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Jun MARUYAMA, Nobutaka FUKUI, Masayuki KAWAGUCHI, Takahiro HASEGAWA, H ...
2011 Volume 79 Issue 5 Pages
318-321
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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A carbon-based noble-metal-free fuel cell cathode catalyst was formed by heat treatment of a mixture of glucose, Fe gluconate, and 1,4-diamino-2,3-dicyano-9,10-anthraquinone as a nitrogen source. The factors for the formation of the active site and the pore development were the heat-treatment temperature and the content of the nitrogen source in the starting mixture. The activity for oxygen reduction was dependent on the active site and the pore development, which were optimized to form the catalyst with the improved activity compared to those formed from various glucose/nitrogen source/Fe salts mixtures
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Minoru INABA, Yu MATSUI, Morihiro SAITO, Akimasa TASAKA, Kenji FUKUTA, ...
2011 Volume 79 Issue 5 Pages
322-325
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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The effects of CO
2 on the performance of an anion-exchange membrane fuel cell were investigated using a three-electrode single cell equipped with a reference electrode. Though the membrane resistance decreased at high current densities in the presence of CO
2 via the self-purging mechanism, the cell voltage was significantly lower than that for pure O
2 especially at low current densities even at a very low CO
2 concentration of 100 ppm. The overpotential at the cathode was hardly changed by the presence of CO
2, while that at the anode significantly increased in the presence of CO
2. It was concluded that carbonate/bicarbonate ions accumulated at the anode during operation, and reduces the ionic conductivity and the pH in the anode catalyst layer, which results in a high overpotential at the anode.
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Zyun SIROMA, Kazuaki YASUDA
2011 Volume 79 Issue 5 Pages
326-328
Published: May 05, 2011
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A simple one-dimensional numerical simulation for cathode catalyst layers was conducted to elucidate the signifi-cance of a structure with a gradient in the ionomer content in the cross-plane direction. First, under an assumption of uniform (one-layer) catalysts, equivalent pairs of the effective ionic conductivity and effective gas diffusion coefficient were identified. Next, results with two-layer catalysts were calculated with two pairs of parameters among the equivalent pairs obtained earlier. Comparison of the performance of the two-layer catalysts revealed that ionic conductivity is more important near the PEM, and gas diffusivity is more important near the GDL.
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Mitsuhiro INOUE, Tatsuya IWASAKI, Minoru UMEDA
2011 Volume 79 Issue 5 Pages
329-333
Published: May 05, 2011
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In this study, we succeeded in measuring the impedance spectra at the anode and cathode during the direct methanol fuel cell power generation using a single cell having a Ag/Ag
2SO
4 reference electrode. When the anode impedance is measured at 20 mA cm
−2, two semicircles are observed in the high and middle frequency ranges, and the magnitude of the latter one increases with the increasing methanol concentration. At the cathode, the impedance spectra at 20 mA cm
−2 show three semicircles, of which the magnitudes decrease with the increasing methanol concentration from 1 mol dm
−3 to 5 mol dm
−3, and increase again at 10 mol dm
−3. These results demonstrate that the increased methanol concentration magnifies the methanol oxidation reaction resistance at the anode and affects the total resistance at the cathode.
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Taro KINUMOTO, Keita NAGANO, Tomoki TSUMURA, Masahiro TOYODA
2011 Volume 79 Issue 5 Pages
334-336
Published: May 05, 2011
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A novel durable electrode catalyst of Pt/Ketjen black decorated with SnO
2 nanoparticles (Pt/SnO
2-KB) was prepared for polymer electrolyte fuel cells (PEFCs). The particle size of SnO
2 and Pt in the catalyst is
ca. 10 nm and 2 nm, respectively. The activity of Pt/SnO
2-KB for oxygen reduction reaction is almost same as that without SnO
2; on the other hand, the durability as the cathode is excellent.
