Kenji Miyatake

University of Yamanashi, Kōhu, Yamanashi, Japan

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Publications (117)518.35 Total impact

  • Junpei Miyake · Ibuki Hosaka · Kenji Miyatake
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    ABSTRACT: The introduction of sulfonated triphenylphosphine oxide moieties improved the oxidative stability of aromatic block copolymer membranes, while other factors such as water affinity also played an important role in determining the membrane properties.
    No preview · Article · Jan 2016 · Chemistry Letters
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    ABSTRACT: A novel series of ammonium-containing copolymers (QPAFs) were synthesized as anion exchange membranes for alkaline fuel cell applications. The precursor copolymers (Mw = 28.3-90.1 kDa) composed of perfluoroalkylene and phenylene groups were obtained by a nickel promoted polycondensation reaction. Chloromethylation and quaternization reactions of the precursors provided thin and ductile QPAF membranes with ion exchange capacity (IEC) ranging from 0.79 to 1.74 meq g-1. The QPAF membranes exhibited a phase-separated morphology based on the hydrophilic/hydrophobic differences in the main chain structure. The QPAF membrane with an optimized copolymer composition and IEC = 1.26 meq g-1 showed high hydroxide ion conductivity (95.5 mS cm-1 in water at 80 °C), excellent mechanical properties (large elongation at break (218%)), and reasonable alkaline stability at 80 °C. An alkaline fuel cell using the QPAF as the membrane and electrode binder achieved the maximum power density of 139 mW cm-2 at a current density of 420 mA cm-2.
    No preview · Article · Oct 2015 · Journal of Materials Chemistry A
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    ABSTRACT: Synthesis and properties of anion conductive aromatic block copolymers, QPE-bl-3, QPE-bl-3 M2, and M4, containing fluorenylidene biphenylene groups as scaffold for ammonium groups are described. These copolymers share the same main chain structure, but the position and the number of ammonium groups on a fluorenyl group differ. High molecular weight quaternized block copolymers were obtained via typical chloromethylation reaction or using preaminated monomers, and were well-characterized by 1H NMR spectra. Self-standing bendable membranes were obtained by solution casting. QPE-bl-3 M4 membranes containing four ammonium groups per hydrophilic repeat unit (highest ammonium density) in the hydrophilic block exhibited well developed phase-separated morphology, while QPE-bl-3 membranes containing two ammonium groups per hydrophilic repeat unit exhibited high anion conductivity. The highest anion conductivity (104 mS/cm) was obtained with QPE-bl-3 membrane (IEC=2.1 meq/g) at 80 °C in water. An H2/O2 alkaline fuel cell was operable with the membrane to achieve 62 mW/cm2 of the maximum power density at 161 mA/cm2 of the current density.
    No preview · Article · Oct 2015
  • Yaojian Zhang · Junpei Miyake · Ryo Akiyama · Kenji Miyatake
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    ABSTRACT: The synthesis and characterization of ladder-type aromatic block copolymers containing sulfonated triphenylphosphine oxide moieties (LadP-SPE) are reported. Through aromatic nucleophilic substitution polycondensation and Pd-catalyzed intrapolymer Heck reaction, the target copolymers LadP-SPE with high molecular weight (Mn = 47-50 kDa, Mw = 289-579 kDa) and different ion exchange capacity (IEC) values (1.04, 1.84 and 2.22 meq g-1, by titration) were prepared. By solution casting method, all the copolymers gave transparent and bendable membranes. The membrane with IEC = 2.22 meq g-1 exhibited high proton conductivity in wide range of relative humidity (RH) at 80 °C (ca. 1.6 mS cm-1 at 20% RH and 351.2 mS cm-1 at 95% RH). Moreover, the stiff ladder structure strengthened the molecular chain which contributed to the membrane with high IEC value and water uptake to have desirable mechanical stability up to 90% RH at 80 °C.
    No preview · Article · Sep 2015 · Polymer
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    ABSTRACT: We developed a new FTIR system with two polarizers in its optics in order to conduct polarization-modulated measurements. Polarization characteristics were examined for the Kretschmann polarization-modulated attenuated total reflectance (ATR) configuration by the use of gold-sputtered films of 10–100 nm thickness on Ge and ZnSe prisms. The marked increase of the polarization characteristics for Au film thicknesses below 30–40 nm is closely associated with a large reflectivity decrease of the p-polarized radiation. A cast film of sulfonated block poly(arylene ether sulfone ketone) membrane was formed on the Au film, and the interfacial spectra were acquired by the use of the ATR FTIR system. The interfacial spectra resemble those of the ATR spectra of the bulk membrane but exhibited strong dependence of the intensity and line shape of the vibrational modes on the Au thickness. The dependence is closely associated with a change of the polarization characteristics of the interface. Electromagnetic as well as chemical effects were concluded to be responsible for the band anomalies and enhancement.
    No preview · Article · Jul 2015 · The Journal of Physical Chemistry C
  • Junpei Miyake · Takashi Mochizuki · Kenji Miyatake
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    ABSTRACT: To elucidate the effect of the hydrophilic component on the properties of aromatic ionomers, we have designed for the first time one of the simplest possible structures, the sulfo-1,4-phenylene unit, as the hydrophilic component. A modified Ni-mediated coupling polymerization produced the title aromatic ionomers composed of sulfonated p-phenylene groups and oligo(arylene ether sulfone ketone)s, as high-molecular-weight polymers (Mw = 202-240 kDa), resulting in the formation of tough, flexible membranes. The aromatic ionomer membranes showed well-developed hydrophilic/hydrophobic phase separation. Comparison with our previous aromatic ionomer membrane containing sulfonated benzophenone groups as a hydrophilic component revealed that the simple sulfophenylene structure (i.e., no polar groups such as ether, ketone, or sulfone groups in the hydrophilic component) was effective for the improvement of the membrane properties, i.e., reduced water uptake and excellent mechanical stability under humidified conditions. Furthermore, because of the high local ion exchange capacity (IEC), the simple structure led to high proton conductivity, especially at low humidity (reaching up to ca. 7.3 mS/cm at 80°C and 20% RH), which is one of the highest values reported thus far. The improved properties of the membranes were also confirmed in an operating fuel cell. (Figure Presented)
