Activated Mesocarbon Microbeads Research Articles

Electrochemical performance of graphene-coated activated mesocarbon microbeads as a supercapacitor electrode.

Hybrid activated carbon/graphene materials are prospective candidates for use as high performance supercapacitor electrode materials, since they have the superior characteristics of high surface area, abundant micro/mesoporous structure due to the presence of activated carbon and good electrical conductivity as a result of the presence of graphene. In this work, the electrochemical performance of facile and low-cost graphene-coated activated mesocarbon microbeads (g-AM) is carefully studied. The results show that g-AM can only be formed at a very high temperature over a long activation time, resulting in the formation of a large pore size and low specific surface area, further resulting in poor electrochemical performance (110 F g−1 at 0.1 A g−1 in 6 M KOH solution). Ball milling for a short time is an effective way to improve the electrochemical performance (191 F g−1 at 0.1 A g−1 in 6 M KOH solution). Moreover, due to the strong resistance to aggregation and good electrical conductivity of graphene flowers, the g-AM had nearly 100% rate capability when increasing the current density from 5 to 50 A g−1. The as-assembled two-electrode symmetric supercapacitor exhibits a high energy and power density (5.28 W h kg−1 at 10 000 W kg−1) in organic LiPF6 electrolyte, due to its better electrical conductivity. It is expected that this type of hybrid structure holds great potential for scalable industrial manufacture as supercapacitor electrodes.

Determination of specific surface of activated mesocarbons by sorption of organic vapors

The determination of specific surface of activated mesocarbons prepared from coal tar pitch by sorption of organic vapors and the operating factors affecting their performances were investigated. Proposed paper deals with alternative experimental method based on weight registration during adsorption of pure vapors of volatile organic compounds VOCs on tested samples. Thermogravimeter TGA-HP50 was used for sorption experiments where activated mesocarbon microbeads were the sorbent and vapors of benzene, toluene, acetone and cyclohexane were used as adsorbate. Primary data were actual weight of the tested sorbent and absolute pressure of organic vapor. Experimental data were fitted by Langmuir model of adsorption isotherm. Specific surface was determined from evaluated parameters. Obtained results were compared with results from standard nitrogen S-BET method. Specific surfaces evaluated from both methods are comparable. The influence of important parameters such as chemical activation, extraction and addition of catalytic agents on activated mesocarbons was studied too. Coal tar pitch as raw material was thermally treated together with Lewis acid (FeCl3). Final solid sorbents were prepared by chemical activation of pyridine-insoluble (PI) matters using potassium hydroxide. Weight ratio of activated agent (potassium hydroxide) to PI matters was 1:5, and temperature of activation was 850 °C. It was found that three samples which were activated had greater specific surface area than the one (B) that was not activated, also as they are appropriate for adsorbing the selected adsorptives.

Preparation of Spherical Sn/SnO2/Porous Carbon Composite Materials as Anode Material for Lithium-Ion Batteries

A novel spherical Sn/SnO2/porous carbon composite anode material was successfully synthesized from activated mesocarbon microbeads (AMCMBs) and SnCl4·5H2O as starting materials by a simple hydrothermal method followed by heat treatment. SnO2 dispersed on AMCMB was partially reduced into metallic Sn favorable for high capacity. The structure, morphology, and electrochemical properties have been studied by x-ray diffraction, scanning electron microscopy, and electrochemical performance test. The results show the porous AMCMB as a supporting matrix surface supports the huge volume expansion and keeps the structural stability of Sn/SnO2 during the insertion/extraction process of lithium ion. The Sn/SnO2/AMCMB sample annealed at 600 °C takes full advantages of the superiorities of porous carbon, SnO2, and metallic Sn and exhibits an excellent cycling performance and rate capability. The specific capacity is 451 mAh g−1 at a current density of 100 mA g−1 after 50 cycles. The Sn/SnO2/AMCMB composite has a large potential application as a high-performance anode material for the lithium-ion batteries.

