Faculty Publications
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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 Tubular array, dielectric, conductivity and electrochemical properties of biodegradable gel polymer electrolyte(Elsevier Ltd, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.A supercapacitor based on a biodegradable gel polymer electrolyte (GPE) has been fabricated using guar gum (GG) as the polymer matrix, LiClO4 as the doping salt and glycerol as the plasticizer. The scanning electron microscopy (SEM) images of the gel polymer showed an unusual tubular array type surface morphology. FTIR, DSC and TGA results of the GPE indicated good interaction between the components used. Highest ionic conductivity and lowest activation energy values were 2.2 × 10-3 S cm-1 and 0.18 eV, respectively. Dielectric studies revealed ionic behavior and good capacitance with varying frequency of the GPE system. The fabricated supercapacitor showed a maximum specific capacitance value of 186 F g -1 using cyclic voltammetry. Variation of temperature from 273 K to 293 K did not significantly influence the capacitance values obtained from AC impedance studies. Galvanostatic charge-discharge study of supercapacitor indicated that the device has good stability, high energy density and power density. © 2013 Elsevier Ltd. All rights reserved.Item Reduced graphene oxide derived from used cell graphite and its green fabrication as an eco-friendly supercapacitor(Royal Society of Chemistry, 2014) Sudhakar, Y.N.; Muthu, M.; Bhat, D.; Senthil Kumar, S.Graphite extracted from a used primary cell was converted into reduced graphene oxide (rGO) using calcium carbonate together with rapid and local Joule heating by microwave irradiation. Electrodes were prepared by ultrasonically dispersing rGO in biodegradable poly(vinylpyrrolidone) (PVP) binder and coating this on recyclable poly(ethyleneterephthalate) (PET) sheet using a low cost screen printing technique. The use of the same polymer (PVP) as a binder, in addition to as the solid polymer electrolyte (SPE), enhances the compatibility and ionic conductivity of the hydrophobic rGO electrode in the supercapacitor system. Further, the phosphoric acid (H3PO4)-doped biodegradable SPE was screen printed for the first time on the rGO electrodes. Ionic conductivity and dielectric studies of the SPE were carried out at different temperatures and different dopant acid concentrations. The morphology, composition and structure of the graphene electrode components were characterized using Fourier transform infrared spectroscopy (FTIR), Raman spectroscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) methods. Transmission electron microscopy (TEM) images showed a single layer or a few layers of rGO sheets and selected area electron diffraction showed the presence of slight defects. The fabricated environmentally friendly, industrially favorable and green supercapacitor showed a specific capacitance of 201 F g-1 and cyclic stability with 97% retention of the initial capacitance over 2000 cycles. Furthermore, the performance of this green supercapacitor is comparable to that of those fabricated using rGO synthesized from commercial graphite and in other literature reports. © 2014 The Royal Society of Chemistry.Item Ionic conductivity and dielectric studies of acid doped cellulose acetate propionate solid electrolyte for supercapacitor(John Wiley and Sons Inc, 2016) Sudhakar, Y.N.; Bhat, D.; Muthu, M.Phosphoric acid doped cellulose acetate propionate (CAP) consisting of poly(ethylene glycol) (PEG) as plasticizer was investigated. Ionic conductivities and dielectric studies were carried at different temperature with varying concentration of H3PO4 using AC impedance method. The highest conductivity was 8.1 × 10-4 S cm-1 at 343 K and a long tail was featured in dielectric studies indicating good capacitance nature of the electrolyte. Interactions between added constituents were observed in FTIR and differential scanning calorimetry studies. Thin and compact fabricated supercapacitor demonstrated specific capacitance of 64 F g-1 using cyclic voltammetry. Furthermore, the supercapacitor properties like AC impedance and charge-discharge were studied. Stability was up to 96% at 1000th cycle. POLYM. ENG. SCI., 56:196-203, 2016. © 2015 Society of Plastics Engineers.Item Supercapacitor studies of activated carbon functionalized with poly(ethylene dioxythiophene): Effects of surfactants, electrolyte concentration on electrochemical properties(Elsevier B.V., 2020) Sudhakar, Y.N.; Muthu, M.; Krishna Bhat, D.; Karazhanov, S.; Raghu, R.Electropolymerization of poly(ethylene dioxythiophene) (PEDOT) on activated carbon (AC) was performed using different surfactants such as anionic surfactant (sodium dodecyl sulfate), protonic surfactant (camphor sulphonic acid) and non-ionic