Browsing by Author "Manjunatha"

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    Physical and Electrochemical Properties of Supercapacitor Electrodes Derived from Carbon Nanotube and Biomass Carbon
    (2015-09-08) Farma, Rakhmawati; Deraman, Mohamad; Awitdrus; Talib; Omar, Ramli; Manjunatha; Ishak; Basri, Nur Hamizah; Dollah, Besek Nurdiana Mohd
    Green monoliths (GMs) were prepared from mixtures of KOH (5% by weight), carbon nanotubes (5%) and self-adhesive carbon grains (90%) from oil palm empty fruit bunch fibers. The GMs were carbonized up to 600, 700 and 800°C under an N2 gas environment, and activated by CO2 gas at 800°C for one hour to produce activated carbon monoliths (ACMs), designated as ACM6, ACM7 and ACM8, respectively. The characterization of the ACMs showed a notable effect of the carbonization temperature on the structure, microstructure, electrical conductivity and porosity of the ACMs. Consequently, three independent methods, galvanostatic charge-discharge, cyclic voltammetry and electrochemical impedance spectroscopy, used for the electrochemical characterization of supercapacitor cells fabricated using the ACMs as their electrodes, consistently found that the ACM7 and ACM8 cells have higher specific capacitance (77 Fg-1 and 85 Fg-1, respectively), specific energy (2.2 Wh kg-1 and 2.1 Wh kg-1, respectively) and specific power (156 W kg-1 and 161 W kg-1, respectively) compared to the ACM6 cell. These results suggest that carbonization should be performed at temperatures closer or equal to the activation temperature for the preparation of supercapacitor electrodes composed of biomass precursors.
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    Preparation of highly porous binderless activated carbon electrodes from fibres of oil palm empty fruit bunches for application in supercapacitors
    (2015-09-07) Farma, Rakhmawati; Deraman, Mohamad; Awitdrus; Taer, Erman; Talib; Basri, Nur Hamizah; Manjunatha; Ishak; Dollah, Besek Nurdiana Mohd; Hashmi
    Fibres from oil palm empty fruit bunches, generated in large quantities by palm oil mills, were processed into self-adhesive carbon grains (SACG). Untreated and KOH-treated SACG were converted without binder into green monolith prior to N2-carbonisation and CO2-activation to produce highly porous binderless carbon monolith electrodes for supercapacitor applications. Characterisation of the pore structure of the electrodes revealed a significant advantage from combining the chemical and physical activation processes. The electrochemical measurements of the supercapacitor cells fabricated using these electrodes, using cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge–discharge techniques consistently found that approximately 3 h of activation time, achieved via a multi-step heating profile, produced electrodes with a high surface area of 1704 m2 g 1 and a total pore volume of 0.889 cm3 g 1, corresponding to high values for the specific capacitance, specific energy and specific power of 150 F g 1, 4.297 Wh kg 1 and 173Wkg 1, respectively
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    Supercapacitors using binderless composite monolith electrodes from carbon nanotubes and pre-carbonized biomass residues
    (2015-09-10) Basri, Nur Hamizah; Deraman, Mohamad; Kanwal; Talib; Manjunatha; Aziz; Farma, Rakhmawati
    Binderless composite monolith (BCM) electrodes prepared from carbon nanotubes (CNTs) and self-adhesive carbon grains (SACGs) were used in a symmetrical supercapacitor. The SACGs were prepared from fibers of oil palm empty fruit bunches (EFBs) from oil palm tree (Elaeis guineensis), Heliotropium dasycarpum (H. dasycarpum) and Guaiacum officinale (G. officinale). For each biomass, the BCMs were prepared by the carbonization and activation of green monoliths (GMs) containing SACGs treated with KOH and a mixture of SACGs and CNTs treated with KOH. Thermal decomposition behavior of all SACGs was found to be slightly different because of the difference in their compositions. In addition, BCMs from H. dasycarpum and G. officinale were found to have SiO2. The BET surface areas were 1656, 1031 and 532 m2 g 1 for the BCMs from EFB, H. dasycarpum and G. officinale, respectively, and these values decreased by 40, 50 and 31% upon CNTs addition. Consequently, the specific capacitance decreased from w124 to w104 and w49 F g 1 to w111, w87 and w31 F g 1, respectively. However, addition of CNTs reduced the equivalent series resistance (ESR) by a factor of 83.9 (EFB), 90.6 (H. dasycarpum) and 38.8 (G. officinale) %. It was also found that CNTs addition contributed to improving the decay of Csp with increasing scan rate if the electrode surface area was sufficiently high.