Updated on 2024/05/20

写真a

 
HANADA, Nobuko
 
Affiliation
Faculty of Science and Engineering, School of Advanced Science and Engineering
Job title
Associate Professor

Research Experience

  • 2017.04
    -
    Now

    Waseda University   School of Advanced Science and Engineering

  • 2010.12
    -
    2017.03

    University of Tsukuba   Graduate School of Systems and Information Engineering

  • 2008.04
    -
    2010.11

    Sophia University   Faculty of Science and Technology Department of Engineering and Applied Sciences

  • 2006.04
    -
    2008.03

    カールスルーエ研究所   ナノテクノロジー研究所   客員研究員

  • 2005.04
    -
    2006.03

    Hiroshima University   Natural Science Center for Basic Research and Development

Education Background

  • 2003.04
    -
    2005.03

    Hiroshima University   Graduate School of Advanced Sciences of Matter  

  • 2001.04
    -
    2003.03

    Hiroshima University   Graduate School of Biosphere Science  

  • 1997.04
    -
    2001.03

    Hiroshima University   School of Integrated Arts and Sciences  

Research Areas

  • Chemical reaction and process system engineering / Structural materials and functional materials

Awards

  • 第19回 日本学術振興会賞

    2022.02   日本学術振興会   高容量水素貯蔵材料の反応速度改善と水素貯蔵・供給プロセスの開発

    Winner: 花田信子

 

Papers

  • Molten-salt synthesis of manganese-doped intermetallic TiFexMn(1−x) nanoparticles from oxide precursors

    Yasukazu Kobayashi, Shohei Yamaoka, Shinichiro Nakagawa, Nobuko Hanada

    Journal of Alloys and Compounds   941   168996  2023.04  [Refereed]

     View Summary

    Manganese-doped intermetallic TiFexMn(1−x) nanoparticles (NPs) were synthesized by a molten-salt synthesis method using TiO2, FeSO4•7H2O, and Mn(NO3)2•6H2O as the raw materials. The Ti–Fe–Mn oxide precursors prepared from the raw materials were efficiently reduced at temperatures as low as 600 °C in molten LiCl in the presence of CaH2 as the reducing agent. This resulted in the formation of TiFexMn(1−x) NPs exhibiting few impurities (e.g., TiFe2 or/and TiFe39). Increase in the Mn content led to peak shifts in the X-ray diffraction (XRD) patterns, indicating good incorporation of Mn into the cubic CsCl-type structure of intermetallic TiFe to form a solid solution. Nano-sized particles of< 100 nm were clearly observed in the obtained powders by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Moreover, homogeneous distribution of the constituent elements (i.e., Ti, Fe, and Mn) was confirmed by energy dispersive X-ray (EDX) spectroscopy. Finally, the hydrogen absorption properties of the prepared TiFe0.7Mn0.3 NPs were analyzed. Notably, with the exception of micron-sized TiFe0.7Mn0.3 prepared by common arc melting, the generated NPs exhibited almost no hydrogen absorption. The results obtained herein demonstrated the importance of particle size in activating TiFe-based hydrogen absorption materials.

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  • Environmentally friendly molten salt synthesis of high-entropy AlCoCrFeNi alloy powder with high catalytic hydrogenation activity

    Yasukazu Kobayashi, Heng Yi Teah, Shota Yokoyama, Ryo Shoji, Nobuko Hanada

    International Journal of Hydrogen Energy    2023  [Refereed]

     View Summary

    A molten salt synthesis method was used to prepare high-entropy AlCoCrFeNi alloy powder with a high specific surface area of 67.5 m2/g, exhibiting remarkable catalytic activity in the hydrogenation of p-nitrophenol by NaBH4. The life cycle assessment of the proposed method indicated that AlCoCrFeNi production was associated with greenhouse gas emission of 125 kgCO2e/kg-product, whose main contributors were CaH2 and citric acid used during the precursor's reduction and formation, respectively. On the other hand, that for a previously reported dealloying method was 277 kg CO2e/kg-product. Thus, a minimum of 54% greenhouse gas emission reduction compared to the conventional dealloying method is achievable in the proposed molten salt method. The results indicated the possible environmentally friendly production of high-surface-area, high-entropy alloy powders suitable for industrial applications.

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  • A Molten Salt Synthesis Method of the High-Entropy Alloy CrMnFeCoNi for High Catalytic Performance and Low Life Cycle GHG Emissions

    Yasukazu Kobayashi, Heng Yi Teah, Shota Yokoyama, Ryo Shoji, Nobuko Hanada

    ACS Sustainable Chemistry &amp; Engineering   10 ( 46 ) 15046 - 15057  2022.11  [Refereed]

     View Summary

    The high-entropy alloy (HEA) CrMnFeCoNi is a prominent catalyst material. High-specific-surface-area HEA powder can be chemically prepared via a conventional direct etching method or a molten salt synthesis method developed in our group. In this study, we compared the catalytic performance in the hydrogenation of p-nitrophenol using the HEA CrMnFeCoNi powders obtained from the etching method and the molten salt method. The results demonstrated a superior catalytic performance for the HEA prepared by the molten salt method at 800 °C. A structural analysis comprising X-ray diffraction, scanning electron microscopy/transmission electron microscopy with energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy revealed that the HEA CrMnFeCoNi prepared by the molten salt method is composed of a homogeneous HEA core covered by an active nickel-rich surface shell, which contributes to the superior catalytic performance. Furthermore, a life cycle GHG emissions assessment was conducted to compare the environmental performances of the two methods. The result showed that the molten salt method accounted for 121 kg CO2e/kg HEA production, which is 20% lower than that for the common etching method. Thus, the molten salt synthesis method is a promising option to industrialize HEA production.

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    6
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  • Systematic investigation of anode catalysts for liquid ammonia electrolysis

    Natsuho Akagi, Keisuke Hori, Hisashi Sugime, Suguru Noda, Nobuko Hanada

    Journal of Catalysis   406   222 - 230  2022.02  [Refereed]

     View Summary

    Liquid ammonia is able to release hydrogen via electrolysis with a theoretical voltage of 0.077 V. However, the actual operation voltage is much higher (around 1–2 V) due to the large overpotential of the anodic reaction. We systematically investigated Pt, Ir, Ru, Ni, Co, Fe, Ta, and Ti as the anodic catalyst, and observed a volcano correlation when plotting the current density against the formation enthalpy of metal nitrides per nitrogen ΔfHMN (kJ/mol-N). ΔfHMN reflects the strength of metal-nitrogen bond, and Ru having a moderate ΔfHMN showed the highest catalytic activity. Then, the activity enhancement via microstructure control was examined. The sputtered Pt and Ni films having a columnar structure with a rough surface showed 7- and 13-times higher current density than the Pt and Ni plates, respectively. An anodic current density of 0.45 mA/cm2 was achieved for the sputtered Ni film at an anodic potential as low as 0.3 V vs H2/NH3.

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  • Fast and stable hydrogen storage in the porous composite of MgH2 with Nb2O5 catalyst and carbon nanotube

    Kosuke Kajiwara, Hisashi Sugime, Suguru Noda, Nobuko Hanada

    Journal of Alloys and Compounds   893   162206 - 162206  2022.02  [Refereed]

     View Summary

    The MgH2-Nb2O5-carbon nanotube (CNT) composite was fabricated to accommodate the volume change of particles during the hydrogen storage cycles by holding the MgH2-Nb2O5 particles within the sponge-like matrix of the CNT. This allowed for preservation of the composite structure and led to more stable hydrogen sorption properties during 20 cycles, as compared to without CNT. To investigate this effect of CNT on the cyclic stability of MgH2-Nb2O5, CNT and expanded graphite (EG) were added to MgH2-Nb2O5 via ball milling. The MgH2-Nb2O5-CNT powder showed stable cyclic performance, similar to the MgH2-Nb2O5-CNT composite, whereas the MgH2-Nb2O5-EG powder exhibited cyclic degradation similar to MgH2-Nb2O5. From SEM-EDS, it was found that the C/Mg ratio of the surface of the MgH2-Nb2O5-CNT powder was higher than that of the MgH2-Nb2O5-EG powder. Thus, the fibrous CNT on the surface of the MgH2 particles could be responsible for the greater cyclic stability of the MgH2-Nb2O5-CNT composite.

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    34
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  • Environmentally friendly chemical synthesis of intermetallic iron aluminide submicrometer particles

    Yasukazu Kobayashi, Heng Yi Teah, Nobuko Hanada

    Journal of Cleaner Production   316   128264 - 128264  2021.09  [Refereed]

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  • Low-temperature chemical synthesis of intermetallic TiFe nanoparticles for hydrogen absorption

    Yasukazu Kobayashi, Shohei Yamaoka, Shunta Yamaguchi, Nobuko Hanada, Shohei Tada, Ryuji Kikuchi

    International Journal of Hydrogen Energy   46 ( 43 ) 22611 - 22617  2021.06  [Refereed]

     View Summary

    Nanosizing of TiFe hydrogen storage alloy is conducted to facilitate its activation. Here, pure intermetallic TiFe nanoparticles (45 nm) were prepared using chemical reduction of oxide precursors at 600 °C, which is the lowest temperature ever used in chemical synthesis. This was achieved using a strong reducing agent (CaH2) in a molten LiCl. When used for hydrogen absorption, the obtained nanoparticles surprisingly exhibited almost no hydrogen absorption. The results demonstrated that TiFe nanoparticles are more difficult to activate than the bulk powder because the oxidized surface layers of the nanoparticles become stabilized, which prevents the morphological change necessary for their activation.

