DOI： 10.1088/1757-899X/375/1/012032

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：TRANS TECH PUBLICATIONS LTD  

Competitive reactions and formation mechanism of microstructures in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation were studied. During initial hydrogenation of Mg/Cu SLCs, hydrogenation of Mg and alloying of Mg with Cu followed by hydrogenation of Mg2Cu are competitive. It is found that microstructures of Mg/Cu SLCs during initial hydrogenation have changed drastically depending on the order of hydrogenation of Mg and Mg2Cu. The microstructures of Mg/Cu SLCs after initial hydrogenation can be categorized in 3 types.

DOI： 10.4028/www.scientific.net/MSF.941.1927

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

To identify the reasons why Ti-Pd alloys for hydrogen storage materials show good hydrogenation properties, X-ray photoelectron spectroscopy and the Suzuki-Miyaura cross-coupling reaction were used to investigate a small amount of Pd added Ti-Pd alloys. Pd in or on Ti oxide films is in a valence state of 0 (Pd-0). Catalytic activity was shown by Pd-0 in the Suzuki-Miyaura cross-coupling reaction. Therefore, the enhanced hydrogenation properties of Ti-Pd alloys for hydrogen storage materials is due to Pd-0's catalytic activity in dissociating hydrogen molecules. In addition, the potential catalytic activity of Ti-Pd alloys was shown to be based on a Pd catalyst.

DOI： 10.2320/matertrans.M2018240

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

The use of redox active organic compounds as an alternative positive electrode material of rechargeable lithium batteries can be a solution for the resource issues of the current battery system. To satisfy both the high capacity and long cycle life of the batteries using organic active materials, naphthazarin (5,8-dihydroxy-1,4-naphthoquinone) derivatives, which potentially exhibit a four-electron transfer redox reaction, were investigated. While the unsubstituted naphthazarin lithium salt (1), having a high theoretical capacity of up to about 550 mAh g(-1), showed only half the expected capacity and a short cycle life as a positive electrode active material, the chloro-substituted ones (1-Cl-2, 1-Cl-4) exhibited improved properties in both their initial capacity utilization and cycle life. In addition, the high stability of a chloro-substituted naphthazarin salt (1-Cl-4) was supported by a reversible electrochromic behavior during the redox reaction. The substituent effect of the naphthazarin derivatives on the cycle stability was discussed with respect to the battery performance and electrochromic behavior. Also, a guide for designing a new organic active material which shows a high capacity and long cycle life is suggested.

DOI： 10.1007/s10853-017-1368-z

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

The formation mechanism of microstructures in Mg/Cu super-laminates composites (SLCs) fabricated by accumulative roll-bonding (ARB) during initial activation was investigated. It is revealed that Mg2Cu can grow with sufficient growth rate at low temperatures (<453 K) in Mg/Cu SLCs. The growth of Mg2Cu layers for short growth length is diffusion-controlled. The activation energies for layer growth process of Mg2Cu layers in Mg/Cu SLCs are 107 +/- 8 kJmol(-1) with acid cleaning prior to ARB and 103 +/- 12 kJmol(-1) without acid cleaning prior to ARB, respectively, which are about 2/3 of those in Mg-Cu diffusion couples. It is considered that the high density of lattice defects in Mg/Cu SLCs fabricated by ARB contributes the much lower activation energies for layer growth process of Mg2Cu layers in Mg/Cu SLCs than in Mg-Cu diffusion couples. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2017.02.193

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ATLANTIS PRESS  

Titanium (Ti) based hydrogen-storage materials can absorb hydrogen under mild conditions. However, the materials could not absorb hydrogen without initial activation, owing to the formation of surface oxide layer. For mitigate the initial activation conditions, addition of Pd to Ti based materials were conducted. In spite of a tiny content of Pd, the addition was effective. In this study, effect of Pd in Ti oxide layer on initial hydrogenation property was investigated. Ti(1-x) Pdx (x=0, 0.002, 0.005, 0.010) alloys were fabricated with an arc-melting machine in an Ar atmosphere. Turnings-like specimens were obtained by milling the ingots with a milling machine for increase of specific surface. Initial hydrogenation properties were carried out with a Sieverts-type apparatus. Surface property of Ti0.990Pd0.010 before hydrogenation was carried out by X-ray photoelectron spectroscopy. Pd-added Ti alloys rapidly formed Ti hydride compared with pure Ti. Pd in the oxide film existed as valence state of 0 (Pd-0). Because metallic Pd was well-known as catalyst for dissociation of molecular hydrogen, Pd-added Ti alloys can faster absorb hydrogen.

