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Tanaka, Nobuyuki; Yamaki, Tetsuya*; Asano, Masaharu*; Terai, Takayuki*
Journal of Membrane Science, 587, p.117171_1 - 117171_9, 2019/10
Times Cited Count：10 Percentile：41.64(Engineering, Chemical)Electro-electrodialysis (EED) has been applied to thermochemical water-splitting iodine-sulfur process for hydrogen production in order to enhance the HI component in the HI-I
-HO mixture (HIx solution). In this paper, HIx solution concentration dependence of the conductivity (
) and transport number (
) as the membrane-performance indexes of Nafion 212 and a styrene-grafted poly(ethylene-co-tetrafluoroethylene) (ETFE) membrane was experimentally investigated. From the theoretical analysis for the measurements based on the new EED model, the effects of the H
and I
content and the diffusion coefficients of H and I in the evaluated membranes on and were as follows: HIx solution concentration dependence of ion contents exhibited a significantly small or different variation in comparison with that of and t
, which indicates that the dominant factors for and would not be ion contents; thereby, the effect of ion diffusion coefficients should not be ruled out. For of Nafion 212, H diffusion is the dominant factor because the existence of I was negligible, whereas for the ETFE-St membrane, the effect of I diffusion should be considered. I diffusion could more strongly affect for the evaluated membranes rather than H diffusion, which indicates that H selectivity of the membranes could be relatively determined by the variation of the I behavior in the membranes.
thermally induced phase separationSawada, Shinichi; Ursino, C.*; Galiano, F.*; Simone, S.*; Drioli, E.*; Figoli, A.*
Journal of Membrane Science, 493, p.232 - 242, 2015/11
Times Cited Count：53 Percentile：88.7(Engineering, Chemical)The replacement of commonly-used substances with non-toxic equivalents is attracting a great amount of attention in membrane preparation processes. In order to address this issue, we prepared porous poly(vinylidene fluoride) (PVDF) membranes via thermally-induced phase separation using the following non-toxic Citroflex as solvents: acetyl tributyl citrate (ATBC); acetyl triethyl citrate (ATEC); and triethyl citrate (TEC). The pore size of the membranes increased in the following solvent order of ATBC 
ATEC TEC, which is the same trend of the PVDF/solvent affinity. During the phase separation process, high-affinity solvent molecules should have enough molecular mobility and easily gather with each other to form the large solvent rich phases, thereby producing the large pores. In the pure water microfiltration test using the PVDF membranes, the water permeability can be controlled in the wide range, depending on the pore size.
-HO mixtureTanaka, Nobuyuki; Yamaki, Tetsuya; Asano, Masaharu; Terai, Takayuki*; Onuki, Kaoru
Journal of Membrane Science, 456, p.31 - 41, 2014/04
Times Cited Count：2 Percentile：8.89(Engineering, Chemical)Electro-electrodialysis (EED) has been applied to thermochemical water-splitting iodine-sulfur process for hydrogen production in order to enhance the HI uptake from a HI-I-HO mixture (HIx solution). In this paper, the constitution of the HIx solution absorbed in grafted membranes and in Nafion 212 is evaluated. The affinity of the membranes for the HIx solution is discussed based on the measurement results. The behavior of each component in the membrane was as follows: The strong affinity of the ETFE-St membrane for I was shown because of the formation of a charge-transfer complex with electron-donating aromatic groups, whereas I absorption by Nafion 212 was minimal. The difference of affinity for the ions can be attributed to the formation of the I
- complex from I- and I absorbed in the grafted membranes, which was precluded in Nafion 212.
Tran, D. T.; Sawada, Shinichi; Hasegawa, Shin; Katsumura, Yosuke*; Maekawa, Yasunari
Journal of Membrane Science, 447, p.19 - 25, 2013/11
Times Cited Count：35 Percentile：74.22(Engineering, Chemical)Relative humidity (RH) dependence of the proton conduction and mechanical properties of poly(ethylene-co-tetrafluoroethylene) (ETFE)-based radiation grafted polymer electrolyte membranes (PEMs) were investigated in a wide ion exchange capacity (IEC) range at 80 
C. The proton conductivities of the ETFE-based PEMs for IECs of 1.3-2.9 mmol/g were 0.001-0.013 S/cm at 30% RH. These PEMs have conductivities that are less dependent on RH than aromatic-hydrocarbon-polymer based PEMs. The ETFE PEM (IEC 2.4 mmol/g) showed higher tensile strength than Nafion at 100% RH. It was revealed that the mechanical strength and proton conductivity were clearly related to PEM crystallinities.
