Kenji Miyatake

University of Yamanashi, Kōhu, Yamanashi, Japan

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Publications (102)465.58 Total impact

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    ABSTRACT: We have utilized m-terphenyl (MTP) moiety as a component of hydrophobic blocks for sulfonated multiblock poly(arylene ether) copolymers. For this purpose, bisphenol-type MTP monomer was polymerized with bis(4-fluorophenyl)sulfone to obtain hydroxyl-terminated hydrophobic oligomers, which were copolymerized with sulfonated hydrophilic blocks to obtain the targeted multiblock copolymers. The block copolymers possessed high apparent molecular weight (Mw=74-180 kDa) and gave bendable membranes by solution casting. Transmission electron microscopic (TEM) images revealed that the membranes exhibited hydrophilic/hydrophobic phase-separated morphology with distinct interfaces. The domain sizes were dependent on the compositions of the multiblock copolymers, indicating the sequenced structure is responsible for the morphology. The introduction of MTP moieties in the hydrophobic blocks resulted in the membrane with the higher ion exchange capacity (IEC) value (2.13 meq/g) and higher proton conductivity (ca. 320 mS/cm at 80 °C and 90% relative humidity) than that of the previous polymers sharing the same hydrophilic but different hydrophobic (p-biphenyl, BP) moieties (1.69 meq/g, ca. 200 mS/cm under the same conditions, respectively). In contrast, humidity dependence of dynamic mechanical properties in MTP membranes was similar to BP membranes, suggesting the introduction of MTP moieties in the hydrophobic segments has minor impact on the mechanical stability and its dependence on the humidity.
    Journal of Membrane Science 02/2015; 476:156-161. DOI:10.1016/j.memsci.2014.11.032 · 4.91 Impact Factor
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    ABSTRACT: A new series of poly(arylene ether sulfone) multiblock copolymers were synthesized by polycondensation of linear and rigid hydrophobic and densely sulfonated hydrophilic oligomers. Thin membranes were prepared therefrom by solution casting and their properties were compared with those of Nation and other poly(arylene ether sulfone) multiblock copolymers containing perfluorinated biphenylene moieties. The membranes showed good water affinity, high proton conductivity, low hydrogen and oxygen permeability, high mechanical strength, and reasonable oxidative stability. These properties are attractive as an electrolyte for polymer electrolyte membrane fuel cells. It was found that the perfluofinated biphenylene moieties as connecting groups for hydrophilic and hydrophobic blocks affected only slightly the properties of poly(arylene ether sulfone) multiblock copolymer membranes.
    Bulletin of the Chemical Society of Japan 01/2015; 88(1):183-191. DOI:10.1246/bcsj.20140237 · 2.22 Impact Factor
  • Tae-Yeol Jeon, Masahiro Watanabe, Kenji Miyatake
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    ABSTRACT: The important roles of Ni in electrocatalytic reactions such as hydrazine oxidation are limited largely by high oxidation states due to its intrinsically high oxophilicity. Here, we report the synthesis and properties of highly metallic Ni nanoparticles (NPs) on carbon black supports. We discovered that the heat treatment of as-prepared Ni NPs with an average particle size of 5.8 nm produced highly metallic Ni NPs covered with thin carbon shells, with negligible particle coarsening. The carbon shells were formed by the segregation of carbons in the Ni lattice to the surface of the Ni NPs, leaving highly metallic Ni NPs. X-ray photoelectron spectroscopic analyses revealed that the atomic ratio of metallic Ni increased from 19.2% to 71.7% as a result of the heat treatment. The NPs exhibited higher electrocatalytic activities toward the hydrazine oxidation reaction in alkaline solution, as compared to those of the as-prepared Ni NPs and commercial Ni powders.
