Electrochemistry
Online ISSN : 2186-2451
Print ISSN : 1344-3542
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79 巻 , 5 号
選択された号の論文の31件中1~31を表示しています
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第45回論文特集号 本格普及へ進展を続ける固体高分子形燃料電池
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Headline
  • Hiroyuki UCHIDA, Hiroshi YANO, Mitsuru WAKISAKA, Masahiro WATANABE
    79 巻 (2011) 5 号 p. 303-311
    公開日: 2012/03/30
    ジャーナル オープンアクセス
    We have clarified for Pt nanoparticles supported on carbon black that the oxygen reduction reaction (ORR) activities are not affected by differences in the particle size. Enhanced activities in the ORR have been demonstrated at Pt alloyed with non-precious metals such as Fe, Co, and Ni. By use of multiple analysis methods, we found that the dissolution of the surface alloy layer was followed by a rearrangement of the remaining Pt layer, resulting in a Pt skin layer, which can protect the underlying bulk alloy. It was shown that a modified electronic structure at the Pt skin layer induced enhanced ORR activity due to an increased coverage of oxygen atoms. These results contribute to establishing a clear strategy for the design of highly active electrocatalysts for fuel cells.
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総合論文
  • Masahiro IDE, Hironosuke IKEDA
    79 巻 (2011) 5 号 p. 312-317
    公開日: 2012/03/30
    ジャーナル オープンアクセス
    A long-term operation test of PEFCs was conducted for single cells having an effective area of 25 cm2. The decay rate of the cell voltage was relatively large in the beginning, decreased to about 4 µV h−1 from 3000 to 6000 h, and about 7 µV h−1 in the later stage from 9000 to 12000 h. In order to clarify the cause of the voltage decay, materials composing membrane electrode assembly (MEA) were analyzed by disassembling a cell every 3000 h. After operation, changes of materials, such as particle size change of Pt-Co cathode catalyst, loss of ionomer layers on Pt-Co/C, decrease in thickness of the polymer electrolyte membrane, pore size changes of the cathode, were observed. Electrochemical active surface area of the electrode showed a decreasing tendency. Based on these results, we focused on the improvement of cathode, and developed a “four-layer electrode catalyst” which consisted of Pt-Co alloy particle, carbon support, ionomer and fluorocarbon resin. A test cell using this new type cathode exhibited better performances than a cell using conventional cathode in the durability test under low humidity or low temperature conditions.
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コミュニケーション
報文
  • Myoungseok LEE, Makoto UCHIDA, Kazuki OKAYA, Hiroyuki UCHIDA, Masahiro ...
    79 巻 (2011) 5 号 p. 381-387
    公開日: 2012/03/30
    ジャーナル フリー
    The objective of this research was to assess the feasibility of the use of highly corrosion resistant graphitized carbon (GC) as a support for Pt nanoparticles in polymer electrolyte fuel cells and to assess the role of the state of Pt dispersion in the maintenance of performance. Three types of 50 wt% Pt-loaded catalysts (commercial Pt/CB, Pt/GC and an in-house-prepared nanocapsule Pt/GC) were subjected to durability testing by means of a standard voltage step protocol (0.9 V↔1.3 V vs. RHE, holding 30 s at each voltage, 1 min for one cycle) at 65°C with H2 (anode) and N2 (cathode), and ambient pressure (0.1 MPa). The durability was estimated on the basis of either 3000 potential cycles (commercial Pt/CB) or 10000 cycles (commercial Pt/GC and nanocapsule Pt/GC). The current-voltage curves were measured initially and after certain numbers of cycles N at 65°C, 100% RH with H2 and air. The electrochemically active surface area (ECA) decreased with increasing N, particularly the commercial Pt/CB, which underwent severe degradation in the cathode. In contrast, commercial Pt/GC and nanocapsule Pt/GC showed slow ECA degradation, due to the high corrosion resistance of GC. Furthermore, it was found that the decrease in cell performance was smaller for the nanocapsule Pt/GC compared to that for the commercial Pt/GC by 10 to 50 mV, because the Pt nanoparticles of the nanocapsule Pt/GC were well dispersed over the whole GC surface. We also examined the changes in the state of dispersion of the Pt nanoparticles by use of transmission electron microscopy (TEM).
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  • Kenji TAKADA, Yuta ISHIGAMI, Satoki HIRAKATA, Makoto UCHIDA, Yuzo NAGU ...
