Mohamad Redwani Mohd Jasni

Supercapacitors using binderless activated carbon monoliths electrodes consisting of a graphite additive and pre-carbonized biomass fibers

Varying amounts of graphite powder (0 to 20 wt%) are mixed as an additive with self-adhesive carbon grains, which are produced from pre-carbonized powder derived from the fibers of oil palm empty fruit bunches, a by-product from palm oil mills. The mixtures are treated with KOH and converted into green monoliths (GMs). The GMs are carbonized and activated via a multistep heating profile to produce activated carbon monolith (ACM) electrodes. X-ray diffraction, field emission scanning electron microscopy and nitrogen adsorption-desorption isotherm analysis demonstrate that the addition of graphite influences the structure, microstructure and porosity of the ACM electrode materials. Electrochemical impedance spectroscopy, cyclic voltammetry and galvanostatic chargedischarge studies show that the best frequency response of the electrodes is obtained using 4 wt% of graphite. A tremendous decrease in the equivalent series resistance (~70%) and response time (~87%) leads to an improvement of specific power by 39 % and an 8-fold increase in the maximum operating frequency (from ~0.13 Hz to ~1 Hz). Furthermore, the cells incorporating the electrodes with 4 wt% of graphite retain 50% of their capacitance up to 1 Hz. These findings show that the cheap graphite powder can be a useful additive for preparing supercapacitor electrodes from activated carbon.

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.

Effect of nano-scale characteristics of graphene on electrochemical performance of activated carbon supercapacitor electrodes

Graphene with its typical nano-scale characteristic properties has been widely used as an additive in activated carbon electrodes in order to enhance the performance of the electrodes for their use in high performance supercapacitors. Activated carbon monoliths (ACMs) electrodes have been prepared by carbonization and activation of green monoliths (GMs) of pre-carbonized fibers of oil palm empty fruit bunches or self-adhesive carbon grains (SACGs) and SACGs added with 6 wt% of KOH-treated multi-layer graphene. ACMs electrodes have been assembled in symmetrical supercapacitor cells that employed aqueous KOH electrolyte (6 M). The cells have been tested with cyclic voltammetry, electrochemical impedance spectroscopy and galvanostatic charge discharge methods to investigate the effect of graphene addition on the specific capacitance (Csp), specific energy (E), specific power (P), equivalent series resistance (ESR) and response time (τo) of the supercapacitor cells. The results show that the addition of graph...

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).

Effect of heat-treatment of manganese oxide deposited on stainless steel 316L current collector surface towards carbon based supercapacitor performance

Manganese oxide was deposited on the surface of stainless steel (SS) foil current collector (CC) using a simple immersion method followed by heat-treatment at three different temperatures (70, 200 and 400 °C) for 3 h. The CC deposited with manganese oxide without and with heat treatment were used in symmetrical supercapacitor cells using highly porous activated carbon electrodes and LiCl electrolyte. The heat-treatment changes the structure (from amorphous to crystalline phase) and surface morphology of manganese oxide deposited on the CC surface as evidenced by X-ray diffraction and field emission scanning electron microscopy studies. The electrochemical impedance spectroscopy, cyclic voltammetry and galvanic charge-discharge characterization results of the supercapacitor cells demonstrate that the heat-treatment temperature of 70 o C results in a maximum increase of ~70 % in specific capacitance, ~140 % in specific power and ~280 % in specific energy compared to the cell using CC deposited with manganese oxide at room temperature. Further, a 10-fold decrement in response time (from ~ 14 to ~ 1.4 s) is achieved for a heat-treatment at 70 o C which implies a ten times faster delivery of energy. These results show the superiority of CC deposited with manganese oxide heat-treated at 70 o C over the manganese oxide deposited at other temperatures.

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.