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Jun SATO, Kazuki HIGURASHI, Katsutoshi FUKUDA, Wataru SUGIMOTO
2011 Volume 79 Issue 5 Pages
337-339
Published: May 05, 2011
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Graphite oxide nanosheets with three different sheet sizes were prepared from different graphite materials. The graphite oxide nanosheets were used as precursors to prepare three 20 mass% Pt/graphene composite electrocatalysts composed of different sizes of graphene. The structure and electrochemical properties in 0.1 M HClO
4 at 60°C of the three Pt/graphene electrocatalysts were studied. Well dispersed Pt nanoparticles with 2.2 nm average diameter and electrochemically active surface area of ∼50 m
2 (g-Pt)
−1 were obtained irrespective of the size of graphene. Despite the similarity in Pt nanoparticle state, the oxygen reduction reaction was strongly affected by the size of graphene. Smaller sized graphene afforded higher mass and specific activity towards the oxygen reduction reaction.
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Keisuke UKITA, Akimitsu ISHIHARA, Yoshiro OHGI, Koichi MATSUZAWA, Shig ...
2011 Volume 79 Issue 5 Pages
340-342
Published: May 05, 2011
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Zirconium oxide-based compounds without partial oxidation of zirconium carbonitride were investigated as nonplatinum cathode for polymer electrolyte fuel cell. Zirconium oxide-based compounds were prepared by solutionprecipitation method and heat-treated at different temperature. In X-ray diffraction patterns tetragonal ZrO
2 peaks decreased whereas monoclinic ZrO
2 peaks increased with increasing temperature. Onset potential for oxygen reduction reaction (ORR) of the specimen heat-treated at 1000°C reached 0.90 V vs. RHE, indicating that the specimen had definite ORR activity. The increase of ORR activity may be explained by the increase of Zr
3+ and/or oxygen vacancies due to the transformation of ZrO
2 from tetragonal to monoclinic structure from the XRD results.
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Yoshiyuki HASHIMASA, Yoshiyuki MATSUDA, Daichi IMAMURA, Motoaki AKAI
2011 Volume 79 Issue 5 Pages
343-345
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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Hydrogen for fuel cell vehicles is likely to contain impurities from its production process, and such impurities may poison the fuel cell catalyst, thus degrading the power generation performance of the polymer electrolyte fuel cell (PEFC) especially when the Platinum(Pt) loading is reduced. The effects of anode Pt loading on power generation performance degradation by H
2S and NH
3 in hydrogen fuel were investigated. The test results indicated that the lower the anode Pt loading, the more rapid the decrease in cell voltage under the influence of H
2S in the hydrogen. The amount of H
2S supplied to the cell until the cell voltage decreased by the same level (30 mV) was proportional to the anode Pt loading regardless of the hydrogen sulfide concentration. The cell voltage decrease by NH
3 in the hydrogen was not dependent on the anode Pt loading, but was influenced by the cathode Pt loading.
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Yoshiki OKAJIMA, Arata YAMAMOTO, Masao SUDOH, Susumu SAKAI, Yutaka MAT ...
2011 Volume 79 Issue 5 Pages
346-348
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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Hydrogen gas reformed from the biogas has recently been paid attention particularly from the point of view of environmental protection. In order to investigate the effect of the biogas on a polymer electrolyte membrane fuel cell, the cell performances using CO
2 containing gas as anode gas were measured by fuel cell experiments and cyclic voltammetry. The membrane-electrolyte assemblies were manufactured with a Pt or PtRu catalyst and Nafion 117 or Nafion 212, and some electrodes were loaded with a Nafion solution. As a result, it was found that the presence of coexisting CO
2 gas decreased the cell performance, while PtRu suppressed the negative effect. In the case of Nafion 212, which was a thinner membrane than Nafion 117 used as the electrolyte, it was more sensitive to the presence of CO
2. It was found that the cathode catalyst in the cell was also poisoned by the crossovered CO
2.
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Tsukasa SAKAI, Sayoko SHIRONITA, Mitsuhiro INOUE, Minoru UMEDA
2011 Volume 79 Issue 5 Pages
349-352
Published: May 05, 2011
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The reaction selectivity of Pt loading carbon electrocatalysts (Pt/C) having different Pt particle sizes was electrochemically evaluated in the presence of methanol and O
2. The electrochemical measurement of these electrocatalysts was performed using a porous microelectrode technique without any binder resin. In this study, we found an electrocatalyst which exhibits a reaction selectivity during the competitive reactions of methanol oxidation and O
2 reduction. For the Pt/C of O
2 reduction, the desired electrocatalyst is required to retain a low Pt loading amount irrespective of Pt particle size. For the methanol oxidation, the electrocatalyst having a Pt particle size around 4 nm is effective.
