Faculty Publications
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Item ZnO/carbon nanotube nanocomposite for high energy density supercapacitors(2013) Aravinda, L.S.; Nagaraja, K.K.; Nagaraja, H.S.; Bhat, K.; Badekai Ramachandra, B.A facile, green and highly efficient method for the decoration of carbon nanotubes with ZnO was developed for the fabrication of binder-free composite electrode for supercapacitor applications. The nano composite was prepared by using reactive magnetron sputtering in Ar/O2 environment. This approach leads to more uniform coating with tuneable thickness, which alters the electrochemical performance of the nano composite electrodes. The structure and surface morphology of the composite film have been studied by means of X-ray diffraction (XRD) analysis, scanning electron microscopy and field emission scanning electron microscopy (FESEM). The XRD study reveals the formation of Wurtzite ZnO structure. The electrochemical performance of nano composite electrode was investigated using cyclic voltammetry, chronopotentiometry and electrochemical impedance measurements in non-aqueous electrolyte. The nano composite electrode shows significant increase in the specific capacitance up to 48 F g-1 with an energy density 13.1 Wh kg-1 in the potential range -2 V to 1 V. © 2013 Elsevier Ltd. All rights reserved.Item Solar exfoliated graphene and its application in supercapacitors and electrochemical H2O2 sensing(Elsevier Ltd, 2015) Moolayadukkam, M.; Huang, N.M.; Nagaraja, H.S.In the present study, graphene nanosheets are synthesized using sunlight irradiation focussed onto graphite oxide. The morphological characteristics of graphene are examined using Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Raman spectroscopy and X-ray diffraction (XRD) are used for the structural characterization of the sample. The electrochemical performance is evaluated using cyclic voltammetry (CV), charge-discharge characteristics and impedance spectroscopy. A high specific capacitance value of 223 F g-1 is obtained using cyclic voltammetry. The electrochemical detection of H2O2, a common biological species using solar graphene is demonstrated. The impedance spectroscopy and CV are used to study the electrocatalytic activity of the material. High sensitivity of 64.79 ?A mM-1 cm-2 is reported. © 2015 Elsevier Ltd. All rights reserved.Item Microwave assisted synthesis of rGO/ZnO composites for non-enzymatic glucose sensing and supercapacitor applications(Elsevier Ltd, 2017) Moolayadukkam, M.; Dhanush, S.; Rossignol, F.; Nagaraja, H.S.Zinc oxide (ZnO) and Graphene Oxide (GO) are known to show good electrochemical properties. In this paper, rGO/ZnO nanocomposites have been synthesised using a simple microwave assisted method. The nanocomposites are characterized using XRD, Raman, SEM and TEM. XRD reveals the wurtzite structure of ZnO and TEM shows the heterogeneous nucleation of ZnO nanocrystals anchored onto graphene sheets. The electrochemical properties of the rGO/ZnO nanocomposite enhanced significantly for applications in glucose sensors and supercapacitors. The non-enzymatic glucose sensor of this nanocomposite tested using cyclic voltammetry (CV) and chronoamperometry, exhibits high sensitivity (39.78 mA cm?2 mM?1) and a lower detection limit of 0.2 nM. The supercapacitor electrode of rGO/ZnO nanocomposite exhibits a significant increase in specific capacitance. © 2017 Elsevier Ltd and Techna Group S.r.l.Item Porous cobalt chalcogenide nanostructures as high performance pseudo-capacitor electrodes(Elsevier Ltd, 2017) Bhat, K.S.; Shenoy, S.; Nagaraja, H.S.; Sridharan, K.Electrochemical supercapacitor is an essential technology that is pivotal for the development of reliable energy storage devices. Herein, we report the fabrication of supercapacitor electrodes using nanostructured porous cobalt chalcogenide (CoTe2 and