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  • Structural Properties of (Ti, Zr)(Mn, Cr)2M0.1 (M = None, Fe, Co, Ni, and Cu) Hydrogen Storage Alloys: Composition Distribution and Occupied Site of Doped Element

    Tessui Nakagawa, Daichi Heshiki, Hiroki Higa, Junko Kawakami, Riki Kobayashi, Nobuko Hanada, Kazutaka Ikeda, Toshiya Otomo, Hironori Ofuchi, Masayoshi Ishida

    MATERIALS TRANSACTIONS   62 ( 6 ) 899 - 904  2021.06  [Refereed]

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  • Numerical simulation of heat supply and hydrogen desorptionby hydrogen flow to porous MgH2 sheet

    Keisuke Yoshida, Kosuke Kajiwara, Hisashi Sugime, Suguru Noda, Nobuko Hanada

    Chemical Engineering Journal   421   129648 - 129648  2021.04  [Refereed]

     View Summary

    We propose using hydrogen as a heat transfer medium to supply waste heat from hydrogen-driven devices to hydrogen storage tanks. In our model, MgH2 is used in the form of porous sheets, set in parallel in the tank, and heat is supplied via hot hydrogen flowed through the interspaces between the porous sheets. Feasibility of the hydrogen desorption reaction in this process was verified numerically. Hydrogen efficiently carried heat to the stack of porous MgH2 sheets via convective heat transfer and then carried heat into the porous MgH2 sheets via conductive heat transfer through the pores owing to its high thermal conductivity. We found that the hydrogen desorption is also fast enough to allow the supplied heat to be used efficiently to drive the endothermic hydrogen desorption reaction. It was understood that the thickness of the MgH2 sheet and hot hydrogen flow speed affected hydrogen desorption. These factors can be evaluated by using the dimensionless number of τs/τh which is the ratio of the space time to the time constant for heat transfer in the MgH2 sheet. Under τs/τh > 0.01 range, both the reaction and heat transfer are fast enough, the hydrogen desorption is limited by heat supply, and hydrogen desorption amount is proportional to the heat supplied to the reactor. The tank structure and operating conditions can be designed by using the dimensionless number of τs/τh.

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  • Chemical synthesis of unique intermetallic TiFe nanostructures originating from the morphology of oxide precursors

    Yasukazu Kobayashi, Heng Yi Teah, Nobuko Hanada

    Nanoscale Advances   3 ( 18 ) 5284 - 5291  2021  [Refereed]

     View Summary

    TiFe nanostructures where prepared at temperatures as low as 600 °C with a Ti–Fe precursor and a CaH2 reducing agent in molten LiCl. For the first time an intermetallic compound with a unique layered morphology was found which could have originated from the FeTiO3 precursor.

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  • Electrolysis of ammonia in aqueous solution by platinum nanoparticles supported on carbon nanotube film electrode

    Nobuko Hanada, Yusuke Kohase, Keisuke Hori, Hisashi Sugime, Suguru Noda

    Electrochimica Acta   341   136027 - 136027  2020.05  [Refereed]

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  • Effect of CO2 on hydrogen absorption in Ti-Zr-Mn-Cr based AB2 type alloys

    Nobuko Hanada, Hirotaka Asada, Tessui Nakagawa, Hiroki Higa, Masayoshi Ishida, Daichi Heshiki, Tomohiro Toki, Itoko Saita, Kohta Asano, Yumiko Nakamura, Akitoshi Fujisawa, Shinichi Miura

    Journal of Alloys and Compounds   705   507 - 516  2017.05  [Refereed]

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  • Material transformation of alumina and influence on leakage current by application of DC high voltage at high temperatures

    Satoshi Kawato, Nobuko Hanada, Masashi Mitsui, Masayoshi Ishida

    IEEJ Transactions on Fundamentals and Materials   137 ( 12 ) 685 - 692  2017

     View Summary

    In order to investigate a material transformation of alumina (Al2O3) and an influence on leakage current by application of high DC voltage at high temperatures, the leakage current of two alumina samples were measured for 100 hours and the elemental analyses were carried out. The leakage current tended to decrease, and the electrical conductivity decreased with increasing applied voltage. The activation energies of electrical conduction of two samples were nearly equal. Thus, the reproducibility of these results was confirmed. After the experiments, deposits of impurities contained in alumina were observed in the surrounding area of the positive electrode. Furthermore, Na, which was contained in Pt paste used for preparing the electrodes, can be a charge career of alumina because it was detected from only negative electrodes. Therefore, the reason why the leakage current decreased is the decrease in the amount of charge careers because of the deposits of impurities.

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  • dc Voltage Insulating Properties of Various Inorganic Materials in Hydrogen Atmosphere at High Temperatures

    Koichi Takahashi, Nobuko Hanada, Masayoshi Ishida

    ELECTRICAL ENGINEERING IN JAPAN   193 ( 4 ) 1 - 8  2015.12  [Refereed]

     View Summary

    In this study, the dc voltage insulating properties in a hydrogen atmosphere at high temperatures (600 degrees C to 850 degrees C) were evaluated for alumina (Al2O3), magnesia (MgO), silicon nitride (Si3N4), and mica (KMg3(Si3Al)O-10(OH)(2)) to comprehend the difference in the insulating properties of oxide, nitride, and minerals. The activation energies of the electrical conductivity of alumina and magnesia in hydrogen were larger than those in air. On the other hand, the electrical conduction values for silicon nitride and mica in hydrogen were the same as those in air. Therefore a low oxygen partial pressure would have some influence on the electrical conduction of oxides. Increasing the temperature did not result in a large change in the electrical conduction mechanism in any of the materials in either atmosphere. The maximum partial discharge (PD) in hydrogen tended to increase compared to that in air at high voltage. The applied voltage at which the maximum amount of PD started to increase rapidly became lower with increasing temperature in all materials and in both atmospheres. The total amount of PD tended to decrease with increasing temperature in all materials and in both atmospheres. However, above a certain temperature, the total amount of PD either increased or showed a slight decrease.

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  • Dependence of constituent elements of AB5 type metal hydrides on hydrogenation degradation by CO2 poisoning

    Nobuko Hanada, Tessui Nakagawa, Hirotaka Asada, Masayoshi Ishida, Keisuke Takahashi, Shigehito Isobe, Itoko Saita, Kohta Asano, Yumiko Nakamura, Akitoshi Fujisawa, Shinichi Miura

    Journal of Alloys and Compounds   647   198 - 203  2015.10  [Refereed]

     View Summary

    LaNi5-based AB(5) type alloy has high tolerance to CO2 poisoning for hydrogen purification and storage from 20 to 25% CO2 mixed gas. To elucidate the CO2 poisoning factors of AB(5) type alloys, which are LaNi5, CaNi5, LaCo5, and MmNi(4.025)Co(0.4)Mn(0.275)Al(0.3) (Mm-Ni), the dependence of the constituent elements has been investigated on hydrogenation degradation by CO2 poisoning. The tendency of CO2 poisoning magnitude is CaNi5 < LaNi5 << Mm-Ni < LaCo5, which was evaluated by the hydrogenation rate and capacity under CO2 partial pressure and after CO2 exposure. The Ni element of B site in CaNi5 and LaNi5 is an important role to maintain higher tolerance of CO2 poisoning compared to Co element in LaCo5. Moreover, the element of A site effects on CO2 poisoning magnitude in AB(5) type alloy. The experimental tendency of CO2 poisoning magnitude is consistent with the theoretical CO2 adsorption energy on the (1010) surface plane of -1.39, -2.05, and -2.68 eV for CaNi5, LaNi5, and LaCo5, respectively. CO2 adsorbs on B site with electron charge transfer from AB(5) alloys to carbon. Not only Ni element in B site but also Ca element in A site decreases the energy of CO2 adsorption on B site in AB(5) type alloys. (C) 2015 Elsevier B.V. All rights reserved.

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  • In-Situ XAS for Niobium Oxide Catalyst on Hydrogen Absorption and Desorption of Magnesium

    Toru Kimura, Hiroki Miyaoka, Nobuko Hanada, Takayuki Ichikawa

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   79 ( 3 ) 107 - 111  2015  [Refereed]

     View Summary

    The variation of the niobium (Nb) oxide catalyst during hydrogen absorption and desorption reactions was investigated by in-situ X-ray absorption spectroscopy (XAS). Results indicated that H-2 was easily dissociated on the catalyst because the hydrogen absorption kinetics was significantly improved, and then the hydrogen atoms were diffused through inside of the catalyst. Thus, the catalytic mechanism of Nb oxides is different from that of conventional metal catalysts, in which the dissociated H is moved on the surface of catalyst.

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  • Mgの水素吸蔵/放出におけるNb酸化物触媒のIn-situ X線吸収分光

    木村通, 宮岡裕樹, 花田信子, 市川貴之

    日本金属学会誌   79 ( 3 ) 107 - 111  2015  [Refereed]

  • Study on the capacity fading of pristine and FePO4 coated LiNi1/3Co1/3Mn1/3O2 by Electrochemical and Magnetical techniques

    Xizheng Liu, De Li, Huiqiao Li, Akira Iyo, Nobuko Hanada, Masayoshi Ishida, Haoshen Zhou

    ELECTROCHIMICA ACTA   148   26 - 32  2014.12  [Refereed]

     View Summary

    Capacity fading mechanism of pristine and FePO4-coated LiNi1/3Co1/3Mn1/3O2 has been studied by electrochemical and magnetic methods. Along with cycles, significant increase of cell polarization and charger transfer resistance (R-ct), which mainly cause the capacity fading at the initial charge/discharge cycles, have been observed according to the cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) analysis. In comparison, the existence of FePO4 coating layer can effectively suppress the deterioration of surface polarization and increase of Rct at the interface of electrode/electrolyte. The coated sample suppress the decrease of Li+ diffusion coefficient with prolonged cycles according to the galvanostatic intermittent titration technique (GITT) tests. It also shows larger Weiss constants (fitting above 130 K) and lower blocking temperatures, which indicate the surface coating can suppress the deterioration of Li/Ni disorder upon repeated cycles. This study may give the researchers some light on understanding the capacity fading mechanism of LiNi1/3Co1/3Mn1/3O2 and the effects of surface coating layer, and thus, give help to the future designing of superior coating layers for layered cathode materials in Li-ion batteries. (C) 2014 Elsevier Ltd. All rights reserved.

