Kenji Miyatake

University of Yamanashi, Kōhu, Yamanashi, Japan

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Publications (89)252.75 Total impact

  • [Show abstract] [Hide abstract]
    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; · 5.01 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. · 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.
    07/2014;
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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; · 5.01 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. · 0.93 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 02/2014; · 7.48 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). · 3.54 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. 01/2014; 137:213–218.
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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. · 2.15 Impact Factor
  • 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; · 5.01 Impact Factor
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    ABSTRACT: The proton conductive spots on the membrane surface of sulfonated poly(arylene ether) multiblock copolymer were successfully imaged by current-sensing atomic force microscopy under the hydrogen atmosphere at various temperatures and humidities. These spots should be connected to the proton conductive paths inside the membrane. The average diameter of the spots was approximately 12 nm, consistent with the size of hydrophilic domains observed by transmission electron microscopy. The size of the proton conducing spots was almost unchanged regardless of the temperature and humidity, whereas the number of the spots increased at higher humidity; the total area of the proton conducting spots increased accordingly on the membrane surface. This increase in the conducting area at high humidity should be related to the bulk ionic conductivity measured by impedance spectroscopy.
    The Journal of Physical Chemistry B 03/2013; · 3.61 Impact Factor
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    ABSTRACT: We have conducted combined time-resolved ATR-FTIR and proton conductivity measurements of a sulfonated block poly(arylene ether sulfone ketone) membrane, to be called a SPE-bl-1 membrane hereafter, during the hydration/dehydration cycle at room temperature. The result was discussed in comparison with the Nafion NRE211 membrane. Dissociation of the sulfonic acid groups and conductivity change were interpreted in terms of different states of water in the membrane characterized by δ(HOH) bands at 1705 and 1637 cm–1, respectively. The former is assigned to hydrated protons produced by the dissociation followed by hydration. Proton conductivity increases significantly, over 0.1–0.2 S cm–1, after the dissociation is completed at the initial stage of hydration, which is common to both membranes. The 1637 cm–1 band contains contributions from the water in the proton conduction channels as well as some water which is hydrogen bonded to the polar groups in the SPE-bl-1 membrane such as ether (COC), sulfonyl (O═S═O), and carbonyl (C═O). The presence of the latter water lowers the effectiveness of the water in promoting proton conduction in the membrane. It is concluded that incomplete dissociation of the sulfonic acid groups coupled by the lower effectiveness is contributing to the lower proton conductivity of SPE-bl-1 than Nafion NRE211 at low hydration levels.
    The Journal of Physical Chemistry C. 02/2013; 117(8):3762–3771.
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    ABSTRACT: The effect of platinum loading on cathode performance in hydrogen/oxygen fuel cells was investigated using perfluorosulfonic acid (Nafion), sulfonated polyimide (SPI-8) and sulfonated poly(phenylene ether ether ketone) (SPEEK) ionomers as the electrode binder. By lowering the platinum loading, the cathode polarization decreased for MEAs using SPI-8 and SPEEK binders at high humidity (90-100% RH (relative humidity)) due to an improvement of mass transport (oxygen supply and/or water discharge) in the catalyst layer. In contrast, at humidity lower than 80% RH, the effect of platinum loading on the cathode performance differed between these two hydrocarbon (HC) ionomers. When SPI-8 was used as the binder, the cathode polarization increased when lowering the platinum loading due to an increase of activation overpotential. When SPEEK was used as the binder, the effect of platinum loading on the cathode performance was smaller. Such differences can be ascribed to the specific adsorbability of these hydrocarbon binders on the platinum catalyst at low humidity. These results point to crucial factors in achieving higher performance at low platinum loadings and low humidity using HC binders.
    Physical Chemistry Chemical Physics 11/2012; · 3.83 Impact Factor
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    ABSTRACT: In situ confocal micro-Raman spectroscopy was used to probe the water distribution in an electrolyte membrane in a polymer electrolyte fuel cell (PEFC) under various cell-operating conditions. The water content, λR (number of water molecules per sulfonic acid group), in a Nafion® membrane was calculated from the intensity of the OH stretching (ν(OH)) band. By analyzing the Raman spectra as a function of the membrane depth in an operating PEFC, the λR distributions in the membrane were obtained under different temperature, humidification, current density and gas-flow rate conditions. The ν(OH) intensity in the electrolyte membrane increased with increasing current density, relative humidity, and gas utilization. The water distribution in the electrolyte membrane can be understood as a balance among back-diffusing water produced from the cathode, electro-osmotic drag, and water removal via the gas diffusion layer (GDL), all of which is information that will be important for the realization of cell operation without humidification in future advanced fuel cell vehicles.
    Electrochimica Acta 11/2012; 82(SI):277–283. · 4.09 Impact Factor
