The addition of nitrophenyl groups to the surface of few-layer epitaxial graphene (EG) by the formation of covalent carbon-carbon bonds changed the electronic structure and transport properties of the EG from near-metallic to semiconducting.

Natural graphite was intercalated, thermally exfoliated, and dispersed in acetone to prepare graphite nanoplatelets (GNPs, G n ) of controlled aspect ratio. Thermal conductivity measurements indicate that few graphene layer G n , where n ∼ 4, with a thickness of ∼2 nm function as a very efficient filler for epoxy composites. When embedded in an epoxy matrix, the G4 GNPs provide a thermal conductivity enhancement of more than 3000% (loading of ∼25 vol %), and a thermal conductivity κ = 6.44 W/mK, which surpasses the performance of conventional fillers that require a loading of ∼70 vol % to achieve these values. We attribute the outstanding thermal properties of this material to a favorable combination of the high aspect ratio, two-dimensional geometry, stiffness, and low thermal interface resistance of the GNPs.

The increased heat generated in high density electronics has intensified the search for advanced thermal interface materials (TIMs) and prompted fundamental studies at the nanoscale level to develop filler materials with enhanced thermal performance. [1][2][3][4] Single-walled carbon nanotubes (SWNTs) considerably improve the heat transport in polymer composites as a result of their one-dimensional (1D) structure, high thermal conductivity and high aspect ratio. [5][6][7][8][9][10][11][12] Recently, two-dimensional (2D) nanostructures such as graphite nanoplatelets (GNPs), have emerged as a promising filler in polymer matrices [13][14][15][16][17][18][19] and it has been shown that they provide even higher thermal conductivity enhancement than SWNTs. [16] In this study we combine 1D-SWNTs and 2D-GNPs to prepare a series of hybrid graphitic nanofillers and we observe a synergistic effect between the GNPs and SWNTs in the enhancement of the thermal conductivity of epoxy composites to the point that at certain filler loadings the hybrid composition outperforms composites utilizing pure GNP or SWNT fillers. The increased thermal conductivity is ascribed to the formation of a more efficient percolating nanoparticle network with significantly reduced thermal interface resistances. The idea of using a hybrid filler comprised of two or more traditional filler materials has already been explored in the literature and it has been demonstrated that improved composite performance can be achieved by combining the advantages of each filler. [20,21] Commercially available thermal greases and adhesives often utilize several components to achieve the desired combination of thermal and electrical conductivities, viscosity and low coefficient of thermal expansion. In our study, we utilize two different nanostructured graphitic fillers for incorporation into epoxy resin: purified SWNTs and graphite nanoplatelets (GNPs) comprised of few graphene layer G n , where n $ 4. The SWNT component of the hybrid filler is electric arc produced purified SWNTs with a typical length of 0.3-1.0 mm and an average diameter of 1.4 nm. The purification process [22] leaves the SWNTs ends and side-walls functionalized with carboxylic acid groups and this facilitates their homogeneous dispersion into the polymer matrix. In addition, the epoxy curing process is accompanied by a cross-linking reaction between the carboxylic acid groups of the SWNTs and the epoxy groups of the polymer, [23] thus improving the integration of SWNTs into the polymer matrix. GNPs are typically prepared by intercalation and exfoliation of graphite; [24][25][26][27][28][29] and by control of the exfoliation conditions we were able to obtain GNPs comprised of 2 to 8 graphene layers with a lateral dimension of 200-1000 nm and an aspect ratio in the range of 50 to 300. [16] This was achieved by thermal shock exfoliation of natural graphite flakes at 800 8C [25,26] followed by high shear mixing and sonication in order to separate the exfoliated graphite flakes into nanoplatelets.[...

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A high energy density supercapacitor device is reported that utilizes hybrid carbon electrodes and the ionic liquid, 1-butyl-3-methylimidazolium tetrafl uoroborate (BMIMBF 4 ) as an electrolyte. The hybrid electrodes are prepared from reduced graphite oxide (rGO) and purifi ed single-walled carbon nanotubes (SWCNTs). A simple casting technique gives the hybrid structure with optimum porosity and functionality that provides high energy and power densities. The combination of SWCNTs and rGO in a weight ratio of 1:1 is found to afford a specifi c capacitance of 222 F g − 1 and an energy density of 94 Wh kg − 1 at room temperature.

International audienceGraphene displays unprecedented electronic properties including room-temperature ballistic transport and quantum conductance, and because of its small spin-orbit interaction, graphene has the potential to function as the building block of future spintronic devices. Theoretical calculations indicate that a defective graphene sheet will be simultaneously semiconducting and magnetic; thus it would act as a room-temperature magnetic semiconductor. Recently, ferromagnetic ordering at room temperature has been observed by magnetometry measurements on bulk samples of reduced graphene oxide

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Fuel cell membrane electrode assemblies with Pt loading of 0.2 mg Pt/cm2 at the anode and ultralow Pt loadings of 6 μg Pt/cm2 and 12 μg Pt/cm2 at the cathode have been fabricated using thin films of multiwalled carbon nanotube supported Pt catalysts (Pt/MWNTs) at the cathode. The Pt/MWNTs have a Pt weight loading of 26.8 wt % and a uniform and small Pt particle size of 2.1 nm. The MWNTs used are 360 μm long. This thin film cathode catalyst layer with a loading of 6 μg Pt/cm2 is about 1.3 μm thick, contains no ionomer, and exhibits surprisingly high performance in a hydrogen proton exchange membrane fuel cell. The peak power density for a membrane electrode assembly with a cathode loading of 12 μg Pt/cm2 when tested at 70 °C with hydrogen and oxygen is 613 mW/cm2. A mass activity (ampere per milligram of Pt) based on the cathode Pt loading greater than 250 A/mg Pt is achieved with 6 μg Pt/cm2, and this is among the highest reported to date.