V. G. Zhigalina

Fabrication and characterization of fluorinated single-walled carbon nanotubes

The optimum conditions for the fluorination of single-walled carbon nanotubes (SWCNT) in the atmosphere of gaseous fluorine with the nanotube structure remaining intact up to a stoichiometry of CFx, x ∼ 0.5 were determined. The kinetics of fluorination was examined. The fluorinated SWCNTs were characterized by various methods, including transmission electron microscopy, measurements of specific surface area and accessible internal volume, NMR spectroscopy, IR spectroscopy, X-ray absorption and photoelectron spectroscopies, thermal stability, and analysis of gaseous products by mass-spectrometry. The structure of fluorinated SWCNT was preserved up to brutto-composition CF0.5 but degree of fluorination of SWCNT bundles was decreased with distance from the SWCNT surface to its core. Such a decrease becomes evident at ∼1.5 nm distance. It means that the degree of fluorination depends on the degree of its dispersion.

Characterization of SWCNT products manufactured in Russia and the prospects for their industrial application

Single-wall carbon nanotubes (SWCNTs) are of the greatest interest for application in materials used for various purposes due to all of their unique properties. However, the practical use of SWCNTs has, until quite recently, been limited by the absence of a cheap industrial process for manufacturing them. Currently, a technology for the synthesis of SWCNTs from hydrocarbon raw materials providing the initial SWCNTs product of a sufficiently high quality has been developed in Russia for the first time in world history. In this work, the results of the characterization of the SWCNT products available in the Russian market are presented and the most promising directions among the technical applications of the materials and products on the basis of SWCNTs are highlighted.

Pt/Pd/C catalysts with ultra low platinum content for oxygen reduction reaction

The activity of Pt/Pd/C ETEK catalysts of the core-shell type with an ultralow content of platinum (0.5–15 μg cm−2) based on a commercial palladium catalyst is shown to exceed the activity of commercial Pt/C ETEK catalysts in the oxygen reduction reaction. The activity sharply increases with the decrease in the platinum content down to values corresponding to monolayer and submonolayer of platinum on palladium. This dependence wasn’t observed for the same amounts of platinum deposited on the carbon support Vulcan XC-72. This makes it possible to conclude that the most probable factor responsible for the high catalytic activity of Pt/Pd/C ETEK is the effect of palladium on the electronic properties of platinum rather than the effect of structural modification of the platinum deposit induced by the decrease in the platinum amount deposited on a foreign metal or a carbon support.

Study of one-dimensional crystal@single wall carbon nanotube nanocomposites using atomic resolution scanning transmission electron microscopy

Abstract1DCuI@SWCNT nanocomposites have been studied by scanning transmission electron microscopy (STEM) using the registration modes of large-angle scattered electrons and bright-field images in combination with the spectroscopy of electron energy losses. A new structure of a 1DCuI@SWCNT nanocomposite has been found. The results of the studies indicate that by using STEM modes it is necessary to obtain simultaneously both the images in a bright field and in high-angle annular dark field (HAADF) imaging. Using the spectroscopy of electron energy losses, the formation of a chemical bond between Cu3d and C2pz states of an intercalated nanocrystal and nanotube with the corresponding transfer of the electron density ∼0.09 e/carbon atom has been shown.

Electron microscopy study of a Pt-Pd bimetallic structure formation on soot for catalytic systems

Bimetallic structures—Pt nanoparticles distributed on the surface of a Pd catalyst on Vulcan XC-72 soot—have been investigated. Several series of bimetallic catalysts with various contents of platinum have been obtained by pulsed electrochemical deposition. Their structure is studied using analytical high resolution transmission electron microscopy with a correction of aberrations. The data allows us to present a scheme of evolution in the bimetallic catalyst structure caused by a change in the ratio of metals Pt : Pd. For the ratio Pt : Pd = 1 : 25, the electrochemical measurements of catalytic activity have shown an extremely high current of oxygen reduction.

Dimensional and phase characteristics of aluminum oxide and titanium dioxide nanoparticles

Aluminum oxide and titanium dioxide nanoparticles obtained by laser evaporation and condensation have been studied using X-ray phase analysis and high-resolution transmission electron microscopy techniques. A dimension-phase dependence in the crystalline structure of nanoparticles has been revealed: a transfer from cubic to orthorhombic phase for aluminum oxide was observed at a particle dimension of 35 nm, while for titanium dioxide the phases of rutile and anatase steadily coexisted at an average particles size of 20.3 and 19.2 nm, respectively.

Diffusion of One-Dimensional Crystals in Channels of Single-Walled Carbon Nanotubes

The transport of one-dimensional CuI crystals in channels of single-walled carbon nanotubes (SWCNTs) has been studied by high resolution electron microscopy. The diffusion kinetics has been investigated by counting the number of CuI atoms escaping from the nanotube channel. The diffusivity is calculated to be 6.8 × 10–21 m2/s, which corresponds to an activation-barrier height of ~1 eV/atom. A comparison with the theoretically estimated height of the energy barrier for molecular transport through a graphene layer is indicative of mass transfer through vacancy defects in graphene.

Structure of One-Dimensional Rubidium and Silver Iodide Crystals in the Channels of Single-Walled Carbon Nanotubes

The structures of one-dimensional (1D) RbI, AgI, and RbAg4I5 crystals inside single-walled carbon nanotube (SWCNT) channels of 1D crystal@SWCNT nanocomposites formed by the capillary technique have been studied by high-resolution (scanning) transmission electron microscopy and computer modeling. 1D RbI crystals form a cubic lattice in a limited space, while 1D AgI crystals form a hexagonal lattice, as in their ternary compounds. The 1D RbAg4I5 structure differs from known bulk analogs and can be described by a distorted cubic lattice formed in two different directions.

Carbon nanofiber paper cathode modification for higher performance of phosphoric acid fuel cells on polybenzimidazole membrane

Entire carbon nanofiber mats (carbon nanofiber paper) based on polyacrylonitrile pyropolymer composite were prepared by the preliminary oxidation (stabilization) of the initial polymer at 250–350°C in air and following pyrolysis at 800–1200°C under vacuum. The mats were tested as cathodes in a fuel cell on polybenzimidazole membrane. Properties of the pyropolymers which were obtained by polymer carbonization could be significantly changed by the addition of specific additives to polyacrylonitrile and also by changing thermal treatment. Particularly, the addition of Ketjen Black® or Vulcan® XC72 carbon blacks and polyvinyl pyrrolidone during electrospinning step resulted in increase of material electrical conductivity and inner porosity, which is important for improving fuel cell performance. Depending on oxidation and pyrolysis temperature, the physical properties of platinated carbon nanofiber paper and the efficiency of a fuel cell on polybenzimidazole membrane significantly change.

Electroforming of Nitrogen-Containing Polymers and Derived Nonfabric Nanofibre Carbon Materials

This is the first report of nonfabric nanofibre materials derived from polyheteroarylenes and polyacrylonitrile obtained by electroforming (electrospinning). Feasibility was demonstrated for the pyrolysis of the starting nonfabric nanofibre materials with retention of integrity and sufficient strength in order to obtain derived nanostructural carbon materials suitable for use in electrochemical devices.