N.H. Basri

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.

Selective Detection of Dopamine in the Presence of Uric Acid Using Polymerized Phthalo Blue Film Modified Carbon Paste Electrode

A convenient and useful method for the voltammetric determination of dopamine (DA) and uric acid (UA) based on poly (Phthalo blue) modified carbon paste electrode (PTBMCPE) is reported in this paper. The PTBMCPE exhibits excellent electro-catalytic activities for the oxidationreduction of DA and UA, as well as eliminating the interference. Factors influencing the detection processes are optimized and the kinetic parameters are calculated. The effects of pH, scan rate and concentration of dopamine on the peak current were investigated, and the results indicated that the peak current of dopamine is the highest in 0.2 M pH 7.0 Phosphate buffer solution (PBS) and the electrode reaction corresponds to a rate-controlled process. The proposed method possesses the distinct advantages of simple, appropriate for operation, good reproducibility and highly selective and sensitive.

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.

Influence of aqueous KOH and H2SO4 electrolytes ionic parameters on the performance of carbon-based supercapacitor electrodes

In this paper, the suitability of aqueous KOH and H2SO4 electrolytes in terms of ionic size, mobility, conductivity and energy of electrolyte ions with the porosity of activated carbon electrodes are demonstrated. These parameters of ions (K+, OH−, H+, SO42−) are found to affect the overall performances of supercapacitor cells as observed from the results of EIS, CV and GCD studies. The cell using H2SO4 electrolyte exhibits better performance with relatively low value of charge transfer resistance (0.57Ω), overall cell resistance, 19Ω (at 10mHz) and high value of specific capacitance 547F g−1 (at 1mV s−1), specific energy 10W h kg−1 (at 0.5A g−1) and specific power, 490W kg−1. These results show that aqueous acid electrolyte is more compatible with carbon electrodes which could be due to the higher ionic energies of H+ and SO42− ions.

Graphene/semicrystalline-carbon derived from amylose films for supercapacitor application

Graphene/semicrystalline-carbon in the form of carbon flakes is produced by carbonization up to 600, 700, 800, 900 and 1000°C, respectively, of the amylose films prepared by a casting method on copper foil substrate. The carbon flakes are characterized by X-ray diffraction (XRD) method to determine their microcrystallite interlayer spacing, width and stack-height; and Raman spectroscopy (RS) method to obtain structural information from the D-, D2- and G-bands peak-intensities. The XRD results show that increase in carbonization temperature lead to ~(1-3%), ~85% and ~30%increase in the microcrystallites interlayer spacing, width and stack-height, respectively, indicating that a larger growth of microcrytallite of carbon flakes occurs in the direction parallel to (001) plane or film planar surface. The specific surface area of carbon flakes estimated from the XRD results in decreases from ~4400 to ~3400 m2/g, corresponding to the specific capacitance between ~500 to ~400 F/g, which are well within the range of specific capacitance for typical electrodes carbon for supercapacitor application. The RS results show that the multilayer graphene co-exist with semicrystalline- carbon within the carbon flakes, with the multilayer graphene relative quantities increase with increasing carbonization temperature.

Preparation and structural characterization of turbostratic-carbon/graphene derived from amylose film

In this study, we report the preparation of turbostratic-carbon/graphene from biomass amylose film by carbonization (N2 gas) and activation (CO2 gas) over different temperatures 600, 700, 800, 900, and 1000 °C, respectively. The Raman spectroscopy results of the produced samples show that the values of the ID/IG ratio ranging from 0.75 to 0.99 are comparable to that of the commercial multilayer graphene and KOH treated multilayer graphene. The X-ray diffraction results of the produced samples show that a small decrease in the d002 (∼0.62 %) and d100 (∼0.57 %) values and a larger decrease in Lc (∼8.6 %) and La (∼27.2 %) values occurs as the carbonization and activation temperature increases, indicating that the increase in temperature has an effect on the growth of microcrystallites during carbonization and activation. This study demonstrates the potential of the amylose film to be used as a precursor for producing graphene flakes.

Review of Energy and Power of Supercapacitor Using Carbon Electrodes from Fibers of Oil Palm Fruit Bunches

Energy and power capability of a supercapacitor is important because of its function to provide backup power or pulse current in electronic/electric products or systems. The choice of its electrode materials, typically such as carbon, metal oxide or conducting polymer determines the mechanism of its energy storage process. This short review focuses on the supercapacitors using porous carbon electrode prepared, respectively, from fibers of oil palm empty fruit bunches. The specific energy and specific power of these supercapacitors were analyzed to observe their trend of change with respect to the electrode preparation parameters affecting the porosity, structure, surface chemistry and electrical conductivity of electrodes, and thence influence the energy and power capability of a supercapacitor. This review found that the trend of change in specific energy and specific power was not in favor of the expectation that both the specific energy and specific power should be in increasing trend with a significant progress.

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.

Electric double-layer capacitors with tea waste derived activated carbon electrodes and plastic crystal based flexible gel polymer electrolytes

We report a novel configuration of symmetrical electric double-layer capacitors (EDLCs) comprising a plastic crystalline succinonitrile (SN) based flexible polymer gel electrolyte, incorporated with sodium trifluoromethane sulfonate (NaTf) immobilised in a host polymer poly (vinylidine fluoride-co-hexafluoropropylene) (PVdF-HFP). The cost-effective activated carbon powder possessing a specific surface area (SSA) of ~ 1700 m2g-1 containing a large proportion of meso-porosity has been derived from tea waste to use as supercapacitor electrodes. The high ionic conductivity (~3.6×10-3 S cm-1 at room temperature) and good electrochemical stability render the gel polymer electrolyte film a suitable candidate for the fabrication of EDLCs. The performance of the EDLCs has been tested by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and galvanostatic charge-discharge studies. The performance of the EDLC cell is found to be promising in terms of high values of specific capacitance (~270 F g-1), specific energy (~ 36 Wh kg-1), and power density (~ 33 kW kg-1).