Synthesis of hollow carbon nanoshells and their application for supercapacitors

Sosunov A.V., Spivak L.V.

The irradiation of metallic films by a nanosecond pulsed laser leads to a self-assembly of nanoparticle arrays. This method has been used to prepare bimetallic Au/Co nanoparticles on a SiO2 substrate. The microstructure and morphology of the bimetallic nanoparticles have been investigated using scanning electron microscopy and transmission electron microscopy. It has been shown that the bimetallic nanoparticles have a hemispherical shape with a single-crystal structure and an average size of ~50 nm. The magnetic properties of these nanoparticles have been examined using a vibrating-sample magnetometer in the transverse and longitudinal directions. It has been found that the direction of the magnetization of the bimetallic nanoparticles lies in the plane of the substrate, and the coercive forces in the transverse and longitudinal directions differ by 25%. The use of the vibrating-sample magnetometer method makes it possible to investigate the differences in the magnetic saturations and the coercive forces of an array of bimetallic nanoparticles on a large surface area. The performed investigations have demonstrated that the anisotropic nanomagnetic materials with the desired magnetic orientation can be easily and quickly prepared by means of thermal laser treatment.

Zhao R., Afaneh T., Dharmasena R., Jasinski J., Sumanasekera G., Henner V.

Here we report in-situ monitoring of electrical transport properties of graphene subjected to sequential and controlled nitrogen plasma doping. The nitrogen is presumed to be incorporated in to the carbon lattice of graphene by making covalent bonding as observed by the swinging of the sign of the thermopower from (initial) positive to (eventual) negative. Electrical transport properties for nitrogen-doped graphene are believed to be governed by the enhanced scattering due to nitrogen dopants and presence of localized states in the conduction band induced by doping. Our results are well supported by Raman and XPS results.

Smith S.C., Rodrigues D.F.

In recent years, significant discoveries related to antimicrobial and adsorption properties of carbon-based nanomaterials have led to new avenues for removal of various biological and organic/inorganic contaminants in drinking water. Furthermore, progress in the synthesis of multifunctional nanocomposites paves the way for their application in advanced water treatment system design. This review article describes and compares the adsorptive and antimicrobial properties of four common classes of carbon nanomaterials: single- and multi-walled carbon nanotubes, graphene, and graphene oxide, as well as some of their most important polymeric and metallic nanocomposites. Barriers for application of these nanomaterials in sustainable water treatment are also addressed.

Xu B., Zheng D., Jia M., Liu H., Cao G., Qiao N., Wei Y., Yang Y.

Nanostructured carbon with different morphologies are easily prepared by a chemical vapor deposition (CVD) process using nano-CaO as template and toluene as carbon precursor and followed by template removal with diluted hydrochloric acid. During the CVD process, the toluene are pyrolyzed to generate carbon atoms and then deposit on the surface of nano-CaO particles. With a CVD growth time less than 10 min, as the surface of the nano-CaO particles are only partly coated with a few layers of carbon atoms, the obtained carbon are small, thin nanosheets with a maximum surface area of 612 m2 g−1. As the CVD growth time prolonged to over 15 min, the pyrolyzed carbon atoms will coat the whole surface of the nano-CaO particles, yielding carbon nanocages with a maximum pore volume as high as 2.618 cm3 g−1 after template removal.

Staaf L.G., Lundgren P., Enoksson P.

In this paper we argue that supercapacitors are the best choice for energy storage in an intelligent wireless sensor system. Furthermore we present recent research on carbon allotropes used as electrode. To compare these materials we introduce a theoretical model to estimate the maximum surface area and maximum capacitance obtainable for carbon electrodes. The purpose of the model is to elucidate what material features are crucial for obtaining a higher energy density in electrochemical double layer capacitors which will particularly benefit energy storage in wireless intelligent sensor systems since a supercapacitor will deliver a higher energy density over time and will have a longer lifespan than a battery. The result of the comparison is that composite materials especially nitrogen-doped graphene nanosheets show great promise with their high capacitance compared to other carbon allotropes.

Wang W., Yuan D.