DOI： 10.2991/ame-17.2017.10

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

Although Mg based hydrogen storage materials absorb hydrogen immediately under appropriate thermodynamic conditions, an obvious incubation period exists for hydrogen desorption. This fact implies that the mechanisms of hydrogen absorption and desorption are different from each other. During hydrogen desorption process, nucleation and growth of Mg are occurring in MgH2. It is considered that free surface is the only nucleation site of Mg in hydrogen desorption process. The nucleation frequency per unit specific surface area should be constant under a fixed temperature and H-2 partial pressure. Therefore, it is estimated that the incubation period is proportional to the inverse of specific surface area.
The relationship between incubation period and specific surface area of MgH2 was investigated in order to understand the mechanism of incubation period on magnesium. hydrogen system. MgH2 with several kinds of specific surface area were manufactured by changing milling time of a planetary ball mill. A primary Gibbs free energy for dehydrogenation was conducted as -1.94 kJ mol(-1) by controlling H-2 pressure for measuring incubation period. The results revealed that the incubation period was proportional to the inverse of specific surface area.

DOI： 10.2320/jinstmet.JD201604

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

A new battery material that is composed of polyglycidol and a redox-active anthraquinone unit (AQ) was prepared and was then used as a positive electrode for lithium ion batteries. Polyglycidol (pGD) is a bio-based polymer that is derived from the waste glycerin that is discarded during bio-diesel processing. The pGD-AQ electrode has a potential plateau at 2.3 V vs. Li+/Li, and a discharge potential that decreased gradually with a capacity of 139 mAh g(-1). The cycle-life stability of pGD-AQ is better than that of chloroanthraquinone, which was used as a reference material. A higher AQ skeleton incorporation rate into pGD leads to a higher battery capacity. These results show that the incorporation of the AQ unit into the polymer is an effective way to improve battery performance in terms of both capacity and cycle-life stability. (C) 2016 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2016.05.027

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

To increase the cycle-stability of rechargeable batteries using an organic positive-electrode material, we synthesized a polymer from a 5,8-dihydroxy-1,4-naphthoquinone (DHNQ) skeleton, which potentially undergoes a four-electron transfer redox reaction. The polymeric material (PDHNQ) was synthesized by the condensation reaction between DHNQ and formaldehyde under acidic media conditions. The initial capacity of the electrode using the monomer (DHNQ), 193 mAh/g, quickly decayed to 56 mAh/g after 100 cycles. On the other hand, the electrode incorporating the prepared PDHNQ showed the higher initial discharge capacity of 256 mAh/g and a longer cycle-life, retaining about 133 mAh/g after 100 cycles. (C) 2016 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2016.05.028

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

In order to understand the solution chemistry of electrolyte solutions at concentrations far from infinite dilution, the solution density, viscosity and ionic conductivity of Li- and Na-TFSI dissolved in GBL and PC were measured at 0.1 <= C/mol.dm(-3) <= 2.0 and 278 <= T/K <= 328, where TFSI = bis(trifluoromethanesulfonyl) imide, GBL = gamma-butyrolactone and PC = propylene carbonate. The results are compared to those of previously determined perchlorate salts. The partial molar volume of the solute, derived from the density, confirmed that the Na-systems occupy more volume in the solution than the Li-systems. On the other hand, the viscosity and ionic conductivity suggested that the Na-systems are more fluid and conductive than the Li-systems. The relative viscosity vs. the molarity follows a modified empirical Jones-Dole equation. The molar conductivity linearly decreased with respect to the cube-root of the molarity, which was analyzed by the pseudolattice model. The Raman spectroscopy revealed that, while the solvation number is comparable at 1-2 for either the Li- or Na-systems, Li+ is more tightly bound to the solvent molecules than Na+. The higher fluidity and conductivity of the Na-systems than those of the Li-systems result from the less occurrence of the solvent-shared ion pairs in the former than in the latter. (C) 2016 The Electrochemical Society. All rights reserved.