CoSe2) electrodes, anticipating an enhanced performance owing to their higher contact area with electrolyte and large pore volume enabling shorter diffusion paths for ion exchange. In this regard, we synthesized CoTe2 and CoSe2 nanostructures via an anion-exchange-reaction between pre-synthesized Co(OH)2 hexagonal nanosheets and chalcogen (tellurium and selenium) ions under hydrothermal conditions. Structural, morphological and compositional properties of the as-synthesized materials are examined using X-ray diffraction, Raman spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Pseudo-capacitive properties of CoTe2 and CoSe2 nanostructures as working electrodes are studied through cyclic voltammetry and galvanostatic charge-discharge methods using an electrochemical workstation. CoSe2 electrode delivered a specific capacitance of 951 F g?1 at a scan rate of 5 mV s?1, which surprisingly is almost three times higher in comparison to CoTe2 electrode (360 F g?1). Both CoTe2 and CoSe2 electrodes exhibited good capacitance retention capability for 2500 CV cycles. The superior electrochemical performance of the nanoporous CoSe2 electrode indicate their applicability for high-performance energy storage device applications. © 2017 Elsevier LtdItem Synthesis and electrochemical properties of silver dendrites and silver dendrites/rGO composite for applications in paracetamol sensing(Elsevier Ltd, 2018) Dhanush, S.; Moolayadukkam, M.; Bindu, K.; Chowdhury, P.; Nagaraja, H.S.Electrochemical sensors are one of the important applications of electrochemistry. In this paper, synthesis, characterization and application of Silver Dendrites and Silver Dendrites/rGO sensors for simple and fast determination of Paracetamol are described. Silver dendrites and their composite with graphene oxide were synthesized by galvanic replacement method. The synthesized samples were characterized by XRD, SEM and TEM. XRD reveals the FCC structure of silver and TEM images show the formation of dendritic silver wrapped in the graphene sheets. The Electrochemical paracetamol sensing properties of these samples were tested using cyclic voltammetry and chronoamperometry. The silver dendrites exhibit a sensitivity of 2.807 × 105?A/mM/g and a lower detection limit of 2.5 ?M, whereas, the composite with graphene oxide exhibits a high sensitivity of 2.511 × 106?A /mM/g with a lower detection limit of 0.025 ?M. © 2018 Elsevier LtdItem Influence of cations in MFe2O4 (M: Fe, Zn, Ni, Sn) ferrite nanoparticles on the electrocatalytic activity for application in hydrogen peroxide sensor(Institute of Physics Publishing helen.craven@iop.org, 2019) Bindu, K.; Nagaraja, H.S.Hydrothermally prepared MFe2O4 (M: Fe, Zn, Ni and Sn) nanoparticles have been characterized by XRD, SEM and BET. The ferrite nanoparticles have been tested for their electrocatalytic activity and application towards the reduction and sensing of hydrogen peroxide using cyclic voltammetry and chronoamperometry techniques. ZnFe2O4 and SnFe2O4 reveal superior H2O2 sensing performance than Fe3O4 and NiFe2O4, which can be attributed to the lower redox potential of Sn2+/Sn4+ couple, lower charge-transfer resistance and higher specific surface area. ZnFe2O4 and SnFe2O4 have a sensitivity of 4.411 and 3.915 ?AmM-1 ?g-1, respectively, which is greater than that of Fe3O4 (0.434 ?AmM-1 ?g-1) and NiFe2O4 (0.644 ?AmM-1 ?g-1). SnFe2O4 has the lowest limit of detection (2.6 (M) with good selectivity towards H2O2 in the presence of other interference agents. © 2019 IOP Publishing Ltd.Item Lower Band Gap Sb/ZnWO4/r-GO Nanocomposite Based Supercapacitor Electrodes(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Brijesh, K.; Nagaraja, H.S.Sb/ZnWO4/r-GO nanocomposite has been prepared by a single step solvothermal method. The crystal structure of the prepared nanocomposite has been characterized using a powder x-ray