Four nanoporous carbons prepared by direct carbonization of non-permanent highly porous MOF [Zn3(BTC)2·(H2O)3]n without any additional carbon precursors. The carbonization temperature plays an important role in the pore structures of the resultant carbons. The Brunauer-Emmett-Teller (BET) surface areas of four carbon materials vary from 464 to 1671 m2 g−1 for different carbonization temperature. All the four carbon materials showed a mesoporous structure centered at ca. 3 nm, high surface area and good physicochemical stability. Hydrogen, methane and carbon dioxide sorption measurements indicated that the C1000 has good gas uptake capabilities. The excess H2 uptake at 77 K and 17.9 bar can reach 32.9 mg g−1 and the total uptake is high to 45 mg g−1. Meanwhile, at 95 bar, the total CH4 uptake can reach as high as 208 mg g−1. Moreover the ideal adsorbed solution theory (IAST) prediction exhibited exceptionally high adsorption selectivity for CO2/CH4 in an equimolar mixture at 298 K and 1 bar (Sads = 27) which is significantly higher than that of some porous materials in the similar condition.

Wang X.X., Tan Z.H., Zeng M., Wang J.N.

Low durability is the major challenge hindering the large-scale implementation of proton exchange membrane fuel cell (PEMFC) technology, and corrosion of carbon support materials of current catalysts is the main cause. Here, we describe the finding of remarkably high durability with the use of a novel support material. This material is based on hollow carbon nanocages developed with a high degree of graphitization and concurrent nitrogen doping for oxidation resistance enhancement, uniform deposition of fine Pt particles, and strong Pt-support interaction. Accelerated degradation testing shows that such designed catalyst possesses a superior electrochemical activity and long-term stability for both hydrogen oxidation and oxygen reduction relative to industry benchmarks of current catalysts. Further testing under conditions of practical fuel cell operation reveals almost no degradation over long-term cycling. Such a catalyst of high activity, particularly, high durability, opens the door for the next-generation PEMFC for “real world” application.

Podila R., Rao R., Tsuchikawa R., Ishigami M., Rao A.M.

Here we examine the effects of folding and scrolling on the Raman spectra of mechanically exfoliated single- and bilayer graphene prepared on SiO(2) substrates. We find that incommensurate folding in bilayer graphene results in a shift of the second-order G' band frequency, similar to that observed in folded single-layer graphene due to fold-induced changes in the phonon/electronic energy dispersion. Importantly, we show that the contrasting Raman shifts reported for the G' band frequency in folded graphene can be rationalized by taking into account the relative strength of fold-induced electron/phonon renormalization. More interestingly, we find that curvature in scrolled graphene lifts the degeneracy of the G band and results in a splitting of the G band and the appearance of low-frequency radial breathing-like (RBLM) modes. This study highlights a variety of Raman signatures for fold-induced and curvature-induced graphene and sets the stage for further theoretical and experimental studies of these novel structures.

Li G., Xu L., Hao Q., Wang M., Qian Y.

Carbon nanocages (CNCs) with diameters of about 200∼500 nm have been synthesized by a simple method. The electrochemical properties of the CNCs as anode materials were evaluated by discharge/charge measurement and electrochemical impedance spectroscopy. Results showed that the CNCs displayed excellent cycling performance and good rate capability with no noticeable capacity fading up to 50 cycles at current densities of 100, 300 and 500 mA g−1. Their electrochemical properties were significantly improved after annealing treatment of the CNCs at 600 °C. For example, the CNCs(2)-annealed exhibited much better electrochemical performance with a high reversible capacity of 520 mAh g−1 after 50 cycles at current density of 100 mA g−1. A discharge capacity of 380 mAh g−1 can be obtained after 50 cycles at high current density of 500 mA g−1. The results of the Raman, thermal gravimetric and electrochemical impedance analysis indicated that the graphitization degree, electronic conductivity and charge-transfer rate of the CNCs have been improved after annealing treatment.

Xie K., Qin X., Wang X., Wang Y., Tao H., Wu Q., Yang L., Hu Z.

Supercapacitor electrode materials: Carbon nanocages are conveniently produced by an in situ MgO template method and demonstrate high specific capacitance over a wide range of charging-discharging rates with high stability, superior to the most carbonaceous supercapacitor electrode materials to date. The large specific surface area, good mesoporosity, and regular structure are responsible for the excellent performance.