    79 巻 (2011) 5 号 p. 388-391
    公開日: 2012/03/30
    ジャーナル フリー
    Gas diffusion layer (GDL) is an important component for the performance of polymer electrolyte fuel cells controlling the gas flow and the water transport. In this study, the real-time formation process of water droplets on two GDLs with different pore sizes was imaged using a CCD camera during the cell operation. A porphyrin luminescent dye was coated on the GDLs to clarify the shape of the water droplets. On the GDL with a smaller pore size, the droplets were distributed uniformly on the GDL in the flow channel at the cathode. On the GDL with a larger pore size, the water droplets were larger and formed mainly near the ribs of the flow channel, and the droplets were observed to move slowly towards the gas outlet. The difference in the formation of water droplets were explained by the difference in the partial air flow inside the GDLs along the gas channel.
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  • Hisaaki GYOTEN, Tetsuaki HIRAYAMA, Jun-ichi KONDO, Akira TAOMOTO, Masa ...
    79 巻 (2011) 5 号 p. 392-398
    公開日: 2012/03/30
    ジャーナル フリー
    We carried out quantitative transmission electron microscopy (TEM) analysis for the Pt morphology in the cathode catalyst layer of polymer electrolyte fuel cells (PEFCs) for investigating the transportation of Pt species during the cell operation. The specimens for the TEM observation were cut offfrom the catalyst layer with approximately 100nm thickness without embedding it in a resin. The size and number of the Pt particles contained in the same volume of the catalyst layer were accumulated to obtain their size distributions. The distributions of Pt surface areas and volumes were also estimated from the size distributions, assuming that the Pt particles are sphere. The total volumes of the Pt particles estimated by the analysis corresponded to 65–86% of those calculated from the Pt loadings at the MEA preparations. The change in the Pt morphology before and after a potential cycling test without power generation was investigated. For the cycled MEA, the Pt surface area per weight (the specific Pt surface area) calculated from the TEM observation was nearly identical to the electrochemically active surface area (ECSA) by cyclic voltammetry(CV). This novel method for the TEM analysis provides the distributions of the Pt concentration in the whole catalyst layer as well as the Pt surface distribution and the Pt volume distribution in a given area of the catalyst layer without chemical analysis or spectroscopy. Those data can be used to understand the dependence of the microstructures of the catalyst layer on the cell performances.
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  • Katsuyoshi KAKINUMA, Yuko WAKASUGI, Makoto UCHIDA, Takeo KAMINO, Hiroy ...
    79 巻 (2011) 5 号 p. 399-403
    公開日: 2012/03/30
    ジャーナル フリー
    We synthesized a Pt catalyst supported on nanometer-size titanium nitride particles (Pt/TiN) by the nanocapsule method. The titanium nitride (TiN) support, which was synthesized by the radio-frequency (RF) plasma method, had high electrical conductivity, up to 850 S cm −1 at room temperature, with a surface area of 40 m2 g−1. The Pt loading on the catalyst was 19.5 wt%. The electrochemically active surface area (ECA) was 72 m2 g(Pt)−1. During the potential step cycling test (0.9∼1.3 V), the ECA values for Pt/TiN remained high and exceeded that of a commercial Pt catalyst supported on carbon black (Pt/CB) for potential step cycle numbers above 300. From the results of linear sweep voltammetry using a rotating disk electrode, we observed that the oxygen reduction reaction activity of the Pt/TiN exceeded that of Pt/CB. We conclude that the nanometer-size TiN might be a good candidate support material for the cathode of the polymer electrolyte fuel cell (PEFC).
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  • Seiho SUGAWARA, Yosuke SUZUKI, Shyam S. KOCHA, Kazuhiko SHINOHARA
    79 巻 (2011) 5 号 p. 404-413
    公開日: 2012/03/30
    ジャーナル フリー
    A simple macrohomogeneous 1-D model of the polymer electrolyte fuel cell (PEFC) cathode catalyst layer incorporating ORR kinetics and including the effects of Pt surface oxide coverage, proton migration, and oxygen diffusion is introduced. In the model, both the site-blocking and the energetic effects of the Pt surface oxide are incorporated and applied to actual fuel cell data. Measured polarization curves are fitted in both the cathodic and anodic directions using a single value of the intrinsic exchange current density (that is independent of the Pt oxide coverage) representing the entire potential range of operation. By fitting with this model, the catalytic activity is broken down into the intrinsic exchange current density, the oxide coverage, and the Temkin parameter. The fitting parameters used in the model are the exchange current density, the Temkin parameter, and the transmissibility of oxygen within catalyst layer. The electrochemically active surface area and the proton conduction resistance within catalyst layer were determined using experimental diagnostic techniques. The surface charge representing oxide species was also measured experimentally and converted into a surface coverage based on an assumed species. The analysis of polarization curves using this modeling approach may help to provide a deeper understanding that could accelerates the development and characterization of new catalysts.
