Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
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75 巻 , 2 号
選択された号の論文の41件中1~41を表示しています
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論文特集号 固体高分子形燃料電池の材料開発と評価技術
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  • Yoshitsugu SONE, Yusuke ARIYAMA, Masatoshi UNO, Hitoshi NAITO, Hiromit ...
    75 巻 (2007) 2 号 p. 197-200
    公開日: 2012/03/20
    ジャーナル フリー
    The proton conductivity of the reinforced perfluorinated membrane was measured under various conditions of humidity and temperature using a four-electrode impedance method. The conductivity of the membrane was over 8×10−2 S cm−1 with 70% relative humidity at 70°C; it varied strongly with both humidity and temperature. A stable conductivity condition was observed when the relative humidity was over 20%. From the results, the activation energy was calculated to be less than 20 kJ mol−1 at any humidity. These results suggested that the Grothuss-type proton conduction might be dominant for the proton migration inside the reinforced membrane at a wide range of humidity.
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  • Eiji ENDOH, Shinji KINOSHITA
    75 巻 (2007) 2 号 p. 201-206
    公開日: 2012/03/20
    ジャーナル フリー
    The effects of the ion exchange capacity (IEC), of the perfluorosulfonic acid polymers, on the performance of PEFC has been investigated quantitatively by a simplified analysis method. It was determined that the IEC of the membrane influences the mass transfer overpotential of the oxygen reduction reaction (ORR). Whereas, it was determined that the IEC of the catalyst coating ionomer influences the activation overpotential of the ORR.
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  • Minoru INABA, Hirohisa YAMADA, Ryota UMEBAYASHI, Masashi SUGISHITA, Ak ...
    75 巻 (2007) 2 号 p. 207-212
    公開日: 2012/03/20
    ジャーナル フリー
    A durability test of a PEFC single cell using perfluorinated ionomer membrane as an electrolyte was carried out at 80°C under low humidification. The observed voltage drop under low humidification was mostly reversible up to 5200 h. However, hydrogen crossover increased with time and fluoride-ion was continuously detected in drain water, which indicated that membrane degradation proceeded steadily during the test under low humidification. Fluoride-ion release rate decreased with increasing current density, which suggested that hydrogen peroxide was formed at the anode catalyst layer upon direct combustion of hydrogen with crossover oxygen. Drain water analysis revealed that large amounts of sulfate ions and Fe(II or III) ions were released in addition to fluoride ions when the cell was temporarily operated under full humidification. From this fact, it was concluded that accumulation of impurities and hydrogen peroxide under low humidification is a reason why low humidification enhances membrane degradation.
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  • Shigehiro KITTA, Tadaoki OKUMOTO, Hiroyuki UCHIDA, Masahiro WATANABE
    75 巻 (2007) 2 号 p. 213-216
    公開日: 2012/03/20
    ジャーナル フリー
    A new design of metal separator coated with corrosion-resistive and electronically conductive carbon/resin composite layers has been developed. A stainless steel flat plate was coated with a thin composite layer, followed by a formation of ribs of the similar composite on the layer as the gas flow field. We found that the electric conductivity was improved by blending carbon fiber with Ketjen black in the carbon/resin composite. The lowest resistivity of 20.6 mΩ cm was obtained at total carbon content of 50 vol.% with blend ratio of the carbon fiber of 75 vol.%. The composite exhibited a good stability in hot water at 90°C for 2000 h, releasing very small amount of ionic impurities.
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  • Kohei MIYAZAKI, Yuhei NISHIDA, Koji MATSUOKA, Yasutoshi IRIYAMA, Takes ...
    75 巻 (2007) 2 号 p. 217-220
    公開日: 2012/03/20
    ジャーナル フリー
    Gold nanoparticles supported on Pt-Sn/C and Pt/C (nano-Au/Pt-Sn/C and nano-Au/Pt/C, respectively) were prepared by the gas-phase grafting method and their catalytic activities for methanol oxidation were evaluated by steady-state polarization measurement. X-ray diffraction measurement revealed that gold nanoparticles had a diameter of ca. 4 nm, and X-ray photoelectron spectroscopy revealed that gold nanoparticles deposited on Pt-Sn/C and Pt/C were in the zero-oxidation state. Electrochemical measurements performed in an aqueous solution of 1 M (M=mol dm−3) HClO4 and 1 M CH3OH demonstrated that the addition of gold nanoparticles to Pt-Sn/C catalyst gave higher catalytic activities for methanol oxidation than Pt-Sn/C catalyst without gold nanoparticles. In contrast, nano-Au/Pt/C and Pt/C showed almost identical catalytic activities. These results showed that the catalytic activities of gold nanoparticles were influenced by the supporting materials.