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  • Concept Proposal and Test Run Results for a Hybrid Electric Energy Storage Method of High Power Capacitor/Large Energy Battery Combination

    Nakayama Tomonori, Mineno Katsuya, Tachihara Wataru, Kawai Yuki, Hasegawa Hiroaki, Hiraoka Kazutaka, Kakizaki Nobuo, Hanada Nobuko, Ishida Masayoshi

    IEEJ Transactions on Power and Energy   134 ( 1 ) 76 - 83  2014  [Refereed]

     View Summary

    Energy storage will be critically important for stabilizing grids with renewable energy power sources; therefore various kinds of high performance devices such as batteries and capacitors are being developed at present. In particular, Li-ion batteries exhibit high energy density, and Li-ion capacitors have high input/output power ability with almost zero self-discharge. The authors have proposed a BAttery/Capacitor Hybrid Energy Storage system (BACHES) which delivers wide-range charge/discharge power with a large capacity by Li-ion capacitors and batteries. In this paper, the authors show the conceptual details and the features of this system. Also, experimental equipment was manufactured as specifications of maximum power of 6kW for connection to a 380V bus. The fundamental performances of the system components of Li-ion capacitors, Li-ion batteries, and converters were evaluated in test runs. This study concluded that the system operates itself by sharing roles between the Li-ion capacitors and the Li-ion batteries according to the characteristics of each, and then can control the bus voltage within 1.2% and 4.4% drops under sudden 0.47kW and 1.8kW power losses, respectively.

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  • A novel tunnel Na0.61Ti0.48Mn0.52O2 cathode material for sodium-ion batteries

    Shaohua Guo, Haijun Yu, Dequan Liu, Wei Tian, Xizheng Liu, Nobuko Hanada, Masayoshi Ishida, Haoshen Zhou

    CHEMICAL COMMUNICATIONS   50 ( 59 ) 7998 - 8001  2014  [Refereed]

     View Summary

    A novel tunnel Na0.61Ti0.48Mn0.52O2 material is explored as a cathode for sodium-ion batteries for the first time. It can deliver a reversible discharge capacity of 86 mA h g(-1) with an average voltage of 2.9 V at 0.2 C rate in a sodium half cell, exhibiting good rate capability and capacity retention at a cut-off voltage of 1.5-4 V. These results indicate that tunnel Na0.61Ti0.48Mn0.52O2 has a great potential application in large scale energy storage.

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  • DC Voltage Insulating Properties of Various Inorganic Materials in Hydrogen Atmosphere at High Temperatures

    Takahashi Koichi, Hanada Nobuko, Ishida Masayoshi

    IEEJ Transactions on Fundamentals and Materials   134 ( 7 ) 466 - 471  2014  [Refereed]

     View Summary

    In this study, the insulating properties on DC voltage in hydrogen atmosphere at high temperatures (600-850°C) were evaluated for alumina (Al2O3), magnesia (MgO), silicon nitride (Si3N4) and mica (KMg3(Si3Al)O10(OH)2) to comprehend the difference in insulating properties of oxide, nitride and mineral. The activation energies of electrical conductivity of alumina and magnesia in hydrogen were larger than those in air. On the other hand, at silicon nitride and mica electrical conduction in hydrogen were same as those in air. Therefore low oxygen partial pressure would have some influence on electrical conduction of oxide. And increasing temperature didnt bring a huge change of electrical conduction mechanism in all materials and both of the atmospheres. The maximum amounts of partial discharge in hydrogen tended to increase compared to those in air at high voltage. Applied voltage, in which the maximum amounts of partial discharge started to increase rapidly, became lower with increasing temperature in all materials and both of the atmospheres. The total amounts of partial discharge tended to decrease with increasing temperature in all materials and both of the atmospheres. However, at exceeding certain temperatures, the total amounts of partial discharge increased or slightly decreased.

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  • A hydrogen purification and storage system using CO adsorbent and metal hydride

    Shinichi Miura, Akitoshi Fujisawa, Shuhei Tomekawa, Yukinobu Taniguchi, Nobuko Hanada, Masayoshi Ishida

    Journal of Alloys and Compounds   580 ( 1 ) S414 - S417  2013

     View Summary

    The CO Selective Adsorbent and Metal Hydride Intermediate Buffer (COA-MIB) method has been proposed as a hydrogen production/supply system with reformer. First, this method thoroughly eliminates carbon monoxide using an adsorption material that strongly selects carbon monoxide, and second it introduces a mixed gas to a metal hydride that purifies and stores hydrogen. A 100 NL/h laboratory scale apparatus was operated in daily start and stop operations for 1000 cycles for a total of 1500 h with quite good efficiency. The metal hydride used in this apparatus was an AB5-type whose hydrogen equilibrium pressure was adjusted to be 0.1 MPa at 25 C. As a result of the basic performance evaluation, we have experimentally verified that pure hydrogen can be produced from methanol reforming gas for 1000 cycles on a daily start/stop operation basis and a high hydrogen recovery rate of over 89% can be achieved. 3 N m3/h Bench scale apparatus was also operated with same mode for 100 cycles for a total of 150 h and shows almost the same performance. The new method enables us to minimize emissions of carbon dioxide by using compact and highly efficient fuel cells as a part of the smart community technologies. © 2013 Published by Elsevier B.V.

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  • Effect of several metal chlorides on the thermal decomposition behaviour of alpha-Mg(BH4)(2)

    Elisa Gil Bardaji, Nobuko Hanada, Oleg Zabara, Maximilian Fichtner

    INTERNATIONAL JOURNAL OF HYDROGEN ENERGY   36 ( 19 ) 12313 - 12318  2011.09  [Refereed]

     View Summary

    Mechanochemical alloying of Mg(BH4)(2) with small amounts of metal chlorides (PdCl2, TiCl3, VCl3, MoCl3, RuCl3, CeCl3 and NbCl5) results in the formation of transition metal doped nanocomposites with different hydrogen desorption properties. The thermal decomposition properties of ball-milled as well as doped alpha-Mg(BH4)(2) have been studied. An amorphization reaction of Mg(BH4)(2) is induced by ball milling, nevertheless a partial recrystallization of the alpha phase takes place after heating up to 150 degrees C. The effect of ball milling Mg(BH4)(2) with each additive has been investigated in detail by using differential scanning calorimetry, thermogravimetric analysis and X-ray diffraction. The onset temperature of Mg(BH4)(2) is lowered by more than 100 degrees C through the addition of Nb- or Ti chloride. Moreover, a mixed Ti-Nb-nanocomposite was also synthesized and investigated. The onset temperature of hydrogen evolution during decomposition of the mixed Ti-Nb-nanocomposite is considerably lowered by up to 125 degrees C. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

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  • Existing State of Hydrogen in Electrochemically Charged Commercial-Purity Aluminum and Its Effects on Tensile Properties

    Hiroshi Suzuki, Daisuke Kobayashi, Nobuko Hanada, Kenichi Takai, Yukito Hagihara

    MATERIALS TRANSACTIONS   52 ( 9 ) 1741 - 1747  2011.09  [Refereed]

     View Summary

    Hydrogen was introduced in commercial-purity (99%) aluminum by electrochemical charging to study the existing state of hydrogen and its effects on the mechanical properties of aluminum. Electrochemical charging was conducted in an aqueous H2SO4 solution with 0.1% NH4SCN as a hydrogen recombination poison. The potential and during the charging were determined from the immune. passive, and corrosive regions in the Pourbaix diagram to determine the optimum conditions or the charging. The maximum amount of hydrogen absorbed was obtained in the immune region. The amount of hydrogen and its existing state were examined using hydrogen desorption curves, which were obtained by thermal desorption spectroscopy. The curves showed distinctive peaks corresponding to trapping sites of hydrogen in the material. One of the peaks was observed at approximately 100 degrees C, and it corresponds to vacancies and dislocations in the material; another peak was observed at approximately 400 degrees C and it corresponds to molecular hydrogen in blisters. It was presumed that charged hydrogen diffuses into the bulk of the material to form hydrogen-vacancy pairs, and then these pairs cluster to form blisters. The fracture strain of charged aluminum in the immune region decreased with decreasing strain rate, showing an inverse dependence on the fracture strain of the uncharged material. This phenomenon was considered to be caused by hydrogen transport by dislocations through the interaction between hydrogen and dislocations. The phenomenon was further confirmed by the observation of hydrogen release during tensile deformation, where the amount of hydrogen was high in the strain rate range where the interaction between dislocations and hydrogen was prominent. [doi: 10.2320/matertrans.M2011035]

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  • Effects of deformation on hydrogen absorption and desorption properties of titanium

    Hiroshi Suzuki, Hisashi Taniguchi, Nobuko Hanada, Kenichi Takai, Yukito Hagihara

    JOURNAL OF ALLOYS AND COMPOUNDS   509   S759 - S762  2011.09  [Refereed]

     View Summary

    In this study, we analyzed the effects of deformation on hydrogen absorption and desorption properties of titanium to improve such properties. Hydrogen was introduced into commercially pure (99.5%) titanium by the electrochemical method. The amount and existing state of hydrogen were examined using hydrogen desorption curves obtained by thermal desorption spectroscopy. Hydrogen absorption was promoted by applying tensile deformation prior to charging, which leads to hydride formation within a short charging time. The amount of hydrogen absorbed decreased when the volume fraction of deformation twins exceeded about 0.2. It was considered that hydrogen was mainly trapped by dislocations forming hydride while a large fraction of deformation twins hindered dislocation motion, thus reducing dislocation density leading to a decrease in the amount of absorbed hydrogen. Almost half the charged hydrogen was released when in-plane compressive stress was applied to a charged plate specimen at room temperature due to hydride decomposition under compressive stress. (C) 2010 Elsevier B.V. All rights reserved.

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  • Liquid ammonia electrolysis by platinum electrodes

    B. -X. Dong, T. Ichikawa, N. Hanada, S. Hino, Y. Kojima

    JOURNAL OF ALLOYS AND COMPOUNDS   509   S891 - S894  2011.09  [Refereed]

     View Summary

    Liquid ammonia was electrolyzed based on a new concept by using metal amide as the supporting electrolyte for generation of hydrogen. Different metal amides including LiNH(2), NaNH(2) and KNH(2) were tested, and the influences of the solubility and the concentration of different electrolytes upon the electrolysis current were investigated. Electrolysis efficiency was evaluated on the basis of chronopotentiometry tests at different current densities. Platinized platinum electrodes with fine structure were introduced in order to improve the electrolysis current and reduce the electrolysis potential. (C) 2010 Elsevier B.V. All rights reserved.

