Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
ISSN-L : 1344-3542
Volume 72 , Issue 9
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  • Tetsuya IWAGISHI, Yuya NAKATSUKA, Hiroaki YAMAMOTO, Koichiro KOYAMA, H ...
    2004 Volume 72 Issue 9 Pages 618-623
    Published: September 05, 2004
    Released: June 08, 2019
    JOURNALS OPEN ACCESS

    The electrodeposition of the Zn-Mg alloys from Lewis basic ZnBr2-MgBr2-1-ethyl-3-methylimidazolium bromide (EMIB) molten salts with glycerin, in which Mg(II) ions were introduced by the chemical reaction of Mg metal with Zn(II) ions, was investigated at 140°C by potentiostatic and galvanostatic electrolyses and cathodic polarization measurements. The molten salts used were prepared by chemical displacement of prescribed amounts of Zn in ZnBr2-EMIB molten salts with glycerin by Mg. The cathodic polarization curves showed that EMI+ cation in the molten salt decomposed below -1.0 V vs. Zn(II)/Zn in ZnBr2-EMIB-glycerin (15: 42.5: 42.5 mol%). Thus the potentiostatic electrolysis was carried out at -0.8 V, and the grayish metallic-colored electrodeposits were obtained. The Mg content in the Zn-Mg electrodeposits was from 12 to 25 mol%. The X-ray diffraction analysis showed the diffraction peaks of Mg2Znli in addition to Zn, CuZn5 and the substrate Cu, and alao suggested the forced dissolution of Mg in the Zn matrix. The, time of generation of red rust for Zn-20 mol% Mg alloy coating steel was about 20 times longer than with that of Zn coating steel in 5 mass% NaCl aqueous solution at 35°C.

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  • Kazuhiro NAGAHARA, Masatoshi SAKAIRI, Hideaki TAKAHASHI, Kazuyoshi MAT ...
    2004 Volume 72 Issue 9 Pages 624-632
    Published: September 05, 2004
    Released: June 08, 2019
    JOURNALS OPEN ACCESS

    Niobium specimens with chemical polishing were anodized in a phosphoric acid solution galvanostatically up to Ea = 100 V, and then potentiostatically at Ea = 100 V. During galvanostatic anodizing, anode potential increased almost linearly with time, while, during potentiostatic anodizing,anodic current decreased with time before tpa = 3.6 ks,and then increased slowly before decreasing again at tpa = 32.4ks. Galvanostatic anodizing allowed compact oxide films to grow at a steady rate, and also micro imperfections to form in the film at the ridge of convex network structure produced by chemical polishing. The imperfections grew during potentiostatic anodizing, showing the cracking and rolling-up of the oxide film as well as the formation of crystalline oxide at the center of the imperfections. Long-term anodizing lead to the coalescence of the imperfections and eventually the covering of all surfaces with imperfections. Parallel equivalent capacitance, Cp, of anodic oxide films decreased with tpa before 3.6 ks, and increased after 3.6 ks, w ile the dielectric dissipation factor, tan δ, remained to a small value before 3.6 ks, and increased with tpa after 3.6 ks. Measurements with higher bias voltages caused less dielectric dispersion of anodic oxide films. The mechanism of structural change of anodic oxide films during potentiostatic anodizing, and the correlation between the structure and dielectric properties of anodic oxide films are discussed.

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  • Hirofumi SUMI, Yasmobu MIZUTANI, Makoto TAKAHASHI, Mitsuhiko HAYASHI, ...
    2004 Volume 72 Issue 9 Pages 633-636
    Published: September 05, 2004
    Released: June 08, 2019
    JOURNALS OPEN ACCESS

    Protonic conductivities of phosphate glasses made by a condensation-polymerization below liquidus temperature were Measured. Phosphate glasses of both the Sr-Ba-Pb and Sr-Zr-Pb series possess a conductivity of 6×10-4 S/cm at 373 K, three order of magnitude as high as that of glasses made by a conventional melt-quenching. The performance of power generation was evaluated with a use of the glasses as electrolyte of fuel cells. Power density of l mW/cm2 was obtained aτ 413K and 0.035atm of water partial pressure. These fuel cells were found to be operative at higher temperature and lower humidity than those of polymer electrolyte fuel cells

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Technological Report
  • Takahiro SHIMIZU, Mohamed MOHAMEDI, Toshiyuki MOMMA, Tetsuya OSAKA
    2004 Volume 72 Issue 9 Pages 637-640
    Published: September 05, 2004
    Released: June 08, 2019
    JOURNALS OPEN ACCESS

    In this work, we describe the fabrication of a room temperature operating direct methanol fuel cell (DMFC) device for portable electronic devices and its performance as an electrical power source for portable phone. The cell stack is completely passive without external pumps or other ancillary devices. It takes oxygen from the surrounding air, whereas the methanol solution is stored in a built-in reservoir. We achieved a maximum power as high as 2 W, which is largely commensurate with cell phone requirements. The DMFC coupled to DC-to-DC converter was capable of powering a cell phone. The maximum power consumption for talk mode was of 1.2 W while 1.8 W was withdrawn from the stack when receiving a call.

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  • Makiko KISE, Shoji YOSHIOKA, Kouji HAMANO, Takashi NISHIMURA, Hiroaki ...
    2004 Volume 72 Issue 9 Pages 641-646
    Published: September 05, 2004
    Released: June 08, 2019
    JOURNALS OPEN ACCESS

    A new concept cathode is proposed to improve the safety of lithium rechargeable batteries. The cathode contains the Positive Temperature Coefficient (PTC) compound that can drastically increase resistivity at more than a specified temperature. A carbon black/polyethylene composite was selected for the PTC compound, because its resistivity increases at the melting point of polyethylene, since it expands and cuts off the conductive network of the carbon black. The PTC cathode containing the PTC compound was fabricated and its temperature dependence of resistivity was evaluated. The resistivity of PTC cathodes increases by several tens of times at 130-140°C, which is the melting point of polyethylene. In lithium rechargeable batteries using this cathode, a level nearly reaching the rated capacity is obtained at 1 C discharge current. The discharge properties of cells using PTC cathode depend on the porosity, the heat treatment, and the PTC compound ratio of the PTC cathodes. Moreover, the cell voltage using the PTC cathode dropped at 138°C under 3 C discharge condition, the same point at which the resistivity of the PTC cathode drastically increases. These results suggest that the PTC cathodes will improve the safety of lithium rechargeable batteries.

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