Facile synthesis of α-MnO2 nanowires/spherical activated carbon composite for supercapacitor application in aqueous neutral electrolyte

One-dimensional (1-D) α-MnO2 nanowires/spherical activated carbon composite, namely the α-MnO2 nanowires growth onto the surface of activated mesocarbon microbeads (a-MCMB), has been prepared by using a simple hydrothermal synthesis method. The α-MnO2 nanowires are found to be less than 50 nm in diameter and have a characteristic length up to 2 μm. The novel α-MnO2 nanowires/a-MCMB composite when used for supercapacitor electrode material exhibits a specific capacitance (C s) of 357 F g−1 in 1 M Na2SO4 aqueous neutral solution. The C s based on the α-MnO2 nanowires is estimated to be as high as 890 F g−1. A good cycling stability of this composite material is also demonstrated for supercapacitor application.

Supercapacitive behaviors of activated mesocarbon microbeads coated with polyaniline

The polyaniline/activated mesocarbon microbeads (PANI/ACMB) composites are prepared by in situ chemical oxidation polymerization. Fourier infrared spectroscopy (FTIR), scanning electron microscope (SEM) and transmission electron microscope (TEM) have been utilized to characterize the structure and morphology of PANI/ACMB composites. It has been found that PANI is uniformly deposited on the surface of the ACMB to form the leechee-like morphology. The supercapacitive behaviors of the PANI/ACMB composites are investigated with cyclic voltammetry (CV), galvanostatic charge/discharge and cycle life measurements. The results obtained from cyclic voltammograms show that the composites have a maximum specific capacitance of 433.75 F g−1. Moreover, the electrochemical performance of the coin supercapacitor used PANI/ACMB composites as electrode active material represents both high specific capacitance and excellent cycle stability, indicating that the PANI/ACMB composites will be a kind of potential electrode active materials with excellent specific capacitance and enhanced cycle life for application in high performance supercapacitors.

Capacitance behavior of KOH activated mesocarbon microbeads in different aqueous electrolytes

A series of microporous carbons with wide scope of porosity development (surface area SDFT=1200–2460m2g−1, micropore volume VDR=0.43–1.2cm3g−1, average micropore width L0=0.9–1.5nm) was prepared by KOH activation of coal-tar pitch derived mesocarbon microbeads (MCMB). The activated MCMB were tested as an electrode material of capacitor in two-electrode system operating in various aqueous electrolytic solutions using galvanostatic, voltammetry and impedance spectroscopy techniques. The study shows that the capability of charge accumulation in electric double layer is controlled primarily by electrolyte properties. Independent of porosity development the capacitance of activated MCMB decreases in the order: 6molL−1 KOH, 1molL−1 H2SO4, 4.5molL−1 KCl, 2molL−1 KNO3 and 0.5molL−1 Na2SO4. The sequence corresponds basically to the solution conductivity. Activated MCMB of moderate surface area (SDFT=1450–1650m2g−1) and relatively narrow micropores (L0=0.9–1.05nm), which were produced from MCMB carbonized at 600–700°C by activation at 700°C using 2:1 KOH/MCMB ratio, seem to be most promising electrode material. They demonstrate superior both the gravimetric and volumetric capacitances (in 6molL−1 KOH 280–300Fg−1 and above 160Fcm−3, respectively) and a good performance at the current density up to 20Ag−1. Apart from the suitable pore size distribution, the specific particle morphology and a high extent of orientation of constituting defective graphene layers seem to contribute to the superior capacitance properties of activated MCMB compared to ordinary activated carbons.