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  • Electrochemical charge and discharge properties for the formation of magnesium and aluminum hydrides

    Nobuko Hanada, Akito Kamura, Hiroshi Suzuki, Kenichi Takai, Takayuki Ichikawa, Yoshitsugu Kojima

    JOURNAL OF ALLOYS AND COMPOUNDS   509   S584 - S587  2011.09  [Refereed]

     View Summary

    The electrochemical properties of Mg + 2LiH and Al + 3LiH are investigated by applying a Li-ion insertion and extraction system to form magnesium and aluminum hydrides. For MgH(2) formation, the voltage-composition (VC) curve for Mg + 2LiH during charging exhibits a plateau voltage at 0.58 V, then the final composition is obtained with 1.05 mol Li extraction at 3.0 V. After the charging, the MgH(2) phase is observed by XRD measurement. Therefore, MgH(2) is produced from Mg and LiH by electrochemical charging. With respect to AlH(3) formation, Al + 3LiH is charged at a plateau voltage of 0.81 V, which corresponds to the reaction of Al with hydrogen in LiH to form AlH(3). And the final composition at 3.0 V is 0.6 mol Li. In the XRD profile after charging, the AlH(3) phase is not detected. (C) 2010 Elsevier B.V. All rights reserved.

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  • The Existing State of Hydrogen in Electrochemically Charged Commercial Purity Aluminum and Its Effect on the Tensile Properties

    Hiroshi Suzuki, Daisuke Kobayashi, Nobuko Hanada, Kenichi Takai, Yukito Hagihara

    JOURNAL OF THE JAPAN INSTITUTE OF METALS   74 ( 2 ) 65 - 71  2010.02  [Refereed]

     View Summary

    Hydrogen is introduced in commercial (99% pure) aluminum by electrochemical charging to study the existing state of hydrogen and its effect on the mechanical properties of aluminum. Electrochemical charging is conducted in an aqueous solution of H2SO4 with 0.1 mass% NIH4SCN as a hydrogen recombination poison. The potential and pH during the charging are chosen from the immune, passive, and corrosive regions on Pourbaix diagram to determine the optimum conditions for the charging. The maximum amount of hydrogen absorbed is obtained in the immune region. The amount of hydrogen and its existing state are examined using hydrogen desorption curves, which are obtained by thermal desorption spectroscopy. The curves show distinctive peaks that correspond to trapping sites of hydrogen in the material. One of the peaks is observed at approximately 100 degrees C and it corresponds to vacancies and dislocations in the material; another peak is observed at approximately 400 degrees C and it corresponds to molecular hydrogen in blisters. It is presumed that charged hydrogen diffuses into the bulk of the material to form hydrogen vacancy pairs, and then these pairs cluster to form blisters. The fracture strain of charged aluminum in the immune region decreased with a slower strain rate, showing an inverse dependence on the fracture strain of the uncharged material. This phenomenon is considered to be caused by the transport of hydrogen by dislocations through the interaction between hydrogen and the dislocations. The phenomenon is further confirmed by the observation of hydrogen release during tensile deformation, where the amount of hydrogen is higher in the strain rate region where the interaction between the dislocations and hydrogen is more prominent.

  • Hydrogen generation by electrolysis of liquid ammonia

    Nobuko Hanada, Satoshi Hino, Takayuki Ichikawa, Hiroshi Suzuki, Kenichi Takai, Yoshitsugu Kojima

    Chemical Communications   46 ( 41 ) 7775 - 7777  2010  [Refereed]

  • 電解チャージにより水素吸蔵した純アルミニウムにおける水素存在状態と引張特性に与える水素の影響

    鈴木啓史, 小林大輔, 花田信子, 高井健一, 萩原行人

    本金属学会誌   74   65 - 71  2010  [Refereed]

  • Hydrogen generation by electrolysis of liquid ammonia”, Chemical Communication

    Nobuko Hanada, Satoshi Hino, Takayuki Ichikawa, Hiroshi Suzuki, Kenichi Takai, Yoshitsugu Kojima

    Chemical Communication   46   3982 - 3984  2010  [Refereed]

  • X-ray Absorption Spectroscopic Study on Valence State and Local Atomic Structure of Transition Metal Oxides Doped in MgH2

    Nobuko Hanada, Takayuki Ichikawa, Shigehito Isobe, Tessui Nakagawa, Kazuhiko Tokoyoda, Tetsuo Honma, Hironobu Fujii, Yosbitsugu Kojima

    JOURNAL OF PHYSICAL CHEMISTRY C   113 ( 30 ) 13450 - 13455  2009.07  [Refereed]

     View Summary

    A valence state and a local structure of transition metals (Nb, V, and Ti) in MgH2 doped with metal oxides (Nb2O5, V2O5, and TiO2nano) by ball milling were examined by X-ray absorption spectroscopy (XAS). The main edge regions of the Nb, V, and Ti K-edges in the X-ray absorption near edge structure (XANES) profiles are located between 0 and +5 in the oxidation states. Since these spectra coincide with those of NbO, VO, and Ti2O3, respectively, the additives are reduced by MgH2 to the metal oxides, which have lower oxidation states than those of the starting materials. Furthermore, in order to examine the local structures around the transition metal atoms, the extended X-ray absorption fine structure (EXAFS) spectra were analyzed. In the Fourier transformation curves of the EXAFS spectra, all samples doped with the metal oxides show two peaks corresponding to metal-oxygen and metal-metal bonds, being the same as the references of NbO, VO, and Ti2O3. The local structure formed after ball milling or dehydrogenation is close to that of each of the reduced metal oxides (NbO, VO, and Ti2O3) but in a more disarrangement state.

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  • Evaluation of enthalpy change due to hydrogen desorption for lithium amide/imide system by differential scanning calorimetry

    Shigehito Isobe, Takayuki Ichikawa, Kazuhiko Tokoyoda, Nobuko Hanada, Haiyan Leng, Hironobu Fujii, Yoshitsup Kojima

    THERMOCHIMICA ACTA   468 ( 1-2 ) 35 - 38  2008.02  [Refereed]

     View Summary

    Enthalpy change (Delta H) due to hydrogen desorption (H-desorption) for the lithium amide/imide system was evaluated by differential scanning calorimetry (DSC) measurement. In order to obtain the accurate and precise value of Delta H, we have paid special attention to following two points for correcting raw experimental data. One is to determine a cell constant of DSC equipment, which was evaluated by using the TiO2-doped MgH2 compound as a reference because of its quite similar hydrogen desorption properties to that of the lithium amide/imide system. The other is to estimate the sample amount corresponding to the H-desorption reaction from weight loss in the thermogravimetric (TG) analysis. By performing both the corrections, the Delta H value due to the H-desorption reaction from LiNH2 + LiH to Li2NH + H-2 was evaluated to be 67 kJ/mol H-2. (c) 2007 Elsevier B.V. All rights reserved.

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  • SEM and TEM characterization of magnesium hydride catalyzed with Ni nano-particle or Nb2O5

    Nobuko Hanada, Enoki Hirotoshi, Takayuki Ichikawa, Etsuo Akiba, Hironobu Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   450 ( 1-2 ) 395 - 399  2008.02  [Refereed]

     View Summary

    The microstructures of MgH2 catalyzed with Ni nano-particle or Nb2O5 mesoporous powders are examined by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. For MgH2 catalyzed with Ni, the Ni particles with the diameter smaller than 1 mu m were detected on the MgH2 particles with the diameter smaller than 5 mu m by the back scattering electron (BSE) microscopy. In details, the TEM micrograph indicates that the Ni particles distribute similar to 20 nm in diameter on MgH2 uniformly, which was the same size as the additive doped in MgH2 before milling. On the other hand, for MgH2 catalyzed with Nb2O5, the additive particles could not be found anywhere in the BSE image. Even in the TEM micrograph by much larger magnification than the SEM micrograph, the particles corresponding to the additive cannot be observed at all. Furthermore, an energy dispersive X-ray (EDX) analysis in spots with a diameter of 20 nm indicated that the existing ratio of Mg to Nb was evaluated to 98:2, being the same as the starting ratio before milling. Therefore, the metal oxide Nb2O5 becomes extremely small particle that could not be observed by the present work after milling compared to metal Ni-nano. (C) 2006 Elsevier B.V. All rights reserved.

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  • Thermal decomposition of Mg(BH(4))(2) under He flow and H(2) pressure

    Nobuko Hanada, Krzysztof Chopek, Christoph Frommen, Wiebke Lohstroh, Maximilian Fichtner

    JOURNAL OF MATERIALS CHEMISTRY   18 ( 22 ) 2611 - 2614  2008  [Refereed]

     View Summary

    The thermal decomposition steps of Mg(BH(4))(2) were investigated under He flow and various hydrogen pressures up to 50 bar. In a He flow, the main decomposition of Mg(BH(4))(2) occurs between 250 and 410 degrees C until 12.2 mass% is lost, with three main peaks of hydrogen desorption. In the first decomposition step the crystalline phase of Mg(BH(4))(2) disappears while a small amount of Mg is detected in the XRD profile. However, the major part of the sample is in an amorphous state. After the second step, crystalline MgH(2) is observed together with the Mg phase. The third step of hydrogen desorption corresponds to the decomposition of MgH(2) and Mg remains the only crystalline phase observed by XRD measurement after heating to 410 degrees C. Further hydrogen evolution of 1.4 mass% is observed from 410 degrees C to 580 degrees C. Only after this hydrogen desorption, MgB(2) appears in the XRD spectra of the sample. These results indicate that amorphous, hydrogen containing boron compounds take part as intermediates in the reaction. Under hydrogen pressure, the decomposition events of Mg(BH(4))(2) shift to higher temperatures in the DSC (differential scanning calorimetry) profiles: while there is only a small shift for steps 1 and 2 there is a clear separation of the succeeding reactions under a background pressure of hydrogen. These data show that the decomposition proceeds via several well defined steps. The final stable decomposition compound of Mg(BH(4))(2) is MgB(2) under both inert and hydrogen gas atmosphere.

