Time-dependent electrical resistivity of carbon

Kavan, Ladislav; Dousek, F.P.; Micka, K.

doi:10.1021/j100375a067

Cited by 37 publications

(46 citation statements)

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“…The most carefully studied perhalogenated precursor is poly(tetrafluoroethylene) (FIFE). [16][17][18][19][20][21][22][23][24] The reaction of PTFE and other perhalogenated molecules with alkali metal amalgams is, however, also "electrochemical" in nature since it is controlled by a spontaneous discharge of an in situ formed galvanic cell with an amalgam anode and continuously renewed carbon cathode. 16•22 Hence we have introduced the term "electrochemical carbon", which is equally usable for the products of cathodic as well as amalgam reduction of perhalogenated (macro)molecules.…”

Section: =C=c=c=c=mentioning

confidence: 99%

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Reductive Preparation of Carbyne with High Yield. An in Situ Raman Scattering Study

Kastner¹,

Kuzmany²,

Kavan³

et al. 1995

Macromolecules

133

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Electrochemical reductive carbonization of poly(tetrafluoroethylene) with alkali metal (Li, Na, K) amalgams leads to a polymeric carbon with a partly carbynoid structure. Raman spectra measured in situ exhibited a strong line at around 2000 cm-1 which was interpreted as the C=C-C stretching mode of a linear carbon chain with alternating carbon-carbon triple and single bonds (polyyne). The intensity and position of this line evidence an unusually high triple bond carbon content in our materials, which leads to relatively large conjugation lengths in the polyyne chains. The triple bond line shifts to higher wavenumbers with increasing laser energy; this can be elucidated in terms of the conjugation length model. A quantum chemical calculation for transition energies and matrix elements of oligoynes with different chain lengths is presented. In addition, the frequency of the mode as a function of chain length is calculated. The conjugation lengths found correspond to 8-14 C atoms in the polyyne chain and increase with increasing atomic number of the alkali metal. The yield of polyyne and its stability against interchain cross-linking increase similarly. This supports our previous conclusions about the polyyne stability which were formulated on the basis of electronic conductivity and UV-vis spectra.

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Section: =C=c=c=c=mentioning

confidence: 99%

“…The amalgam preparation, purification, chemical analysis, and other experimental details are described elsewhere. 22 Transmission UV-vis measurements were performed in situ using evacuated quartz optical cells and a Zeiss M40 or a Hewlett-Packard 8452A spectrometer. A schematic drawing of the optical cell used is shown in Figure 1.…”

Section: =C=c=c=c=mentioning

confidence: 99%

Reductive Preparation of Carbyne with High Yield. An in Situ Raman Scattering Study

Kastner¹,

Kuzmany²,

Kavan³

et al. 1995

Macromolecules

133

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“…By Kaixue Wang, Mingdeng Wei, Michael A. Morris, Haoshen Zhou,* and Justin D. Holmes* Mesoporous titania and titania nanotubes, with high surface-to-volume ratios, have recently been reported to demonstrate improved properties compared to colloids, films and other forms of titania in applications such as photocatalysts, [1,2] gas sensors, [3] photovoltaic cells [4][5][6] and rechargeable lithium batteries. [7][8][9][10] Therefore, particular attention has been paid to the preparation of titania nanotubes, or arrays of tubes, and many methods have been developed including the hydrothermal treatment of TiO 2 nanoparticles with alkali solution, [8][9][10][11][12][13] anodization of titanium foil, [14,15] deposition of sol-gels within templates, [16][17][18] hydrolysis of TiF 4 under acidic conditions, [19] sonication of titania particles in aqueous NaOH solution, [20] and surfactant-assisted templating methods. [21,22] Materials with mesoporous structures possess an extraordinarily high surface area.…”

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confidence: 99%

Mesoporous Titania Nanotubes: Their Preparation and Application as Electrode Materials for Rechargeable Lithium Batteries

et al. 2007

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Mesoporous titania and titania nanotubes, with high surface-to-volume ratios, have recently been reported to demonstrate improved properties compared to colloids, films and other forms of titania in applications such as photocatalysts, [1,2] gas sensors, [3] photovoltaic cells [4][5][6] and rechargeable lithium batteries. [7][8][9][10] Therefore, particular attention has been paid to the preparation of titania nanotubes, or arrays of tubes, and many methods have been developed including the hydrothermal treatment of TiO 2 nanoparticles with alkali solution, [8][9][10][11][12][13] anodization of titanium foil, [14,15] deposition of sol-gels within templates, [16][17][18] hydrolysis of TiF 4 under acidic conditions, [19] sonication of titania particles in aqueous NaOH solution, [20] and surfactant-assisted templating methods. [21,22] Materials with mesoporous structures possess an extraordinarily high surface area. The synthesis of titania nanotubes, with mesoporous walls and hence high surface areas, will be invaluable for all applications employing the wide bandgap semiconductor. Therefore, there is a requirement for the development of a facile and reproducible way to prepare titania nanotubes with well-defined mesoporous wall structures. We have previously shown that one-dimensional mesoporous silica nanotubes and nanowires can be fabricated inside the pores of anodic aluminum oxide (AAO) membranes.[23] Recently, Chae et al. reported the preparation of titania nanofibres with wormhole-like mesoporous structure using AAO as a 'hard template'. [24] Even though mesoporous SiO 2 nanotubes and titania nanofibres have been prepared, the fabrications of TiO 2 nanotubes with well ordered mesopores are still a challenge because of the complexity of sol-gel chemistry. Herein, we report the preparation of titania nanotubes with mesoporous walls within AAO membranes and their application in a high rate rechargeable lithium battery. Well-aligned titania nanotube arrays were fabricated via a drying process utilizing supercritical CO 2 after the dissolution of the membranes. These mesoporous titania nanotubes, with a 3-dimensional (3D) network structure, were investigated as the electrode material of a rechargeable lithium battery. The structure of the mesoporous nanotubes was specifically designed to allow efficient transport of both lithium ions and electrons, which are necessary for a high rate rechargeable battery. The experimental results obtained proved that the mesoporous nanotube structure plays an important role in the efficiency of the high rate performance of the battery. Scanning electron microscope (SEM) images of the titania nanotubes annealed at 150°C are shown in Figure 1. Well-defined nanotubes are observed occupying most of the pores of the AAO. The size and uniformity of the nanotubes fabricated by this templating method are closely related to the pore size and quality of the alumina membranes employed.[17] Nanotubes prepared within a 0.2 lm Whatman AAO membrane have an outer diameter of approximately 200 nm...

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“…X-Ray diffraction [37], electrical conductivity [36], UVjVIS spectra [34] and solid state I3C-NMR studies [30] indicate a superposition of graphitic, diamond-like and also carbynoid structures for the products derived from dehalogenation of PTFE. Carbynes are further characterized by IR-spectroscopy [27, 281, especially by the C-C stretching mode (vCGc) at 2100-2200 cm-'.…”

Section: Oligoynes Oligoenynesmentioning

confidence: 99%