Faculty Publications
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Item Electrochemical study of graphene-NiCo2O4 nanocomposite prepared through solvothermal approach(American Institute of Physics Inc. subs@aip.org, 2019) Sethi, M.; Krishna Bhat, D.A green approach was employed for the synthesis Graphene-NiCo2O4 nanocomposite and its electrochemical property has been studied. The formation of phase and morphology was studied by diffraction and microscopic analysis. The prepared material was studied as an electrode material for supercapacitor application in a 2 M KOH electrolyte. In order to examine the electrochemical behavior of the prepared material cyclic voltammetry (CV), Galvanostatic charge-discharge (GCD) and electrochemical impedance spectroscopy (EIS) measurements were carried out in a 3-electrode system. Electrochemical studies revealed a high specific capacitance of 242 F g-1 and 165 F g-1 were obtained at a high scan rate of 10 mV s-1 and at an applied current density of 0.5 A g-1, respectively. A high initial capacitance retention value and coulombic efficiency of about 96% and 98% was retained after a long 1000 discharge cycles. Hence, the prepared material can be a potential candidate for high performance supercapacitor applications. © 2019 American Institute of Physics Inc.. All rights reserved.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 Novel porous graphene synthesized through solvothermal approach as high performance electrode material for supercapacitors(American Institute of Physics Inc. subs@aip.org, 2020) Sethi, M.; Bhat, D.K.A facile solvent mediated chemical route is employed for the fruitful synthesis of porous graphene (PG). The formation of PG is thoroughly characterized by microscopic and spectroscopic techniques. Elemental analysis showed the presence of carbon and oxygen only as elements in the PG sample, indicating the purity of the product. The as synthesized sample is utilized as an energetic electrode material for supercapacitor in 2M KOH aqueous electrolyte. The fabricated symmetrical supercapacitor exhibited a capacitance value of 248.0 F g-1 at an applied current density of 1 Ag-1, and 220.0 F g-1 at a scan rate of 5 mV s-1. The supercapacitor provided an energy density value of 7.3 Wh kg-1 while maintaining a power density of 6405.0 W kg-1 at an applied current density of 8 A g-1. Apart from these values, the supercapacitor device can sustain up to 5000 charge-discharge cycles at a higher applied current density of 8 A g-1, with 96% of initial capacitance retention demonstrating the good rate profile. Hence, considering the above facts, it can be suggested that this material can have high practical utility in supercapacitor application. © 2020 Author(s).Item Engineered porous nanopillars of Co3O4: Hydrothermal synthesis and energy storage application(American Institute of Physics Inc. subs@aip.org, 2020) Sethi, M.; Bhat, D.K.The ever increasing demand of energy for daily needs is knocking globally and in this scenario the energy storage devices were paid more attention as they store more charge and release it efficiently which can be used in many applications. Nanopillars like porous Co3O4 nanostructures were synthesized by using a facile hydrothermal method which could be a potential candidate for energy storage applications. The as synthesized Co3O4 nanostructures are thoroughly analyzed by diffraction and microscopic tools which corroborated its successful synthesis. The porous Co3O4 nanostructures when utilized as an electrode material for supercapacitor application, a high capacitance value of 495.5 F g-1 is obtained at a scan rate of 5 mV s-1 from cyclic voltammetry (CV) data and 275 F g-1 (110 C g-1) at a current density of 1 A g-1 from charge-discharge (CD) data in 6 M KOH electrolyte. The charge bearing capacity of porous Co3O4 in other electrolytes like 4 M and 2 M KOH electrolyte is also studied and a capacitance value of 361.7 and 349.5 F g-1 is obtained in 4 M, and 2 M KOH electrolyte, respectively at a scan rate of 5 mV s-1. From the experiment it is found that the charge storage capacity is decreasing as the electrolyte concentration decreases and the value is 220 F g-1 (88 C g-1), and 214 F g-1 (86 C g-1) at a current density of 1 A g-1 for 4 M and 2 M KOH, respectively. Similarly the resistance value also decreases as the electrolyte concentration is increasing and vice-versa. The exciting result produced by this novel material suggests its suitable utility for energy storage applications. © 2020 Author(s).