Papers by Author: Ramli Omar

Abstract: Activated carbon monoliths (ACMs) electrodes for supercapacitor application were prepared from the green monoliths (GMs) containing KOH treated self-adhesive carbon grains (SACG) added with KOH treated graphene at its weight percentages of 0, 2, 4, 6, 8 and 10 %, respectively. The SACG were prepared from fibers of oil palm empty fruit bunches by a low carbonization temperature method. The ACMs were produced by the carbonization and activation of the GMs. The surface area, structure and specific capacitance of the ACMs electrodes were found affected by the graphene addition. The highest surface area of the ACMs electrode was observed for the addition of 6% graphene, which corresponds to the carbon turbostratic structure of the ACMs electrodes with the values of its crystallites interlayers spacing (d₀₀₂ and d₁₀₀) at 0.352 nm and 0.205 nm, and its crystallites stack-width (L_a) and stack-height (L_c) at 43.21 nm and 10.06 nm, respectively. The specific capacitance of the cell using this electrode was 112 F / g.

Abstract: Supercapacitor electrodes in the monolithic form were prepared by carbonization and activation of green monoliths (GMs). The GMs and composite GMs were prepared from self-adhesive carbon grains (SACG) of oil palm empty fruit bunches and SACG added with 2 wt.% of multi-layers graphene, respectively. Both GMs and composite GMs were subjected to 18 h and 36 h milling time, respectively. The structure and porosity of the electrodes observed in the Raman spectroscopy and nitrogen adsorption-desorption results, respectively, indicated the effects of graphene addition and doubling the milling times. Galvanic charge discharge results of the supercapacitor cells fabricated using these electrodes showed that the greatest improvement due to the graphene addition occurred for the electrodes prepared based on the lower milling time. The results obtained from the electrochemical characterization showed that specific capacitance, specific power and specific energy of the cell with electrodes from the composite GMs produced from the mixture milled for 18 h were 46 F g^-1, 165 W kg^-1 and 1.2 W h kg^-1, which were ~500 %, ~25 % and ~1100 % better than the other cells.

Abstract: Supercapacitor electrodes in the form of activated carbon monoliths (ACMs) were prepared by carbonization and activation of three different composite of green monoliths (GMs) consisting of (a) self-adhesive carbon grains (SACG) derived from pre-carbonized oil palm empty fruit bunches, KOH and graphite additive, (b) KOH-treated SACG and HNO₃-treated graphite additive, and (c) SACG and HNO₃-treated graphite additive. The ACM1, ACM2 and ACM3 electrodes produced from their respective GMs were characterized using nitrogen adsorption-desorption technique and the supercapacitor cell fabricated using these electrodes were characterized by galvanostatic charge discharge method. The results showed that the change in the condition of material component in the GMs by acid/alkaline treatment moderately changed the pore characteristics of the electrodes, for example only around 10 % change occurred in the specific surface area of the samples. However, such change gave a larger change in the electrochemical performance of the cells, where the ACM3 exhibit the specific capacitance (119 F g^-1) and specific energy (3.5 W h kg^-1), which were (66 – 71) % and (28 – 75) % higher than the other cells, and the specific power (63.3 W kg^-1), which was 33 % lower than the other cells. These results demonstrate a non-linear dependency of electrochemical performances of the cells on the porosity characteristics of the electrodes resulted from the modification of component materials in the GMs.

Abstract: Green Monoliths (GMs) of self-adhesive carbon grain from fibers of oil palm empty fruit bunches were prepared by compression pressure at 1.43 × 107, 1.91 × 107 and 2.39 × 107 kg/m2, respectively. Activated carbon monoliths ACM-A, ACM-B and ACM-C prepared by CO2 activation from these GMs, respectively, were used as electrodes in supercapacitor cells which employed stainless steel 316L current collector and H2SO4 electrolyte. Evaluation of the electrochemical properties showed that ACM-A, ACM-B and ACM-C cells had specific capacitance of 30, 9 and 5 F/g, total ESR of 3.21, 4.95 and 7.33 Ω, specific power (maximum) of 173.41, 107.58 and 33.82 W/kg, and specific energy (maximum) of 0.67, 0.15 and 0.09 Wh/kg. These properties are directly associated with the surface area of the ACMs, i.e. 419, 336 and 302 m2/g for the ACM-A, ACM-B and ACM-C, respectively, indicating a direct effect of compression pressure on the physical and electrochemical properties of ACMs electrodes.