One of the key issues in the utilization of carbon nanotubes (CNTs) for basic researches as well as their applications is to develop a methodology to solubilize/disperse them in solvents. In this review articles, we first summarize individual solubilization of single-walled carbon nanotubes (SWNTs) in solvents using surfactants, polycylcic aromatic molecules, DNA and condensed polymers. We then describe a novel method determining the electronic states of individually dissolved SWNTs having an own chirality index based on the analysis of Nernst equation. We also introduce our recent approach toward the fabrication of a novel catalyst for fuel cell that works at a nonhumid atmosphere using solubilized CNTs as material.
In the purely academic interests to find new and high oxide ion conductors, we investigated on the electrical conduction in the substituted scheelite- and spinel-type oxides. In the former, the substitution methods shown by Pb1−xLnxWO4+x/2 and Pb1−xLn2x/3WO4 (Ln: Lanthanoid element) to intend to increase the concentration of defects brought about formation of the PbWO4-based scheelite-type solid solutions, where the enhanced oxide ion conductivities were observed compared with that of the based material. From the structural and density measurements, the charge carriers in those phases were considered to be interstitial oxide ions. On the other hand, electrical conduction was also studied in many substituted spinel type oxides. Although the oxide ions would be generally hard to move considering from their cubic-packed form, the enhanced oxide ion conductivities were observed in the inverse spinel type solid solutions based on Zn2TiO4. A typical sample was Zn2−x/2Ti1−xTaxO4, the ionic conduction of which was considered to be due to the interstitialcy oxide ion migration. These results are mentioned in relation to the defect crystal phases.
LiNizCo1−2zMnzO2 materials have been investigated as promising positive electrode materials for lithium-ion secondary batteries, in which cobalt ions are simultaneously substituted with nickel and manganese ions while preserving the α-NaFeO2 structure. The materials can be regarded as solid solutions of LiNiO2, LiCoO2, and LiMnO2, in which the transition metals are trivalent in all three materials, whereas the transition metals found in LiNizCo1−2zMnzO2 materials are Ni2+, Co3+, and Mn4+. The electrochemical lithium deintercalation-intercalation processes of these materials are mainly accompanied by the Ni2+/4+ and Co3+/4+ redox reactions, whereas Mn4+ ions do not participate in the electrochemical redox reaction. Recently, Li+ substitution for transition metals in Li1+x(NizCo1−2zMnz)1−xO2, so called overlithiation, has been introduced to improve their structural integrity and electrochemical performances. In this paper, we introduce the overlithiation effects on the structural and electrochemical properties of the Li1+x(NizCo1−2zMnz)1−xO2 materials having diffrrent x- and z-values in the ranges from x=0.00 to x=0.17 and z=0.00 to z=0.50.
From the viewpoint of reducing carbon dioxide emissions, the practical use of electric buses has been expected to be one of the effective solutions to global warming. Even though lithium-ion batteries using lithium manganese oxide have been studied for use in electric vehicles, it is still necessary to improve their characteristics such as energy density, maximum operating temperature and cycle performance. Manganese oxide lithium-ion batteries for an electric bus developed by internal-combustion spray pyrolysis methods and its performance in an actual road test have been studied. The performance of the electric bus was satisfactory; the bus could run for 74 km on a full charge.
The effect of temperature and adsorption potential towards the electro-oxidation of pre-adsorbed carbon monoxide (COad) on carbon supported platinum-ruthenium alloy catalyst was studied by COad stripping voltammetry and chronoamperometry. The current transient during the CO adsorption process was analyzed at various adsorption potential to understand the catalytic reaction during the CO adsorption process. A clear correlation with the charge associated with CO oxidation during the CO adsorption process and potential was obtained. A linear decrease in the COad oxidation potential with a slope of −2.7 mV K−1 and an apparent activation energy of 126 kJ mol−1 was observed with increasing temperature when full CO coverage is achieved.
In previous study, proton conductivity increased with increasing pressure under water electrolysis, so the effects of pressure on the stability of Nafion 117 have been studied. It was found that conductivity of Nafion 117 drastically decreased at initial few h and then gradually decreased in the following period under electrolysis condition. Decrease in conductivity can be explained by decomposition of Nafion 117. Decomposition of Nafion 117 is accelerated by increasing pressure. Solid state NMR, IR, and Raman spectroscopy suggested that the electrochemical oxidation of sulfo group was occurred at initial period followed by decomposition of CFn main or side chain. Therefore, initial increase in resistance can be explained by desorption of sulfo group in Nafion 117. Desorption of sulfo group also forms pin hole in Nafion membrane which may cause gas leakage under water electrolysis. Mechanical strength of Nafion membrane is also drastically decreased at initial electrolysis period. Consequently, chemical stability of Nafion 117 may cause serious problem for water electrolysis application and this study reveals that increasing pressure strongly accelerates the decomposition of Nafion 117.