Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 69 , Issue 9
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Technical Papers
  • G. M. ABOU-ELENIEN, A. O. ABDELHAMIDE, N. A. ISMAIL, A. A. EL-MAGHRABY ...
    2001 Volume 69 Issue 9 Pages 652-658
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    The redox characteristics of 5-aroyl-2-imino-3-phenyl-2, 3-dihydro-1, 3, 4-thiadiazoles (1a-e), 5-benzoyl-2-imino-3-aryl-2, 3-dihydro-1, 3, 4-thiadiazoles (2b-e) and 2-imino-3, 5-disubstituted-2, 3-dihydro-1, 3, 4-thiadiazoles (3b-e) has been investigated in nonaqueous acetonitrile at platinum and gold electrodes. Through controlled potential electrolysis, the oxidation and reduction product of each class of compound can be separated and identified. The product of oxidation of substituted thiadiazoles 1-3(a-e) was found to be a dimer while that of reduction is a stable anion radical.

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  • Chiaki IWAKURA, Naoji FURUKAWA, Toshiyuki OHNISHI, Kouichi SAKAMOTO, S ...
    2001 Volume 69 Issue 9 Pages 659-663
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    Alkaline polymer gel electrolyte with high ionic conductivity was prepared from potassium salt of crosslinked poly(acrylic acid) and KOH aqueous solution in order to investigate the applicability of the polymer gel electrolyte to alkaline secondary batteries such as nickel/metal hydride (Ni/MH) battery. An experimental Ni/MH cell was assembled using the polymer gel electrolyte and its charge-discharge and capacity retention characteristics were tested. A similar type of Ni/MH cell was also assembled using a 6 M KOH aqueous solution for comparison. The former cell was found to exhibit rather better charge-discharge and capacity retention characteristics than the latter cell.

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  • Jun-ichi YAMAKI, Minato EGASHIRA, Shigeto OKADA
    2001 Volume 69 Issue 9 Pages 664-669
    Published: September 05, 2001
    Released: September 25, 2019
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    Lithium intercalation materials are widely used in lithium ion cells as cathode and anode active materials. Lithium intercalation materials show sometimes phase separation as a function of the amount of inserted Li+. The thermodynamic criterion of the phase separation of binary mixtures is already known using Gibbs free energy. The criterion of the phase separation was applied to that of lithium intercalation materials. We demonstrated the phase separation condition of the Li cathode for the cases of Gas Model and Coulomb Potential Model. By using Gas Model, the cathode potential is written as E = E0 + Ky + (RT/F) ln [(1−y)/y], where E is the cathode potential (V vs. Li), y is Li occupancy. In this case, two phase area is exp (−KF/2RT)<y<1−exp (−KF/2RT) and the potential is E0 + K/2. We have been considering the contribution of the internal energy change to the cell voltage (E vs. Li/Li+) assuming that the cathode material was completely ionic and only the Coulomb potential was effective in terms of changing the internal energy. From this model, we calculated E0 = 3.879 V and K = 1.020 V for LixNiO2 where y = 4 x (0<x<0.25). In this case, two phase area is 2.396 × 10−9 < y < 1 − 2.396 × 10−9 and the potential is 4.384 V.

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  • Kazuhiro TACHIBANA, Yukihiro SATO, Tatsuo NISHINA, Takashi ENDO, Kenzo ...
    2001 Volume 69 Issue 9 Pages 670-680
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    Formation process of passivating film and film formation mechanism of aluminum current collector as lithium secondary batteries in typical orgphenomenarolytes for lithium secondary batteries have been investigated using galva-nostatic and potentiostatic condition with some surface analysis methods such as XRD and XPS. These data were also compared with the phenomena in aqueous solution system. Aluminum current collector formed compact passivating film of barrier type, and this film consisted of AlF3 related compounds as main components. The formation of passivating film followed the high field model, which was similar to that for the aluminum anodic oxide formation in neutral aqueous solution.

