1. Journal Articles
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Item Tubular array, dielectric, conductivity and electrochemical properties of biodegradable gel polymer electrolyte(2014) Sudhakar, Y.N.; Selvakumar, M.; Bhat, D.K.A supercapacitor based on a biodegradable gel polymer electrolyte (GPE) has been fabricated using guar gum (GG) as the polymer matrix, LiClO4 as the doping salt and glycerol as the plasticizer. The scanning electron microscopy (SEM) images of the gel polymer showed an unusual tubular array type surface morphology. FTIR, DSC and TGA results of the GPE indicated good interaction between the components used. Highest ionic conductivity and lowest activation energy values were 2.2 � 10-3 S cm-1 and 0.18 eV, respectively. Dielectric studies revealed ionic behavior and good capacitance with varying frequency of the GPE system. The fabricated supercapacitor showed a maximum specific capacitance value of 186 F g -1 using cyclic voltammetry. Variation of temperature from 273 K to 293 K did not significantly influence the capacitance values obtained from AC impedance studies. Galvanostatic charge-discharge study of supercapacitor indicated that the device has good stability, high energy density and power density. � 2013 Elsevier Ltd. All rights reserved.Item Volumetric, acoustic, and refractometric study of cyclic alanylalanine in aqueous cobalt chloride solutions at temperatures T = (293.15 to 313.15) K(2013) Karanth, V.R.; Bhat, D.K.Density, refractive index, and speed of sound values of cyclic alanylalanine + aqueous CoCl2 systems have been reported as a function of concentrations of cyclic alanylalanine and that of CoCl2 at temperatures T = (293.15, 298.15, 303.15, 308.15, and 313.15) K. The values of partial molar volumes, isentropic compressibilities, and partial molar isentropic compressibilities of the cyclic alanylalanine + aqueous CoCl 2 systems have been calculated from the speed of sound and density data obtained from the experiment at various temperatures. The decreasing value of isentropic compressibility with respect to the molal concentration of cyclic alanylalanine and temperature indicated the presence of strong solute-solvent interaction operative in the present system. The variations in partial molar volumes as well as partial molar isentropic compressibilities have been discussed in terms of ionic, hydrophilic, and hydrophobic interactions present in the system. � 2013 American Chemical Society.Item Reduced graphene oxide derived from used cell graphite and its green fabrication as an eco-friendly supercapacitor(2014) Sudhakar, Y.N.; Selvakumar, M.; Bhat, D.K.; 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.Item Preparation and characterization of phosphoric acid-doped hydroxyethyl cellulose electrolyte for use in supercapacitor(2015) Sudhakar, Y.N.; Selvakumar, M.; Bhat, D.K.A new borax cross-linked biodegradable solid polymer electrolyte based on hydroxyethyl cellulose and phosphoric acid (H3PO4) was prepared. Characterizations of doped and undoped SPE were done using Fourier transform infrared spectroscopic and electrochemical studies. The ionic conductivity of the films increased with increase in acid concentration and the ionic conductivity obtained at 303 K was 4.1 10-3 S cm-1. Furthermore, effects of acid concentration on ionic conductivity and activation energy were discussed. Dielectric studies showed long tail-like feature indicating capacitive nature. A supercapacitor was fabricated and its electrochemical characteristics were studied. The supercapacitor showed a fairly good specific capacitance of 83 F g-1 at 2 mV s-1 and galvanostatic charge-discharge studies showed the mirror-like pattern with 98 % columbic efficiency. Cyclic stability was measured up to 2000 cycles. 2015 The Author(s).Item Partial molar volumes and compressibilities of glycine betaine in aqueous NaCl solutions at temperatures T=(288.15-318.15)K(2014) Karanth, V.R.; Bhat, D.K.The partial molar volumes, partial molar isentropic compressibilities, transfer molar volumes and transfer molar isentropic compressibilities of the system: glycine betaine in aqueous (0.1, 0.2, 0.3, 0.4 and 0.5molkg-1) NaCl solutions at different temperatures were determined using the experimental values of density and speed of sound. The positive transfer molar volumes of the systems indicated the presence of strong solute-solvent interactions. The electrostatic charge-charge interactions (among Na+/Cl- ions and amino/carboxylic groups of glycine betaine) were found to be predominant over the ionic-hydrophobic interactions (among Na+/Cl- ions and CH2/CH3 groups of the glycine betaine) in aqueous solutions. Size of the metal ion was found to influence the volumetric properties to an appreciable extent. 2014 Elsevier B.V.Item Partial molar volume and partial molar isentropic compressibility study of glycine betaine in aqueous and aqueous KCl or MgCl2 solutions at temperatures T = 288.15-318.15 K(2013) Karanth, V.R.; Bhat, D.K.Partial molar volume, ?v0, isentropic compressibility, ?s, and partial molar isentropic compressibility, ?k0 of glycine betaine in aqueous and aqueous KCl or MgCl2 solutions have been computed using the experimental density and speed of sound data at temperatures, T = 288.15-318.15 K. The transfer partial molar volumes, ?tr?v0, and transfer partial molar isentropic compressibilities, ?tr?k0, have also been evaluated using the experimental data. The partial molar volumes of glycine betaine were computed using the usual equation as well as the equation employed by Pitk nen et al. So obtained values have been compared with literature values. The variations in experimental and computed parameters have been discussed in terms of solute-solvent and solute-solute interactions. 