Park, J.; Enomoto, Kazuyuki; Yamashita, Takashi*; Takagi, Yasuyuki*; Todaka, Katsunori*; Maekawa, Yasunari
Journal of Membrane Science, 438, p.1 - 7, 2013/07
Times Cited Count：15 Percentile：43.24(Engineering, Chemical)Alicyclic polyimides (APIs) were successfully applied to radiation-induced graft polymerization for developing polymer electrolyte membranes for fuel cells. The grafting into fully aromatized polyimide barely proceeded (grafting degrees (GDs) of less than 5%), whereas that of styrene into the API films proceeded with styrene GDs of up to 70%. In combination of electron spin resonance measurements and ultraviolet-visible (UV-VIS) spectroscopy, the radical species was identified as a long-lived intermediate and 10% of the radicals were consumed as grafting initiators. The moderate reaction conditions allowed for selective sulfonation on the polystyrene grafts, and not on the API substrates, to give API-based polymer electrolyte membranes (PEMs) with ion exchange capacities (IEC) of 1.7-2.8 mmol/g. The PEMs exhibited appropriate proton conductivity and low water uptake, together with excellent mechanical properties, compared with conventional PEMs such as Nafion.
Enomoto, Kazuyuki; Takahashi, Shuichi; Rohani, R.; Maekawa, Yasunari
Journal of Membrane Science, 415-416, p.36 - 41, 2012/10
Times Cited Count：15 Percentile：46.12(Engineering, Chemical)Polymer electrolyte membranes (PEM) consisting of ion conducting alkylsulfonic acid and hydroxyl groups were successfully synthesized by radiation-induced graft polymerization of vinyl acetate (VAc) into a poly(ethylene-
-tetrafluoroethylene) (ETFE) film, followed by alkylsulfonation with 1,3-propanesulfone. The prepared PEM showed higher conductivity under 30% relative humidity at 80C than that of the conventional poly(styrenesulfonic acid)-grafted ETFE. Furthermore, the prepared PEM also showed better mechanical properties than those of Nafion. Thus, the PEM with hydroxyl groups possesses sufficient mechanical and electrochemical properties, required for a fuel cell, operating at a high temperature and low humidity.
-HO mixture using ion exchange membranesTanaka, Nobuyuki; Yamaki, Tetsuya; Asano, Masaharu; Maekawa, Yasunari; Terai, Takayuki*; Onuki, Kaoru
Journal of Membrane Science, 411-412, p.99 - 108, 2012/09
Times Cited Count：14 Percentile：43.73(Engineering, Chemical)In the thermochemical water-splitting iodine-sulfur process for hydrogen production, an electro-electrodialysis was applied to increase the HI molality of a HI-I-HO mixture. In order to investigate the temperature dependence of the membrane performance for increasing the HI concentration, a theoretical formula for the performance indexes (proton transport number, initial cell voltage, and ratio of water permeation to proton permeation in the membrane) was derived on the basis of the Nernst-Planck equation and electrophoresis theory. The obtained formula could reproduce the experimental values of the grafted membranes and Nafion 212 in the temperature range 313-373 K and was validated.
N117CS membranesIwai, Yasunori; Hiroki, Akihiro; Tamada, Masao
Journal of Membrane Science, 369(1-2), p.397 - 403, 2011/03
Times Cited Count：19 Percentile：53.45(Engineering, Chemical)The successful formation of radiation-induced crosslinking in Nafion N117CS membranes was clearly demonstrated by tensile testing, a methanol uptake measurement, thermo-mechanical analysis (TMA) and fluorine-19 MAS NMR (
F NMR). The possibility of radiation-induced crosslinking of Nafion never had been considered with regard to the thermal stability of Nafion membranes, since the scission of PFAE pendant-chains in Nafion membranes in their protonated form begins at 523 K. To improve the thermal stability of Nafion membranes, Nafion membranes were soaked in sodium chloride prior to irradiation. The sodium-exchange Nafion membranes were irradiated with 
rays in an argon atmosphere at temperatures ranging from room temperature to 618 K. The irradiated membranes were re-exchanged to the protonated form. Fluorine-19 MAS NMR results for the alcohol-swollen membranes indicate peaks which originated due to radiation-induced crosslinking. An increase in percent elongation at break, a decrease in methanol uptake, and a decrease in the softening temperature at a differential TMA peak for membranes irradiated at 598 K compared to received membranes also add support for our new finding.
