Faculty Publications
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Item NiO nanoplates for energy storage application: Role of electrolyte concentration on the energy storage property(Elsevier Ltd, 2020) Sethi, M.; Bhat, D.K.Here in, synthesis of NiO nanoplates by employing a mixed solvent system under solvothermal method followed by calcining the obtained product nickel hydroxide in air is reported. Diffraction, microscopic, and spectroscopic results confirmed the formation of NiO phase. The as synthesized NiO nanoplates are tested as a robust material for energy storage applications. The effect of electrolyte concentration on the capacitive behavior of NiO is studied thoroughly. The outcome from the electrochemical analysis reveals that NiO nanoplates have a high specific capacity value of 108.4 C g-1 (270 F g-1) in 6 M KOH electrolyte and the value decreases to 85.0 C g-1 (212.5 F g-1) and 78.2 C g-1 (195.5 F g-1) for 4 M, and 2 M KOH electrolyte, respectively. The resistance values also decreased with increase in the KOH concentration. The better electrochemical performance depicted by the 6 M KOH electrolyte is mainly ascribed to the availability of plenty of OH- ions in the electrolyte solution, which helped in the proper wettability of the sample so that the OH- ions can participate to higher extent during the electrochemical redox reactions, due to which the observed charge storage capacity is more in higher electrolyte concentration and vice-versa. Thus, the results suggest the usefulness of this material for energy storage applications. © 2019 Elsevier Ltd. All rights reserved.Item LiClO4-doped plasticized chitosan as biodegradable polymer gel electrolyte for supercapacitors(2009) Muthu, M.S.; Bhat, D.K.Studies on redox supercapacitors using electronically conducting polymers are of great importance for hybrid power sources and pulse power applications. In this study, electrochemical properties of a chitosan-based biodegradable polymer gel electrolyte (PGE) and a p/p polypyrrole supercapacitor fabricated using this electrolyte have been investigated. The variation of conductivity and dielectric properties of the electrolyte film with temperature has also been measured. The PGE film chosen for the study exhibited a specific conductivity of 5.5 × 10-3 S cm~. The electric modulus of the electrolyte film exhibits a long tail feature indicative of good capacitance. The fabricated supercapacitor showed a fairly good specific capacitance of 120 F g-1 and a time constant of 1 s. © 2009 Wiley Periodicals, Inc.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 LiClO4-doped plasticized chitosan and poly(ethylene glycol) blend as biodegradable polymer electrolyte for supercapacitors(Institute for Ionics, 2013) Sudhakar, Y.N.; Muthu, 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.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 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.