2013 Elsevier B.V. All rights reserved.Item Novel one-pot green synthesis of graphene in aqueous medium under microwave irradiation using a regenerative catalyst and the study of its electrochemical properties(2015) Subramanya, B.; Bhat, D.K.In this work we report an economic, eco-friendly, high yielding and facile one-pot method for the large scale synthesis of few layer graphene (FLG) nanosheets directly from graphite in aqueous medium using a regenerative catalyst, sodium tungstate. This method is fast and makes use of environmental friendly chemicals and microwave radiation. The as-synthesized FLG nanosheets are characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and Brunauer-Emmett-Teller (BET) surface area analysis. Raman analysis indicates that the as-synthesized graphene is bilayered with a smaller domain size of 3.9 nm which is responsible for a higher specific surface area of FLG nanosheets (1103.62 m2 g-1). Moreover, XPS analysis of FLG nanosheets shows a high C:O ratio (?9.6) which is the best among the graphene prepared from green chemicals. The electrochemical performance of as-synthesized FLG nanosheets is analysed by cyclic voltammetry (CV), chronopotentiometry and electrochemical impedance spectroscopy (EIS) in neat 1-ethyl-3-methylimidazolium tetrafluoroborate (EMIMBF4) electrolyte. The superior capacitive performance with large capacitance (219 F g-1), high energy density (83.56 W h kg-1) and excellent cyclability (3000 cycles) exhibited by these graphene nanosheets make them an excellent candidate for supercapacitor material. The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015.Item Novel eco-friendly synthesis of graphene directly from graphite using 2,2,6,6-tetramethylpiperidine 1-oxyl and study of its electrochemical properties(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.Item Novel Co-Ni-graphene composite electrodes for hydrogen production(2015) Subramanya, B.; Ullal, Y.; Shenoy, S.U.; Bhat, D.K.; Hegde, A.C.Active, stable and cost-effective electrocatalysts are key to water splitting for hydrogen production through electrolysis. Herein, we report the facile preparation of highly porous Co-Ni-graphene (Co-Ni-G) composite electrodes by electrodeposition for electrocatalytic applications. The incorporation of graphene into the Co-Ni matrix enhances the catalyst's activity for the hydrogen evolution reaction (HER) in an alkaline solution. The best coating exhibits a maximum current density of -850 mA cm-2 at -1.6 V, which is approximately 4 times better than that of the binary Co-Ni alloy indicating higher activity for hydrogen production. The addition of graphene to an electrolyte bath results in a porous encapsulated bundle of alloy nano-particles within the graphene network which effectively increases the electrochemically active surface area. As indicated by XPS analysis results, on addition of graphene the Co(0) and Ni(0) content in the deposit increases and as a result both cobalt/cobalt oxide and nickel/nickel oxide sites are evenly distributed on the Co-Ni-G electrode surface which is responsible for increased HER activity. The Tafel slope analysis showed that the HER follows a Volmer-Tafel mechanism. The structure-property relationship of the Co-Ni-G composite coating has been discussed by interpreting field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis results. The Royal Society of Chemistry 2015.Item Novel Fe-Ni-Graphene composite electrode for hydrogen production(2015) Badrayyana, S.; Bhat, D.K.; Shenoy, S.; Ullal, Y.; Hegde, A.C.We have developed a novel, efficient and economical composite electrode for hydrogen production. The electrode has been formed by embedding graphene in the Fe-Ni matrix via room temperature electrodeposition. The obtained active coatings have been tested for their efficiency and performance as electrode surfaces for hydrogen evolution reaction (HER) in 6 M KOH by cyclic voltammetry and chronopotentiometry techniques. The coating obtained at 60 mA cm-2 exhibited approximately 3 times higher activity for hydrogen production than that of binary Fe-Ni alloy. Addition of graphene to electrolyte bath resulted in porous 3D projections of nano-sized spheres of Fe-Ni on the surface of graphene, which effectively increased the electrochemically active surface area. XPS analysis results showed the equal distribution of both Ni metal and NiO active sites on the composite. The addition of graphene favoured the deposition of metallic nickel, which accelerated the rate determining proton discharge reaction. All these factors remarkably enhanced the HER activity of Fe-Ni-Graphene (Fe-Ni-G) composite electrode. The Tafel slope analysis showed that the HER follows Volmer-Tafel mechanism. The structure-property relationship of Fe-Ni-G coating has been discussed by interpreting field emission scanning electron microscopy (FESEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) analysis results. 2015 Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.