We have developed a new type of nanostructured anode material and studied its performance for catalyzing the oxygen evolving half reaction (OER) associated with electrolysis of water. The hybrid material, comprising a hierarchical iron oxide/nitrogen doped carbon nanotube structure, was used as a direct electrode for electrochemical water splitting without any further modification. The electrode is prepared in a bottom up process by CVD growth of NCNTs on the fibers of a conductive carbon paper, followed by a hydrothermal growth of iron hydroxide nanorods on the surface of the nitrogen doped carbon nanotubes (NCNTs). The iron hydroxide nanorods are then transformed to maghemite. The resulting hierarchical nanostructure exhibit large surface area, and ideal attachment of maghemite nanorods to NCNTs which are further well attached to the carbon paper. The hybrid electrode demonstrates very good electrochemical water oxidation activities in 0.1 M KOH. For a current density of 1 mA cm-2 (geometric surface) an overpotential of only 392 mV is needed. By combining electrochemical water oxidation with isotope ratio mass spectrometry we show that only water is oxidized.
Aluminum matrix composites with significantly enhanced mechanical and physical properties are expected by using the carbon nanotube (CNT) as the reinforcement, due to its good mechanical properties (extremely high strength ~30 GPa, modulus ~ 1 TPa) as well as good electrical and thermal conductivity. However, it is a challenging task to individually disperse CNTs into the metal matrix due to the entangling or bundling of CNTs resulting from large aspect ratio and the strong Vander force. The CNT clusters in the CNTs reinforced metal matrix (CNT/metal) composites would reduce either mechanical or physical properties of the resultant composites. Individual dispersion of CNTs, relatively long CNT length and good CNT-metal interface bonding are the keys to obtain high-performance CNT/metal matrix composites.
In this work, 1.5-4.5vol.% CNTs reinforced 2009Al (CNT/2009Al) composites were fabricated by means of friction stir processing (FSP) technique and subsequent rolling, and subjected to detailed microstructural investigation and property evaluation. Firstly, the CNT/2009Al composites were fabricated by multi-pass FSP. Microstructural observations indicated that the CNTs were uniformly and randomly dispersed in the aluminum matrix after 3-pass FSP. The CNTs were cut shorter as the FSP pass increased and it was found that the reciprocal of CNT length exhibited a linear relationship with the number of FSP passes. The grains of the matrix were significantly refined due to the effective pinning of CNTs on the growth of recrystallized grains, and the grain size tended to stable after 3-pass FSP. The maximum strength of the composites was obtained with 3-pass FSP. This is attributed to the combined effect of CNT cluster reduction, grain refinement and CNT shortening.
Secondly, in order to align CNTs in the aluminum matrix, the FSP CNT/2009Al composites with randomly arranged CNTs were subjected to hot-rolling with a reduction of 80%. Microstructural observations indicated that CNTs were directionally aligned along the rolling direction in the composites after hot-rolling. The tube structure of the CNTs was retained and the CNT-Al interface was well bonded without pores after FSP and rolling. As a result, both the strength and modulus of the composites were significantly enhanced compared to the 2009Al and increased with increasing the CNT volume fraction. In particular, 3vol.% CNT/2009Al composite exhibited an ultimate tensile strength of 600 MPa and elongation of 10%, much higher than the corresponding values for CNT/Al composites fabricated by other processes.
A designer polysiloxane-based stabilizer for graphene was used as the polymer matrix to prepare a highly conductive polymer film. To synthesize the stabilizer, 1-ethynylpyrene was grafted to the backbone of a poly(dimethylsiloxane)-co-(methylhydrosiloxane) random copolymer by Pt-catalyzed hydrosilylation with a SiH:ethynyl ratio of 1.0:1.3. Graphene was stabilized in chloroform through the π-π interactions with the pyrene groups of the resulting copolymer. A graphene/polymer film was cast from the dispersion in chloroform. SEM and TEM images confirmed the homogeneous distribution of the graphene sheets in the film. The conductivity of this film with 4 wt% loading of graphene was measured to be 220 S/m, the first case of a melt-processable, conductive graphene/polymer film reported in the literature. When the ratio of SiH:ethynyl was changed to 1.7:1.0, the copolymer self-crosslinked at 110 ⁰C and resulted in a direct production of a conductive graphene/silicon elastomeric composite. The crosslinking reaction was observed by FT-IR spectroscopy and the network formation was confirmed by swelling and extraction of the product.
