Faculty Publications
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Item Fabrication and performance evaluation of hybrid supercapacitor electrodes based on carbon nanotubes and sputtered TiO2(Institute of Physics Publishing michael.roberts@iop.org, 2016) Aravinda, L.S.; Nagaraja, K.K.; Nagaraja, H.S.; Bhat, K.U.; Badekai Ramachandra, B.R.We report a simple and eco-friendly method for the fabrication of a titanium dioxide/functionalized multiwalled carbon nanotube (TiO2/FMWCNT) composite electrode for use in supercapacitors. The nanocomposite electrodes were formed by depositing titanium dioxide onto FMWCNTs using reactive magnetron sputtering, thus providing a green roue for the formation of the binder-free composite electrode. It is shown that the electrochemical performance of the fabricated electrodes can be altered by tuning the thickness of the titanium dioxide overlayer. The integrated nanocomposite electrode showed an improved specific capacitance of 90 Fg-1 in two-electrode configuration. © 2016 IOP Publishing Ltd.Item Microwave assisted growth of stannous ferrite microcubes as electrodes for potentiometric nonenzymatic H2O2 sensor and supercapacitor applications(Elsevier Ltd, 2016) Bindu, K.; Sridharan, K.; Ajith, K.M.; Lim, H.N.; Nagaraja, H.S.Electrochemical sensors and supercapacitors are two noteworthy applications of electrochemistry. Herein, we report the synthesis of SnFe2O4 microcubes and Fe2O3 nanorods through a facile microwave assisted technique which are employed in fabricating the electrodes for nonenzymatic hydrogen peroxide (H2O2) sensor and supercapacitor applications. SnFe2O4 microcubes exhibited an enhanced specific capacitance of 172 Fg?1 at a scan rate of 5 mVs?1 in comparison to Fe2O3 nanorods (70 Fg?1). Furthermore, the H2O2 sensing performance of the fabricated SnFe2O4 electrodes through chronopotentiometry studies in 0.1 M PBS solution (at pH 7) with a wide linear range revealed a good sensitivity of 2.7 mV ?M?1 ?g?1 with a lowest detection limit of 41 nM at a signal-to-noise ratio of 3. These results indicate that SnFe2O4 microcubes are excellent materials for the cost effective design and development of efficient supercapacitors as well as nonenzymatic sensors. © 2016 Elsevier LtdItem Melt quenched vanadium oxide embedded in graphene oxide sheets as composite electrodes for amperometric dopamine sensing and lithium ion battery applications(Elsevier B.V., 2017) Moolayadukkam, M.; Shenoy, S.; Sridharan, K.; Kufian, D.; Arof, A.K.; Nagaraja, H.S.Electrochemical sensors and lithium-ion batteries are two important topics in electrochemistry that have attracted much attention owing to their extensive applications in enzyme-free biosensors and portable electronic devices. Herein, we report a simple hydrothermal approach for synthesizing composites of melt quenched vanadium oxide embedded on graphene oxide of equal proportion (MVGO50) for the fabrication of electrodes for nonenzymatic amperometic dopamine sensor and lithium-ion battery applications. The sensing performance of MVGO50 electrodes through chronoamperometry studies in 0.1 M PBS solution (at pH 7) over a wide range of dopamine concentration exhibited a highest sensitivity of 25.02 ?A mM ?1 cm ?2 with the lowest detection limit of 0.07 ?M. In addition, the selective sensing capability of MVGO50 was also tested through chronoamperometry studies by the addition of a very small concentration of dopamine (10 ?M) in the presence of a fairly higher concentration of uric acid (10 mM) as the interfering species. Furthermore, the reversible lithium cycling properties of MVGO50 are evaluated by galvanostatic charge-discharge cycling studies. MVGO50 electrodes exhibited enhanced rate capacity of up to 200 mAhg ?1 at a current of 0.1C rate and remained stable during cycling. These results indicate that MVGO composites are potential candidates for electrochemical device applications. © 2017 Elsevier B.V.Item Porous nickel telluride nanostructures as bifunctional electrocatalyst towards hydrogen and oxygen evolution reaction(Elsevier Ltd, 2017) Bhat, K.S.; Barshilia, H.C.; Nagaraja, H.S.Electrochemical water splitting technology has attracted researchers for the development of next generation fuels. Herein, we report the synthesis of nanostructured porous hollow nickel telluride nanosheets and their use as bifunctional electrocatalyst towards hydrogen and oxygen evolution reaction, anticipating an enhanced performance owing to their 2D sheet like morphology, conductivity, porous nature providing larger catalytic surface for water splitting reaction. In this regard, nickel telluride nanostructures were synthesized via an anion-exchange-reaction between pre-synthesized nickel hydroxide hexagonal nanosheets and tellurium ions under hydrothermal conditions. The as-synthesized