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  • Comparison of the calculated and experimental scenarios for solid-state reactions involving Ca(AIH(4))(2)

    Nobuko Hanada, Wiebke Lohstroh, Maximilian Fichtner

    JOURNAL OF PHYSICAL CHEMISTRY C   112 ( 1 ) 131 - 138  2008.01  [Refereed]

     View Summary

    Solid-state reactions of Ca(AIH(4))(2) and various additives were investigated experimentally for hydrogen desorption. The Ca(AIH(4))(2) + Si, Ca(AIH(4))(2) + 2MgH(2), Ca(AIH(4))(2) + 2LiH, and Ca(AIH(4))(2) + 2LiNH(2) systems were chosen among reactions proposed theoretically(1) to study their hydrogen storage capacity and an appropriate reaction enthalpy. For all systems investigated, the reversible reactions proposed should have more than 6.5 mass % hydrogen capacity and reaction enthalpies in the range of 30-55 kJ/mol H-2. However, most of the experimentally observed reactions do not conform to theoretical propositions because different final products were obtained in all cases but one. Two tendencies were observed in the experiments. One is that the reaction comprises several distinct steps at different temperatures as observed in the Ca(AIH(4))(2) + Si and Ca(AIH(4))(2) + 2 MgH2 systems. In this case, Ca(AIH(4))(2) decomposes first and is followed by a reaction of the remaining compounds. The same kinetic reaction barriers are encountered here as in pure Ca(AIH(4))(2). Second, LiH and LiNH2 additions yield exothermic reactions of Ca(AIH(4))(2) and the other reactant as early as in the ball milling or annealing steps, leading to final products not considered in the reactions calculated.

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  • Hydrogen absorption kinetics of the catalyzed MgH2 by niobium oxide

    Nobuko Hanada, Takayuki Ichikawa, Hironobu Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   446   67 - 71  2007.10  [Refereed]

     View Summary

    The hydrogen absorption kinetics of magnesium hydride (MgH2) composite doped with 1 mol% Nb2O5 prepared by ball milling was examined under various temperatures and pressures. The composite after dehydrogenation at 200 degrees C absorbs gaseous hydrogen of similar to 4.5 mass% within 15 s even at room temperature under 1.0 MPa hydrogen pressure or at 0 degrees C under 3.0 MPa, and finally their capacities reach up to 5 mass%. At 150 and 250 degrees C, a large amount of hydrogen gas of more than 5.0 mass% is absorbed within 30 s and their capacity reach up to 5.7 mass% under 1.0 MPa. Interestingly, the absorption kinetics of the catalyzed Mg shows two unusual behaviors in the initial reaction stage of the time scale within 30 s. One is that the kinetics decreases with increase in the temperature from 150 to 250 degrees C under any pressures (0.2, 1.0 and 3.0 MPa). The other is that the amount of hydrogen absorption drastically increases with increase in the initial pressure from 1.0 to 3.0 MPa at 0 degrees C or from 0.2 to 1.0 MPa at room temperature (similar to 20 degrees C). These behaviors may be explained by taking into account heat generation of Mg due to fast hydrogen uptake in such a short time. (C) 2006 Elsevier B.V. All rights reserved.

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  • Thermal analysis on the Li-Mg-B-H systems

    Tessui Nakagawa, Takayuki Ichikawa, Nobuko Hanada, Yoshitsugu Kojima, Hironobu Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   446   306 - 309  2007.10  [Refereed]

     View Summary

    Thermal analyses of the mixture of MgH(2) and LiBH(4) doped with TiCl(3), and each element MgH(2) or LiBH(4) doped with TiCl(3) were performed under an inert gas flow and 0.5 MPa H(2)-gas conditions. It was indicated that the hydrogen desorption reaction of MgH(2) + 2LiBH(4) to MgB(2) + 2LiH + 4H(2) phases proceeded at temperature above 400 degrees C under 0.5 MPa hydrogen, whereas, under an inert gas atmosphere, the reaction of the same mixture was transformed into Mg + 2B + 2LiH + 4H(2) phases in a temperature range from 350 to 430 degrees C. Before these reactions, the dehydrogenation of MgH(2) and the melting of LiBH(4) took place under both hydrogen and the inert gas atmospheres with increasing temperature. In addition, the molten LiBH(4) did not decompose into LiH, B and H(2) below 450 degrees C under 1 MPa H(2), while the LiBH(4) decomposed even below 450 degrees C under an inert gas atmosphere. From these results, it is deduced that the reaction producing MgB(2) is a solid-liquid reaction between solid Mg and liquid LiBH(4) above 400 C without decomposition of molten LiBH(4) Under a hydrogen atmosphere, while MgH(2) dehydrogenate. A characteristic solid-liquid reaction is realized under a hydrogen atmosphere for proceeding of the MgB(2) producing reaction in this system. (C) 2007 Elsevier B.V. All rights reserved.

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  • Recent development on hydrogen storage properties in metal-N-H systems

    T. Ichikawa, H. Y. Leng, S. Isobe, N. Hanada, H. Fujii

    JOURNAL OF POWER SOURCES   159 ( 1 ) 126 - 131  2006.09  [Refereed]

     View Summary

    In this paper, we review our recent results on hydrogen storage properties in light metals(M)-nitrogen(N)-hydrogen(H) systems prepared by mechanochemical method. At first, the composite mixture of LiH and LiNH2 doped with TiCl3 as a catalyst was prepared by ball milling for 2 h under a H-2 gas pressure of 1 MPa. The TDS profile indicated that similar to 6 mass% H-2 was desorbed by the reaction LiH + LiNH2 &lt;-&gt; Li2NH + H-2 in the temperature range from 150 to 250 degrees C under a He gas flow at a heating rate of 5 degrees C min(-1), but the H-desorption equilibrium pressure P-H2 was similar to 0.1 MPa at 250 degrees C. This temperature is too high for onboard use, indicating that further improvement is necessary to destabilize the above Hstorage reaction. For that, we clarified the H-desorption mechanism by the isotopic exchange experiments, on the basis of which we designed a new Li-Mg-N-H composite system with the reaction 8LiH + 3Mg(NH2)(2)&lt;-&gt; 4Li(2)NH + Mg3N2 + 8H(2). This composite materials desorbed similar to 7 mass% H-2 in the range from 120 to 200 degrees C and the H-desorption equilibrium pressure P-H2 was higher than 5 MPa at 200 degrees C, indicating that this system has an excellent potential for onboard applications. (c) 2006 Elsevier B.V. All rights reserved.

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  • Remarkable improvement of hydrogen sorption kinetics in magnesium catalyzed with Nb2O5

    Nobuko Hanada, Takayuki Ichikawa, Satoshi Hino, Hironobu Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   420 ( 1-2 ) 46 - 49  2006.08  [Refereed]

     View Summary

    Kinetics of hydrogen absorption and desorption reactions was investigated on the MgH2 composite doped with 1 mol% Nb2O5 as a catalyst by ballmilling. The composite after dehydrogenation at 200 degrees C absorbed gaseous hydrogen of similar to 4.5 mass% even at room temperature under lower pressure than I MPa within 15 s and finally its capacity reached more than 5 mass%. On the other hand, the catalyzed MgH2 after rehydrogenation desorbed similar to 6 mass% hydrogen at 160 degrees C under purified He flow, which followed the first order reaction. From the Kissinger plot, the activation energy for hydrogen desorption was estimated to be similar to 71 kJ/mol H-2, indicating the product was significantly activated due to the catalytic effect of Nb2O5. (c) 2005 Elsevier B.V. All rights reserved.

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  • Catalytic effect of niobium oxide on hydrogen storage properties of mechanically ball milled MgH2

    Nobuko Hanada, Takayuki Ichikawa, Hironobu Fujii

    PHYSICA B-CONDENSED MATTER   383 ( 1 ) 49 - 50  2006.08  [Refereed]

     View Summary

    We examined a catalytic effect of niobium oxide (Nb2O5) on the hydrogen storage properties of MgH2 prepared by mechanical ball milling method. The MgH2 composite doped with I mol% Nb2O5 by ball milling for 20 h desorbed hydrogen up to similar to 6 mass% in the temperature range from 200 to 250 degrees C at the heating rate of 5 degrees C/min under a purified helium flow. After dehydrogenation at 200 degrees C, the product showed remarkable hydrogen absorption kinetics. A large amount of gaseous hydrogen up to similar to 4.5 mass% was absorbed even at room temperature under 1 MPa hydrogen pressure within 15 s and finally its capacity reached up to 5 mass%. Furthermore, the valence state of Nb2O5 doped in MgH2 was examined by X-ray absorption near edge structure (XANES) measurement. The results indicated that additive Nb2O5 was reduced by MgH2 during mechanical milling. This suggests that the Nb compound, in which the valence state of Nb atom is less than 5 +, acts as a catalyst for the hydrogen absorbing/desorbing kinetics. (c) 2006 Elsevier B.V. All rights reserved.

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  • Synthesis and decomposition reactions of metal amides in metal-N-H hydrogen storage system

    HY Leng, T Ichikawa, S Hino, N Hanada, S Isobe, H Fujii

    JOURNAL OF POWER SOURCES   156 ( 2 ) 166 - 170  2006.06  [Refereed]

     View Summary

    The synthesis and decomposition properties of some metal amides M(NH2)(x) such as LiNH2, NaNH2, Mg(NH2)(2) and Ca(NH2)(2) were investigated, which play important roles for designing a new family of metal-N-H hydrogen storage systems. Both the gas chromatographic examination and X-ray diffraction measurement indicated that the reaction between alkali or alkaline earth metal hydride MHx (such as LiH, NaH, MgH2 and CaH2) and gaseous NH3 could quickly proceed at room temperature by ball milling and the corresponding metal amides were easily synthesized in high quality. The kinetics of these kind of reactions is faster in the order of NaH &gt; LiH &gt; CaH2 &gt; MgH2, which is consistent with the inverse order of electronegativity of those metals, i.e. Na &lt; Li = Ca &lt; Mg. The thermal decomposition properties indicated that both Mg(NH2)(2) and Ca(NH2)(2) decomposed and emitted NH3 at lower temperature than LiNH2. (c) 2005 Elsevier B.V. All rights reserved.