surfactant (Triton) in 0.1 M H2SO4. The effects of concentration of different surfactants for electrodeposition of PEDOT on AC were analyzed using electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and SEM techniques. Supercapacitors (SC) were fabricated using AC/PEDOT composite electrodes and 0.1 M H2SO4 as an electrolyte. The specific capacitance (Cs) values were calculated using CV at different concentrations of surfactants, electrolytes and variation of potential. The electrolyte containing 0.1 M H2SO4 and 0.02 M camphor sulphonic acid showed to have the highest specific capacitance value of 240 Fg?1 than other surfactant based SCs. Galvanostatic charge/discharge at varying current density were performed on SCs containing different surfactant based electrodes to study their cyclic stability. © 2020Item Pyrene-based chalcones as functional materials for organic electronics application(Elsevier Ltd, 2023) Kagatikar, S.; Dhanya, D.; Kekuda, D.; Satyanarayana, M.N.; Kulkarni, S.D.; Sudhakar, Y.N.; Vatti, A.K.; Sadhanala, A.Though new generation organic electronic devices have evolved from mere scientific perceptions to real-life marketed applications, considerably less research attention has been focused on n-type or electron transporting small molecule semiconductors. The present study is focused on the exploration of structural, thermal, electrochemical, electrical, and optical properties of two pyrene-based chalcones: PC1 and PC2, synthesized through Claisen Schmidt condensation reaction. The chalcones displayed good thermal stability and wide bandgap n-type semiconducting behaviour with high charge carrier concentration and dielectric constant. The experimental evidences including fluorescence measurements, nanoaggregate size, and morphology analysis, supported by DFT calculations and molecular dynamic simulations advocated the intramolecular charge transfer and aggregation-induced enhanced emission features of the molecules. Successful fabrication of a diode in combination with the current-voltage characteristics established the candidature of PC1 and PC2 for electro-optical devices. The dielectric studies were performed to measure dielectric constant and AC conductivity at different frequency ranges. The cyclic voltammetry and AC impedance response of PC2 differed from PC1 due to the inclusion of a fluorine atom in the molecular scaffold. Further, the functional implication of PC2 as an electrode material was explored by constructing a supercapacitor, which offered a specific capacitance of 220 Fg-1 at a scan rate of 10 mV s−1. Moreover, these chalcone-based organic semiconductors displayed high thermal and charge carrier concentration as well as compatibility with other layers in an OLED device. Hence PC1/PC2 can be further investigated as dopants along with other emissive layers as host materials in OLEDs. © 2022 Elsevier B.V.Item Unveiling the mass-loading effect on the electrochemical performance of Mn3O4 thin film electrodes: a combined computational and experimental study(Institute of Physics, 2024) Pramitha, A.; Hegde, S.S.; Badekai Ramachandra, B.R.; Yadav K, C.; Chakraborty, S.; Ravikumar, A.; George, S.D.; Sudhakar, Y.N.; Raviprakash, Y.The remarkable storage performance of manganese oxide (Mn3O4) makes it an appealing option for use as electrodes in electrochemical capacitors. However, the storage kinetics were significantly influenced by the mass loading of the electrode. Herein, we have inspected the dependency of mass loading on the storage performance of the spray pyrolyzed Mn3O4 thin film electrodes along with the correlation of structural and morphological characteristics. X-ray diffraction and Raman spectroscopic studies proven the formation of spinel Mn3O4 with a tetragonal structure. Morphological analysis revealed that all films exhibited fibrous structures with interconnected patterns at higher mass loadings. Moreover, the surface roughness and wettability of the electrode surface were influenced by variations in mass loading. Notably, thin-film electrode with a mass loading of 0.4 mg cm?2 exhibited the highest specific capacitance value of 168 F g?1 at 5 mV s?1 in a three-electrode system. Further, electrochemical impedance spectroscopic studies showed that there were noticeable changes in the capacitive behaviour of the electrode with respect to variations in mass loading. Moreover, the Dunn approach was employed to differentiate the underlying storage mechanism of the Mn3O4 electrode. Additionally, first-principles Density Functional Theory (DFT) studies were carried out in connection with the experimental study to comprehend the structure and electronic band structure of Mn3O4. This study underscores the critical importance of mass loading for enhancing the storage performance of Mn3O4 thin-film electrodes. © 2024 The Author(s). Published by IOP Publishing Ltd.