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    ABSTRACT: Synthesis and properties of aromatic block copolymers composed of highly sulfonated phenylene ether sulfone ketone units as hydrophilic blocks and phenylene ether biphenyene sulfone units as hydrophobic blocks are reported. High molecular weight block copolymers 4 (Mw = 275–362 kDa and Mn = 76–144 kDa) with different compositions (number of repeat unit in the hydrophobic blocks (X) = 15, 30, or 60, and that of hydrophilic blocks (Y) = 4, 8, or 12) were synthesized. Transparent and bendable membranes were obtained by casting from the solution of 4. Due to the rigid rod-like structure of the hydrophilic blocks, the nanophase-separated morphology was not as distinct as that of the conventional sulfonated aromatic block copolymer membranes. Highly sulfonated hydrophilic blocks, which contained phenylene rings with sulfonic acid groups and electron-withdrawing sulfone or ketone groups, contributed to the high proton conductivity and improved oxidative stability of 4 membranes. The 4 (X60Y12) membrane with low IEC (1.18 mequiv g−1) showed comparable or higher conductivity than that of Nafion at >80% relative humidity (RH).
    Polym. Chem. 07/2012; 3(9).
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    ABSTRACT: A sulfonated aromatic block copolymer (SABC), consisting of hydrophobic and hydrophilic blocks, was analyzed by heteronuclear single-quantum correlation (HSQC), heteronuclear multiple-bond correlation (HMBC) and HSQC total correlation spectroscopy (HSQC–TOCSY). Because of its complicated chemical structure with five different phenylene rings, 12 types of 1H signals and 24 types of 13C signals were observed in a narrow chemical shift range (7.0–8.0 p.p.m. for 1H and 118–162 p.p.m. for 13C). To improve the 1H signal separation, the temperature conditions for the 1H nuclear magnetic resonance (NMR) experiments were optimized. Moreover, 1H and 13C NMR signal assignments for the hydrophobic blocks were performed using HSQC and HMBC, with reference to the assignments of a model oligomer. For the hydrophilic blocks, furthermore, HSQC–TOCSY techniques were applied. As a result of these studies, complete 1H and 13C NMR signal assignments were made for the SABC. The ion-exchange capacity (IEC) and the copolymerization composition were calculated using the 1H NMR assignments for the SABC, and the IEC value obtained in this way was consistent with that obtained via titration.
    Polymer Journal. 06/2012; 44:845–849.
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    ABSTRACT: Sulfonated polybenzophenone/poly(arylene ether) block copolymers were designed and synthesized via Ni-mediated coupling polymerization. The block copolymers were obtained as high-molecular-weight (M(n) = 70-110 kDa, M(w) = 150-230 kDa) with low polydispersity index (M(w)/M(n) = 2.0-2.3). The block copolymer membranes showed well-developed hydrophilic/hydrophobic phase separation and high proton conductivity and low gas permeability. The membrane showed better fuel cell performance and durability compared with those with Nafion, state-of-the-art proton conducting membrane.
    ACS Applied Materials & Interfaces 06/2012; · 5.01 Impact Factor
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    ABSTRACT: A versatile synthetic method of superacid-modified poly(arylene ether sulfone)s via post-bromination has been developed. Three kinds of high molecular weight poly(arylene ether sulfone)s, in which differences lie in the main chain structures, were synthesized and brominated. Careful control of the reaction conditions enabled selective and quantitative bromination of the polymers. The bromo groups were converted to superacid groups via Ullmann coupling reaction to obtain the title ionomers (FSPE-1a, 1b, and 1c). The chemical structure and the ion exchange capacity (IEC) of the FSPE-1s were characterized by 1H and 19F NMR spectra. Tough, flexible, and transparent membranes with IEC ranging from 0.87 to 1.09 meq g−1 were obtained by solution casting. The FSPE-1 membranes showed comparable properties (chemical stability, phase-separated morphology, water absorbability, and proton conductivity,) to those of our previous version of the superacid-modified poly(arylene ether sulfone) (FSPE) synthesized from brominated monomers (pre-bromination method). The advantages of the post-bromination method have been proven by significant improvement in the mechanical strength of the FSPE-1 membranes since it could provide superacid-modified aromatic ionomers with much higher molecular weight.
    RSC Advances 05/2012; 2(12):5199-5204. · 3.71 Impact Factor
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    ABSTRACT: In situ confocal micro-Raman spectroscopy was used to probe the interior of the electrolyte membrane of a polymer electrolyte fuel cell (PEFC) at various temperatures (40–110°C) and humidities (dry–90% RH). No changes in the Raman spectra for functional groups involved in the polymer were found under humidified and dry conditions, except for the sulfonic acid group. With increasing relative humidity, the band intensity for S–O stretching (ν(S–O)) in the latter increased, and the peak shifted toward lower wavenumber. By analyzing the Raman peaks, water distributions through the Nafion membrane thickness were successfully evaluated in the operating PEFC. It was found that the back-diffusion of water produced at the cathode to the anode, humidifying the membrane, was clearly detectable, and also the rate of water transport in the membrane increased with increasing cell temperature.
    Electrochimica Acta 12/2011; 58:449-455. · 4.09 Impact Factor
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    ABSTRACT: Sulfonated polyimide (SPI-8) ionomers were used as binders in the catalyst layers, and their fuel cell performance was evaluated. SPI-8 ionomers functioned well in the anode with only minor overpotential even at low humidity (50% relative humidity (RH)). In contrast, the cathode performance was significantly dependent on the content and molecular weight of the ionomers and humidity of the supplied gases. Higher molecular weight of the ionomer caused larger potential drop at high current density at 80 and 100% RH since oxygen supply and/or water discharge became insufficient due to higher water uptake (swelling) of the ionomer. Similar results were obtained at higher ionomer content, because of the increase of thickness in the catalyst layer. The mass transport was improved with decreasing humidity, however, proton conductivity became lower. While the maximum values of j(@0.70 V) for all membrane electrode assemblies (MEAs) were ca. 0.35 A/cm(2), each electrode could have the different appropriate operating conditions. The results suggest that the parameters such as oxygen supply, proton conductivity, and water uptake and discharge need to be carefully optimized in the catalyst layers for achieving reasonable cathode performance with hydrocarbon ionomers.
    ACS Applied Materials & Interfaces 12/2011; 4(2):730-7. · 5.01 Impact Factor