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  • Hydrogen storage properties in Ti catalyzed Li-N-H system

    T Ichikawa, N Hanada, S Isobe, HY Leng, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   404   435 - 438  2005.12  [Refereed]

     View Summary

    The Li-N-H system expressed by LiNH2 + LiH &lt;-&gt; Li2NH + H-2 can be expected as a promising candidate for the hydrogen storage materials because of possessing a large amount of reversible hydrogen (6.5 wt.%), a satisfactorily fast kinetics and a relatively small enthalpy change. In this work, we investigated the hydrogen storage properties of the Li-N-H system from three different points of view. Firstly, we claim that the ball milled 1: 1 mixture of lithium amide (LiNH2) and lithium hydride (LiH) containing a small amount (I mol %) of titanium chloride (TiCl3) shows superior hydrogen storage properties; a large amount of H-2 gas desorbs in the temperature range from 150 to 250 degrees C at a heating rate of 5 degrees C/n-dn and it reveals an excellent reversibility. Secondly, we clarify that the above hydrogen desorption reaction is composed of two kinds of elementary reactions: The one is that 2LiNH(2) decomposes to Li2NH and emits ammonia (NH3). The other is that the emitted NH3 reacts with LiH and transforms into LiNH2 and H-2, indicating that NH3 plays an important role on this H-2 desorption reaction. Finally, we examined the reaction of LiH and LiOH to clarify the influence of exposing the product to air. This is because due to the fact that LiOH is easily produced by exposing LiH and LiNH2 to air. The reaction between LiH and LiOH indicated better kinetics but worse durability and an extra H2 desorption due to transforming into Li2O. (c) 2005 Elsevier B.V. All rights reserved.

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  • Catalytic effect of Ni nano-particle and Nb oxide on H-desorption properties in MgH2 prepared by ball milling

    N Hanada, T Ichikawa, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   404   716 - 719  2005.12  [Refereed]

     View Summary

    We examined the catalytic effect of Ni nano-particle and Nb oxide on hydrogen desorption (HD) properties in MgH2 prepared by mechanical ball milling under a hydrogen gas atmosphere of 1 MPa. The MgH2 composite with 2 mol% Ni nano-particle prepared by milling for a short time of 15 min at 200 rpm desorbed a large amount of hydrogen (similar to 6.5 wt.%) in the temperature range from 150 to 250 degrees C at heating rate of 5 degrees C/min. On the other hand, the MgH2 Composite with I mol% Nb-2 O-5 prepared by milling for a long time of 20 h at 400 rpm desorbed similar to 6.0 wt.% H-2 in the temperature range from 200 to 250 degrees C at heating rate of 5 degrees C/min. After second hydrogen absorption/desorption cycles at 200 degrees C, the HD properties of the Ni-catalyzed MgH2 composite became worse than those before cycling, while the Nb2O5-catalyzed composite showed better HD properties than those before cycling. (c) 2005 Elsevier B.V. All rights reserved.

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  • Effect of Ti catalyst with different chemical form on Li-N-H hydrogen storage properties

    S Isobe, T Ichikawa, N Hanada, HY Leng, M Fichtner, O Fuhr, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   404   439 - 442  2005.12  [Refereed]

     View Summary

    The effect of some different type Ti additives on kinetics of the reaction, LiH + LiNH2 &lt;-&gt; Li2NH + H-2, was intensively investigated in this work. The mixture of LiH and LiNH2 powders with the 1: 1 molar ratio and Ti additives with different chemical form were mechanically ball milled under a hydrogen gas atmosphere of I MPa at 400 rpm for 2 It and the measurements of thermal hydrogen desorption spectrum (TDS), thermogravimetry (TG) and X-ray diffraction (XRD) were performed. Here, we used Ti (nano particle), Ti (micro particle), TiCl3, TiO2 (nano particle) and TiO2 (micro particle) as the additives. The results indicated that the Ti-nano, TiCl3 and TiO2nano doped composites revealed a superior catalytic effect on the TDS properties, while the Ti-micro and TiO2micro did not show so good catalytic effect being similar to the sample without any additives. In the XRD profiles, there are traces of Ti and TiO2 phases in the Ti-micro and TiO2micro doped composites, respectively, whereas no trace of Ti, TiCl3 and TiO2 was found in the Ti-nano TiCl3 and TiO2nano doped composites. These results indicate that the uniform distribution of nano particle Ti metal between LiH and LiNH2 plays an important role for catalytic effect. (c) 2005 Elsevier B.V. All rights reserved.

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  • Desorption behaviours from metal-N-H systems synthesized by ball milling

    HY Leng, T Ichikawa, S Isobe, S Hino, N Hanada, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   404   443 - 447  2005.12  [Refereed]

     View Summary

    Three metal amides LiNH2, NaNH2 and Mg(NH2)(2) were synthesized by ball milling the metal hydrides under gaseous ammonia NH3 at room temperature. The decomposition behaviours from these metal amides were investigated by thermal desorption mass spectroscopy and thermogravimetry analysis methods. The results showed that LiNH2 decomposed at T &gt; 230 degrees C and was transformed into the imide Li2NH with emitting NH3, while Mg(NH2)(2), decomposed at T &gt; 180 degrees C and was transformed into MgNH and finally into Mg3N2 with emitting NH3 within 500 degrees C. Then, a new metal-N-H system composed of Mg(NH2)(2) and LiH with a molar ratio of 3:8 was designed by ball milling treatment and examined the hydrogen storage properties. The results showed that this system could reversibly absorb/desorb a large amount of hydrogen (similar to 7 wt.%) at a moderate temperature and pressure, which was better than the system of LiNH2 and LiH for hydrigen storage. (c) 2005 Elsevier B.V. All rights reserved.

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  • Catalytic effect of nanoparticle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH2 prepared by mechanical milling

    N Hanada, T Ichikawa, H Fujii

    JOURNAL OF PHYSICAL CHEMISTRY B   109 ( 15 ) 7188 - 7194  2005.04  [Refereed]

     View Summary

    We examined the catalytic effect of nanoparticle 3d-transition metals on hydrogen desorption (HD) properties of MgH2 prepared by mechanical ball milling method. All the MgH2 composites prepared by adding a small amount of nanoparticle Fe-nano, Co-nano, Ni-nano, and Cu-nano metals and by ball milling for 2 h showed much better HD properties than the pure ball-milled MgH2 itself. In particular, the 2 mol % Ni-nano-doped MgH2 composite prepared by soft milling for a short milling time of 15 min under a slow milling revolution speed of 200 rpm shows the most superior hydrogen storage properties: A large amount of hydrogen (similar to 6.5 wt %) is desorbed in the temperature range from 150 to 250 degrees C at a heating rate of 5 degrees C/min under He gas flow with no partial pressure of hydrogen. The EDX micrographs corresponding to Mg and Ni elemental profiles indicated that nanoparticle Ni metals as catalyst homogeneously dispersed on the surface of MgH2. In addition, it was confirmed that the product revealed good reversible hydriding/dehydri ding cycles even at 150 degrees C. The hydrogen desorption kinetics of catalyzed and noncatalyzed MgH2 could be understood by a modified first-order reaction model, in which the surface condition was taken into account.

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  • Composite materials based on light elements for hydrogen storage

    T Ichikawa, N Hanada, S Isobe, HY Leng, F Hironobu

    MATERIALS TRANSACTIONS   46 ( 1 ) 1 - 14  2005.01  [Refereed]

     View Summary

    In this paper, we review our recent experimental results on hydrogen storage properties of light elements Li, C and Mg based nanocomposite materials. The results are summarized as follows: In the Li-N-H system, such as the ball milled 1: 1 mixture of Li amide and Li hydride containing a small amount of TiCl3 (1 mol%), a large amount of hydrogen (similar to 6 mass%) is absorbed and desorbed in the temperature range from 150 to 250 degrees C with good reversibility and high reaction rate. Furthermore, in the ball milled mixture of 3Mg(NH2)(2) and 8LiH, similar to 7 mass% of hydrogen is reversibly stored in the temperature from 140 to 220 degrees C, indicating one of the suitable hydrogen storage materials. In graphite containing a small amount of nanometer sized Fe (similar to 2at.%), a large amount of hydrogen (similar to 7 mass%) is chemisorbed by ball milling for 80 h under less than 1 MPa of H-gas pressure. However, the chemisorbed hydrogen capacity decreases with increase in the milling pressure for the 80 h ball milled graphite (down to similar to 4.1 mass% at 6 MPa), while the physisorbed hydrogen capacity in graphite increases with increase in the milling pressure, reaching up to 0.5 similar to 1.0 mass% at 6 MPa. Unfortunately, the desorption temperature of chemisorbed hydrogen is higher than 300 degrees C. Therefore, some break-through is necessary for the development of carbon-based materials as one of the hydrogen storage systems'. On the other hand, some nano-composite Mg catalyzed by Ni nano-particle or Nb oxide reveals superior reversible hydrogen storage properties: similar to 6.5 mass% of hydrogen is reversibly stored in the temperature range from 150 to 250 degrees C. Especially, the Nb metals uniformly dispersed in nanometer scale on the surface of MgH2, which was produced by reduction of Nb2O5, is the best catalyst we have studied so far. Thus, it seems that some Mg nano-composites catalyzed by nano-particles of d-electron transition metals is acceptable for practical applications.

