M. M. Ishak

Preparation of highly porous binderless activated carbon electrodes from fibres of oil palm empty fruit bunches for application in supercapacitors

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 3h of activation time, achieved via a multi-step heating profile, produced electrodes with a high surface area of 1704m(2)g(-1) and a total pore volume of 0.889cm(3)g(-1), corresponding to high values for the specific capacitance, specific energy and specific power of 150Fg(-1), 4.297Whkg(-1) and 173Wkg(-1), respectively.

Supercapacitor Electrodes from Activated Carbon Monoliths and Carbon Nanotubes

Binderless monoliths of supercapacitor electrodes were prepared by the carbonization (N2) and activation (CO2) of green monoliths (GMs). GMs were made from mixtures of self-adhesive carbon grains (SACG) of fibers from oil palm empty fruit bunches and a combination of 5 & 6% KOH and 0, 5 & 6% carbon nanotubes (CNTs) by weight. The electrodes from GMs containing CNTs were found to have lower specific BET surface area (SBET). The electrochemical behavior of the supercapacitor fabricated using the prepared electrodes were investigated by electrochemical impedance spectroscopy (EIS) and galvanostatic charge-discharge (GCD). In general an addition of CNTs into the GMs reduces the equivalent series resistance (ESR) value of the cells. A cell fabricated using electrodes from GM with 5% CNT and 5% KOH was found to have the largest reduction of ESR value than that from the others GMs containing CNT. The cell has steeper Warburgs slope than that from its respective non-CNT GM, which reflect the smaller resistance for electrolyte ions to move into pores of electrodes despite these electrodes having largest reduction in specific BET surface area. The cell also has the smallest reduction of specific capacitance (Csp) and maintains the specific power range despite a reduction in the specific energy range due to the CNT addition.

Effect of Compression Pressure on the Physical and Electrochemical Properties of Activated Carbon Monoliths Electrodes for Supercapacitor Application

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.

Binderless Composite Electrode Monolith from Carbon Nanotube and Biomass Carbon Activated by H2SO4 and CO2 Gas for Supercapacitor

Binderless composite electrodes in the monolithic form prepared from carbon nanotubes (CNTs) and self‐adhesive carbon grains (SACG) from fibers of oil palm empty fruit bunch were studied as an electrode in a supercapacitor. The green monoliths (GMs) were prepared from three different types of precursors, SACG, SACG treated with 0.4 Molar H2SO4 and mixture of SACG and 5% CNTs (by weight) treated with 0.4 Molar H2SO4, respectively. These GMs were carbonized at 600 °C in N2 gas environment and activated by CO2 gas at 800 °C for 1 hour to produce activated carbon monoliths (ACMs). The properties of the ACMs (density, porosity, microstructure, structure and electrical conductivity) were found affected by CNTs addition and acid treatment. The acid treatment did not improve the electrochemical behavior of the ACMs used as electrodes (specific capacitance, specific energy and specific power of the supercapacitor) in the supercapacitor cells but CNTs addition improves the equivalent series resistance of the cell.

Carbon/Carbon Nanotubes (CNTs) Composites from Green Pellets Contain CNTs and Self‐adhesive Carbon Grains from Fibres of Oil Palm Empty Fruit Bunch

Nano composites green pellets (GPs) were prepared from the mixtures of carbon nanotubes (CNTs) at varying percentage (0, 2, 4, 6, 8 and 10%) and self‐adhesive carbon grains (SACG) from fibres of oil palm empty fruit bunch. These GPs were carbonized and CO2 activated to produce activated carbon/CNTs composites in the form of pellets (ACPs). It was found that the density (ρ) and electrical conductivity (σ) of the ACPs varied nonlinearly with CNTs content; as for the CNTs content of 3–5%, we observed the peak values of ρ and σ at 1.3781 gcm−3 and 3.4146 (Ωcm)−1 respectively. The presence of the agglomerated and individual particles of CNTs in the pores of the ACPs was clearly shown by the micrograph of the Field Emission Scanning Electron Microscope (FESEM). The nitrogen adsorption isotherm data showed the decrease in surface area, volume and diameter of pores due to the effect of CNTs. The effect of CNTs on the electrochemical behavior of the ACPs were investigated from the supercapacitor cells fabricated u...

Effect of KOH Treated Graphene in Green Monoliths of Pre-Carbonized Biomass Fibers on the Structure, Porosity and Capacitance of Supercapacitors Carbon Electrodes

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 (La) and stack-height (Lc) at 43.21 nm and 10.06 nm, respectively. The specific capacitance of the cell using this electrode was 112 F / g.

Electrochemical Characterization of Supercapacitor Electrodes Prepared by Activation of Green Monoliths Consist of Self-Adhesive Carbon Grains and Lignin

Self-adhesive carbon grains (SACG) and lignin were prepared from fibres of oil palm empty fruit bunches by a low carbonization temperature and chemical treatment methods, respectively. Green monoliths were prepared from the KOH-treated SACG mixed with the organosolv-treated lignin with their weight percentages of 0%, 5%, 10%, 15% and 20%, respectively. The green monoliths were carbonized and activated into highly porous activated carbon monoliths (ACMs) electrodes for supercapacitor applications. The electrochemical characterization using galvanostatic charge-discharge (GCD) technique was carried out on the supercapacitor cell fabricated using these electrodes. The results show that the addition of 5 wt.% lignin was optimum, corresponding to the higher values of the specific capacitance (137 Fg-1), specific energy (4.13 Wh kg-1), specific power (192 W Kg-1), and a satisfactory value of equivalent series resistance (0.467 Ω) of the supercapacitor.

Electrical conductivity of carbon pellets prepared from mixtures of pyropolymers from oil palm bunches and petroleum green coke

Green pellets (GPs), prepared at different compression pressures (cs = 6, 7.5 and 12 metric tonne) from mixtures containing self‐adhesive carbon grains (sacg) from the oil palm empty fruit bunch (EFB) and different percentages (pr = 0 to 90%) of a non self‐adhesive powder of petroleum green coke (ppgc), were carbonized (800° C) and activated with CO2 to produce carbon pellets (CPs). The measured electrical conductivity (σ) of the CP for all cs showed a curve having a minimum value at pr around 50%, indicating that the conducting phase displays a nonlinear σ‐ pr relationship. A significant increase in the σ due to CO2 activation was observed. For a sufficienctly high cs, an existence of a pr range in which the σ varies linearly with the density was also observed. These results provide some new information for modifying the electrical conductivity of carbon derived from the sacg from EFB or other types of biomass.