    ACS Applied Materials & Interfaces 10/2014; 6(21). DOI:10.1021/am5058635 · 5.90 Impact Factor
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    ABSTRACT: A novel series of aromatic block copolymers composed of fluorinated phenylene and biphenylene groups, and diphenyl ether (QPE-bl-5) or diphenyl sulfide (QPE-bl-6) groups as scaffold for quaternized ammonium groups are reported. The block copolymers were synthesized via aromatic nucleophilic substitution polycondensation, chloromethylation, quaternization, and ion exchange reactions. The block copolymers were soluble in organic solvents and provided thin and bendable membranes by solution casting. The membranes exhibited well-developed phase-separated morphology based on the hydrophilic/hydrophobic block copolymer structure. The membranes exhibited mechanical stability as confirmed by DMA (dynamic mechanical analyses) and low gas and hydrazine permeability. QPE-bl-5 membrane with the highest ion exchange capacity (IEC = 2.1 meq. g(-1)) exhibited high hydroxide ion conductivity (62 mS cm(-1)) in water at 80 °C. A noble metal-free fuel cell was fabricated with the QPE-bl-5 as the membrane and electrode binder. The fuel cell operated with hydrazine as a fuel exhibited the maximum power density of 176 mW cm(-2) at a current density of 451 mA cm(-2).
    ACS Applied Materials & Interfaces 09/2014; 6(19). DOI:10.1021/am5046586 · 5.90 Impact Factor
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    ABSTRACT: Microscopic proton conductivity at surfaces of a hydrocarbon-type polymer electrolyte membrane of sulfonated poly(arylene ketone) block copolymers (SPK-bl-1) was investigated by current-sensing atomic force microscopy (CS-AFM) under a hydrogen atmosphere. The distributions of proton-conductive regions on the SPK-bl-1 membrane surfaces were different on two surface sides of the membrane: the substrate side and the air side after being cast on a poly(ethylene terephthalate) substrate. After a liquid-water treatment of the membrane at 60 °C, the surface morphology of both sides changed. The proton-conductive area and the “pseudo current density” increased especially on the substrate side, and the difference between two sides of the membrane became very small. The scanning transmission electron microscopy inside the membrane showed no structural change after the hot-water treatment, and the water uptake and conductivity of the membrane were also unchanged. This hot liquid-water treatment activating the membrane surfaces should be related to the conditioning processes of the membrane-electrode assemblies of polymer electrolyte fuel cells.
    Electrochimica Acta 08/2014; 143:383-389. DOI:10.1016/j.electacta.2014.08.031 · 4.09 Impact Factor
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    ABSTRACT: We have developed new composite membranes of sulfonated polyimide containing triazole groups (SPI-8) as a matrix ionomer and SiO2 nanoparticles. The incorporation of SiO2 nanoparticles remarkably improved the fuel cell performances during low humidity operation at 53% RH and 80 °C. Among the cells with SPI-8 membranes with uniformly dispersed SiO2 from 0 to 15 wt%, the single cell with 10 wt% SiO2/SPI-8 was found to exhibit the highest I − E performance, with the highest mass activity at 0.85 V and the smallest oxygen-transport overpotential (O2-gain) as well as the lowest ohmic resistance. This strongly indicates that SiO2 nanoparticles were able to promote the back-diffusion of water produced in the cathode catalyst layer to the anode catalyst layer, maintaining high water content in the membrane during the operation. It was found that the cell with a bilayer SPI-8 membrane having 10 wt% SiO2 in the anode-side layer and 3 wt% SiO2 in the cathode-side layer exhibited performance superior to that with a uniform dispersion of 10 wt% SiO2, especially in the higher current density region at low RH, which can be ascribed with certainty to the fact that the concentration gradient of SiO2 in the SPI-8 led to enhancement of the back-diffusion of water through the membrane
    Electrochimica Acta 08/2014; 137:213–218. DOI:10.1016/j.electacta.2014.05.159 · 4.09 Impact Factor
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    ABSTRACT: a b s t r a c t The hydrated structures of the proton exchange membranes were theoretically investigated using long-range corrected density functional theory to make clear why perfluorinated polymer membrane Nafion is superior to other membranes in the proton conductivity at low humidity. For exploring the possibility of the proton conductance in the vehicle mechanism with low hydration numbers, we examined the relay model of protonated water clusters between the sulfonic acid groups in Nafion and concluded that this relay model may contribute to the high proton conductivity of Nafion with less-hydrated sulfonic acid groups. Ó 2014 Elsevier B.V. All rights reserved.
