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2015, 30(1): .

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Research progress on fibrous carbon materials as anode materials for lithium ion batteries

NAN Ding, HUANG Zheng-hong, KANG Fei-yu, SHEN Wan-ci

2015, 30(1): 1-11.

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Fibrous carbon materials have a variety of dimensions and structures. However, these materials were earlier restricted for use as anode materials for lithium ion batteries due to their cost and performance. With the development of nanotechnology, some modified and new forms of carbon fibers have emerged, which show good performance as anode materials. This paper reviews recent domestic and foreign research progress on fibrous carbon materials as anode materials. The electrochemical performance and prospective use of graphite fibers, carbon fibers and carbon nanofibers for this purpose are summarized. Research has ranged from non-graphitized to graphitized carbon fibers, from micron to nanometer diameter, and has focused on the parameters of their preparation to the design of their microstructure. Fibrous carbon materials are likely to be important alternatives for carbon anode materials in the future based on their high capacity, high rate capability, low cost and ease of industrialization.

Fuels for direct carbon fuel cells: present status and development prospects

LIU Guo-yang, ZHANG Ya-ting, CAI Jiang-tao, ZHANG Xiao-qian, QIU Jie-shan

2015, 30(1): 12-18.

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The direct carbon fuel cell (DCFC) has been considered an efficient way to mitigate the energy crisis and environmental pollution issues, owing to its high energy conversion efficiency, low pollution, and abundant and readily available resources, but its performance is closely related to the fuel used. We give a brief introduction to the development of DCFCs and a review of the current status of DCFC fuels, with an emphasis on the impact of different carbonaceous materials, such asgraphite, coal, activated carbon, solid waste, and cokeon DCFC performance. We also systematically analyze the relation between the electrochemical reaction activity of the fuels and their characteristics. For carbonaceous fuels, defects in the crystal structure and surface oxygen functional groups can promote the anodic electrochemical reaction, and their wettability by the electrolyte. Their pore structure, conductivity and particle size can affect mass transfer and charge transfer in the anodic electrochemical reaction. We discuss the function of anodic catalysts in the DCFC, which accelerate the conversion of carbon from solid to gas and improve the anodic electrochemical reaction rate. Based on the current research on DCFC fuels, we forecast development trends and key issues relating to DCFC fuels.

Transformation of carbon black into carbon nano-beads and nanotubes: the effect of catalysts

Vijayshankar Asokan, Dorte Nørgaard Madsen, Pawel Kosinski, Velaug Myrseth

2015, 30(1): 19-29. doi: 10.1016/S1872-5805(15)60172-X

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Structural transformation of carbon black (CB) into carbon nano-beads and nanotubes was achieved at 1 000 ℃ using ferrocene and nickelocene as catalyst precursors using a simple and single step chemical vapor deposition method. The samples were characterized by XRD, SEM, TEM, HR-TEM and Raman spectroscopy. Results indicate that different morphological and high quality nano carbon structures were obtained using different weight ratios of catalyst to precursor. The use of bimetallic catalysts provides many different morphologies and a higher degree of crystal order of the carbon nanostructures than the use of mono-metallic catalysts. The nanotubes were mostly filled with metal nanoparticles and the degree of metal-filling is dependent on the weight ratio of catalyst precursor to CB. Metal-filled multi-walled carbon nano-bead structures with a high degree of crystalline order are also obtained at weight ratios of CB:ferrocene:nickelocene of 1:2:2.

Self-assembled graphene monoliths: properties, structures and their pH-dependent self-assembly behavior

WANG Gang, JIA Li-tao, HOU Bo, LI De-bao, WANG Jun-gang, SUN Yu-han

2015, 30(1): 30-40. doi: 10.1016/S1872-5805(15)60173-1

Abstract(1204)

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Fabricating self-supporting, three dimensional graphene macroscopic structures from two dimensional graphene sheets by self-assembly has been an intriguing subject in exploring the performance of graphene structures for practical advanced applications. Monolithic graphene hydrogels (GHs) with quite good mechanical properties and excellent resilience were self-assembled from graphene oxide (GO) dispersions under hydrothermal conditions by changing the pH value. The structure-property relationships and the self-assembly behavior of GHs were investigated. It was found that the formation of GHs was pH-dependent. The charge state of carboxyl groups on the graphene was the key factor that influenced the balance of attraction and repulsion interactions of the GO and consequently determined the self-assembly behavior. Both the graphene molecular structure and colloidal interactions were correlated with the unique self-assembly behavior, which can be used to design graphene arrangements with various structures, functions and mechanical properties. This method is superior to the conventional method that adjusts the concentration and reduction time of the GO dispersion.