DOI： 10.1149/2.0931606jes

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Other Link： http://orcid.org/0000-0002-7223-2295

Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Formation mechanism of micro/nano-structures through competitive reactions in Mg/Cu super-laminate composites (SLCs) during initial hydrogenation was investigated experimentally. Three types of MgCu2 structures, an open network, a sheathed network and a layer, were observed after initial hydrogenation of Mg/Cu SLCs under the conditions of 573 K, 86.4 ks in H-2 atmosphere of 3.3 MPa. Hydrogenation of Mg (1) and alloying Mg with Cu to form Mg2Cu (2) followed by hydrogenation of Mg2Cu (3) should be competitive. It is proposed that an open network of MgCu2 can be formed when (1) occurs later than (3), a sheathed network when (1) occurs later than (2) and earlier than (3), and a layer when (1) occurs earlier than (2). However, the reaction of MgH2 to Cu under H-2 atmosphere is not known in general. Therefore, in order to prove the existence and the generality of this reaction, pellets of MgH2 and Cu powder were heated under the condition of 673 K, 86.4 ks in H-2 atmosphere of 8.0 MPa. The formation of a layer of MgCu2 was confirmed by SEM observations, EDS analyses and XRD measurements. (C) 2015 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2015.01.196

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The micro/nano-structural transition and hydrogen absorption mechanism in Mg/Cu super-laminate composites (SLCs) were investigated. Differential scanning calorimetry (DSC) measurements were performed on Mg/Cu SLCs at several heating rates and till several repetition cycles up to twenty cycles, and micro/nano-structures of Mg/Cu SLCs were examined with stereomicroscope, digital-microscope, scanning electron microscope (SEM), and scanning transmission electron microscope (STEM). It is found that the micro/nano-structures of Mg/Cu SLCs change drastically at early cycles and reach a steady state after around the tenth cycle. The detailed examination of DSC profiles, and SEM and STEM observations of Mg/Cu SLCs suggest that the hydrogen absorption process consists of a fast and a slow reaction which shows a sharp exothermic peak around at 610 K and a broad exothermic peak around at 570 K connected with it in DSC profiles, respectively.

DOI： 10.2320/jinstmet.J2015034

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：IOP PUBLISHING LTD  

A variety of microstructures in Mg/Cu super-laminate composites (SLCs) caused by competitive reactions during hydrogenation has been shown experimentally. Two types of MgCu2 structures, three-dimensional (3-D) network and layer, were observed after initial hydrogenation of Mg/Cu SLCs under the conditions of 573K, 86.4ks in H-2 of 3.3MPa. It was proposed that Mg/Cu SLCs could be hydrogenated by two kinds of processes. The one is alloying Mg with Cu to form Mg2Cu followed by hydrogenation of Mg2Cu, leading to the formation of 3-D network of MgCu2. The other is hydrogenation of Mg followed by the reaction of MgH2 to Cu, leading to the formation of layer MgCu2. SEM observations revealed that there existed Mg2Cu nano-crystals at the interface between Mg and Cu in as-rolled Mg/Cu SLCs, and layer MgCu2 at the interface between MgH2 and Cu in pellets of MgH2 powder and Cu powder heated under the conditions of 673K, 86.4ks in H-2 of 8.0 MPa. The existence of Mg2Cu nano-crystals enables alloying Mg with Cu at low temperatures (<473K).

DOI： 10.1088/1757-899X/82/1/012078

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

We have been proposing that there are competitive two kinds of pathways in the hydrogenation of Mg/Cu super-laminate composites. The one is that Mg reacts with Cu to form Mg2Cu and then Mg2Cu is hydrogenated to form MgH2 and MgCu2. The other is that Mg is hydrogenated and then MgH2 and Cu reacts to form MgCu2 together with H-2 gas, according to a hypothesis that the reaction of MgH2 + 2Cu -> MgCu2 + H-2 occurs. In the present study, the reaction conditions such as pressure and temperature were investigated in order to confirm that the hypothesis is true. Well-mixed MgH2 and Cu powder was compressed to a pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Following results were obtained from the experiments at 673 K. The above-mentioned alloying accompanied by H-2 emission occurs at pressures higher than 6.6MPa of H-2 pressure, which is higher than lower limit for the hydrogenation of Mg2Cu. On the other hand, Mg2Cu is formed at 3.3 MPa which is lower than the limit. The reaction of MgH2 with Cu also occurs at 573K in 3.3 MPa H-2. But it requires very long time such as 691.2 ks, although the existence of MgCu2 is confirmed in 86.1 ks of heating time in the case of Mg/Cu super-laminate composites.