    Chemical Physics Letters 07/2014; 608. DOI:10.1016/j.cplett.2014.05.076 · 1.99 Impact Factor
  • Junpei Miyake, Masahiro Watanabe, Kenji Miyatake
    Polymer Journal 07/2014; 46(10):656-663. DOI:10.1038/pj.2014.56 · 1.55 Impact Factor
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    ABSTRACT: A double layer ionomer membrane, thin-layer Nafion (perfluorinated sulfonic acid polymer) on a sulfonated aromatic block copolymer (SPK-bl-1), was prepared for improving fuel cell performance. Each component of the double layer membrane showed similar phase-separated morphologies to those of the original membranes. A fuel cell with the double layer membrane exhibited lower ohmic resistance and higher cathode performance than those with the original SPK-bl-1 membrane, despite their comparable water uptake and proton conductivity. Detailed electrochemical analyses of fuel cell data suggested that the thin Nafion interlayer contributed to improving the interfacial contact between the SPK-bl-1 membrane and the cathode catalyst layer and to mitigating excessive drying of the membrane. The results provide new insight on designing high performance fuel cells with non-fluorinated ionomer membranes such as sulfonated aromatic polymers.
    ACS Applied Materials & Interfaces 07/2014; 6(16). DOI:10.1021/am503295y · 5.90 Impact Factor
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    ABSTRACT: Proton conductive spots on the membrane surface of sulfonated poly(arylene ketone) multiblock copolymer were investigated by current-sensing atomic force microscopy (CS-AFM) under the hydrogen atmosphere with changing relative humidity, temperature, and bias voltage. The bright spots, where the hydrophilic clusters should be effectively connected inside the membrane, were distributed rather inhomogeneously on the surface at low temperature and humidity but became more homogeneous at higher temperature and humidity. The average diameter of the spots was approximately 10 nm at 40% RH, which increased to 13 nm at 70% RH. The total area of the proton conducting spots, as well as current at each spot, on the membrane surface increased at high humidity and temperature. In addition, the diameter of the proton-conductive spots and the ratio of proton-conductive area on the membrane surface continuously increased with increasing the bias voltage. This increase of the conducting area and the current should be related to the change of the bulk ionic conductivity.
    Electrochemistry -Tokyo- 05/2014; 82(5):369-375. DOI:10.5796/electrochemistry.82.369 · 0.98 Impact Factor
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    ABSTRACT: We report herein temperature- and humidity-controlled small-angle X-ray scattering (SAXS) analyses of proton-conductive ionomer membranes. The morphological changes of perfluorosulfonic acid polymers (Nafion and Aquivion) and sulfonated aromatic block copolymers (SPE-bl-1 and SPK-bl-1) were investigated and compared under conditions relevant to fuel cell operation. For the perfluorinated ionomer membranes, water molecules were preferentially incorporated into ionic clusters, resulting in phase separation and formation of ion channels. In contrast, for the aromatic ionomer membranes, wetting led to randomization of the ionic clusters. The results describe the differences in the proton-conducting behavior between the fluorinated and nonfluorinated ionomer membranes, and their dependence on the humidity.
    ChemSusChem 03/2014; 7(3). DOI:10.1002/cssc.201301322 · 7.12 Impact Factor
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    ABSTRACT: By using a current-sensing atomic force microscope (CS-AFM) under a hydrogen atmosphere, microscopic proton-conductive areas on the membrane surface of sulfonated poly(arylene ether sulfone ketone) block copolymer were investigated. With increasing the bias voltage during the CS-AFM scans, the number and the diameter of proton-conductive spots on the membrane surface continuously increased. Both reversible/irreversible changes in the proton-conductive area on the surface were found. The reversible change indicates that the proton-conductive paths are dynamically rearranged during the power generation in a polymer electrolyte fuel cell. The irreversible change might be related to the enhancement of the performance of the membrane electrode assemblies after being "conditioned" prior to the operation.