Li G., Yu H., Xu L., Ma Q., Chen C., Hao Q., Qian Y.

Carbon nanocages (CNCs) have been synthesized through a simple approach using different alcohols and ferrous oxalate as reactants at 550 °C for 12 h in a sealed autoclave. The lengths of the sides of the CNCs are about 200-350 nm and the wall thicknesses are about 10-15 nm. The formation mechanism of the CNCs is also discussed, based on the experimental results. These CNCs show excellent removal efficiency for phenolic compounds, ammonia, and total particulate matter from cigarette smoke. The adsorption capability of CNCs prepared from ethanol is much higher than that of other samples. For example, the efficiency of 5 mg CNCs (ethanol) for removing the six phenolic compounds p-dihydroxybenzene, m-dihydroxybenzene, o-dihydroxybenzene, phenol, m-cresol, and o-cresol can reach 57.31%, 62.25%, 65.58%, 75.95%, 54.34% and 59.43%, respectively, while that of the commercial activated carbon (5 mg) can only reach 29.02%, 33.93%, 35.00%, 36.00%, 20.33% and 36.19%, respectively, under the same conditions.

Teng S.J., Wang J.N., Wang X.X.

Carbon nanocages (CNCs) with a hollow core and a thin wall of a few graphitic layers have a wide range of applications. However, the preparation of such a material remains a great challenge. In this study, we report the preparation of thin-walled CNCs through the pyrolysis of a mixture composed of pyridine and liquid iron pentacarbonyl, subsequent heat treatment in the presence of NH4Cl at a low temperature, and finally washing and filtering in water. The finding that pyridine is completely mutually soluble with liquid iron pentacarbonyl in any proportion stands out to be a crucial advantage for reducing the thickness of the graphitic wall formed on a metal core. To obtain hollow CNCs, heat-treatment proves to be simple and effective in removing the metal core and, more importantly, maintaining the thin graphitic wall when compared with conventional boiling in a strong oxidant, such as HNO3. The thin-walled hollow CNCs are demonstrated to be suitable nanocontainers for encapsulating iodine, as iodine can easily get into and out of the CNCs when it is heated at a relatively low temperature. Considering the large internal space and thin graphitic wall, the hollow CNCs could be widely used in many fields, such as biology, medicine and chemistry.

Miller J.R., Outlaw R.A., Holloway B.C.

Extending the Capability of Supercapacitors Supercapacitors have porous electrodes that can store more charge per volume in electrical double layers than conventional parallel plate capacitors. However, the porous electrodes cause poor performance in filter circuits that eliminate residual alternating current ripple from rectified direct current. Miller et al. (p. 1637 ) fabricated electrodes with a high surface area for ionic adsorption by growing graphene sheets in the vertical direction off a metal surface. Such capacitors may be able to perform the same filtering tasks as conventional capacitors but take up less space.

Zheng M., Liu Y., Zhao S., He W., Xiao Y., Yuan D.

This study reports a simple method for the controlled synthesis of uniformly shaped carbon hollow structures by an ethanol-assisted thermolysis of zinc acetate. The experimental evidence reveals that the generated zinc oxide nanostructures act as in-situ templates to form the carbon hollow structures. The morphologies, including the shell thickness, cavity size, and aspect ratio, can be controlled by the reaction time and the heating procedure, and hollow nanospheres, nanocapsules, nanorods, and microtubes can be obtained. Experimental results show that the as-synthesized carbon hollow structures exhibit excellent thermal and structural stability to temperatures as high as 1200 °C.

Dresselhaus M.S., Jorio A., Saito R.

Recent advances in Raman spectroscopy for characterizing graphene, graphite, and carbon nanotubes are reviewed comparatively. We first discuss the first-order and the double-resonance (DR) second-order Raman scattering mechanisms in graphene, which give rise to the most prominent Raman features. Then, we review phonon-softening phenomena in Raman spectra as a function of gate voltage, which is known as the Kohn anomaly. Finally, we review exciton-specific phenomena in the resonance Raman spectra of single-wall carbon nanotubes (SWNTs). Raman spectroscopy of SWNTs has been especially useful for understanding many fundamental properties of all sp2 carbons, given SWNTs can be either semiconducting or metallic depending on their geometric structure, which is denoted by two integers (n,m).