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 Eco-friendly synthesis of porous graphene and its utilization as high performance supercapacitor electrode material(Elsevier Ltd, 2019) Sethi, M.; Bantawal, H.; Shenoy, U.S.; Bhat, D.K.The successful application of porous graphene (PG) is hindered due to the lack of efficient and cost-effective method for its synthesis. Herein, we report a facile and eco-friendly method to produce PG through a low temperature solvothermal method. The structural and morphological characteristics of PG samples were investigated thoroughly. The as synthesized material is found to be a few layers thick (?4–6 layers) with a surface area of 420 m2 g?1 and consisting of hierarchical pores on the surface of the sheets. A high specific capacitance of 666 F g?1 was obtained at a scan rate of 5 mV s?1, apart from longer cyclic stability with 87% retention of initial capacitance value after 10000 cycles for the PG 28 sample. The fabricated supercapacitor displayed an energy density of 26.3 Wh kg?1 and power density of 6120 W kg?1. Density functional theory calculations were also carried out to qualitatively support the enhanced capacitance by providing theoretical insight from electronic structure and density of states of PG. These results open a new avenue for greener synthesis of high-quality PG using environmentally friendly solvents, without the use of toxic chemicals, for excellent supercapacitor performance. © 2019 Elsevier B.V.Item Porous Graphene Wrapped SrTiO3 Nanocomposite: Sr-C Bond as an Effective Coadjutant for High Performance Photocatalytic Degradation of Methylene Blue(American Chemical Society service@acs.org, 2019) Bantawal, H.; Sethi, M.; Shenoy, U.S.; Bhat, D.K.Porous graphene-SrTiO3 (PGST) composite prepared by a facile solvothermal method was tested for its photocatalytic activity in degradation of methylene blue (MB) dye. First-principles density functional theory calculations were also carried out to study the effect of nanocomposite formation on the electronic structure and density of states. The combined experimental and theoretical study gave insights regarding the formation of the Sr-C bond which enhanced the charge transport, effectively separating the charge carriers and reduced their recombination rate. The formation of PGST nanocomposite favorably tuned the electronic structure with decreased band gap due to introduction of the hybridized states extending the absorption to the visible region of electromagnetic spectrum. The microscopy studies revealed loofah like PG wrapped SrTiO3 nano structures with contusions providing high surface area facilitating adsorption of MB dye. Degradation of ?92% was obtained by 7.5 PGST in 120 min with high cyclic stability indicating its suitability as an efficient photocatalyst for the treatment of pollutants. © 2019 American Chemical Society.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 Facile solvothermal synthesis of NiFe2O4 nanoparticles for high-performance supercapacitor applications(Higher Education Press, 2020) Sethi, M.; Shenoy, U.S.; Muthu, M.; Bhat, D.K.We report a green and facile approach for the synthesis of NiFe2O4 (NF) nanoparticles with good crystallinity. The prepared materials are studied by various techniques in order to know their phase structure, crystallinity, morphology and elemental state. The BET analysis revealed a high surface area of 80.0 m2·g?1 for NF possessing a high pore volume of 0.54 cm3·g?1, also contributing to the amelioration of the electrochemical performance. The NF sample is studied for its application in supercapacitors in an aqueous 2 mol·L?1 KOH electrolyte. Electrochemical properties are studied both in the three-electrode method and in a symmetrical supercapacitor cell. Results show a high specific capacitance of 478.0 F·g?1 from the CV curve at an applied scan rate of 5 mV·s?1 and 368.0 F·g?1 from the GCD analysis at a current density of 1 A·g?1 for the NF electrode. Further, the material exhibited an 88% retention of its specific capacitance after continuous 10000 cycles at a higher applied current density of 8 A·g?1. These encouraging properties of NF nanoparticles suggest the practical applicability in high-performance supercapacitors. © 2020, Higher Education Press.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.