A simple method for the reduction of graphene oxide by sodium borohydride with CaCl₂ as a catalyst

YANG Zhen-zhen, ZHENG Qing-bin, QIU Han-xun, LI Jing, YANG Jun-he

2015, 30(1): 41-47. doi: 10.1016/S1872-5805(15)60174-3

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Graphene oxide (GO) prepared by a modified Hummers method was reduced by NaBH₄ at room temperature for 12 h in a 0.5 mg/mL GO water suspension to obtain reduced GO (RGO), using CaCl₂ as a catalyst. The GO and RGO were characterized by XPS, FT-IR, UV-Vis and electrical resistivity measurements. Results show that CaCl₂ improves the reduction ability of NaBH₄ for oxygen-containing functional groups on the GO. After reduction, the C/O atomic ratio increased, most of the oxygen-containing functional groups were eliminated, and the electrical resistance decreased significantly. The highest C/O atomic ratio was 5.38 and the lowest electrical resistance of RGO was 18.6 kΩ/sq, the latter being about two orders of magnitudes lower than the RGO prepared without CaCl₂. This reduction method opens a possibility of reducing GO under ambient conditions without using a toxic/corrosive reducing agent and an organic solvent.

Effect of thermal reduction temperature on the electrochemical performance of reduced graphene oxide/MnO₂ composites

WANG Ling-yun, WANG Yong, ZHANG Hai-xia, WANG Xiao-min

2015, 30(1): 48-53. doi: 10.1016/S1872-5805(15)60175-5

Abstract(959)

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Thermally reduced graphene oxide (RGO)/MnO₂ composites were prepared by the thermal reduction of graphene oxide (GO)/MnO₂ composites. The structure, electrical conductivity and specific capacitance of the composites before and after thermal reduction were investigated by SEM, XRD, FT-IR,the four-pointprobe method and cyclic voltammetry. Results showed that the GO and RGO significantly decreased the agglomeration of MnO₂. The RGO/MnO₂ composites had higher specific capacitances than pure MnO₂ or GO/MnO₂ composites. A RGO/MnO₂ composite reduced at 600 ℃ had the highest specific capacitance of 321 F·g^-1 and good stability upon cycling. The presence of an optimum reduction temperature could be accounted for by the fact that the thermal reduction decreased the amount of oxygen-containing functional groups that contribute to pseudocapacitance in GO and increased its electrical conductivity which favors a capacitance increase.

Synthesis of carbon nanofiber monoliths by chemical vapor deposition

GE Xiang, WU Xiao-long, WANG Ji-tong, LONG Dong-hui, QIAO Wen-ming, LING Li-cheng

2015, 30(1): 54-62.

Abstract(1043)

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Carbon nanofiber (CNF) monoliths with excellent properties were prepared by catalytic chemical vapor deposition, using ethylene (C₂H₄) and a non-supported Cu-Ni alloy as carbon source and catalyst, respectively. The structure, mechanical properties, and specific surface area of the CNF monoliths were characterized for various preparation conditions. The formation of CNF monoliths mainly depended on the Cu/Ni ratio, growth temperature and time. A CNF monolith synthesized at 580℃ for 3 h from a Cu-Ni catalyst with a Cu/Ni mass ratio of 0.25 exhibited a bulk density of 0.28 g/cm³, a compressive elastic modulus of 1.7 kPa, and a specific surface area of 117 m²/g. SEM images of the CNF monoliths in the initial growth stage further indicated that they were composed of thick octopus-like nanofibers and thin nanofibers that were interwoven with each other to form a three dimensional CNF network and finally the CNF monolith.

Preparation and characterization of large diameter pitch based carbon fiber/ABS resin composites with high thermal conductivities

YI Jing, YUAN Guan-ming, LI Xuan-ke, DU Hong-da, DONG Zhi-jun, LI Bao-liu, LIN Jian-feng

2015, 30(1): 63-70.