DOI： 10.2320/matertrans.M2014426

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The micro/nano-structural transition and hydrogen absorption mechanism in Mg/Cu super-laminate composites (SLCs) were investigated. Differential scanning calorimetry (DSC) measurements were performed on Mg/Cu SLCs at several heating rate and till several repetition cycles up to twenty cycles, and micro/nano-structures of Mg/Cu SLCs were examined by stereomicroscope, digital-microscope, scanning electron microscope (SEM), and scanning transmission electron microscope (STEM). It is found that the micro/nano-stractures of Mg/Cu SLCs change drastically at early cycles and reach a steady state after around the tenth cycle. The detailed examination of DSC curves, and SEM and STEM observations of Mg/Cu SLCs suggest that the hydrogen absorption process consists of a fast and a slow reaction which shows a sharp exothermic peak around at 610K and a broad exothermic peak around at 570K connected with it in DSC profiles, respectively.

DOI： 10.2320/matertrans.MG201413

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELSEVIER SCIENCE BV  

The applicability of the redox reactions of 5,8-dihydroxy-1,4-naphthoquinone (1) and its lithium salt, 5,8-dihydroxy-1,4-naphthoquinone dilithium salt (2), as positive electrode active materials for rechargeable lithium batteries was investigated. The prepared electrodes showed initial discharge capacities of 170 mAh g(1) (1) with an average voltage of 2.2 V vs. Li+/Li, and 247 mAh g(2) (1) with an average voltage of 2.1 V vs. Li+/Li for 1 and 2, respectively. The obtained discharge capacities correspond to their two-electron redox behaviors. While the electrode using 1 suffered from a poor cycle-stability, the one using 2 underwent many cycles; i.e., after a small drop in the capacity at the first cycle, the capacity of the latter electrode hardly decayed during the subsequent 100 cycles. The effects of the introduction of ionic groups on the physical properties including the cycle stability were discussed along with quantum chemistry calculation results. (C) 2014 Elsevier Ltd.

DOI： 10.1016/j.egypro.2014.07.153

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Japan Institute of Metals (JIM)  

The hydrogen absorption and desorption reactions of pure MgH2were investigated by pressure-time measurements using a Sieverts' type instrument in the temperature and pressure ranges of 653683K and 0.51.7 MPa, respectively. The absorption and desorption behaviors were analyzed using a fraction of the reaction product during the hydrogen absorption and desorption. The fraction was evaluated based on the amount of absorbed and desorbed hydrogen. The hydrogen absorption of pure Mg immediately occurs when the thermodynamic condition in which the reaction can proceed is reached at 653683 K, but the hydrogen desorption does not start immediately when it can thermodynamically proceed at the same temperatures. Incubation periods were observed and had varied values in the range from 0.15 to 1.5 ks under the above-mentioned pressure and temperature conditions. In order to clarify the hydrogen desorption mechanism, the data obtained were analyzed by the Kolmogorov-Johnson-Mehl-Avrami (KJMA) equation. The obtained values of the Avrami exponents varied from 3 to 0.6 with the increasing fraction of Mg. The hydrogen desorption process was classified into four stages based on the KJMA plots of the hydrogen desorption curves of MgH2measured in this study. These values indicated that the Mg nuclei generate and three-dimensional grow during the initial stage, then the growth is restricted to a two- or one-dimensional.

DOI： 10.2320/matertrans.MG201405

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The effect of initial structures of Mg/Cu super-laminates on hydrogen absorption/desorption properties was investigated experimentally. Mg/Cu super-laminates were prepared by a repetitive fold and roll method using a conventional two-high roll mill. Three types of specimens were prepared by changing rolling reduction in cold rolling. Each of them had a fine, medium, coarse microstructure, respectively. Hydrogen absorption/desorption properties were measured with HP-DSC and a Sieverts' type instrument. Microstructures were observed with SEM. Two types of MgCu2 forms, 3D-network and layered forms, were observed after hydrogenation under the conditions of 573 K, 86.4 ks and 3.3 MPa of H-2, respectively. This implies that Mg/Cu super-laminates can be hydrogenated by two kinds of processes. The dominant process depends on the initial structures of Mg/Cu super-laminates. Repetitive hydrogenation/dehydrogenation tests using HP-DSC indicate that, even after 20 cycles, the initial microstructures of Mg/Cu super-laminates can affect their hydrogen absorption/desorption properties. (C) 2013 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2013.03.155