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  • Atsuhiko ONUMA, Makoto MORISHIMA, Yoshiyuki TAKAMORI, Iwao FUKUCHI, Ta ...
    79 巻 (2011) 5 号 p. 414-418
    公開日: 2012/03/30
    ジャーナル フリー
    To improve the proton conductivity of an aromatic polymer electrolyte membrane (PEM), the relationship between the size of a micro-phase-separated structure and the proton conductivity of the membrane were investigated. Micro-phase-structures, which are comprised of hydrophilic and hydrophobic domains, were measured by using the stained small-angle X-ray scattering (SAXS) method in wet conditions. Periodic sizes calculated from SAXS profiles in a dry state were as large as those measured by scanning transmission electron microscopy (STEM), which indicates that micro-phase-separated structures can be effectively evaluated by using SAXS. The membranes with the larger periodic size showed higher proton conductivity; however, water content was not simply increased with the increasing in the periodic size. Conceivably, the periodic size of the phase-separated-structure had an effect on both the proton conductivity at the same water content and on the water content itself, and the proton conductivity was increased by these two factors. The results indicated that the optimum periodic size of micro-phase-separated structures between proton conductivity and water content was 35 nm in this study, and it may be possible to develop a membrane with high proton conductivity and low water content by controlling the size of the phase-separated-structure.
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  • Koichi MATSUZAWA, Tomoaki TAKAHASHI, Akimitsu ISHIHARA, Shigenori MITS ...
    79 巻 (2011) 5 号 p. 419-423
    公開日: 2012/03/30
    ジャーナル フリー
    In order to develop a principle of the materials design for the high CO2 generation efficiency during the C2H5OH electrooxidation, the reaction pathways during the electrooxidation of C2H5OH and CH3CHO which is a by-product during the electrooxidation of C2H5OH have been quantitatively analyzed. As a result, a direct pathway from C2H5OH to CO2 and a pathway via CH3CHO toward CO2 coexisted at 0.4 V, 70°C. At 0.6 V, 70°C, the both pathways from C2H5OH to directly CO2 and from C2H5OH via CH3COOH to CO2 existed. Especially in the latter pathway, the activity of Pt was found to be deteriorated by the adsorbed species which would be formed as an intermediate of CH3COOH formation.
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ノート
  • Jun YANO, Yushi TAKATSUKA, Yutaka HARIMA, Akira KITANI
    79 巻 (2011) 5 号 p. 424-427
    公開日: 2012/03/30
    ジャーナル フリー
    To develop better and less expensive electrocatalysts for the oxidation of ethanol in direct ethanol fuel cells, several combinations of a conductive polymer polyaniline (PANI), dispersed Pt particles and pre-dispersed metal particles, such as Sn and Fe, were examined. The anodic current for the ethanol oxidation (iEtOH) was gained in larger quantities using the glassy carbon electrode covered with the Pt-dispersed PANI film than using the naked glassy carbon electrode. The enhancement of iEtOH strongly depended on the morphology and the electrical conductivity of the five PANI films with different dopant anions: SO42−, NO3 and Cl. The highest activity was achieved for the SO42−-doped PANI film. To reduce the amount of the expensive Pt particles, inexpensive base metal particles were pre-dispersed on the PANI film, and the Pt particles were then dispersed on the film. Among the investigated pre-dispersed metal particles (Sn, Cu, Zn and Fe), the highest activity was obtained with Sn particles for the ethanol oxidation. When the ratio of the dispersed Pt to Sn particles ranged from 10:90 to 100:0, iEtOH was higher than that measured with the dispersed Pt particle PANI films without the Sn particles. This meant that utilizing dispersed Sn particles could reduce the amount of the dispersed Pt particles needed.
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