Faculty Publications
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Publications by NITK Faculty
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Item Polyvinyl alcohol-polystyrene sulphonic acid blend electrolyte for supercapacitor application(2009) Muthu, M.S.; Bhat, D.K.A new polymer blend electrolyte based on poly vinyl alcohol and poly styrene sulphonic acid has been studied as an electrolyte for supercapcitors. A carbon-carbon supercapacitor has been fabricated using this electrolyte and its electrochemical characteristics and performance have been studied. The conductivity has been calculated using the bulk impedance obtained through impedance spectroscopy. The real and imaginary parts of the electrical modulus of samples show a long tail feature, which can be attributed to high capacitance of the material. The super capacitor showed a fairly good specific capacitance of 40 F g- 1 and a time constant of 5 s. © 2008 Elsevier B.V. All rights reserved.Item 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.Item 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.Item Effect of acid dopants in biodegradable gel polymer electrolyte and the performance in an electrochemical double layer capacitor(Institute of Physics Publishing custserv@iop.org, 2015) Sudhakar, Y.N.; Muthu, 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.Item Novel Fe-Ni-Graphene composite electrode for hydrogen production(Elsevier Ltd, 2015) Badrayyana, S.; Bhat, D.K.; Shenoy, U.S.; Ullal, Y.; Hegde, A.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.Item RGO/ZnWO4/Fe3O4 nanocomposite as an efficient electrocatalyst for oxygen reduction reaction(Elsevier B.V., 2017) Mohamed, M.; Mutyala, S.; Mathiyarasu, J.; Bhat, D.K.Development of low cost, environmental friendly and noble metal free catalyst materials with excellent performance is essential for commercialization. In fact, this is the need of the day too. Herein, we report a facile microwave irradiation method for the synthesis of novel RGO/ZnWO4/Fe3O4 cathode catalysts for the oxygen reduction reaction (ORR) in alkaline medium. The structural and morphological features of synthesized materials are fully examined using transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM). The chemical composition and elemental analysis of the catalyst is investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy techniques. Efficiency of RGO/ZnWO4/Fe3O4 catalyst material for oxygen reduction reaction (ORR) in 0.1 M KOH is reported. The activity of catalyst is determined by linear sweep voltammogram (LSV) and rotating disk electrode (RDE) measurements in O2 saturated 0.1 M KOH electrolyte. RGO/ZnWO4/Fe3O4 catalyst exhibits higher ORR activity than RGO, ZnWO4, RGO/ZnWO4 and its electrocatalytic performance is comparable to Pt/C material and is superior to it in stability and methanol tolerance. Further, it is determined that process follows a direct four electron reaction pathway. These combined results strongly signpost that RGO/ZnWO4/Fe3O4 composite can function as an economic noble metal free ORR cathode catalyst for energy applications. © 2017 Elsevier B.V.Item Facile solvothermal synthesis and high supercapacitor performance of NiCo2O4 nanorods(Elsevier Ltd, 2019) Sethi, M.; Bhat, D.K.NiCo2O4 nanorod arrays were synthesized employing a facile low-temperature solvothermal approach, followed by post-calcination treatment. The structural, morphological and elemental characterizations were done by diffraction, microscopic and spectroscopic techniques. The prepared sample was studied as an active electrode material for supercapacitor application in 2 M KOH aqueous electrolyte. The cyclic voltammetry (CV), galvanostatic charge-discharge (GCD) and electrochemical impedance spectral (EIS) studies were carried out to know the electrochemical activity of the prepared material. From the CV study, a high capacitance value of 440 F g?1 was obtained at a scan rate of 5 mV s?1 in a 3-electrode method. Apart from high capacitance value, the prepared electrode depicted 94% initial capacitance retention value after 2000 charge-discharge cycles at a current density of 8 A g?1. The fabricated symmetrical supercapacitor depicted a high energy density of 12.6 Wh kg?1 and a high power density of 4003 W kg?1. This was attributed to the better electrical conductivity of NiCo2O4 nanorods. © 2018 Elsevier B.V.Item Porous graphene-NiCo2O4 nanorod hybrid composite as a high performance supercapacitor electrode material(Royal