    Journal of Electroanalytical Chemistry 03/2014; 716:156-163. DOI:10.1016/j.jelechem.2013.11.035 · 2.87 Impact Factor
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    ABSTRACT: Five kinds of ammonium groups functionalized partially fluorinated poly(arylene ether) block copolymer membranes were prepared for investigating the structure–property relationship as anion exchange membranes (AEMs). Consequently, the pyridine (PYR)-modified membrane showed the highest alkaline and hydrazine stability in terms of the conductivity, water uptake, and dry weight. The chloromethylated precursor block copolymers were reacted with amines, such as trimethylamine, N-butyldimethylamine, 1-methylimidazole, 1,2-dimethylimidazole, and PYR to provide the target quaternized poly(arylene ether)s. The structures of the polymers, as well as model compounds and oligomers were well characterized by 1H NMR spectra. The obtained AEMs were subjected to water uptake and hydroxide ion conductivity measurements and stabilities in aqueous alkaline and hydrazine media. The pyridinium-functionalized quaternized polymers membrane showed the highest alkaline and hydrazine stability with minor losses in the conductivity, water uptake, and dry weight. © 2013 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014, 52, 383–389
    Journal of Polymer Science Part A Polymer Chemistry 02/2014; 52(3). DOI:10.1002/pola.27011 · 3.54 Impact Factor
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    ABSTRACT: The relay model in the vehicular mechanism is found to be one of the most probable for the conductance of protonated water clusters in Nafion membrane at low humidity.
    Chemical Physics Letters 01/2014; 608:11–16. · 1.99 Impact Factor
  • Junpei Miyake, Masahiro Watanabe, Kenji Miyatake
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    ABSTRACT: A novel polymer synthetic method, the intrapolymer Heck reaction, provided ladder-type ionomer membranes with excellent proton conductivity (221 mS cm−1 at 80 °C and 90% relative humidity) and mechanical strength over a wide range of humidity (ca. 0-90% relative humidity) at 80 °C.
    RSC Advances 01/2014; 4(40):21049. DOI:10.1039/c4ra02582b · 3.71 Impact Factor
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    224th ECS Meeting; 10/2013
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    224th ECS Meeting; 10/2013
  • Junpei Miyake, Masahiro Watanabe, Kenji Miyatake
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    ABSTRACT: The introduction of triphenylphosphine oxide moiety into the hydrophilic segments of aromatic multiblock copolymers provided outstanding oxidative stability and high proton conductivity. Our designed multiblock copolymers are composed of highly sulfonated phenylene ether phosphine oxide ketone units as hydrophilic blocks and phenylene ether biphenylene sulfone units as hydrophobic blocks. High molecular weight block copolymers (Mw = 204-309 kDa and Mn = 72-94 kDa) with different copolymer compositions (number of repeat unit in the hydrophobic blocks (X) = 30, and that of hydrophilic blocks (Y) = 4, 6, or 8) were synthesized, resulting in self-standing, transparent, and bendable membranes by solution casting. The block copolymer membranes exhibited well-developed hydrophilic/hydrophobic phase separation, high proton conductivity, and excellent oxidative stability due to the highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing phosphine oxide or ketone groups.
    ACS Applied Materials & Interfaces 06/2013; 5(13). DOI:10.1021/am401625j · 5.90 Impact Factor
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    ABSTRACT: Synthesis and properties of aromatic block copolymers containing fluorinated phenylene and biphenylene groups and ammonium-substituted fluorene groups are reported. High-molecular-weight poly(arylene ether) block copolymers were prepared from the corresponding telechelic oligomers and were chloromethylated. Quaternization reaction of the chloromethylated precursors with trimethylamine provided the title ammonium-substituted block copolymers (QPE-b1-4). The QPE-b1-4 membrane with the highest ion-exchange capacity (IEC = 1.3 mequiv g(-1)) showed high hydroxide ion conductivity (45 mS cm(-1)) at 80 degrees C due to its phase-separated morphology with interconnected ion-transporting pathway. The accelerated stability test in aqueous KOH solution containing hydrazine revealed that the ammonium groups decomposed to certain extent while the polymer main chains were rather robust to maintain the self-supporting membranes.
    Bulletin of the Chemical Society of Japan 05/2013; 86(5):663-670. DOI:10.1246/bcsj.20130017 · 2.22 Impact Factor
  • 223th ECS Meeting; 05/2013