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  • Tomoyuki TADA, Nobuhito TOSHIMA, Yumi YAMAMOTO, Masahiko INOUE
    75 巻 (2007) 2 号 p. 221-230
    公開日: 2012/03/20
    ジャーナル フリー
    To investigate the effect of fuel cell operating conditions on catalyst agglomeration of a platinum catalyst, several single cell life tests were carried out under different conditions. It was found that catalyst agglomeration was accelerated by higher temperature operation, while it was not accelerated by higher current density (∼1.5 A/cm2) nor by higher potential (∼0.85 V) when the operating temperature was 100°C. Catalyst agglomeration was much more severe in the cathode, and the surface area of the platinum catalyst was decreased from 58.9 m2/g to 30.6 m2/g after a life test for 4000 hours. Because there was no sign of platinum dissolution/precipitation in the ionomer phase and there was a peak tail in the direction of larger particles in the particle distribution after 4000 hours, this catalyst agglomeration may be caused by a crystallite migration mechanism and a coalescence growth mechanism. In addition, to investigate the degradation of the CO-tolerance performance of a platinum-ruthenium catalyst, 5000-hour life tests and several life tests for shorter periods were carried out. It was found that the CO-tolerance performance was gradually decreased with time and that one of the reasons for the degradation was considered to be decomposition of the platinum-ruthenium alloy. It was also found that an air-bleeding technique could reduce the loss of cell performance due to the degradation of the CO-tolerance performance but may slightly accelerate the catalyst material degradation.
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  • Arata GOTO, Yusuke KAWAGOE, Yasushi KATAYAMA, Takashi MIURA
    75 巻 (2007) 2 号 p. 231-237
    公開日: 2012/03/20
    ジャーナル フリー
    The Nafion membrane impregnated with various room-temperature ionic liquids have been prepared and characterized as the electrolytes for polymer electrolyte fuel cells (PEFCs) operated at elevated temperature (100∼200°C). The continuous proton transportation in the membrane was confirmed under dry hydrogen atmosphere at 160°C. The ionic conductivity of the membrane was determined by both DC and AC measurements under dry hydrogen atmosphere and found to reach the order of 10−2 S cm−1 at 200°C without humidification. It is suggested that the high ionic conductivity of the membrane is caused mainly by free ionic liquids in the membranes. The continuous operation of the PEFC using the membrane was found to be possible without humidification at 120°C. However, the overpotential at the cathode was found to be large compared with the anode probably due to the sluggish electrode reaction and/or the slow diffusion of HTFSI in the membranes.
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  • Hiroki CHIBA, Shin-ichi KOMAZAKI, Masao WATANABE, Yutaka KOHNO
    75 巻 (2007) 2 号 p. 238-242
    公開日: 2012/03/20
    ジャーナル フリー
    AMPS polymer membranes containing various amounts of water were fabricated to simulate the material degradation of in-service membranes in PEFC. The life time of PEFC was measured along with measurements of tensile properties and swelling of the membranes. It was concluded that (1) the failure of PEFC is caused by fracture of the AMPS membrane; (2) the tensile strength of the AMPS membrane decreases with increasing water content due to a softening of the membrane; and (3) a high concentration of the cross-linker molecules is very effective for improving the mechanical strength of the membrane and the resistive force against the swelling, which results in the longer durability of PEFC.
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技術報文
  • Yong Ming LI, Kazuhiro NODA, Koichiro HINOKUMA
    75 巻 (2007) 2 号 p. 243-247
    公開日: 2012/03/20
    ジャーナル フリー
    The nano-composite of the phosphoric acid derivative of fullerene ([PO(OH)2]2CC60) with SiO2 was synthesized using the in-situ reaction from [PO(OH)2]2CC60 with tetraethoxysilane (TEOS). The nano-composite was characterized using FT-IR measurements, and its morphology was observed using SEM. The humidity dependence of their proton conductivity for both [PO(OH)2]2CC60 and its nano-composite was investigated. The proton conductivity of the nano-composite is increased more than one order of magnitude higher than that of [PO(OH)2]2CC60 under low relative humidity. This is probably because the more proton conductive sites are generated by SiO2. However its proton conductivity is lower in the humidity range above 60%, probably because the number of the highly dissociative protons from phosphoric acid is decreased after being combined with silica.
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  • Taro KINUMOTO, Yoshiharu UCHIMOTO, Xiaoming XIAO, Katsumi KATAKURA, Ke ...
    75 巻 (2007) 2 号 p. 248-257
    公開日: 2012/03/20
    ジャーナル フリー
    Meniscus formation and hydrogen oxidation on partially immersed Nafion® coated and uncoated electrodes were investigated as a model of the reaction sites in polymer electrolyte fuel cells. Hydrogen oxidation current was measured at 0.4 V with raising the electrode, and simultaneously the optical microscope observation was carried out. The intrinsic meniscus developed from the boundary between Nafion®-coated (Pt-loaded) and the uncoated parts. A liquid thin film, which would have sub-micron order thickness, was observed above the intrinsic meniscus on the uncoated electrode under hydrogen atmosphere after development of the intrinsic meniscus was terminated. At the same time, hydrogen oxidation current was further increased. Therefore, the liquid thin film behaved as an effective supermeniscus on the uncoated electrode. On Nafion®-coated electrode, hydrogen oxidation current was small in the intrinsic meniscus region; however, it became larger with an increase in the exposed area of Nafion®-coated part to the gas phase. This fact showed that hydrogen oxidation reaction occurred mainly in the exposed Nafion®-coated part. The current distribution in the supermeniscus region was discussed, and it was found that the effective area is controlled by the ohmic drop in the Nafion® coating.
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