Graphene-polymer hydrogels and aerogels hold interest for both fundamental studies of graphene-polymer interactions as well as the production of nano-enhanced polymeric materials. Flexible, compressible, and self-healing pristine graphene/polymer hydrogels were synthesized via in-situ polymerization of the monomer in the polymer-stabilized graphene dispersion. The graphene sheets act as physical cross-linkers and permit gelation without the presence of any chemical cross-linker. Rheological measurements indicate that these physically cross-linked gels have higher storage modulus and toughness compared to the chemically cross-linked baseline. These gels are turned into conductive aerogels (or cryogels) by critical point drying or freeze drying. The aim is to create percolating composites with ultralow filler content by utilizing aerogels or cryogels as a conductive template. This is done by backfilling and polymerizing epoxy resin into the scaffold. The infusion of the resin does not disrupt the monolithic structure or conductive network. Three different aerogel systems (inorganic, organic and polymer aerogel) are investigated with both graphene and carbon nanotubes loading, with successful percolation in each case. A percolation threshold as low as 0.012 vol. % is obtained for graphene loaded organic aerogel/epoxy composite. This is the lowest reported threshold of any graphene based nanocomposites.
Atomic Carbon Chains: A Perfectly One-Dimensional Carbon Phase Beyond Nanotubes
F. Banhart1, O. Cretu1, A. La Torre1, A. Botello-Mendez2, J.-C. Charlier2
1Institut de Physique et Chimie des Matériaux, University of Strasbourg, France
2Institute of Condensed Matter and Nanosciences, Université catholique de Louvain, Belgium
Carbon chains can be considered as sp1-hybridized strings of carbon atoms of monoatomic thickness, constituting the logical one-dimensional phase of carbon. They have been proposed since a long time until they were observed by electron microscopy. Recent experiments show that, by using a measuring system with an STM tip in a TEM specimen stage, carbon chains can not only be made but also characterized (O. Cretu et al., Nano Lett. 13, 3487 (2013)). By passing a current through the chains, their electrical properties have been measured for the first time. The chains are obtained by unraveling carbon atoms from nanotubes or graphene ribbons while an electrical current flowed through the tubes or ribbons and, successively, through the chain. The electrical conductivity of the chains was found to be much lower than predicted for ideal chains. First-principles calculations show that strain in the chains determines the conductivity in a decisive way. Indeed, carbon chains are always under varying non-zero strain that transforms their atomic structure from cumulene (double bonds throughout the chain) to polyyne (alternating single/triple bonds), thus inducing a tunable band gap. New experiments show the bonding characteristics at contacts between metals and carbon chains as well as characteristic current-voltage curves, depending on the type of contact. The experiments show a perspective toward the synthesis of carbon chains and their application as the smallest possible interconnects or even as one-dimensional semiconducting devices.
Electronic properties in moiré superlattice in rotationally stacked atomic layers
Mikito Koshino1, Pilkyung Moon2
1Department of Physics, Tohoku University,
2Korean Institute for Advanced Study
We report recent theoretical studies on the electronic properties of rotationally stacked atomic layer systems, including graphene-graphene bilayer, and graphene-hBN (hexagonal boron nitride) composite bilayer. The misoriented atomic structure gives rise to a moiré superlattice structure with a long spatial period, and it strongly modifies the band structure in the low-energy region. We develop an effective continuum model based the tight-binding Hamiltonian, which correctly describes the electronic structure of moiré superlattice . In a magnetic field, the coexistence of the moiré pattern and the Landau quantization causes the fractal energy spectrum so-called Hofstadter’s butterfly. We calculate the spectral evolution as a function of magnetic field, and demonstrate that the quantized Hall conductivity changes in a complicated manner in changing Fermi energy and the magnetic field amplitude . We also calculate the optical absorption in the fractal band regime, and find that the absorption spectrum and the optical selection rule exhibit recursive self-similar structure as well, reflecting the fractal nature of the energy spectrum.
