M. Suleman

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.

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.

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).

Preparation and characterization of graphene/turbostratic carbon derived from chitosan film for supercapacitor electrodes

Electrochemical capacitors or supercapacitors are the potential energy storage devices which are known for having higher specific capacitance and specific energy than electrolytic capacitors. Electric double-layer capacitors (EDLCs) also referred as ultracapacitors is a class of supercapacitors that employ different forms of carbon like activated carbon, CNT, graphene etc., as electrodes. The performance of the supercapacitors is determined by its components namely electrolyte, electrode, etc. Carbon electrodes with high surface area and desired pore size distribution are always preferred and which can be tailored by varying the precursor and method of preparation. In recent years, owing to their low cost, ease of synthesis, high stability and conductivity, the activated carbons derived from biomass precursors have been investigated as potential electrode material for the EDLCs. In this report, we present the preparation and characterization of graphene/turbostratic carbon monolith (CM) electrodes from the carbon grains (CGs) obtained by carbonization (under the flow of nitrogen, N2 gas and over a temperature range from 600 °C to 1000 °C) of biomass precursor chitosan film. The procedure to prepare the chitosan film is described elsewhere. The carbon grains are characterized using Raman spectroscopy (RS) and X-ray diffraction (XRD). We expect that the CGs would have the similar characteristics as graphene and would be a potential electrode material for EDLCs application.Electrochemical capacitors or supercapacitors are the potential energy storage devices which are known for having higher specific capacitance and specific energy than electrolytic capacitors. Electric double-layer capacitors (EDLCs) also referred as ultracapacitors is a class of supercapacitors that employ different forms of carbon like activated carbon, CNT, graphene etc., as electrodes. The performance of the supercapacitors is determined by its components namely electrolyte, electrode, etc. Carbon electrodes with high surface area and desired pore size distribution are always preferred and which can be tailored by varying the precursor and method of preparation. In recent years, owing to their low cost, ease of synthesis, high stability and conductivity, the activated carbons derived from biomass precursors have been investigated as potential electrode material for the EDLCs. In this report, we present the preparation and characterization of graphene/turbostratic carbon monolith (CM) electrodes from th...

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 impedance spectroscopy study of carbon electrodes prepared from date pits and fibers of oil palm empty fruit bunches

In this study, we produced pre-carbonized date pits (PDP) and self-adhesive carbon grains (SACGs) from oil palm empty fruit bunches (EFB) by a low temperature (200°C for DP and 280°C for SACGs, respectively) carbonization method followed by KOH treatment to obtain KOH treated PDP (T-PDP) and KOH treated SACGs (T-SACGs). Four sets of green monolith (GMs) denoted as GM-A, GM-B, GM-C and GM-D were prepared respectively from SACGs (100 wt. %), mixture of PDP and SACGs (50:50 wt. %), T-SACGs (100 wt. %), and mixture of T-SACGs and T-PDP (50:50 wt. %), respectively. From these GMs the respective activated carbon monolith (ACMs) electrodes namely ACM-A, ACM-B, ACM-C and ACM-D were prepared via carbonization (N2 carbonization) and activation (CO2 environment). These ACMs electrodes were used to fabricate the corresponding EDLC cells: Cell-A, Cell-B, Cell-C and Cell-D, respectively. The electrochemical impedance spectroscopy tests conducted on the cells found that the Cell-D showed the maximum value of specific ca...