Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
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77 巻 , 2 号
選択された号の論文の22件中1~22を表示しています
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論文特集号 低温作動化が進む固体酸化物形燃料電池
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  • Tatsumi ISHIHARA, Hiroyuki ETO, Hao ZHONG, Hiroshige MATSUMOTO
    77 巻 (2009) 2 号 p. 115-122
    公開日: 2012/03/22
    ジャーナル オープンアクセス
    Solid Oxide Fuel Cells (SOFCs) show a great promise as new power generators with high energy conversion efficiency. Decreasing operating temperature is critically requested for the further improvement in SOFC performance, in particular, for improving stability. Perovskite oxide of LaGaO3, doped with La and Mg exhibits the high oxide ion conductivity over wide PO2 range; the value is higher than that of Y2O3 stabilized ZrO2 by an order of magnitude at 773 K and useful for electrolyte of SOFC operating at intermediate temperature range. When LaGaO3-based oxide was used as the electrolyte of SOFC, the power density could be improved greatly, in particular in low temperature range. In this study, power generation property of SOFC using LaGaO3 electrolyte and also the improvement in power density of the cell by using a LaGaO3 thin film is also introduced. The maximum power density of the cell using LaGaO3 based oxide is as high as 0.6 W/cm2 at 773 K. This suggests that SOFC could be operable at temperature lower than 773 K. Tubular type cell stack using LSGM thin film is also introduced.
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  • Takanori ITOH, Saori SHIRASAKI, Yoshinori FUJIE, Naoto KITAMURA, Yasus ...
    77 巻 (2009) 2 号 p. 161-168
    公開日: 2012/03/22
    ジャーナル オープンアクセス
    In this study, we have analyzed the mechanism of mixed conduction due to electrons and oxygen ions in (La0.75Sr0.25)MnO3.00 (LSM) and (Ba0.5Sr0.5)(Co0.8Fe0.2)O2.33 (BSCF) by using the Rietveld refinement technique and the maximum entropy method (MEM). Using neutron diffraction measurements, we showed that the site occupancies of the O1 (4c) and O2 (8d) sites in BSCF are 0.59 and 0.87, respectively. Further, the MEM analysis of synchrotron X-ray diffraction measurements revealed that the Mn-O plane in LSM has a strong, isotropic covalent bond that enables conduction of electrons. The (Co,Fe)-O2 plane with a covalent bond and a low concentration of oxygen vacancies in BSCF can also conduct electrons. On the other hand, the (Ba,Sr)-O1 plane in BSCF, which has a high concentration of oxygen vacancies, large isotropic displacement parameter (Uiso) values, and a strong ionic bond, is responsible for the diffusion of oxygen ions.
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  • Takeshi OHZEKI, Yoichiro OGATA, Kenji TSUDA, Takuya HASHIMOTO
    77 巻 (2009) 2 号 p. 169-177
    公開日: 2012/03/22
    ジャーナル オープンアクセス
    Construction of structural phase diagram of LaGa1−xMgxO3−δ has been attempted by using synchrotron X-ray diffraction, high temperature X-ray diffraction, dilatometry and differential scanning calorimetry. Existence of long-period anti-phase domain structure(LPAPDS) observed in the specimens with x larger than 0.10 by using electron diffraction analysis was considered for the phase diagram construction. Existence of four phases has been proposed and their phase relationship has been evaluated. For the specimen with x≈0.00, orthorhombic phase free from LPAPDS and rhombohedral phase without LPAPDS were detected. In LaGa1−xMgxO3−δ with x larger than 0.10, orthorhombic phase and rhombohedral phase with LPAPDS were proposed. It was suggested that the slow kinetics of the phase transition from orthorhombic phase with LPAPDS to rhombohedral with LPAPDS was the origin of region, where mixture of orthorhombic phase and rhombohedral phase was observed. Existence of two-phase region, where phase free from LPAPDS and one with LPAPDS coexist, has been clarified. The compositional region, where x is around 0.05, is revealed to be the two-phase region from room temperature to 800°C.