Society of Chemistry, 2020) Sethi, M.; Shenoy, U.S.; Bhat, D.K.The template free low temperature solvothermal synthesis of high capacitive porous graphene-NiCo2O4 nanorod composites has been carried out. Solvothermal synthesis followed by calcination in air led to the development of a highly porous hybrid nanocomposite, which acts as a buffering channel for fast ion diffusion and provides robust mechanical strength. Advantages of using porous graphene to enhance the capacitance of the material were studied theoretically using First principles calculations. High capacitance values of 1533 F g-1 at a scan rate of 5 mV s-1 and 1684 F g-1 at a current density of 1 A g-1 are obtained from cyclic voltammetry data and galvanostatic charge discharge data, respectively. The electrode material possesses good cyclic stability with the retention of 94% of its initial capacitance even after 10000 charge-discharge cycles at a current density of 8 A g-1 in 2 M KOH electrolyte. The fabricated supercapacitor exhibited a high energy density of 45.3 W h kg-1 and a high power density of 17843.5 W kg-1 due to the synergistic effect of the composite components. The enhanced electrochemical function of the composite makes it a potential candidate for supercapacitor application and future studies. This journal is © 2020 The Royal Society of Chemistry and the Centre National de la Recherche Scientifique.Item A porous graphene-NiFe2O4nanocomposite with high electrochemical performance and high cycling stability for energy storage applications(Royal Society of Chemistry orders@rsc.org, 2020) Sethi, M.; Shenoy, U.S.; Bhat, D.K.It is well agreed that supercapacitors form an important class of energy storage devices catering to a variety of needs. However, designing the same using eco-friendly and earth abundant materials with high performance is still the dire need of the day. Here, we report a facile solvothermal synthesis of a porous graphene-NiFe2O4 (PGNF) nanocomposite. Thorough elemental, diffraction, microscopic and spectroscopic studies confirmed the formation of the PGNF composite, in which the NF nanoparticles are covered over the PG surface. The obtained 10 PGNF composite showed a surface area of 107 m2 g-1, with large pore volume which is favorable for charge storage properties. When utilizing the material as an electrode for a supercapacitor in a 2 M KOH aqueous electrolyte, the electrode displayed an impressive specific capacitance value of 1465.0 F g-1 at a scan rate of 5 mV s-1 along with a high capacitance retention of 94% after 10?000 discharge cycles. The fabricated symmetrical supercapacitor device exhibited an energy density of 4.0 W h kg-1 and a power density of 3600.0 W kg-1 at a high applied current density of 14 A g-1. The superior electrochemical performance is attributed to the synergetic effect of the composite components which not only provided enough electroactive channels for the smooth passage of electrolyte ions but also maintained the hybrid structure intact in the ongoing electrochemical process. The obtained results underpin the promising utility of this material for future electrochemical energy storage devices. © The Royal Society of Chemistry.Item Exploring the potential of CoAl2O4 nanoflakes in supercapacitor applications(Elsevier B.V., 2025) Ramesh, T.P.; Shenoy, U.S.; Bhat, D.K.Spinel structured nanoparticles with binary and ternary metal oxide combinations have recently been identified as a viable material for use in supercapacitors. Two mixed-valence metal cations provide easy electron transport between various metal cations. High-performance CoAl2O4 spinel nanoflakes were synthesized using a mixed-solvent solvothermal method, followed by calcination. First principles calculations revealed high density of states near the Fermi level indicating its potential for supercapacitor applications. These nanostructured materials were then experimentally explored as promising electrode candidates for supercapacitor applications, using a 2 M KOH aqueous electrolyte. The results were impressive: the material demonstrated a high specific capacitance of 851.9 F/g at a current density of 1 A/g and the fabricated supercapacitor exhibited a power density of 14940.0 W/kg at a current density of 12 A/g. Even under more demanding conditions, the electrode maintained strong durability, in terms of cyclic stability along with high energy and power density values making it a strong contender for next-generation energy storage devices. © 2025 Elsevier B.V.