  • Hydrogen Storage Properties in Ti Catalyzed Li-N-H Ststem”, Journal of Alloys and Compounds

    Takayuki Ichikawa, Nobuko Hanada, Shigehito Isobe, Haiyan Leng, Hironobu Fujii

    Journal of Alloys and Compounds   404-406   716 - 719  2005

  • New metal-N-H system composed of Mg(NH2)(2) and LiH for hydrogen storage

    HY Leng, T Ichikawa, S Hino, N Hanada, S Isobe, H Fujii

    JOURNAL OF PHYSICAL CHEMISTRY B   108 ( 26 ) 8763 - 8765  2004.07  [Refereed]

     View Summary

    We have investigated the hydrogen storage properties of a ball-milled mixture of 3Mg(NH2)(2) and 8LiH after first synthesizing Mg(NH2)(2) by ball milling MgH2 under an atmosphere of NH3 gas at room temperature. The thermal desorption mass spectra of the mixture without any catalysts indicated that a large amount of hydrogen (similar to7 wt %) was desorbed from 140 degreesC, and the desorption peaked at similar to190 degreesC under a heating rate of 5 degreesC/min with almost no ammonia emission. Moreover, the reversibility of the hydrogen absorption/desorption reactions was confirmed to be complete. The above results indicate that this system is one of the promising metal-N-H systems for hydrogen storage.

    DOI

  • Mechanism of novel reaction from LiNH2 and LiH to Li2NH and H-2 as a promising hydrogen storage system

    T Ichikawa, N Hanada, S Isobe, HY Leng, H Fujii

    JOURNAL OF PHYSICAL CHEMISTRY B   108 ( 23 ) 7887 - 7892  2004.06  [Refereed]

     View Summary

    The mechanism of the hydrogen desorption (HD) reaction from the 1:1 mixture of lithium amide (LiNH2) and lithium hydride (LiH) to lithium imide (Li2NH) and hydrogen (H-2) has been proposed on the basis of our experimental results in this paper. The proposed model is constituted by 2 kinds of elementary reactions: the one is that 2LiNH(2) decomposes to Li2NH and ammonia (NH3) the other is that the emitted NH3 reacts with LiH and transforms into LiNH2 and H-2. Since the former and the latter reactions are, respectively, endothermic and exothermic, the HD reaction corresponding to the latter reaction occurs as soon as LiNH2 has decomposed into Li2NH and NH3. Therefore, the HD reaction can be understood by the following processes: at the first step, LiNH2 decomposes into Li2NH/(2) + NH3/2, and then the emitted NH3/2 quickly reacts with LiH/2, transforming into LiNH2/2 + H-2/2; at the second one, the produced LiNH2/2 decomposes to Li2NH/4 + NH3/4, and then NH3/4 + LiH/4 transform to LiNH2/4 + H-2/4, and such successive steps continue until LiNH2 and LiH completely transform into Li2NH and H-2, even at low temperatures, by the catalytic effect of TiCl3.(.)

  • Catalytic effect of nano-particle 3d-transition metals on hydrogen storage properties in magnesium hydride MgH2 prepared by mechanical milling

    Hanada Nobuko, Ichikawa Takayuki, Fujii Hironobu

    Journal of Physics and Chemistry of Solids   65 ( 2 ) 535 - 539  2004.03

    DOI CiNii

  • Correlation between hydrogen storage properties and structural characteristics in mechanically milled magnesium hydride MgH2

    N Hanada, T Ichikawa, SI Orimo, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   366 ( 1-2 ) 269 - 273  2004.03  [Refereed]

     View Summary

    In this work, we clarified the correlation between hydrogen storage and crystallographic properties in nanostructural magnesium hydride MgH2 prepared by mechanical milling under hydrogen gaseous atmosphere. At the early stage within 2h milling, the amount of desorbed hydrogen decreases similar to16% from 7.3 to 6.1 wt.% and the onset temperature of dehydrogenation decreases by 70 K from 670 K, while both the powder size and the crystallite size in powder decrease with increasing the milling time down to 1 mum and 15 nm, respectively, and the lattice strain of 0.3% is rapidly introduced. At the middle stage with longer milling time than 2 h, however, the crystallite size hardly change, but the lattice strain is once released at 2-5 h milling and again increases for longer milling time than 5 h. On the other hand, the amount of desorbed hydrogen suddenly increases from 2 to 5 h, and again decreases with a little increase of lattice strain during 5-80 h milling. At the final stage, the hydrogen capacity and desorption temperature reach to saturation of, respectively, 6.5 wt.% and 600 K, whereas the crystallite size and lattice strain reach to saturation of similar to7 nm and 0.2%, respectively. The results obtained indicate that the reduction of crystallite size as well as the introduction of lattice strain in MgH2 during milling gives rise to the decrease in hydrogen storage capacity. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    113
    Citation
    (Scopus)
  • Lithium nitride for reversible hydrogen storage

    T Ichikawa, S Isobe, N Hanada, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   365 ( 1-2 ) 271 - 276  2004.02  [Refereed]

     View Summary

    In this paper, we examined the basic properties in the 1:1 mixture of lithium amide LiNH2 and lithium hydride LiH as a candidate of reversible hydrogen storage materials. The thermal desorption mass spectra of the ball milled mixture without any catalysts indicated that hydrogen H-2 is released in the temperature range from 180 to 400degreesC while emitting a considerable amount of ammonia NH3. On the other hand, the ball milled mixture containing a small amount of TiCl3 as a catalyst showed the most superior hydrogen storage properties among the 1: 1 mixtures with a small amount of catalysts, Ni, Fe, Co metals and TiCl3 (I mol.%). That is, the product desorbs a large amount of hydrogen (similar to5.5 wt.%) in the temperature from 150 to 250degreesC under the condition of a heating rate of 5 degreesC/min, but it does not desorb ammonia at all within our experimental accuracy. In addition, we confirmed that the product shows an excellent cycle retention with an effective hydrogen capacity of more than 5 wt.% and a high reaction rate until at least 3 cycles. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

    Scopus

    306
    Citation
    (Scopus)
  • Hydriding properties of ordered-/disordered-Mg-based ternary Laves phase structures

    N Hanada, S Orimo, H Fujii

    JOURNAL OF ALLOYS AND COMPOUNDS   356   429 - 432  2003.08  [Refereed]

     View Summary

    Ternary Laves phase structures with compositions MgYNi4, MgCaNi4 and CaYNi4 were prepared, and the relationship between the structures and hydriding properties was studied in detail. Only in MgYNi4 are Mg and Y found to be ordered and a plateau pressure is clearly observed in the P-C isotherm during the dehydriding process. In MgCaNi4, however, Mg and Ca are disordered, and hydrogen content of MgCaNi4 is similar to30% larger than that of MgYNi4. Control of their order/disorder in Laves phase structures may provide the hydriding properties with higher hydrogen concentrations and flatter plateau regions. (C) 2003 Elsevier B.V. All rights reserved.

    DOI

  • マグネシウムを含む3元系Laves相構造の規則化・不規則化と水素化特性

    花田信子, 折茂慎一, 藤井博信

    日本金属学会誌   66   466 - 469  2002  [Refereed]

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Research Projects

  • Overvoltage decrease of liquid ammonia electrolysis by electrode of nitrogen absorbing material with electrocatalysts

    Project Year :

    2016.04
    -
    2018.03
     

     View Summary

    The anode reaction with nitrogen desorption has much larger overpotential than that of a cathode reaction in the electrolysis of liquid ammonia for hydrogen generation. The anode reaction properties were investigated using mono catalyst and binary catalyst electrodes. The catalyst effect on anode reaction was investigated by focusing on the metal nitride formation enthalpy which corresponds to the strength of metal-nitrogen bond. By plotting the current density at the low potential against the metal nitride formation enthalpy, the volcano plot was obtained. The binary metal catalysts of Fe and Pt (Fe-Pt) composited in nanoparticle size or atomic size (alloyed) were prepared. The current density of both Fe-Pt electrodes were lower than that of mono-Fe and mono-Pt at the low potential

  • Dielectrical reliability improvement for increasing output of solid oxide fuel cell system

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2015.04
    -
    2018.03
     

    Ishida Masayoshi

     View Summary

    The electrical insulation properties and morphological change of alumina in redox gas atmosphere of solid oxide fuel cells (SOFC) at high temperatures (600-900℃) were evaluated. It is shown that difference of gases greatly effects these properties. In the study on distance dependence of creepage electrical insulation properties, it was clarified that properties are not proportional to creepage distance. In applying inorganic materials to space charge distribution measurement, the distribution tended to reverse in most materials. Such a tendency was not observed in some inorganic materials which have different electrical properties, and this suggests the electrical properties have a large effect as a factor

  • Design of high efficiency electrolysis cell for liquid ammonia utilization as hydrogen storage carrier

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2012.04
    -
    2014.03
     

    HANADA Nobuko

     View Summary

    The overvoltage reduction effects of electrode morphology and materials on liquid ammonia electrolysis were investigated to design high efficiency electrolysis cell for generating hydrogen from liquid ammonia. For Pt-black electrodes prepared by electrodeposition, it is clarified that the overvoltage reduction does not relate to the electrode surface area, but relates to both of Pt deposition amount and size of deposited Pt particles. For the electrolysis by using Pt plate electrode, anode overvoltage is five times as large as cathode one. Ammonia electrolysis with the emission of hydrogen gas was performed at 0.1 V around theoretical electrolysis voltage by adapting Pt-Ru electrode which can reduce the anode overvoltage

  • Insulating design for solid oxide fuel cells based on dielectrical properties at high temperatures

    Japan Society for the Promotion of Science  Grants-in-Aid for Scientific Research

    Project Year :

    2011.04
    -
    2014.03
     

    ISHIDA Masayoshi, HANADA Nobuko

     View Summary

    The dielectric properties of inorganic materials in anode gas atmosphere of solid oxide fuel cells (SOFC) at high temperatures (600-850 deg C) were evaluated, and design concepts of primary insulation of SOFC are proposed. The evaluation of DC voltage insulating properties for various inorganic materials shows that magnesia is the best insulation material among them because it has the largest insulation resistance. The effects of anode gas component on dielectric properties were investigated for primary insulation of SOFC composed of magnesia mainly. It is clarified that hydrogen gas itself or heat and flame of hydrogen combustion generated by hydrogen leak degrade primary insulation performance

