Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 85 , Issue 2
Showing 1-13 articles out of 13 articles from the selected issue
  • Kei NISHIKAWA, Nobuyuki ZETTSU, Katsuya TESHIMA, Kiyoshi KANAMURA
    2017 Volume 85 Issue 2 Pages 72-76
    Published: February 05, 2017
    Released: February 05, 2017
    The intrinsic electrochemical characteristics of needle-like LiCoO2 crystals with a hexagonal cylindrical shape were studied by the single particle measurement technique. The needle-like LiCoO2 crystals were synthesized by the flux growth method. Single-particle Raman spectroscopy and galvanostatic charge-discharge tests at different electrical contact points in one needle-like LiCoO2 crystal revealed that the crystal has homogeneous intercalation/deintercalation characteristics throughout the long axis. This suggests that the electron conductivity is high on a 100 µm scale along that axis and that lithium ions are efficiently transferred from the electrolyte to the layer structure of the crystal. The charge rate characteristics of the needle-like LiCoO2 crystals were also evaluated and compared to those of powdered LiCoO2. The polarization curve analysis indicates that the needle-like LiCoO2 particles had almost same exchange current density, i0, as powdered LiCoO2, which has a much smaller volume. These excellent electrochemical characteristics are considered to be due to the orientation of the {104} crystal face on the crystal sides, which is the preferential face for lithium ion transfer, and the larger effective surface area of the particles.
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  • Jungo WAKASUGI, Hirokazu MUNAKATA, Kiyoshi KANAMURA
    2017 Volume 85 Issue 2 Pages 77-81
    Published: February 05, 2017
    Released: February 05, 2017
    Thermal stability of LiCoO2, LiMn2O4 and LiFePO4 with Li6.25Al0.25La3Zr2O12 (Al-LLZ) solid electrolyte was investigated at 300–800°C. In the case of LiCoO2/Al-LLZ mixture, the XRD patterns and charge-discharge behavior did not change after the heat treatment at 800°C. In contrast, the formation of impurities and degradation of cathode performance were observed for LiMn2O4/Al-LLZ mixture and LiFePO4/Al-LLZ mixture. The decomposition of Al-LLZ and the formation of some impurities were observed from 600°C for LiMn2O4/Al-LLZ mixture, leading to decrease in the discharge capacity. In the case of LiFePO4/Al-LLZ mixture, the decomposition of both materials was started at 400°C. These results indicate that the limit of heat treatment temperature for the formation of electrode/solid electrolyte system strongly depends on the kind of electrode material.
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    2017 Volume 85 Issue 2 Pages 82-87
    Published: February 05, 2017
    Released: February 05, 2017
    Direct electron transfer (DET)-type bioelectrocatalytic waves of bilirubin oxidase (BOD)-catalyzed O2 reduction and [NiFe] hydrogenase (H2ase)-catalyzed H2 oxidation are very small and un-detectable using glassy carbon (GC) electrodes, respectively; however, clear catalytic waves are observed when the enzymes are adsorbed on Ketjen black-modified GC (KB-GC) electrodes, in which KB provides mesopores for DET-type bioelectocatalysis. To explain the phenomena, we focus on the curvature effect of mesoporous structures on long range electron transfer kinetics and simulate steady-state voltammograms catalyzed by model redox enzymes adsorbed with a random orientation on planar and mesoporous electrodes based on a three-dimensional model. In the simulation, we assume a spherical enzyme with a radius of r, an active site located at a certain distance from the center of the enzyme, and a spherical pore with a radius of Rp in mesoporous electrodes in which the enzyme is trapped and adsorbed. The simulation reveals that mesoporous electrodes provide platforms suitable for DET-type bioelectrocatalysis of enzymes when Rp becomes close to r. Such curvature effects of mesoporous electrodes become especially notable for larger sized enzymes. Furthermore, the simulation reproduces the experimental data of BOD- and H2ase-catalyzed DET-type waves by considering the crystal structures of the enzymes. This work will open a route to improve the kinetic performance of the DET-type bioelectrocatalysis that has become very important in its practical application to a variety of bioelectrochemical devices.
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  • Akihiro WATANABE, Genki KOBAYASHI, Naoki MATSUI, Masao YONEMURA, Akiko ...
    2017 Volume 85 Issue 2 Pages 88-92
    Published: February 05, 2017
    Released: February 05, 2017
    Recently, hydride ion (H) has come to be recognized as new charge carrier for the transport of hydrogen in solids by realization of pure H conduction in BaH2 and La2−xySrx+yLiH1−x+yO3−y oxyhydride system (LSLHO). In this study, the H conductive oxyhydride, LaSrLiH2O2 (x = 0, y = 1 in LSLHO), was synthesized by a conventional solid-state reaction at ambient pressure. The crystal structure of LaSrLiH2O2, as well as the H conductivity and bonding state of hydrogen, was examined by Rietveld analysis using X-ray and neutron diffraction data, attenuated total reflection Fourier transform spectroscopy (ATR-FTIR), and electrochemical impedance spectroscopy (EIS). The sample synthesized at ambient pressure had a K2NiF4-type layered perovskite structure composed of alternately stacked tetragonal (LiH2) and (LaSrO2)+ layers, and exhibited a conductivity of H of 3.2 × 10−6 S cm−1 at 300°C, which were the same structure and property as that reported previously for a sample synthesized by high-pressure synthesis.
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