Chen, J.; Li, D.; Koshikawa, Hiroshi; Asano, Masaharu; Maekawa, Yasunari
Journal of Membrane Science, 362(1-2), p.488 - 494, 2010/10
Times Cited Count：39 Percentile：75.41(Engineering, Chemical)An aromatic hydrocarbon polymer electrolyte membrane (PEM) was prepared by direct modification of polyetheretherketone (PEEK) film using the radiation-induced crosslinking and grafting techniques. The crosslinking structure induced by the electron-beam irradiation enhanced the insolubility of the PEEK base film. The film shape of the crosslinked PEEK (cPEEK) was well maintained under sulfonation. A small amount of divinylbenzene was introduced into the cPEEK film to enhance the radiation-induced styrene-grafting. The styrene-grafted film was sulfonated under a mild sulfonation condition to obtain the PEM. The PEM with different ion exchange capacity was prepared by changing the grafting yield of styrene. The new PEM exhibited lower methanol permeability and higher mechanical properties, and was proven to be durable in a direct methanol fuel cell at high temperature, reaching a high maximum power density.
-HO solutionTanaka, Nobuyuki; Onuki, Kaoru
Journal of Membrane Science, 357(1-2), p.73 - 79, 2010/06
Times Cited Count：18 Percentile：51.94(Engineering, Chemical)The equilibrium potential across Nafion 117 in a HIx solution (HI-I-HO mixture) was measured for an electro-membrane process (electro-electrodialysis, EED) in the thermochemical water-splitting Iodine-Sulfur process. The experimental results were correlated with a theoretical formula derived on the basis of the electrochemical reaction, the Donnan equilibrium and the Nernst-Planck equation. The obtained empirical formula could reproduce the experimental equilibrium potential within 
0.03 V. Also, the obtained regression parameter agreed well with that calculated from the vapor liquid equilibrium data of a HIx solution reported by Hodotsuka et al. (2008).
-HO mixture using radiation-grafted polymer electrolyte membranesTanaka, Nobuyuki; Yamaki, Tetsuya; Asano, Masaharu; Maekawa, Yasunari; Onuki, Kaoru
Journal of Membrane Science, 346(1), p.136 - 142, 2010/01
Times Cited Count：21 Percentile：56.37(Engineering, Chemical)In the thermochemical water-splitting Iodine-Sulfur process used to produce hydrogen new polymer electrolyte membranes were applied in an electro-membrane process (Electro-electrodialysis, EED) to increase the HI molality of HIx solution (HI-I-HO mixture) to be over quasi-azeotropic. Radiation grafting of a styrene monomer into a poly (ethylene--tetrafluoroethylene) base film and subsequent sulfonation provided electrolyte membranes that had ion exchange capacities (IECs) of 1.1-1.6 mmol/g. With the EED of the HIx solutions using [HI]=[I]=10 mol/kg at 40 C the transport number of protons, ratio of permeated quantities of water to the protons, and current efficiency all appeared to depend on the IEC of the resulting membranes. When compared to Nafion the tested membranes exhibited lower electric cell resistance, and thereby decreasing the overall energy required in the concentration operation.
Hasegawa, Shin; Sato, Ken*; Narita, Tadashi*; Suzuki, Yasuyuki; Takahashi, Shuichi; Morishita, Norio; Maekawa, Yasunari
Journal of Membrane Science, 345(1-2), p.74 - 80, 2009/12
Times Cited Count：33 Percentile：70.33(Engineering, Chemical)Radiation-induced graft polymerization of styrene into poly(ether ether ketone) (PEEK) with 32% crystallinity was investigated with DSC, TGA, XRD, and ESR. Endothermic heats of melting of the original and styrene-grafted PEEK (grafted PEEK) films were similar, indicating the crystallinity was almost completely maintained up to a grafting degree of 51%. Lower glass transition temperature of the grafted PEEK film in the DSC, and the absence of an extra halo originating from amorphous polystyrene grafts in the XRD strongly indicate the grafting of styrene to crystalline PEEK films proceeded in the amorphous region of PEEK. This is probably because polystyrene grafts have hydrocarbon structures similar to a base PEEK polymer, resulting in compatibility to the amorphous phase of the PEEK films. The grafted PEEK films can be converted to PEEK-based electrolyte membranes by subsequent sulfonation, and had conductivity of more than 0.01 S/cm and exhibited higher water content above 100%.