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Eiji HIGUCHI, Akihiro TAGUCHI, Kiyoaki HAYASHI, Hiroshi INOUE
2011 Volume 79 Issue 5 Pages
353-356
Published: May 05, 2011
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Pt-carbonyl cluster complexes were prepared just by bubbling CO in various acetonitrile- or ethanol-water mixed solutions containing PtCl
62−. They had compositions of [Pt
3(CO)
3(μ-CO)
3]
n2− (
n=3–6) complexes in which a Pt
3(CO)
3(μ-CO)
3 unit composed of triangular Pt atoms and two types of CO ligands was stacked. The number of Pt
3(CO)
3(μ-CO)
3 units tended to decrease as water content in the mixed solutions increased. Pt nanoparticles prepared from the Pt-carbonyl cluster complexes had much smaller mean particle size (1.8–2.0 nm) and narrower size distribution (
ca. 0.3 nm) than commercial ones. The Pt nanoparticles-loaded carbon black (Pt/CB) catalysts improved mass activity at 0.9 V for oxygen reduction reaction compared to the commercial catalyst (Pt/CBTKK). In particular, the mass activity for Pt/CB prepared from the [Pt
3(CO)
3(μ-CO)
3]
52− complex produced in a water-ethanol mixed solution (water content: 50 vol.%) was
ca. 1.7 times higher than that of the Pt/CB-TKK.
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Hirohisa YAMADA, Toru IKEDA, Daisuke SHIMODA, Akimasa TASAKA, Minoru I ...
2011 Volume 79 Issue 5 Pages
357-360
Published: May 05, 2011
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Pure Pt, Pure Ru, and Pt-Ru alloy thin films of different compositions (Ru:Pt=0.5–2.0) were prepared by magnetron sputtering. These thin films were characterized by Cu stripping voltammetry at different deposition potentials. Furthermore, we developed a novel technique to determine the surface Ru/Pt ratio of Pt-Ru alloys using Cu stripping voltammetry. The Ru/Pt ratios calculated from Cu stripping data agreed well with those measured by EDX in the Ru/Pt range of 0.6 to 2.0.
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Tsuneyoshi NAKASHIMA, Hiroyuki SAITO, Katahiro MURANO, Choji FUKUHARA, ...
2011 Volume 79 Issue 5 Pages
361-363
Published: May 05, 2011
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To improve the catalyst utilization and reduce the catalyst amount, we designed the anode structure. The superior catalyst utilization of direct methanol fuel cell (DMFC) was obtained by localized catalyst loading on the reaction sites. Hence the multi-layer anode with localized catalyst loading was prepared by the sputtering method. The designed multi-layer electrode showed a high cell performance and mass activity because of the good contact at the interface between the catalyst and the electrolyte membrane and low mass transfer resistance. The ultra-low catalyst loading electrode preparing by the sputtering method was a very effective method for reducing the catalyst amount and enhancing the mass activity.
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Wataru IWAYA, Satoko TAKASE, Youichi SHIMIZU
2011 Volume 79 Issue 5 Pages
364-366
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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Metal-sulfides with high chemical stability in acidic condition were tried to develop as an alternative none-noble metal electrocatalyst for polymer electrolyte fuel cell (PEFC). In particular, various types of Ni-based sulfides have synthesized by wet-chemical method and analyzed for the cathodic performances. Among the NiS, NiS
2, and Ni
3S
4, nickel-mono sulfide (NiS) system showed high oxygen reduction performance in 2N-H
2SO
4 at 70°C. In addition, Ni
0.9Cu
0.1S was found to show the highest oxygen reduction performance in the Ni-mono sulfide based catalysts.
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Haryo Satriya OKTAVIANO, Keiko WAKI
2011 Volume 79 Issue 5 Pages
367-370
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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The electrochemical oxidation of ethanol on novel Pt-natural zeolite electrocatalyst has been studied. It was found that Pt/Zeolite (Pt mean size, 4.14 nm) had higher electrocatalytic activity and CO-tolerance suggested by the increase of oxidation current density and the onset potential of Pt/Zeolite, 0.06 V, which is much lower than that of Pt/MWCNTs.