diffractometer (XRD). The optical properties of the prepared nanocomposite were studied using UV–visible spectroscopy and photoluminescence. The energy band gap of 3.52 eV is obtained for the ZWS-5 nanocomposite using Tauc plots. For both Sb/ZnWO4 and Sb/ZnWO4/r-GO nanocomposite XRD shows the monoclinic Wolframite structure. The supercapacitor performance of the prepared samples was carried out using electrochemical techniques such as cyclic voltammetry, galvanostatic charge–discharge and electrochemical impedance spectroscopy. The nanocomposite ZWS-5 exhibits a specific capacitance of 102 F/g, which is higher than pristine ZWS specific capacitance of 64 F/g. Both ZWS and ZWS-5 electrodes show good capacitance retention proficiency even after 1000 cycles. © 2019, The Minerals, Metals & Materials Society.Item Morphology-dependent electrochemical performances of nickel hydroxide nanostructures(Indian Academy of Sciences, 2019) Bhat, K.S.; Nagaraja, H.S.Electrochemical capacitors form part of the developing technologies in the field of alternative energy sources. In the present work, nickel hydroxide (Ni(OH) 2) nanosheets and microflowers are hydrothermally prepared employing different chemical precursors. Structure, morphology and chemical analysis are conducted using powder X-ray diffraction, field emission scanning electron microscopy and energy-dispersive X-ray spectroscopy measurements. Electrochemical performances as supercapacitor electrodes of the synthesized nanostructures are evaluated through cyclic voltammetry and galvanostatic charge–discharge measurements with three-electrode configurations. The results indicated the specific capacitance of 180 and 417Fg-1 at a scan rate of 5mVs-1 for Ni(OH) 2 nanosheets and microflowers, respectively. The higher specific capacitances for Ni(OH) 2 microflowers could be attributed to the higher specific surface area, morphology, electronic conductivity and porosity. Both Ni(OH) 2 nanostructures exhibited good capacitance retention for 1500 cycles. © 2019, Indian Academy of Sciences.Item ZnWO4/SnO2 composite for supercapacitor applications(Elsevier B.V., 2020) Vinayaraj, S.; Brijesh, K.; Dhanush, P.C.; Nagaraja, H.S.The pristine ZnWO4 and ZnWO4/SnO2 composite was synthesized by solvothermal method. The crystal structure of the ZnWO4 and ZnWO4/SnO2 composite is determined by powder X-ray diffraction (XRD) pattern. The morphology of the samples investigated using SEM and found to be agglomerated structure. The samples are tested as an electrode material for supercapacitor using electrochemical techniques like cyclic Voltammetry (CV), Galvanostatic Charge-Discharge (GCD) and Electrochemical Impedance Spectroscopy (EIS). The ZnWO4/SnO2 composite reveals 56.7 F/g specific capacitance at 1 mV/s scan rate which is higher than that of pristine material and also ZnWO4/SnO2 composite exhibits good cyclic stability than pure ZnWO4. © 2020 Elsevier B.V.Item Electrochemical hydrogen-storage performance of copper sulfide micro-hexagons(Elsevier Ltd, 2021) Bhat, K.S.; Nagaraja, H.S.Electrochemical hydrogen-storage is one of the prominent energy storage systems. In this work, the hydrothermally synthesized copper sulfide (Cu2S) revealed a unique morphology of micro-hexagons as envisioned through scanning electron microscopy measurements. Electrochemical hydrogen storage (EHS) performance was evaluated using various electrochemical techniques, such as cyclic voltammetry, galvanostatic charge-discharge, and impedance spectroscopy measurements. The hydrogen discharge capacity of ~59.32 mAh g?1 was obtained at an applied current density of 1 A g?1. Further, the analysis of the charge-storage mechanism indicates foremost contributions from the redox processes. The prominent hydrogen storage performance is complimented with reasonable cyclic retention for 2500 cycles. © 2020 Hydrogen Energy Publications LLC