Manganese dioxide-coated activated mesocarbon microbeads for supercapacitors in organic electrolyte

MnO 2 nanostructures are successfully coated onto activated mesocarbon microbeads (a-MCMB) by a simple chemical coprecipitation method. The structure and morphology of the as-prepared a-MCMB/MnO 2 composite were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The results showed that the nano-MnO 2 is of short fiber-like structures with about 200 nm in length and 60 nm in width. A growing mechanism was also proposed for the nano-MnO 2 on the surface of a-MCMB. This novel composite was used as an electrode material for supercapacitors. Electrochemical measurements showed that the composite electrode has a maximum specific capacitance of 183 F g −1 in 1 M LiPF 6 (EC + DMC) organic electrolyte with an operating voltage up to 3.0 V. The specific capacitance base on the MnO 2 is estimated to be as high as 475 F g −1, corresponding to a considerable energy density of 106 wh kg −1.

Facile synthesis of activated carbon/carbon nanotubes compound for supercapacitor application

A large number of carbon nanotubes (CNTs) have been produced commingled in activated mesocarbon microbeads (AMCMBs) activated by potassium hydroxide in a stainless steel container at 900 °C, in which an especial buried-protection method with petroleum coke powders was used to protecting the product during activation. The CNTs were found to be about 50 nm in diameter and characteristic length more than 10 μm. In addition, the AMCMBs/CNTs compound when used for electrode material of electrochemical double-layer capacitors exhibited a specific capacitance of 243 F g −1 in 6 M KOH aqueous solution.

Separation of Hydrogen and Carbon Dioxide in Activated Mesocarbon Microbeads with High Specific Surface

On the basis of experimental data,double-Langmuir(DL)model was used to investigate the adsorption and separation of hydrogen and carbon dioxide in activated mesocarbon microbeads with high specific surface.Pure and binary adsorption isotherms of carbon dioxide and hydrogen(mole ratio is 1:9)in activated mesocarbon microbeads were measured using the high-precision intelligent gravimetric analyzer at temperature of 298,273 and 268 K,and the pressure ranging from 0 to 1.8 MPa.In order to get adsorption amount of the single component of mixture gas,the DL model and the ideal adsorbed solution theory(IAST)were combined.The combined method can be applied to carbon dioxide and hydrogen binary systems perfectly.The calculated results indicated that the selectivity of carbon dioxide can reach 73.4 at 268 K and 1.7 MPa,which suggests that the activated mesocarbon microbead was an excellent candidate for the removal of carbon dioxide in hydrogen/carbon dioxide mixtures.

Adsorption separation of CH4/CO2 on mesocarbon microbeads: Experiment and modeling

AbstractA novel meso‐porous material, the activated mesocarbon microbeads (a‐MCMBs) prepared by this group, is used for the separation of the CH4/CO2 mixture by experiment and modeling. First, the adsorption isotherm of nitrogen at 77K was measured to characterize the a‐MCMBs by the IGA‐003 gravimetric analyzer. Then, the adsorption experiments of pure CH4 and CO2 at ambient temperature of 298.15 K were carried out. A CH4/CO2 mixture is prepared at the mole ratio of 85:15, corresponding to the gas composition of the Ya‐13 gas field in the Qiongdongnan basin, China. Although only the total adsorption amount of the gas mixture on a‐MCMBs is available, the single adsorption amount for CH4 and CO2, also including the selectivity of CO2 over CH4, can be obtained by the Zhou, Gasem, and Robinson Equation of State (ZGR EOS). Finally, the adsorption behavior over a wide range of variables was predicted by the ZGR EOS method. The predicted greatest selectivity of CO2 over CH4 is 3.70 at 3.0 MPa, 258.15 K for the feed gas mole composition of CH4:CO2 = 40:60. Our results demonstrate that a‐MCMBs is not only suitable for CH4 storage, but also a promising adsorbent for separation of CH4/CO2. © 2005 American Institute of Chemical Engineers AIChE J, 2006

Adsorption of Methane and Hydrogen on Mesocarbon Microbeads by Experiment and Molecular Simulation