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  • Masashi MORI, Yu LIU, Shin-ichi HASHIMOTO, Katsuhito TAKEI
    77 巻 (2009) 2 号 p. 178-183
    公開日: 2012/03/22
    ジャーナル オープンアクセス
    In this work, current leakage of the micro-tubular cells with a 10-µm Ce0.9Gd0.1O1.95 (GDC) electrolyte based on cathode- and anode-supported configurations was investigated at 500 and 550°C. It was found that the open circuit voltage (VOC) of the GDC membrane cell greatly corresponds to the cell structure, particularly influenced by the electrode polarization. Calculations derived from the experimental results showed that the leak current through the GDC electrolyte gradually vanished as the external current increased to certain degree, which accordingly related to the polarizations, due to the cell structures. The anode-supported cell can be capable of generating a high power density with a reasonable maximum-efficiency. On the other hand, not only VOC but also cell output and efficiency were significantly lowered for the cathode-supported cell. It suggests that an appropriate cell structure is necessary to make the doped ceria a promising electrolyte for low-intermediate temperature power-generation applications.
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  • Masashi MORI, Yu LIU, Shuhua MA, Shin-ichi HASHIMOTO, Kenji YASUMOTO
    77 巻 (2009) 2 号 p. 184-189
    公開日: 2012/03/22
    ジャーナル オープンアクセス
    The compatibility of bismuth compounds as a sintering aid for (ZrO2)0.89(ScO1.5)0.1(CeO2)0.01 (ScSZ) electrolyte in intermediate-temperature solid oxide fuel cells (IT-SOFCs) has been discussed. Addition of 3 mol% BiO1.5 considerably decreased the sintering temperature of ScSZ of approximately 200°C and achieved the densification with a relative density above 95% at 1200°C. The solid solubility limit of BiO1.5 in ScSZ was less than 2 mol%. Dispersion of Bi2O3 at the grain boundaries correspondingly accelerated the growth of ScSZ grains and increased the grain boundary resistance at temperatures below 450°C. At elevated temperatures of 450–750°C, the electrical conductivity of the ScSZ after doping remained almost unchangeable in air and under reducing atmospheres. The results suggested that bismuth addition is promising to be applicable to a low-temperature co-firing fabrication of ScSZ based components for IT-SOFCs.
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  • Haruo KISHIMOTO, Katsuhiko YAMAJI, Teruhisa HORITA, Yue-Ping XIONG, Ma ...
    77 巻 (2009) 2 号 p. 190-194
    公開日: 2012/03/22
    ジャーナル オープンアクセス
    The reaction process for the Ni-SDC cermet anode on the ScSZ electrolyte was examined by impedance spectrometry with wet hydrogen fuels and results were compared with previously obtained data for the Ni-ScSZ anode. Area specific conductivities (σSDC) for each rate controlling steps were obtained from the impedance spectra. Hydrogen and water vapor pressure (PH2 and PH2O, respectively) dependencies and temperature (T) dependence of σ for the Ni-SDC are compared with those of the Ni-ScSZ. Three rate controlling steps were observed for the Ni-SDC anode. The σSDC obtained at the lowest frequency region (σLSDC) shows slightly negative dependence on the T and it was proportional to the PH2O. The σMSDC obtained in the middle frequency region is activated with increasing PH2, PH2O and T. This process should be associated with the electrochemical oxidation reaction step accompanied with charge transfer. The σHSDC obtained at the highest frequency region is independent on both PH2 and PH2O, but it is activated with increasing temperature. This process appears only in the Ni-SDC anode, and therefore, it is reasonable to assume formation of proton at the Ni/SDC interface. The difference in reaction processes between the Ni-SDC anode and the Ni-ScSZ anode is discussed.
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