Tsiberkin K.B., Sosunov A.V., Govorina V.V., Neznakhin D.S., Henner V.K., Sumanasekera G.

Tsiberkin K., Kovycheva E.

The study presents an analysis of free induction decay (FID) in the ensemble of ring spin clusters using the formalism of collective modes similar to the spin waves. A dispersion relation for the waves is obtained. FID from a spin cluster is estimated and averaged over system parameters to simulate the signal given by a spherical structure or by an ensemble of rings withrandom orientation. There exists a fast relaxation according to the Gaussian law in the initial time interval. After T2, the signal decays as a power function which matches the direct numerical simulations of the signal from the ring clusters.

Li Y., Cao J., Wang L., Qiao Y., Zhou Y., Xie H., Li J.

Metal-organic frameworks (MOFs) derived carbon materials have great potential to be utilized as electrode materials in the field of energy storage and conversion. In the present work, nitrogen-doped hollow carbon polyhedron and hollow carbon sphere are synthesized using MOFs coated with carboxylated polystyrene (PS) microspheres as precursors. The morphology evolution of the hollow carbon has been discussed, which are subject to the reactant concentration and solvothermal temperature. The as-prepared hollow carbon has superior electrochemical performances for supercapacitors, owning to the hollow structure, high specific areas and nitrogen doping. The discharge specific capacitances of the hollow carbon polyhedron and hollow carbon sphere are respectively 160.2 F/g and 186.4 F/g under 0.2 A/g current density. Furthermore, the capacitance retentions of the hollow carbon polyhedron and hollow carbon sphere are 96.4 % and 98.9 % after 10,000 cycles, presenting excellent cycling stability. This work could provide new insight into the controllable design and synthesis of hollow carbon materials for energy storage. • Nitrogen-doped hollow carbon polyhedrons and hollow carbon spheres were successfully prepared using MOFs as precursors. • The morphology evolution of the hollow carbon is subject to the reactant concentration and solvothermal temperature. • The hollow carbon materials have superior electrochemical performances for supercapacitors.

Sosunov A.V., Rajapakse M., Rudakov G.A., Ponomarev R.S., Henner V.K., Jasinski J.B., Buchberger D.A., Reza M.S., Karki B., Sumanasekera G.

High capacity (>200 F/g) supercapacitor electrodes have been fabricated by blending high surface area microporous carbon and polyaniline. The incorporation of a conducting polymer is expected to stabilize the microporous graphitic layers to form a conductive porous composite to increase the capacitance. Well-organized nano- and micropores are believed to facilitate rapid ion diffusion especially when the micropore size is comparable to the ionic radii in the electrolyte solution thereby greatly boosting the capacitance. The initial capacitance of ~110 F/g of the microporous carbon network was found to increase to ~224 F/g (>100% increase) after the incorporation of polyaniline in the 1 M H2SO4 aqueous electrolyte. The non-linear behavior in the charge/discharge galvanostatic curve and the appearance of additional redox peaks in the capacitance-voltage curves confirm the presence of pseudocapacitance in the microporous carbon/ polyaniline composite in addition to the electrical double layer capacitance of pristine microporous carbon. The composite material shows the capacitance retention percentage over 80% after 1000 cycles implying a promise for novel supercapacitors with long-lasting ultra-high capacitance and power density.

Karki B., Rajapakse M., Sumanasekera G.U., Jasinski J.B.

Here, we report the structural and temperature-dependent transport properties of AsxP1–x (x = 0, 0.2, 0.5, 0.83, and 1) alloys. It is observed that black phosphorous-related phonon modes in the all...

Abuhimd H.M., Kiyashko M.V., Grinchuk P.S.

Abstract The effect of the thickness of a catalytic nickel coating deposited on a copper substrate by an electrochemical method on the intensity of formation of carbon nanomaterials in the CVD process was investigated. It was found that the dependence of the specific nanostructured carbon yield on the coating thickness is extremal, with a maximum near 1.5 μm. Qualitative interpretation of the obtained data is proposed on the basis of the carbon growth mechanisms on the catalytic coating.

Sosunov A.V., Henner V., Sumanasekera G.

Fluorination process was carried out on carbon nanocages in the CFx range at 0