Faculty Publications
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Publications by NITK Faculty
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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 Preparation and characterization of phosphoric acid-doped hydroxyethyl cellulose electrolyte for use in supercapacitor(SpringerOpen, 2015) Sudhakar, Y.N.; Muthu, M.; Bhat, D.K.A new borax cross-linked biodegradable solid polymer electrolyte based on hydroxyethyl cellulose and phosphoric acid (H3PO4) was prepared. Characterizations of doped and undoped SPE were done using Fourier transform infrared spectroscopic and electrochemical studies. The ionic conductivity of the films increased with increase in acid concentration and the ionic conductivity obtained at 303 K was 4.1 × 10-3 S cm-1. Furthermore, effects of acid concentration on ionic conductivity and activation energy were discussed. Dielectric studies showed long tail-like feature indicating capacitive nature. A supercapacitor was fabricated and its electrochemical characteristics were studied. The supercapacitor showed a fairly good specific capacitance of 83 F g-1 at 2 mV s-1 and galvanostatic charge-discharge studies showed the mirror-like pattern with 98 % columbic efficiency. Cyclic stability was measured up to 2000 cycles. © 2015 The Author(s).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.