Abstract(906)

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Parallel, stretched and evenly arranged mesophase pitch based graphitized carbon fibers with diameters of 50-53 μm were coated with different amounts of acrylonitrile butadiene styrene (ABS) resin, and hot-pressed to produce carbon fiber/ABS resin composites. The morphology, optical texture and crystal structure of the carbon fibers and their composites were characterized by scanning electron microscopy, polarized light microscopy and X-ray diffraction. The influence of the graphitization temperature and fiber content on the thermal conductivity of the composites was investigated. The thermal diffusivity and thermal conductivity of the composites along both fiber axial and radial directions showed an obvious difference, owing to the high orientation of the graphite crystals along the axial direction of the carbon fibers. The thermal diffusivity of the composites along the carbon fiber axial direction increased both with the graphitization temperature and fiber content. The composite with 54 vol.% carbon fibers graphitized at 2 900 ℃ showed the highest thermal conductivity.

Adsorption of low-concentration methylene blue onto a palygorskite/carbon composite

WU Xue-ping, XU Yan-qing, ZHANG Xian-long, WU Yu-cheng, GAO Peng

2015, 30(1): 71-78. doi: 10.1016/S1872-5805(15)60176-7

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A palygorskite/carbon composite was prepared through hydrothermal treatment of palygorskite and cellulose, and its adsorption behavior for methylene blue (MB) was investigated. The effect of adsorption conditions on the capacity and kinetics was also investigated. The adsorption kinetics of MB onto the composite is best described by a pseudo-second-order equation. The adsorption isotherms conform to the Langmuir isothermal adsorption equation. The adsorption thermodynamic parameters calculated from the isotherms indicate that the adsorption of MB on the composite is endothermic.

Fluorinated graphene as a cathode material for high performance primary lithium ion batteries

XU Yao, ZHAN Liang, WANG Yun, WANG Yan-li, SHI Yun-hai

2015, 30(1): 79-85. doi: 10.1016/S1872-5805(15)60177-9

Abstract(1209)

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A free-standing fluorinated graphene (F-graphene) was fabricated by the simple liquid exfoliation of a fluorinated graphite (F-graphite) in a 2-propanol/water mixture, and was used as the cathode material of primary lithium ion batteries. As-prepared F-grapheneh as a very high fluorine content (49.7 at%), and an amorphous-like two-dimensional nanostructure. These features facilitate the rapid diffusion of lithium ions during discharging. The F-graphene exhibits better electrochemical performance, especially, a higher specific power density than the F-graphite.

Microwave-assisted preparation of peanut shell-based activated carbons and their use in electrochemical capacitors

WU Ming-bo, LI Ru-chun, HE Xiao-jun, ZHANG He-bao, SUI Wu-bin, TAN Ming-hui

2015, 30(1): 86-91. doi: 10.1016/S1872-5805(15)60178-0

Abstract(1161)

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Activated carbons (ACs) were prepared from peanut shells by KOH activation under microwave heating and were used as electrode materials for electrochemical capacitors (ECs). The pore structure of the ACs was characterized by nitrogen adsorption andthe electrochemical performance by galvanostatic charge-discharge and cyclic voltammetry. Results show that the ACs' specific surface area, total pore volume, specific capacitance, as well as energy density are maximized using anactivation time from 6 to 10 min or KOH/peanut shell mass ratio from 0.6 to 2.0 under otherwise identical conditions. When the KOH/peanut shell mass ratio was 1.0, microwave power was 600 W and activation time was 8 min, the specific surface area of the resulting AC was 1 277 m²/g and its energy density was 8.38 Wh/kg after 1 000 cycles. The KOH activation of peanut shells with microwave heating is an efficient approach for the rapid preparation of low cost ACs for ECs.

Properties of silicon carbide-reinforced graphite composites prepared by a reactive sintering method

HAN Yong-jun, LI Qing-bin, YAN Qing-zhi, TANG Rui

2015, 30(1): 92-96.

Abstract(1050)

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Silicon carbide-reinforced graphite composites were prepared by hot-pressing mixtures of flake graphite and Si powder with various mass ratios under vacuum. The microstructure and phase compositions were characterized by SEM and XRD. Results indicated that SiC, resulting from the reaction between graphite and silicon, was uniformly dispersed in the graphite matrix. The bend strength of the composites increased from 112 to 206 MPa with increasing silicon content from 28.06 to 37.94 mass%. The oxidation resistance of the composites increased with their silicon content. The coefficient of friction of the composites remainedat a low constant value of about 0.1 when the Si content was below 31.46 mass%.

2015 Vol. 30, No. 1

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