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  • Shinji UESUGI, Tetsurou KATSUMATA, Futoshi MATSUMOTO, Nobuyuki KOURA, ...
    2001 Volume 69 Issue 9 Pages 681-685
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    Acceleration of the reduction of hydrogen peroxide (H2O2) and electrochemical oscillatory phenomena during the reduction of H2O2 on Hg adatom-modified Au polycrystalline electrodes in acidic, neutral and alkaline aqueous solutions were first observed. The observed acceleration of the reduction of H2O2 was explained by taking into account the electrode potential-dependent electrocatalytic behavior of the adsorbed species of OH (OHad) on the Hg adatom-modified Au electrode surface. The negative differential resistance (NDR) was observed in the potential region from 0.4 to 0.8 V vs. Ag/AgCl, which is indeed characteristic of electrochemical oscillatory phenomena. Moreover, the oscillatory behavior was found to depend on the electrode rotation rate, the direction of potential scan, pH of the solution and the concentration of H2O2, similar to that previously observed on Au [100] and Ag polycrystalline electrode surfaces during the reduction of H2O2. A probable explanation for the observed current oscillation is given based on the comparision with the current oscillation behavior on Au [100] and Ag polycrystalline electrodes. The reduction of H2O2 catalyzed by OHad (H2O2 + H+ + OHad + e → 2 OHad + H2O) is an autocatalytic reaction which is characteristic of electrochemical oscillatory phenomena and is controlled by the formation and disappearance of OHad on the Hg adatom-modified Au electrode surface.

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  • Hidetoshi HONBO, Yasushi MURANAKA, Fusaji KITA
    2001 Volume 69 Issue 9 Pages 686-691
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    The thermal decomposition reactions of lithium-intercalated graphite electrodes with the electrolyte solution have been investigated by DSC measurements. Three exothermic reaction peaks appeared in the DSC curves around 130°C (peak 1), 260°C (peak 2) and 300°C (peak 3), respectively. The total amount of generated exothermic heat increased linearly with the amount of intercalated lithium, not depending on specific surface area of graphite powder. The increase of specific surface area reduced temperatures of peak 2 and peak 3, and magnified the amount of heat generated at peak 1. The increase of specific surface area is considered to accelerate the thermal decomposition reactions of lithium-intercalated graphite with the electrolyte solution and reaction at peak 1, which was associated with passivation film formation. The reaction around 130°C has been investigated by GC and FT-IR measurements. Li2CO3 was produced on the graphite surface and CO2 gas was evolved during lithium-intercalated graphite heating at 130°C. It was supposed that lithium alkyl carbonate was created on the graphite surface at first and lithium alkyl carbonate was decomposed immediately to Li2CO3, which was more stable.

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Technological Report
  • Koichi TAKIZAWA, Akifusa HAGIWARA
    2001 Volume 69 Issue 9 Pages 692-698
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    Li-Co-Ni mixed metal oxide is expected to be as stable in molten carbonates as LiCoO2 and attain conductivity as good as lithiated NiO. The present study examined the behavior of Li-Co-Ni mixed metal oxide in molten carbonates and its characterization as an alternative cathode material for molten carbonate fuel cells. It was found that phase separation occurred if the partial pressure of carbon dioxide was high. In this case, formation of NiO is dominant. The concentrations of Ni and Co in molten carbonates approach to respective solubilities of NiO and LiCoO2 as the decomposition reaction progresses. Also this oxide has no substantial solubility suppression effect. The conductivity of this material is affected by phase separation, therefore care must be directed to the partial pressure of carbon dioxide. As a result of a single cell test for 10000 hours using mixed metal oxide as cathode, it was recognized that Co deposited on the anode surface, though its effect of cell performance was left uncertain.

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Note
  • Hiroshi INOUE, Takeshi ITO, Chiaki IWAKURA
    2001 Volume 69 Issue 9 Pages 699-701
    Published: September 05, 2001
    Released: September 25, 2019
    JOURNALS OPEN ACCESS

    A new hydrogenation system, which combined electrochemical production of atomic hydrogen with hydrogenation of unsaturated organic compounds with the atomic hydrogen, was used for the hydrogenation of crotonaldehyde, butyraldehyde and crotyl alcohol. The sole hydrogenation product of crotonaldehyde was butyraldehyde when Pd black was deposited on the substrate-side of the Pd sheet in this system. 1-Butanol and crotyl alcohol together with butyraldehyde as a main product were produced on the Pt black-loaded palladized Pd sheet. In the hydrogenation of butyraldehyde, 1-butanol was a sole hydrogenation product. On the contrary, in the hydrogenation of crotyl alcohol, not only 1-butanol as a hydrogenation product but also butyraldehyde as an isomerization product was produced. The ratio of the rate of 1-butanol production to butyraldehyde production varied with the electrolytic current for the production of atomic hydrogen and the concentration of crotyl alcohol, suggesting that the product selectivity can be strictly controlled by appropriate combination of these two factors.

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Micro-Chip Capillary Electrophresis—Frontier of m-TAS (2)
Techniques in Electrochemical Measurements
Salon
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