Misc

  • 酸化ニオブ添加水素化マグネシウムの触媒機構解明へのアプローチ

    市川貴之, 花田信子, 日野聡, 礒部繁人, 藤井博信, 小島由継

    日本金属学会講演概要   140th  2007

    J-GLOBAL

  • New metal-N-H system composed of Mg(NH2)(2) and LiH for hydrogen storage (vol 108, pg 8763, 2004)

    HY Leng, T Ichikawa, S Hino, N Hanada, S Isobe, H Fujii

    JOURNAL OF PHYSICAL CHEMISTRY B   108 ( 33 ) 12628 - 12628  2004.08

    Other  

    DOI

 

Syllabus

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Sub-affiliation

  • Faculty of Science and Engineering   Graduate School of Advanced Science and Engineering

Research Institute

  • 2022
    -
    2024

    Waseda Research Institute for Science and Engineering   Concurrent Researcher

  • 2022
    -
    2024

    Waseda Center for a Carbon Neutral Society   Concurrent Researcher

Internal Special Research Projects

  • Mg ナノ粒子を用いた触媒添加 Mg 水素吸蔵材料の簡易合成プロセスの開発

    2023   森岡柚衣

     View Summary

     水素貯蔵材料の中でマグネシウムは、マグネシウム水素化物(MgH2)を形成して7.6 mass%、109 kgH2/m3と高容量の水素を吸蔵する。水素吸蔵放出の反応速度が遅いことが欠点であったが、これまでにMgH2に金属酸化物であるNb2O5をボールミリング法によりナノレベルで高分散させることで、反応速度の向上に成功した。これを水素貯蔵タンクに搭載する場合にはkgオーダーで大量に合成する必要がある。ボールミリング法はスケールアップには向いておらず、触媒添加Mgの新たな合成プロセス開発が必要となる。本研究ではMgを出発材料として、Mgナノ粒子を連続的に合成し、触媒を担持するビルドアッププロセスによる触媒添加Mgの合成を目的とする。Mgナノ粒子を連続的に作製する方法として不活性ガスフローによる熱プラズマ法を用いる。作製したMgナノ粒子の表面に少量の触媒を一様に添加するために、蒸気圧の低いNb塩化物を用いて昇温によりMgナノ粒子表面に蒸着させ、水素吸蔵放出特性を評価した。まず熱プラズマ法を用いて、Mgを電極としてアーク放電により蒸発させ、同時にArガスを流すことによりMg粒子を作製した。Mg粒子は作製できたが、0.1-0.5μm程度の粒径でのばらつきが見られ、水素吸蔵量も2mass%程度と低かった。そこで、アーク放電時のラインに整流管を設置して、粒子の流れを改善した。その結果、0.1-0.2μm程度の一様な小さい粒子を作製でき、水素吸蔵量も4mass%程度まで増加した。次に、このMg粒子に触媒源としてNbCl5を蒸着させた。しかし、Mgナノ粒子の水素吸蔵量が2mass%に減少し、水素吸蔵速度も改善しなかった。NbCl5が表面でMgに還元されて、Nbが触媒効果を示す効果を期待していたが、Mg粒子表面のMgO上にNbCl5がそのまま蒸着されたため、むしろ水素吸蔵放出特性を阻害したことが分かった。今後は、触媒効果を示すNb単体もしくは価数の低いNb酸化物などをMg粒子表面に添加する方法を検討する。

  • 液体アンモニア電解のための高活性なRuナノ粒子担持カーボンナノチューブ膜電極の開発

    2022   宮越すみれ

     View Summary

    液体アンモニアは17.8 mass%の質量水素密度を持ち、室温で電解反応が進行し水素生成が可能である。窒素発生反応であるアノード側で高い反応過電圧を持つことが課題である。本研究では、カーボンナノチューブ(CNT)膜の3次元スポンジ構造に触媒活性の高いRuナノ粒子を担持したRu-CNT電極により、触媒表面積増大による電流密度向上および水素アニール処理によるRuナノ粒子の還元の電極触媒性能への影響を評価した。Ru-CNT電極を用いた液体アンモニアのアノード反応領域では、Ru plate 電極に対し電流密度の増加が確認され触媒表面積増加の効果が見られた。さらに水素アニール後電極の電流密度が2.0倍増加し追加還元によってRuナノ粒子の触媒活性が向上することが分かった。

  • アンモニア電気分解におけるアノード反応の高電流密度・高効率化

    2021   野田優, Patil Neel, 沓抜佳奈, 宮越すみれ

     View Summary

    高容量水素貯蔵のキャリアとしてアンモニアに着目し、液体アンモニアから電気分解により水素を生成するシステム開発を目指している。理論分解電圧は0.077 Vであるが、窒素発生反応であるアノード側で高い反応過電圧を持つことが課題である。本研究では、活性なアノード触媒電極の低電位での電流効率評価を行った。高い触媒活性を持つNi電極を用いた場合のアノード反応(窒素発生反応)の電流効率を調べた。ガスの定量評価によりH2/N2の比がおおよそ3となり、アンモニアの分解を確認した。窒素発生反応の電流効率は90%と高いが、100%ではないため副反応が一部起こっていることが分かった。副反応としてNiの腐食が確認されたが、電流効率に対してNiの腐食が占める割合は0.74%であり、影響は小さいことが分かった。

  • Ruナノ粒子担持カーボンナノチューブ膜電極による液体アンモニアの電気分解

    2021   宮越すみれ

     View Summary

    液体アンモニアは17.3 mass%の質量水素密度を持ち、エネルギーキャリアとして優れている。室温で電解反応が進行し、水素生成が可能である。理論分解電圧は0.077 Vであるが、窒素発生反応であるアノード側で高い反応過電圧を持つことが課題である。これまでにRu電極がアノード反応に対して高い活性を持つことが分かっている。Ruナノ粒子を担持した3次元電極により電極触媒表面積を増加させ低電位での電流密度の向上を目的とした。Ruナノ粒子をCNT上に担持したRu-CNT電極を作製し、液体アンモニア電解のアノード反応への活性評価を行った。CNT上に1-2 nmのRu粒子の担持が確認され、ポリオール法によりCNT上へのRuナノ粒子の担持に成功した。触媒表面積増加の効果によりRu-CNT電極ではRu板電極に対し電流密度が6.1倍向上した。

  • 液体アンモニア電気分解のカソード反応機構解明および高電流効率化

    2020   佐々木隆一

     View Summary

    高容量水素貯蔵のキャリアとしてアンモニアに着目し、液体アンモニアから室温で電気分解により水素生成を行った。電気分解が起きていることは確認されているが、電流効率は85%程度であり100%に達していない。この原因がカソード反応における溶媒和電子発生の副反応にあるという仮説のもと、電流効率と溶媒和電子発生の関係を調べた。液体アンモニア電気分解の定電位測定において電位を-0.3、-0.5、-0.7 V vs H2/NH3 と変化させた結果、低電位であるほど溶媒和電子が多く発生することが観察された。しかし、-0.3 Vと-0.5 Vでの定電位測定の電流効率は82.9 %、82.5%とほとんど同じであったことから、低電流効率の要因は他にも存在することが示唆された。

  • オンボード水素供給に向けたアンモニア電気分解の高電流密度・高効率化

    2020   野田優, 赤木夏帆, Patil Neel, 佐々木隆一, 沓抜佳奈

     View Summary

    高容量水素貯蔵のキャリアとしてアンモニアに着目し、液体アンモニアもしくはアンモニア水溶液から電気分解により水素を生成する。本研究では、高電流密度を低電圧で出力するために、2元系アノード電極触媒の検討を行った。液体アンモニア電気分解反応に対して、比較的窒素との結合強さが近い金属の組み合わせであるNi-Pt触媒を適用した。Ni板にPtをスパッタしてアニール処理した電極を用い、表面積変化の影響を除去して評価を行った。Pt単体触媒比べてNi-Pt&nbsp;の二元系触媒はアノード反応に対して効果が見られなかった。Ni&nbsp;とPt&nbsp;の組み合わせでは、N&nbsp;との結合が強いNi&nbsp;に律速が支配されてしまい二元系の効果が見られない可能性が高い。

  • 水素生成のための液体アンモニアおよび水溶液中アンモニア電気分解特性の向上

    2019   野田優, 小長谷優佑, 赤木夏帆, Patil Neel

     View Summary

    高容量水素貯蔵のキャリアとしてアンモニアに着目し、液体アンモニアもしくはアンモニア水溶液から電気分解により水素を生成した。本研究では、高電流密度を低電圧で出力する高効率な電気分解セル構築のための基礎検討を行った。液体アンモニア電気分解反応に対して、過電圧の高いアノード反応特性の向上のために、触媒金属の窒素との結合のしやすさに着目した。窒素との結合が中間の強さである触媒金属が高電流密度を示すことが明らかになった。また、アンモニア水溶液電気分解反応に対しては、電極の反応場を3次元的に拡張するために白金ナノ粒子を担持したカーボンナノチューブ膜電極を適用し、アノード電流密度の増大を実現した。

  • 液体アンモニア電気分解への電極触媒を内包したカーボンナノチューブ膜電極の適用

    2017  

     View Summary

    Ammonia (NH3), which has high volumetric hydrogen density and high gravimetric hydrogen density, is one of the promising media to store and transport hydrogen. We have performed the direct electrolysis of liquid ammonia for hydrogen generation. This method would be able to decompose ammonia itself by keeping high hydrogen density at room temperature. In this study 3D structured electrode with platinum nanoparticles supported on carbon nanotube (CNT) film was fabricated to increase the current density and decrease anode over potential for liquid ammonia electrolysis. The platinum nanoparticles were loaded on CNT by reducing Pt ion in Ethylene Glycol at 100 to 180 ºC. The smaller Pt nanoparticles were synthesized by increasing loading temperature. The average particle size of Pt nanoparticles on CNT was 3.6 nm and surface area of Pt was several hundred times of the electrode area. The electrode of Pt nanoparticles on CNT decreased anode overpotential and increased the current density&nbsp;at lower potential&nbsp;in ammonia electrolysis.

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