 P. Moon and M. Koshino, Phys. Rev. B 87, 205404 (2013)
 P. Moon and M. Koshino, Phys. Rev. B 85, 195458 (2012).
 P. Moon and M. Koshino, Phys. Rev. B 88, 241412(R) (2013).
Milestones in Synthesis, Dispersion, and Applications that Realized Single-walled Carbon Nanotubes Industrialization
Nanotube Research Center, National Institute of Advanced Industrial Science and Technology (AIST) and TASC: Technology Research Association for Single Wall Carbon Nanotubes
After two decades of extensive research, single-walled carbon nanotubes (SWNT) are going to be industrialized at last. By the time of the conference, Nippon-Zeon will have announced that they will launch the first commercial SWNT production plant based on the super-growth technology in 2015. Concurrently, a couple of applications such as SWNT super-capacitors and composites would hit the market. To realize this, not only the development of mass production technique was necessary but also new concepts in CNT dispersion were crucial to keep the length of the long SWNTs and development of new application were required. Indeed, I envision that the “first” SWNT industrial applications are going to be very different from what we researchers had thought CNT would be useful for. In this talk I will present milestones, new concepts, new directions and aspects in synthesis, dispersion and applications of long SWNTs that have led to industrialization.
Towards large-area monocrystalline graphene: Growth and observations
Young Hee Lee1
1Center for Integrated Nanostructure Physics, Institute for Basic Science, Sungkyunkwan University,Suwon, Kyunggi-do 440-746, South Korea
2Department of Energy Science, Department of Physics, Sungkyunkwan University,Suwon, Kyunggi-do 440-746, South Korea
E-mail address: firstname.lastname@example.org
Grain boundaries in graphene are formed via the stitching of islands during the initial growth stage, and these boundaries govern transport properties and related device performance. Graphene can be ideally grown from a single nucleation seed, but its growth to large-area graphene can be terminated by several unknown self-limiting growth factors. Another approach is to start with numerous nucleation seeds and allow them to grow and coalesce together to produce large-area graphene. However, graphene grain boundaries (GGBs) are inevitably formed via stitching of graphene flakes, consequently limiting the graphene quality. We will describe several growth factors to achieve monocrytalline graphene growth during CVD. Another issue is how to confirm grain boundary-free large-area graphene in centimetre scales. We will present several methods of identifying monocrytallinity of graphene in large area together with local transport phenomena at the grain boundaries.
Carbon Nanotubes: From Basic Research to Commercialization
1Department of Physics & Tsinghua‐Foxconn Nanotechnology Research Center, Tsinghua University, Beijing, China 100084.
Carbon nanotube (CNT) is a promising nanomaterial for real applications due to its excellent mechanical, electrical, and thermal properties. The real products of CNT are expected after long time intensive research efforts on it. In this talk, I will present our research works on CNTs in the past two decades, including studies on the growth mechanism, controllable synthesis, physical properties, and real applications of CNTs. In particular, I will show that a unique macroscopic form of CNTs, the super‐aligned CNTs, can bridge the gap between nano‐world and macro‐world and lead CNTs into real applications1‐7. Many real applications, such as field and thermionic emission electron sources,8‐12 high strength CNT yarns,2,6,7 electrodes for batteries and supercapacitors,13‐17 loudspeakers,18,19 displays,20‐22 SERS substrate23, IR detector24 etc. have been demonstrated. Real products of CNT TEM grids25, 26 and CNT touch panels4 have already been commercialized. More products based on super‐aligned CNTs are expected to go to the market in the near future27.
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Carbon Nanotube Sorting via Molecular Interactions in Liquid Phases
National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
Chirality control is one of the most challenging problems in the carbon nanotube field. Over a decade ago, we and others began to explore separation of single-wall carbon nanotubes by exploiting chirality-dependent molecular interactions in liquid phases. By now, efforts from many groups around the world have resulted in a number of effective ways to achieve metal/semiconductor separation and single-chirality purification, enabling fundamental studies and application development. In this presentation, I will review various separation methods developed so far, discuss common physical mechanism underlying these methods, and highlight a polymer-based liquid two-phase extract method we have recently reported (J. Am. Chem. Soc. 2013, 135, p6822; Adv. Mat. 2014, DOI: 10.1002/adma.201304873). I will give examples to illustrate the versatility of the new method, and provide an outlook for its future development to enable carbon nanotube-based applications.