nanostructures were characterized for structural, morphological and compositional properties using X-ray diffraction, X-ray photoelectron spectroscopy, scanning electron microscopy, high resolution transmission electron microscopy and energy dispersive X-ray spectroscopy. Nickel telluride modified electrodes were tested as bifunctional electrocatalyst under acidic and alkaline conditions, through linear sweep voltammetry and constant current chronopotentiometry methods. The modified electrodes revealed an onset potential of ?422 mV and 87.4 mV dec?1 Tafel slope towards HER and overpotential of 679 mV and 151 mV dec?1 Tafel slope towards OER. The lower onset potentials are complimented with excellent electrocatalytic stability. © 2017 Hydrogen Energy Publications LLCItem 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 Effect of oxygen substitution and phase on nickel selenide nanostructures for supercapacitor applications(Institute of Physics Publishing helen.craven@iop.org, 2018) Bhat, K.S.; Nagaraja, H.S.Electrochemical supercapacitors are the eminent technology for the progress of energy storage devices. The current manuscript deals with the formation of oxygen substituted nickel selenide nanostructures and their use as active electrode material for supercapacitor, expecting an enhanced performance owing to their sheet-like geometry, high specific surface area and porous assembly. In this context, Ni(OH)2 (nickel hydroxide) nanostructures were synthesized employing one-pot hydrothermal method and the ion-exchange reaction of Ni(OH)2 nanostructures with selenium resulted in cubic-NiSe2 (nickel selenide) nanostructures. Further, annealing NiSe2 nanostructures at intermediate pressure (10-3 Torr) has realized the partial oxygen substitution in place of selenium, resulting in NiSe/NiO nanostructures along with phase change from cubic-NiSe2 to hexagonal-NiSe. Supercapacitor electrodes fabricated using NiSe/NiO nanostructures delivered the specific capacitance of 83.5 F g-1 at the scan rate of 2 mV s-1, which is surprisingly more than a double as compared with pristine NiSe2 electrodes (37.4 F g-1). Annealing at intermediate pressure and high temperature significantly enhanced the specific capacitances of the nanostructured electrodes and also accompanied with the good capacitance retention of 94% for 5000 CV cycles. © 2018 IOP Publishing Ltd.Item Chemically prepared Polypyrrole/ZnWO 4 nanocomposite electrodes for electrocatalytic water splitting(Elsevier Ltd, 2019) Brijesh, K.; Bindu, K.; Shanbhag, D.; Nagaraja, H.S.ZnWO 4 , PPy, and PPy/ZnWO 4 nanoparticles were prepared using chemical synthesis. The structural, compositional and morphological properties of the prepared samples have been investigated using XRD, FTIR, SEM, and HRTEM respectively. The powder XRD reveals the monoclinic wolframite structure for both ZnWO 4 and PPy/ZnWO 4 nanocomposite. SEM confirms the wrapping of ZnWO 4 with PPy. The electrodes of ZnWO 4 , PPy, and PPy/ZnWO 4 have been tested as bifunctional electrocatalyst towards HER and OER using constant current chronopotentiometry (CP) and Linear Sweep Voltammetry (LSV). The electrochemical surface area and the electrocatalytic activity PPy/ZnWO 4 nanocomposite towards HER and OER are greater than that of pure ZnWO 4 and PPy. The Tafel slope of PPy/ZnWO 4 nanocomposite is 76 and 84 mV dec ?1 in 0.5 M H 2 SO 4 and 1 M KOH at room temperature for HER and OER respectively. The results suggest that PPy/ZnWO 4 nanocomposite is a good candidate for the bifunctional electrocatalyst for water splitting. © 2018 Hydrogen Energy Publications LLCItem 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 Two-Dimensional Cadmium Hydroxide Nanosheets for Electrochemical Capacitors Under High Operating Voltage(Springer, 2020) Bhat, K.S.; Huvinahalli, B.R.; Nagaraja, H.S.Abstract: Electrochemical capacitors are deemed to be the most prospective energy storage devices in the field of alternative energy sources. Here, cadmium hydroxide (Cd(OH)2) nanosheets are hydrothermally synthesized and used as electrodes for supercapacitors. Physiochemical properties of the as-synthesized materials are examined using powder x-ray diffraction, scanning electron microscopy, high-resolution transmission electron microscopy and energy-dispersive x-ray spectroscopy measurements. Electrochemical investigations reveal an excellent operating potential window of 1.5 V, with the specific capacitance of ? 71 F g?1 at a scan rate of 2 mV s?1. In addition, the Cd(OH)2 electrodes are complemented by good cyclic retention for 2000 cycles. Further, the analysis of the type of charge-storage mechanism reveals prominent contributions from the diffusion-controlled processes. Graphic Abstract: [Figure not available: see fulltext.]. © 2019, The Minerals, Metals & Materials Society.