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Takahiro SAIDA, Yoshio TAKASU, Wataru SUGIMOTO
2011 Volume 79 Issue 5 Pages
371-373
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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The electrochemical behavior of anhydrous rutile-type RuO
2, hydrous rutile-type RuO
2 (RuO
2·0.6H
2O), and ruthenate nanosheets derived from layered ruthenium oxide (H
0.2RuO
2.1) in CH
3OH containing 0.5 M H
2SO
4 was studied. The pseudo-capacitance of rutile-type RuO
2 nanoparticles decreased under the presence of methanol when cycled between 0.05–1.2 V vs. RHE (60°C), which is attributed to the adsorption of methanol onto the oxide surface. In contrast, the pseudo-capacitance for ruthenate nanosheets was not influenced by the presence of methanol. The results suggest that methanol adsorbs on the surface of RuO
2 nanoparticles while no adsorption occurred on ruthenate nanosheets in potential regions of interest for the anodic reaction in direct methanol fuel cells. Thus, ruthenate nanosheets should act as a more efficient co-catalyst for methanol electro-oxidation.
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Toshihiko ITO, Ukyo MATSUWAKI, Yuji OTSUKA, Masahiro HATTA, Katsuichir ...
2011 Volume 79 Issue 5 Pages
374-376
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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The Fuel Cell Electrode (FCE), consisting of platinum particles or platinum alloy particles supported on carbon substrates, is one of the key components in the polymer electrolyte fuel cells (PEFCs). In order for the detailed characterization, it is crucial to determine three-dimensional (3D) morphologies of Pt nanoparticles on carbon substrates (Pt/C). In this communication, 3D structures of Pt/C with two different kinds of substrates have been examined using a nano-scale 3D imaging technique, transmission electron microtomography. It was found that the TEC10V50E had Pt catalytic nanoparticles located only at the substrate surface, while the TEC10E50E showed Pt nanoparticles both inside and at the surface of the carbon substrate.
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Daisuke INOUE, Shigenori MITSUSHIMA, Koichi MATSUZAWA, Seung-Yul LEE, ...
2011 Volume 79 Issue 5 Pages
377-380
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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In order to improve the fuel cell performance using a diethylmethylammonium trifluoromethanesulfate ([dema] [TfO]) absorbed sulfonated polyimide membrane, the effects of H
3PO
4 addition to the [dema] [TfO] and the loading amount of [dema] [TfO] in the gas diffusion electrode have been investigated. The ohmic resistance decreased with an increase in the [dema] [TfO] loading, which would correspond to the ohmic resistance between the electrode and the electrolyte membrane. The 5 mol% of H
3PO
4 addition enhanced the cell performance by accelerating the mass transfer, and the reaction polarization was a minimum at a 2.1 mg cm
−2 the [dema] [TfO] loading.
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Myoungseok LEE, Makoto UCHIDA, Kazuki OKAYA, Hiroyuki UCHIDA, Masahiro ...
2011 Volume 79 Issue 5 Pages
381-387
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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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 H
2 (anode) and N
2 (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 H
2 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 ...
2011 Volume 79 Issue 5 Pages
388-391
Published: May 05, 2011
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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 ...
2011 Volume 79 Issue 5 Pages
392-398
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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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 ...
2011 Volume 79 Issue 5 Pages
399-403
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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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 m
2 g
−1. The Pt loading on the catalyst was 19.5 wt%. The electrochemically active surface area (ECA) was 72 m
2 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
2011 Volume 79 Issue 5 Pages
404-413
Published: May 05, 2011
Released on J-STAGE: March 30, 2012
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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 ...
2011 Volume 79 Issue 5 Pages
414-418
Published: May 05, 2011
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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 ...
2011 Volume 79 Issue 5 Pages
419-423
Published: May 05, 2011
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In order to develop a principle of the materials design for the high CO
2 generation efficiency during the C
2H
5OH electrooxidation, the reaction pathways during the electrooxidation of C
2H
5OH and CH
3CHO which is a by-product during the electrooxidation of C
2H
5OH have been quantitatively analyzed. As a result, a direct pathway from C
2H
5OH to CO
2 and a pathway via CH
3CHO toward CO
2 coexisted at 0.4 V, 70°C. At 0.6 V, 70°C, the both pathways from C
2H
5OH to directly CO
2 and from C
2H
5OH via CH
3COOH to CO
2 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 CH
3COOH formation.
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