Chen, J.; Li, D.; Koshikawa, Hiroshi; Zhai, M.*; Asano, Masaharu; Oku, Hiroyuki*; Maekawa, Yasunari
Journal of Membrane Science, 344(1-2), p.266 - 274, 2009/11
Times Cited Count：15 Percentile：46.49(Engineering, Chemical)An ultrathin polyetheretherketone (PEEK) film was modified by thermal grafting of divinylbenzene (DVB) followed by radiation grafting of ethyl styrenesulfonate (ETSS), to develop a polymer electrolyte membrane (PEM) for use in direct methanol fuel cells (DMFCs). The DVB-grafting yield by thermal polymerization was less than 7%, but was sufficient to enhance the subsequent ETSS-grafting. The ETSS units were converted to styrenesulfonic acid (SS) units by hydrolysis in hot water, resulting in an ultrathin PEEK-g-DVB-g-SS PEM. FT-IR and TG analysis as well as measurements for the ion exchange capacity, water uptake, proton conductivity, mechanical strength, and methanol permeability were performed. Furthermore, this new PEM was tested in a DMFC, and a high maximum power density was confirmed. Therefore, we conclude that this modified PEEK film can be used as the PEM for the application in DMFCs.
Qiu, J.*; Zhai, M.*; Chen, J.; Wang, Y.*; Peng, J.*; Xu, L.*; Li, J.*; Wei, G.*
Journal of Membrane Science, 342(1-2), p.215 - 220, 2009/10
Times Cited Count：77 Percentile：91.1(Engineering, Chemical)A novel ETFE-based amphoteric ion exchange membrane (AIEM) was prepared through a two-step radiation induced grafting technique. ETFE film was first grafted with styrene (St) (denoted as ETFE-
-PS), followed with a sulfonation treatment to obtain a cation exchange membrane (ETFE--PSSA). The ETFE--PSSA membrane was subsequently grafted with dimethylaminoethyl methacrylate (DMAEMA) and then protonated, resulting in an AIEM with both anionic and cationic groups. The obtained AIEM exhibited high ion exchange capacity (IEC) and conductivity, as well as significantly reduced permeability of vanadium ions. Vanadium redox flow battery (VRFB) assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.3V after placed for 300h, and exhibited higher columbic efficiency and energy efficiency than that with Nafion117 membrane.
Qiu, J.*; Zhang, J.*; Chen, J.; Peng, J.*; Xu, L.*; Zhai, M.*; Li, J.*; Wei, G.*
Journal of Membrane Science, 334(1-2), p.9 - 15, 2009/05
Times Cited Count：90 Percentile：93.15(Engineering, Chemical)Poly(vinylidene difluoride) (PVDF) film was grafted with styrene (St) and dimethylaminoethyl methacrylate (DMAEMA) using irradiation techniques. Through subsequent sulfonation and protonation processes, a new kind of amphoteric ion exchange membrane (AIEM) was synthesized. The grafting yield (
) increased with absorbed dose and leveled off at about 60 kGy. The properties of the AIEM strongly depended on the composition and of the film, i.e. higher content of DMAEMA brought lower permeability of vanadium ions and conductivity. Finally, an AIEM was assembled and tested in the vanadium redox flow battery (VRFB) system. It was found that the VRFB assembled with the AIEM maintained an open circuit voltage (OCV) higher than 1.2V after placed for 68h, which was much longer than that with the Nafion117 membrane. Therefore, this work provides a novel method to develop potential substitute of Nafion membranes to be applied in VRFB system.
Koshikawa, Hiroshi; Usui, Hiroaki*; Maekawa, Yasunari
Journal of Membrane Science, 327(1-2), p.182 - 187, 2009/02
Times Cited Count：3 Percentile：17.12(Engineering, Chemical)Hybrid membranes consisting of polyimide (PI) films embedded with copper wires were prepared by electroplating copper into the etched pores of ion track membranes. Electrical resistance of single copper wire, measured by the four-point probe, did not show significant difference with the value estimated from the bulk resistivity. It was also found that the resistance, as well as the hybrid membrane structure, remains stable against thermal treatment of at least up to 400C. Such anisotropically conducting membranes with high thermal stability are expected to have wide application in microelectronics devices.
