Faculty Publications
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Item Microwave synthesized nanostructured TiO 2 -activated carbon composite electrodes for supercapacitor(Elsevier B.V., 2012) Muthu, M.; Bhat, D.K.Electrochemical properties of a supercapacitor based on nanocomposite electrodes of activated carbon with TiO 2 nano particles synthesized by a microwave method have been determined. The TiO 2 /activated carbon nanocomposite electrode with a composition of 1:3 showed a specific capacitance 92 Fg -1 . The specific capacitance of the electrode decreased with increase in titanium dioxide content. The p/p symmetrical supercapacitor fabricated with TiO 2 /activated carbon composite electrodes showed a specific capacitance of 122 Fg -1 . The electrochemical behavior of the neat TiO 2 nanoparticles has also been studied for comparison purpose. The galvanostatic charge-discharge test of the fabricated supercapacitor showed that the device has good coulombic efficiency and cycle life. The specific capacitance of the supercapacitor was stable up to 5000 cycles at current densities of 2, 4, 6 and 7 mA cm -2 . © 2012 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 h-MoO 3 /Activated carbon nanocomposites for electrochemical applications(Institute for Ionics ww@tf.uni-kiel.de, 2019) Sangeetha, D.N.; Krishna Bhat, D.; Muthu, M.MoO 3 nanorods were synthesized through the microwave method and the nanocomposites of MoO 3 /activated carbon were prepared for supercapacitor and hydrogen evolution reaction (HER). The XRD pattern revealed that the prepared MoO 3 has a hexagonal phase (h-MoO 3 ). The as-prepared h-MoO 3 was composited with activated carbon (AC) and tested for supercapacitor studies. The fabricated supercapacitor exhibited an appreciable specific capacitance, power density, and energy densities. Further, dedoping of nitrogen in the doped AC creates defects on AC (DAC). These DAC/MoO 3 nanocomposites were prepared and tested for its electrocatalytic activity towards hydrogen evolution reactions. DAC/MoO 3 nanocomposite showed much higher electrocatalytic activity than the neat MoO 3 . [Figure not available: see fulltext.]. © 2018, Springer-Verlag GmbH Germany, part of Springer Nature.Item High power density and improved H2 evolution reaction on MoO3/Activated carbon composite(Elsevier Ltd, 2020) Sangeetha, D.N.; Holla, R.S.; Badekai Ramachandra, B.; Muthu, M.The formation of hexagonal MoO3 (h- MoO3) microrods was favoured at lower pH in the hydrothermal synthesis method. Symmetric and Hybrid supercapacitors were fabricated using h-MoO3/plastic bottle derived activated carbon (PAC) composite in 1 M Na2SO4 aqueous electrolyte. The operating voltage for the aqueous electrolyte was maximized to 1.6 V with this combination. The wide operating voltage led to a maximum specific capacitance of 211 Fg-1, power density of 287 W kg?1 and 79% efficiency even at 5000 charge-discharge cycles for the hybrid supercapacitor combination. The combined effect of PAC micropores along with the 1-D rod-shaped h-MoO3, helped in faster charge-transfer, hence increasing the efficiency of supercapacitors. Further, the composites of defective PAC (PDAC) together with the h-MoO3 when tested for hydrogen evolution reactions (HER), provided lesser onset potential and Tafel slope values of ?0.23 mV and ?93 mVdec?1. There was a change in the structural environment of carbon due to the heteroatom doping and dedoping producing defects in PAC, termed as PDAC. These defects together with the hexagonal microrods of MoO3 provided fast electron transfer towards hydrogen adsorption/desorption hence effectively producing H2. © 2019 Hydrogen Energy Publications LLCItem Improving hydrogen evolution reaction and capacitive properties on CoS/MoS2 decorated carbon fibers(Elsevier Ltd, 2020) Sangeetha, D.N.; Krishna Bhat, D.; Senthil Kumar, S.; Muthu, M.We report a facile method to transform abundantly dumped banana stem fibers into carbon fibers (CFs) useful for energy applications. The CFs surface area is increased by varying the quantity of KOH activation to 488 m2g-1. The solvothermal method is used to synthesize CoS, CoS/MoS2 and also grown on the activated carbon fibers (ACFs). Nano nodules of CoS arranged into sheets and layers of MoS2 stacked together were found in FESEM analysis. The morphology of the CoS/MoS2 differs when grown on ACFs. The growth of CoS/MoS2 along the ACFs length prevents any stacking of the pseudocapacitance materials. The ternary composite ACFs/CoS/MoS2 exhibits superior supercapacitor behavior as well as hydrogen evolution reaction (HER) due to the synergetic effect of the conducting ACF surface and redox active CoS/MoS2. A maximum specific capacitance of 733 Fg-1, energy and power density of 33 WhKg?1 and 999 WKg-1 respectively are obtained. A low Tafel slope value of 61 mVdec?1 is obtained for the ACFs/CoS/MoS2 ternary composite electrode. The present work therefore offers a fresh insight into the effective conversion of waste materials into electrode material for energy storage and conversion applications. © 2019 Hydrogen Energy Publications LLCItem 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. © 2020