The simple preparation of a hierarchical porous carbon with high surface area for high performance supercapacitors
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Abstract Used tea leaves are utilized for preparation of carbon with high surface area and electrochemical properties. Surface area and pore size of tea leaves derived carbon are controlled by varying the amount of KOH as activating agent. The maximum surface area of 2532 m 2 g −1 is observed, which is much higher than unactivated tea leaves (3.6 m 2 g −1 ). It is observed that the size of the electrolyte ions has a profound effect on the energy storage capacity. The maximum specific capacitance of 292 F g −1 is observed in 3 m KOH electrolyte with outstanding cyclic stability, while the lowest specific capacitance of 246 F g −1 is obtained in 3 m LiOH electrolyte at 2 mV s −1 . The tea leaves derived electrode shows almost 100% capacitance retention up to 5000 cycles of study. The symmetrical supercapacitor device shows a maximum specific capacitance of 0.64 F cm −2 at 1 mA cm −2 and about 95% of specific capacitance is retained after increasing current density to 12 mA cm −2 , confirming the high rate stability of the device. An improvement over 35% in the charge storage capacity is seen when increasing device temperature from 10 to 80 °C. The study suggests that used tea leaves can be used for the fabrication of environment friendly high performance supercapacitor devices at a low cost.
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In this paper, porous carbon nanospheres (PCS) were prepared by carbonization at 1000 ℃ and KOH activation at 750 ℃ of polypyrrole (PPy) nanospheres. Then the post treatment of PCS was carried out by solvothermal reaction with p-Aminothiophenol (PATP) to prepare PATP functionalized PCS with high density (PATP-PCS). The results showed that after functionalization with PATP, low-density porous carbon material turned into high-density functionalized carbon material.The volumetric capacitance of PATP-PCS was up to 183.6 F/cm3 at 0.5 A/g; when the current density increased to 20 A/g, the volumetric capacitance is still 123.14 F/cm3, showing excellent rate performance.After 3 000 cycles of charge and discharge at the current density of 10 A/g, the cycle life is up to 94.7%, indicating a prominent cycle stability. Keywords: functionalized, porous carbon nanospheres, volumetric capacitance, supercapacitors
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Hollow carbon nanofibers with hierarchical porous shells were prepared by NaOH activation of the electrospinning SiCNO fibers, followed by carbonization treatment. By adjusting the carbonization temperature, porous hollow carbon nanofibers with different Brunauer-Emmett-Teller (BET) specific surface areas and total pore volumes are obtained, both of which are explored as electrode materials for supercapacitors. It was found that the obtained products (HCF800) possess the highest BET specific surface area of 2628.10 m2/g and the largest pore volume of 2.32 cm3/g when the carbonized temperature was designed at 800 °C, thus displaying the best supercapacitor performance. The electrochemical results in a three-electrode system show that HCF800 exhibits a high specific capacitance of 330.11 F/g as the discharge current density is 1 A/g and still maintains 65.3% of its original specific capacitance when the current density reaches 20 A/g. Moreover, in a two-electrode system, HCF800 also exhibits an excellent specific capacity of 259.86 F/g at a current density of 1 A/g, marvelous cyclic stability with the specific capacitance retention of 95.3% even after 10,000 cycles, and a large energy density of 12.99 W h/kg at 1.0 A/g. Significantly, the supercapacitor performance of these porous hollow carbon nanofibers is also superior to that of many previously reported carbon materials, which proved them to be worthy candidates for high-performance electrode materials.
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Phenolic resin based activated carbon cloths(ACCs) were prepared by steam activation treatment,and were used as electrodes of supercapacitors.The pore structure and the electrochemical properties of the resultant ACCs were investigated by means of N2 adsorption,AC impedance and constant current discharge techniques.The relationship of pore structure and the activated conditions,as well as the relationship between the pore structure and electrochemical performance in 1M(CH2CH3)3CH3NBF4/PC were discussed in details.Results showed that the BET surface area,average pore width and mesoporous surface area dramatically increased with the increase of activation temperature and/or activation time.It was also found that the specific capacitance of ACCs increased with the increase of BET surface area,especially the specific capacitance of the sample activated under 950℃ for 90min reached 158F·g-1 at current density of 50mA·g-1.Besides,the capacitance retention of ACCs at high current density increased with the increase of mesoporous surface area,of which the capacitance retention(C500/C50) of the sample with the largest mesoporous specific surface area reached 91.1%.IR drop reduced sharply in the pores less than 2nm with the increase of average pore width.
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To design high specific surface area and optimize the pore size distribution of materials, we employ a combination of carbonization and KOH activation to prepare activated carbon derived from ground grain hulls. The resulting carbon material at lower temperature (800, BSAC-A-800) exhibits a porous structure with a high specific surface area of 1037.6 m
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In this paper, hollow-tubular porous carbons were synthesized from abundant biomass Cycas fluff (CF) through simple carbonization followed by an NaHCO3 mild activation process. After activation, the tubular structure of the CF was retained, and a hierarchical structure of micropores, mesopores and macropores was formed. When the optimal mass ratio of NaHCO3/CF is 2, the obtained porous carbon CF-HPC-2 sample has a large specific surface area (SSA) of 516.70 m2 g-1 in Brunauer-Emmett-Teller (BET) tests and a total pore volume of 0.33 cm3 g-1. The C, O, N and S contents of CF-HPC-2 were tested as 91.77 at%, 4.09 at%, 3.54 at%, and 0.6 at%, respectively, by elemental analysis. Remarkably, CF-HPC-2 exhibits a high volume capacitance (349.1 F cm-3 at 1 A g-1) as well as a higher rate capability than other biomass carbon materials (289.1 F cm-3 at 10 A g-1). Additionally, the energy density of the CF-HPC-2 based symmetric supercapacitor in 2 M Na2SO4 electrolyte at 20 kW kg-1 is 27.72 W h kg-1. The particular hollow tubular morphology and activated porous structure determine the excellent electrochemical performance of the material. Hence, this synthetic method provides a new way of storing energy for porous carbon as high volumetric capacitance supercapacitor materials.
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It is a big challenge to improve the energy density of the carbon-based supercapacitors for wide applications. In this work, considering the properties of redox electrolytes, functionalized porous carbon has been synthesized with interconnected pores and oxygen functional groups, which is employed to well hold the redox electrolyte ions. As a result, the functionalized porous carbon shows a high capacitance of 454 F g-1 at a current density of 1 A g-1 and can maintain 88% of the initial capacitance after 10 000 charge-discharge cycles at 10 A g-1. Especially, the as-prepared asymmetric supercapacitor obtains high energy density of 36.9 W h kg-1 at the power density of 225 W kg-1. This new design strategy by coordinating carbon materials with the redox electrolytes will guide the development of high-energy density supercapacitors.
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Facile synthesis of hierarchically porous carbon for supercapacitor derived from water-soluble pitch
Abstract Hierarchical porosity carbons have been synthesized via carbonization and activation using water-soluble pitch as carbon source. By further introducing potassium acetate as an activation agent, the obtained materials have a high specific BET surface area of 1108 m 2 g -1 with N, O and S doping. The effects of different activation temperatures on the pore structure and composition of the carbon were investigated. The obtained carbon samples exhibits a maximum gravimetric capacitance of 208 F g -1 when evaluated as an electrode material in 6 mol L -1 KOH aqueous solution and good rate capability of 69.5% retention at 20 A g -1 . Furthermore, it demonstrates good cyclic stability, showing a high capacitance retention of 96.3% over 10000 charge-discharge cycles at a current density of 2 A g -1 .
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