The activated mesocarbon microbeads (a-MCMBs) with high BET specific surface area of 3180m2/g are prepared. Experimental characterization of a-MCMBs is carried out in terms of the adsorption isotherm of nitrogen at 77 K by the ASAP-2010 apparatus. Then, methane and hydrogen adsorption isotherms on a-MCMBs are measured by the IGA-003 gravimetric analyzer at 298 K and 77 K. The pores of a-MCMBs are described as slit-shaped with a pore size distribution (PSD). The PSD is determined by a combined method of grand canonical Monte Carlo (GCMC) simulation and statistics integral equation (SIE) from the experimental isotherm of nitrogen on a-MCMBs. In GCMC simulation, methane and hydrogen molecules are modeled as the Lennard-Jones spherical molecules, and the well-known Steele's 10-4-3 potential is used to represent the interaction between the fluid molecule and the solid wall. Good agreement between simulated and experimental data indicates that our model represents well the mechanism of adsorption on a-MCMBs. Th...

04/00192 Treatment of fly ash-based additive to increase compressive strength of cement binder: Lakshmanan, V. et al. U.S. Pat. Appl. Publ. US 2003 79,656 (Cl 106–705; C04B18/06), 1 May 2003, US Appl. PV299,644

In this study, activated mesocarbon microbeads (AMCMBs) with high mesopore content were prepared from the chemical activation of mesocarbon microbeads (MCMBs) with KOH. The resulting activated mesocarbon microbeads possess well-developed pore structure. The maximum value of the total pore volume is 2.45 cm3/g, and BET surface area can reach 3182 m2/g. Especially, the resulting mesoporous activated microbeads also have mesopore content ranging from 56.1% to 65.7%. It can be seen from the isotherms of N2 at −196 °C that the resulting activated mesocarbon microbeads have high adsorption capacity.

04/00184 Preparation of activated mesocarbon microbeads with high mesopore content: Shen, Z. and Xue, R. Fuel Processing Technology, 2003, 84, (1–3), 95–103

04/00184 Preparation of activated mesocarbon microbeads with high mesopore content: Shen, Z. and Xue, R. Fuel Processing Technology, 2003, 84, (1–3), 95–103

Preparation of activated mesocarbon microbeads with high mesopore content

In this study, activated mesocarbon microbeads (AMCMBs) with high mesopore content were prepared from the chemical activation of mesocarbon microbeads (MCMBs) with KOH. The resulting activated mesocarbon microbeads possess well-developed pore structure. The maximum value of the total pore volume is 2.45 cm 3/g, and BET surface area can reach 3182 m 2/g. Especially, the resulting mesoporous activated microbeads also have mesopore content ranging from 56.1% to 65.7%. It can be seen from the isotherms of N 2 at −196 °C that the resulting activated mesocarbon microbeads have high adsorption capacity.

Anomalous Magnetism of Activated Carbon Having Ultra High Surface Area

The brief explanations on the relationship between the atomic structure and magnetism of various carbon materials such as graphite, fullerene, nanotube, and amorphous carbon were given in order to show the characteristic structure and magnetism of activated mesocarbon microbeads (a-MCMB). a-MCMB which has a greater surface area than 2630m2·g-1 has a highly isolated-nanographitic structure. This a-MCMB shows an anomalous random magnetism having a long relaxation time.

Surface and physical properties of microporous carbon spheres

The surface area of activated mesocarbon microbeads (activated MCMBs) was determined by N 2 adsorption using the subtracting pore effect (SPE) method. The microcrystalline graphitic structure of activated MCMBs was determined by X-ray diffraction. Electron spin resonance (ESR) spectra and magnetic susceptibility were measured for analysis of structure and magnetic properties. Spin concentration and spin-lattice relaxation time ( T 1) were determined from ESR data. The spin concentration of activated MCMB increased with the increase of surface area. The higher the surface area of activated MCMB, the longer the T 1. The longer T 1 indicates that micrographitic units of activated MCMB of higher surface area should be more isolated. A single electron spin was presumed to be situated on each micrographitic unit. The isolated spin system gave a random magnetism of a long magnetic relaxation (>3000 s).