Exceptional progress has been made with chemical vapor deposition (CVD) of graphene in the past few years. Not only has good monolayer growth of graphene been achieved, but large-area synthesis of graphene sheets has been successful too. However, the polycrystalline nature of CVD graphene is hampering further progress as graphene property degrades due to presence of grain boundaries. This review will cover factors that affect nucleation of graphene and how other scientists sought to obtain large graphene domains. In addition, the limitation of the current research trend will be touched upon as well.
Pitch is an attractive raw material for carbon fiberprecursors due to its low cost stemming from its availability as a residue of coking and petroleum processes. Ford Motor Company reported a carbon fibertarget price of 11.0/kg by using a fast cycle-time manufacturing method with carbon fiberin an inexpensive format, allowing for an average retail price of gasoline of 3.58/gallon. They also recommended the use of carbon fiberwith strength of 1700 MPa, modulus of 170 GPa, and 1.5% elongation. This study introduced a ca. 5.5 μm carbon fiberwith 2000 MPa tensile strength obtained from a precursor through simple distil-lation of petroleum residue. Petroleum pitch based carbon nanofibersprepared via electros-pinning were characterized and potential applications were introduced on the basis of their large specific surface area and relatively high electrical conductivity.
An attempt was made to investigate the effect of the preparation temperature on the electro-capacitive performance of polypyrrole (PPY)/graphene oxide (GO) nanocomposites (PNCs). For this purpose, a series of PNCs were prepared at various temperatures by the cetyltrimeth-ylammonium bromide-assisted dilute-solution polymerization of pyrrole in presence of GO (wt%) ranging from 1.0 to 4.0 with ferric chloride as an oxidant. The formation of the PNCs was ascertained through Fourier-transform infrared spectrometry, X-ray diffraction spectra, scanning electron microscopy and simultaneous thermogravimetric-differential scanning calorimetry. The electrocapacitive performance of the electrodes derived from sulphonated polysulphone-bound PNCs was evaluated through cyclic voltammetry with reference to Ag/AgCl at a scan rate (V/s) ranging from 0.2 and 0.001 in potassium hydroxide (1.0 M). The incorporation of GO into the PPY matrix at a reduced temperature has a pronounced effect on the electrocapacitive performance of PNCs. Under identical scan rates (0.001 V/s), PNCs prepared at 10 ± 1°C render improved specificconductivity (526.33 F/g) and power density (731.19 W/Kg) values compared to those prepared at 30 ± 1°C (217.69 F/g, 279.43 W/Kg). PNCs prepared at 10 ± 1°C rendered a capacitive retention rate of ~96% during the first500 cycles. This indicates the excellent cyclic stability of the PNCs prepared at reduced tempera-tures for supercapacitor applications.
This study highlights a novel method and mechanism for the rapid and effective milling of carbon fibers (CFs) in silicon carbide (SiC) powder, and also the dispersion of CFs in SiC powder. The composite powders were prepared by chopping and exfoliation of CFs, and ball milling of CFs and SiC powder in isopropyl alcohol. A wide range of CFs loading, from 10 to 50 vol%, was studied. The milling of CFs and SiC powder was checked by measuring the average particle size of the composite powders. The dispersivity of CFs in SiC powder was checked through scanning electron microscope. The results show that the usage of exfoliated CF tows resulted in a rapid and effective milling of CFs and SiC powder. The results further show an excellent dispersion of CFs in SiC powder for all CFs loading without any dispersing agent.
This study reports on the influenceof N-butyl-N-methylpyrrolidinium tetrafluoroborat (PYR14BF4) ionic liquid additive on the conducting and interfacial properties of organic solvent based electrolytes against a carbon electrode. We used the mixture of ethylene carbonate/dimethoxyethane (1:1) as an organic solvent electrolyte and tetraethylammo-nium tetrafluoroborate(TEABF4) as a common salt. Using the PYR14BF ionic liquid as additive produced higher ionic conductivity in the electrolyte and lower interface resis-tance between carbon and electrolyte, resulting in improved capacitance. The chemical and electrochemical stability of the electrolyte was measured by ionic conductivity me-ter and linear sweep voltammetry. The electrochemical analysis between electrolyte and carbon electrode was examined by cyclic voltammetry and electrochemical impedance spectroscopy.
A hierarchical pore structured novolac-type phenol based-activated carbon with micropores and mesopores was fabricated. Physical activation using a sacrificialsilicon dioxide (SiO2) template and chemical activation using potassium hydroxide (KOH) were employed to pre-pare these materials. The morphology of the well-developed pore structure was character-ized using field-emissionscanning electron microscopy. The novolac-type phenol-based activated carbon retained hierarchical pores (micropores and mesopores); it exhibited high Brunauer-Emmett-Teller specificsurface areas and hierarchical pore size distributions. The hierarchical pore novolac-type phenol-based activated carbon was used as an electrode in electric double-layer capacitors, and the specificcapacitance and the retained capacitance ratio were measured. The specificcapacitances and the retained capacitance ratio were en-hanced, depending on the SiO2 concentration in the material. This result is attributed to the hierarchical pore structure of the novolac-type phenol-based activated carbon.
Amorphous agglomerates of carbon nanospheres (CNS) with a diameter range of 10-50 nm were synthesized using the solution combustion method. High-resolution transmission elec-tron microscopy (HRTEM) revealed a densely packed high surface area of SP2-hybridized carbon; however, there were no crystalline structural components, as can be seen from the scanning electron microscopy, HRTEM, X-ray diffraction, Raman spectroscopy, and ther-mal gravimetric analyses. Electrochemical and thermo catalytic decomposition study results show that the material can be used as a potential electrode candidate for the fabrication of energy storage devices and also for the production of free hydrogen if such devices are used in a fluidized bed reactor loaded with the as-prepared CNS as the catalyst bed.
The adsorption of volatile organic compounds (VOCs) was carried out using an activated carbon fiber (ACF) filter in an automobile. The adsorption capacities of formaldehyde, toluene, and benzene on an ACF filter were far better than those of a polypropylene (PP) mat filter and combined (PP+activated carbon) mat filter by batch adsorption in a gas bag. In a continuous flow of air containing toluene vapor through an ACF packed bed, the breakpoint time was very long, the length of the unused bed was short, and sharp "S" -type breakthrough curve was plotted soon after breakpoint, showing a narrow mass transfer zone of toluene on the ACF. The adsorption amount of toluene on the ACF filter was proportional to the specific surface area of the ACF; however, the development of mesopores 2-5 nm in size on the ACF was very effective with regard to the adsorption of toluene. The ACF air clarifier filter is strongly recommended to remove VOCs in newly produced automobiles.
Nitrogen-doped microporous carbons were prepared using a polyvinylidene fluoridemelamine mixture. The electrochemical performance of the nitrogen-doped microporous carbons after being subjected to different carbonization conditions was investigated. The nitrogen to carbon ratio and specificsurface area decreased with an increase in the carbon-ization temperature. However, the maximum specificcapacitance of 208 F/g was obtained at a carbonization temperature of 800°C because it produced the highest microporosity.
A filtration-tapingmethod was demonstrated to fabricate carbon nanotube (CNT) emitters. This method shows many good features, including high mechanical adhesion, good electrical contact, low temperature, organic-free, low cost, large size, and suitability for various CNT materials and substrates. These good features promise an advanced fieldemission performance with a turn-on fieldof 0.88 V/mm at a current density of 0.1 mA/cm2, a threshold fieldof 1.98 V/mm at a current density of 1 mA/cm2, and a good stability of over 20 h. The filtratio-taping technique is an effective way to realize low-cost, large-size, and high-performance CNT emitters.