    No preview · Article · Jul 2015 · ACS Macro Letters
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    ABSTRACT: A rigid, planar dibenzofuran in the hydrophobic parts provided sulfonated aromatic block copolymer with improved membrane properties, i.e., well-developed phase separation, effective water uptake, high proton conductivity, and moderate mechanical strength at wide range of humidity.
    No preview · Article · Jul 2015 · Chemistry Letters
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    ABSTRACT: A sulfonated polybenzophenone/polyimide block copolymer membrane exhibited high proton conductivity, good dimensional and mechanical stabilities, and low gas permeability, which are attractive for fuel cell applications.
    No preview · Article · Jun 2015 · RSC Advances
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    ABSTRACT: To improve the performances of fuel cells at low humidity, we have prepared composite electrolyte membranes by incorporating SiO2 nanoparticles into poly(arylene ether sulfone ketone) (SPESK) membrane. SiO2 particles were able to be dispersed in SPESK highly uniformly on the nanometer scale by the use of a commercial SiO2-dimethylacetamide sol. The SiO2/SPESK cell exhibited improved I-E performance at 53% relative humidity (RH) and 80°C. It was found that such an improvement was due to the reduction of the ohmic resistance and the oxygen-transport overpotential at high current densities, probably because the SiO2 nanoparticles promoted the back-diffusion of water generated at the cathode catalyst layer toward the anode. Both the ohmic resistance and the oxygen-transport overpotential were reduced further by using a thin (ca. 12 µm) SiO2/SPESK membrane, resulting in remarkably high performances at 53% RH and 30% RH.
    Preview · Article · Mar 2015 · Electrochemistry -Tokyo-
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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.
    No preview · Article · Feb 2015 · Journal of Membrane Science
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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.
    No preview · Article · Jan 2015 · Bulletin of the Chemical Society of Japan
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    ABSTRACT: The synthesis and properties of anion conductive aromatic copolymers containing oligophenylene moieties as a scaffold for quaternized ammonium groups are reported. Our new hydrophilic components consist of a chemically robust oligophenylene main chain modified with a high density of ionic groups. A partially fluorinated oligo(arylene ether) was employed as a hydrophobic block. The targeted copolymers (QPE-bl-9) were synthesized via nickel-mediated coupling polymerization, followed by chloromethylation, quaternization, and ion exchange reactions. QPE-bl-9 provided tough, bendable membranes by solution casting. The resulting membrane with the highest ion exchange capacity (IEC = 2.0 mequiv g-1) exhibited high hydroxide ion conductivity (138 mS cm-1) in water at 80 °C. Reasonable alkaline stability of QPE-bl-9 membrane was confirmed in 1 M KOH aqueous solution for 1000 h at 40 °C. A noble metal-free fuel cell with QPE-bl-9 used as the membrane and electrode binder was successfully operated. A maximum power density of 510 mW cm-2 was achieved at a current density of 1.20 A cm-2 with hydrazine as the fuel and O2 as the oxidant.
    No preview · Article · Dec 2014 · Macromolecules
  • 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.
    No preview · Article · Oct 2014 · ACS Applied Materials & Interfaces
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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).
    No preview · Article · Sep 2014 · ACS Applied Materials & Interfaces
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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.
    Full-text · Article · Aug 2014 · Electrochimica Acta
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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
    No preview · Article · Aug 2014 · Electrochimica Acta
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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.
    Full-text · Article · Jul 2014 · Chemical Physics Letters
  • Junpei Miyake · Masahiro Watanabe · Kenji Miyatake
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    ABSTRACT: The recent progress of our research on anion-exchange membranes (AEMs) for alkaline fuel cell applications is reviewed. The anion conductivity and the mechanical, thermal and chemical stability of AEMs are insufficient. To address these issues, we have designed and synthesized a novel series of poly(arylene ether)-based AEMs with quaternized ammonium groups. First, the effect of the sequence of the polymer main chain (random or block) on the AEM properties, especially the anion conductivity, is discussed. We emphasize that fluorenyl groups serve effectively as scaffolds for the ammonium groups. We then discuss the alkaline stability of both the polymer backbone and the quaternized ammonium groups. Partial fluorination improves the alkaline stability of the polymer main chains. Among the several ammonium groups investigated, we propose that pyridinium groups are seemingly more stable than the typical aliphatic ammonium (for example, trimethylammonium) groups. The results imply that aromatic AEMs are potentially applicable to alkaline fuel cells that use hydrogen or hydrazine as a fuel. © 2014 The Society of Polymer Science, Japan (SPSJ) All rights reserved.
    No preview · Article · Jul 2014 · Polymer Journal
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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.
    No preview · Article · Jul 2014 · ACS Applied Materials & Interfaces
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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.
    Full-text · Article · May 2014 · Electrochemistry -Tokyo-