Takahashi, Shuichi*; Okonogi, Hiroyuki*; Hagiwara, Tokio*; Maekawa, Yasunari
Journal of Membrane Science, 324(1-2), p.173 - 180, 2008/10
Times Cited Count：37 Percentile：72.79(Engineering, Chemical)Polymer electrolyte membranes (PEM) consisting of alkylsulfonic acid were successfully synthesized by radiation-induced graft polymerization of methyl acrylate (MA) into a poly(ethylene-co-tetrafluoroethylene) (ETFE) film, followed by sulfonation at an 
-carbonyl carbon of the MA units in the grafting chain using an equimolar complex of chlorosulfonic acid and dioxane (ClSOH-Complex). The ion exchange capacity and ion conductivity of the MA-grafted PEM were controlled in the respective ranges of 0.54-1.47 mmol/g and 0.014-0.14 S/cm by changing the grafting degree. It has been confirmed by titrimetric and gravimetric analyses of sulfonic and carboxylic acids in the film that the sulfonation reaction is accompanied with decarboxylation of the MA units equimolar to the substituted sulfonic acids (substitution of carboxylic acid with sulfonic acid), that the sulfonation degree was about 30%.
Iwai, Yasunori; Hiroki, Akihiro; Tamada, Masao; Yamanishi, Toshihiko
Journal of Membrane Science, 322(1), p.249 - 255, 2008/09
Times Cited Count：29 Percentile：65.9(Engineering, Chemical)Soaking Nafion N117 in oxygen-saturated distilled water was irradiated by g-rays or electron beam at various dose ranging to 1600 kGy at room temperature or 343K to obtain detailed information on the effect of oxygen on radiation deterioration in Nafion mechanical properties and ion exchange capacity. The contribution of reactions that boar no relation to oxygen to radiation deterioration in mechanical property was dominant for the irradiation in oxygen-saturated distilled water at room temperature. The effect of oxygen was not significant due to little oxygen concentration in distilled water. Irradiated Nafion N117 became a weak and brittle material at 343K. The effect of oxygen became negligible at 343K. The ion exchange capacity irradiated at the dose of 1600kGy was only 20% decrease of initial capacity at room temperature.
Chen, J.; Asano, Masaharu; Maekawa, Yasunari; Yoshida, Masaru
Journal of Membrane Science, 319(1-2), p.1 - 4, 2008/07
Times Cited Count：35 Percentile：71.11(Engineering, Chemical)Polyetheretherketone (PEEK)-based polymer electrolyte membrane (ssPEEK) was prepared by successive grafting of divinylbenzene and ethyl styrenesulfonate onto PEEK film, followed by hydrolysis of the graft chains to form styrenesulfonate graft chains. In comparison with the commercial Nafion membrane, the obtained ssPEEK membrane possesses superior proton conductivity and mechanical property, comparable fuel cell performance at a lower temperature and higher relative humidity, and substantially better fuel cell performance at a higher temperature and lower relative humidity. Furthermore, the ssPEEK membrane maintains good performance in a fuel cell after operation for more than 250 h, while the Nafion membrane deteriorated under such conditions.
-styryltrimethoxysilane into poly(ethylene--tetrafluoroethylene) filmsChen, J.; Asano, Masaharu; Maekawa, Yasunari; Yoshida, Masaru
Journal of Membrane Science, 296(1-2), p.77 - 82, 2007/06
Times Cited Count：36 Percentile：71.52(Engineering, Chemical)In order to prepare a polymer electrolyte hybrid membrane with both high proton conductivity and high thermal stability, the -styryltrimethoxysilane was first grafted into ETFE film by -ray preirradiation. The grafted film was then sulfonated to attach sulfonic acid groups onto the aromatic rings of the graft chains, and finally hydrolyzed and condensed to introduce silane-crosslinking between the graft chains. The preparation conditions for grafting and sulfonation, and the properties of the resulting polymer electrolyte membrane, such as ion exchange capacity, proton conductivity, water uptake, and thermal stability, were investigated with respect to its application in fuel cells. It is concluded that the properties of the new polymer electrolyte hybrid membrane are comparable to Nafion, and are superior to a styrene-grafted membrane.
