biodegradable gel polymer (GPE) consisting of Xanthan gum (XG), glycerol, lithium salts like lithium perchlorate and lithium tetraborate were prepared. Using Fourier transform infrared spectroscopy (FTIR), thermal and scanning electron microscopy characterizations the interactions between the components in the gel matrix were studied. Furthermore, a unique electrochemical property was exhibited by GPEs as measured by AC impedance and dielectric studies. The role of anion in the enhancement of conductivity was important in the present study and highest conductivity of 6.4 10-2 S cm-1 at 333K was achieved among lithium salts. Supercapacitor was fabricated using GPE and tested for its electrochemical properties. Supercapacitor showed specific capacitance of was 82 Fg-1 at a scan rate of 5 mV s-1 for Li2B4O7 and 74 Fg-1 at a scan rate of 5 mV s-1. specific energy and specific power. Galvanostatic charge-discharge studies showed excellent cyclic stability.
Microwave synthesized nanostructured TiO 2 -activated carbon composite electrodes for supercapacitor
(2012) Selvakumar, M.; Bhat, D.K.
Electrochemical properties of a supercapacitor based on nanocomposite electrodes of activated carbon with TiO 2 nano particles synthesized by a microwave method have been determined. The TiO 2 /activated carbon nanocomposite electrode with a composition of 1:3 showed a specific capacitance 92 Fg -1 . The specific capacitance of the electrode decreased with increase in titanium dioxide content. The p/p symmetrical supercapacitor fabricated with TiO 2 /activated carbon composite electrodes showed a specific capacitance of 122 Fg -1 . The electrochemical behavior of the neat TiO 2 nanoparticles has also been studied for comparison purpose. The galvanostatic charge-discharge test of the fabricated supercapacitor showed that the device has good coulombic efficiency and cycle life. The specific capacitance of the supercapacitor was stable up to 5000 cycles at current densities of 2, 4, 6 and 7 mA cm -2 . 2012 Elsevier B.V.
Miscibility of poly(methylmethacrelate) and cellulose acetate butyrate blends in dimethyl formamide
(2008) Selvakumar, M.; Bhat, D.K.
The miscibility of poly(methylmethacrelate) (PMMA) and cellulose acetate butyrate (CAB) blends in dimethyl formamide (DMF) have been investigated by viscosity, density, refractive index and ultrasonic velocity studies. The polymer-solvent and blend-solvent interaction parameters and heat of mixing have been calculated using the viscosity, density and ultrasonic velocity data. The results indicated the existence of positive interactions in the blend polymer solutions and that they are miscible in dimethyl formamide in the entire composition range between 303-323 K. The study also revealed that variation in the temperature does not affect the miscibility of PMMA and CAB blends in DMF significantly. The presence of hydrogen bonding in the blends in the solid state has also been indicated by FTIR studies. SEM images also supported the miscibility of blends.
Miscibility of polymethylmethacrylate and polyethyleneglycol blends in tetrahydrofuran
(2009) Selvakumar, M.; Bhat, D.K.; Renganathan, N.G.
The miscibility of polymethylmethacrylate (PMMA) and polyethyleneglycol (PEG) blends in tetrahydrofuran. (THF) has been investigated by viscosity, density, refractive index, and ultrasonic velocity studies. Various interaction parameters such as polymer-solvent and blend-solvent interaction parameters and heat of mixing have been calculated using the viscosity, density, and ultrasonic velocity data. The results indicated the existence of positive interactions in the blend polymer solutions and that they are miscible in THF in the entire composition range. The study also revealed that variation in the temperature does not affect the miscibility of PMMA and PEG blends in THF significantly. The presence of hydrogen bonding in the blends in the solid state has also been indicated by FTIR studies. 2008 Wiley Periodicals, Inc.
Miscibility studies of chitosan and starch blends in buffer solution
(2012) Sudhakar, Y.N.; Sowmya; Selvakumar, M.; Bhat, D.K.
The miscibility of chitosan (CS) and starch in buffer solution (CH 3COOH and CH 3COONa) has been investigated by viscosity, density and refractive index methods at 303K, 313K, and 323K. Various interaction parameters such as polymer-polymer and blend-solvent interaction parameters and heat of mixing have been calculated using viscosity and density data. The results indicated the existence of positive interactions in the blend polymer solutions and that they are miscible below 40% of starch compositions. The study also revealed that variation of temperature does have significant effect on the miscibility of chitosan and starch blends. 2012 Copyright Taylor and Francis Group, LLC.
Miscibility studies of starch and poly(4-styrene sulfonic acid) blend system
(2014) Sudhakar, Y.N.; Krishna, Bhat, D.; Selvakumar, M.
Polymeric solutions were prepared using blends of starch with poly(4-styrene sulfonic acid) (PSSA) in water and their miscibility was determined by viscosity studies at 30 C, 40 C and 50 C. Using interaction parameters such as Krigbaum s (?b), Hong s (?kAB), Chee s (?), Sun s (?), polymer-polymer, blend-solvent and heat of mixing there was the existence of positive interactions in the blend polymer solutions only up to 80% PSSA content. A significant variation of miscibility was observed with increase in temperature in the sample containing 70% PSSA content. Polymer blend films obtained by solution casting showed hydrogen bonding in Fourier transform infrared (FTIR) studies. Differential thermal analysis (DTA) and thermogravimetric analysis (TGA) studies also supported the results. A uniform surface of the miscible blend films were observed in scanning electron microscopy images, whereas segregation was observed for the immiscible blends. 2014, Sphinx Knowledge House. All Rights Reserved.
Molecular interactions of polymethyl methacrylate and polyethyeleneglycol solutions in tetrahydrofuran
(2008) Selvakumar, M.; Krishna, Bhat, D.
The ultrasonic velocity, density and viscosities of the polymethylmethacrylate (PMMA) and polyethyleneglycol (PEG) solutions in tetrahydrofuran (THF) have been measured in the temperature range 293-313K. Using these data, free energy of mixing, solvation number and different polymer-solvent interaction parameters for the solution systems have been calculated to know the presence of molecular interactions in the system. The trends in the variation of the solution property parameters indicate the existence of positive molecular interactions between the polymer and the solvent in solutions. The results also show the presence of higher degree of interaction between PEG and THF in solution compared to PMMA and THF.
Molecular interactions of polyvinylpyrrolidone and cellulose acetate butyrate solutions in dimethylformamide
(2008) Selvakumar, M.; Krishna, Bhat, D.; Renganathan, N.G.
The ultrasonic velocity, density, and viscosities of polyvinylpyrrolidone (PVP) and cellulose acetate butyrate (CAB) solutions in dimethylformamide (DMF) have been measured in the temperature range, 303K-323 K. Using these data, free energy of mixing, solvation number and different polymer-solvent interaction parameters for the solution systems have been calculated to know the presence of molecular interactions in the system. The trends in the variation of the solution property parameters indicate the existence of positive molecular interactions between the polymer and the solvent in solutions. The results also show the presence of higher degree of interaction between PVP and DMF in solution compared to CAB and DMF.