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

The solution density, viscosity and conductivity of MClO4 (M = Li and Na) solutions in propylene carbonate and gamma-butyrolactone are measured at the concentrations of < 1.5-2.0 mol dm(-3). The partial volume of the solute, derived from the density, of NaClO4 is greater than that of LiClO4 as expected. NaClO4 produces less viscous and more conductive solutions than LiClO4 throughout the examined concentration range. Notably, the conductivity of the NaClO4 solutions is 10-20% higher than that of the LiClO4 solutions at T/K = 298. The validity of the empirical cubic root law, Lambda(C) = Lambda(0) - AC(1/3), is examined, where Lambda and Lambda(0) are the molar conductivities at the molarity C and at infinite dilution. The meaning of the slope A is interpreted in the theoretical framework of the pseudolattice model. (C) 2012 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jpowsour.2012.09.039

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS & MATERIALS  

We proposed that there are two kinds of competitive processes in the hydrogenation of Mg/Cu super-laminate composites; the one in which alloying (formation of MgCu2 fromMg and Cu) occurs in advance and Mg2Cu is hydrogenated to form MgH2 and MgCu2, and the other in which Mg is hydrogenated and then MgH2 and Cu react to form MgCu2 together with H-2 gas, according to a hypothesis that the reaction of MgH2+2Cu -> MgCu2+H-2 occurs. In order to confirm that the hypothesis is true, we investigated the conditions such as H-2 pressure and temperature at which the above-mentioned reaction proceeds. Well-mixed MgH2 and Cu powder was compacted to form pellet at 1.73 GPa and then heated at various hydrogen pressures and temperatures. Experimental results at 673 K indicated that the above-mentioned reaction occurs at pressures higher than 6.5 MPa, approximately the lower limit for the hydrogenation of Mg2Cu, whereas both Mg2Cu and MgCu2 are formed at 3.3 MPa.

DOI： 10.2320/jinstmet.JC201308

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：John Wiley and Sons Inc.  

We proposed that there are competitive two kinds of pathways in the hydrogenation of Mg/Cu super-laminate composites
the one is that alloying (formation of MgCu2 from Mg and Cu) occurs in advance and Mg 2Cu is hydrogenated to form MgH2 and MgCu2, and the other is that Mg is hydrogenated and then MgH2 and Cu reacts to form MgCu2 together with H2 gas, according to a hypothesis that the reaction of MgH2+2Cu -&gt
MgCu2+H2 occurs. In order to confirm that the hypothesis is true, we investigated the conditions such as pressure and temperature at which the above-mentioned reaction proceeds. Well-mixed MgH2 and Cu powder was compacted to form pellet at 1.73GPa and then heated at various hydrogen pressures and temperatures. Experimental results at 673K indicated that the above-mentioned reaction occurs at pressures higher than 6.5MPa, approximately lower limit for the hydrogenation of Mg2Cu, whereas Mg2Cu is formed at 3.3MPa.

DOI： 10.1007/978-3-319-48764-9_28

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：John Wiley and Sons Inc.  

Existence and generality of competitive reactions during hydrogenation of Mg/Cu super-laminate composites were investigated experimentally. Two types of MgCu2 forms, 3D-network and layered ones, were observed after hydrogenation of the composites under the conditions of 573K, 86.4ks and 3.3MPa of H2. We proposed that Mg/Cu super-laminate composites could be hydrogenated by two kinds of processes. The one is alloying Mg with Cu to Mg2Cu followed by hydrogenation of Mg2Cu, leading to the formation of 3D-network MgCu2. The other is hydrogenation of Mg followed by a reaction of MgH2 to Cu, leading to the formation of layered MgCu2. However, the reaction of MgH2 to Cu under hydrogen atmosphere is not known in general. Therefore, in order to prove the existence and the generality of this reaction, pellets of MgH2 and Cu powder were heated under the conditions of 673K, 86.4ks and 8.0MPa of H 2. The formation of layered MgCu2 was confirmed by SEM observations.

DOI： 10.1007/978-3-319-48764-9_13

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

In this study, we used the Sieverts' method to measure the hydrogen pressure-composition isotherms of LiH and LiNH2 mixed in a molar ratio of 2 : 1 in order to obtain the standard reaction enthalpy and entropy of the hydrogenation reaction. The amounts of hydrogen absorbed and desorbed by the mixture were equal to the theoretical value at temperatures ranging from 653 K to 873 K (which were higher than the melting temperature of the mixture), where the standard reaction enthalpy and entropy were -3 +/- 3 kJ . (mol H-2)(-1) and -68 +/- 4 J . K-1.(mol H-2)(-1), respectively. On the other hand, the amounts were less than the theoretical value at 553 K and 623 K (which were lower than the melting temperature) due to the incomplete reaction, indicating that these isotherms would not afford reliable estimates of the standard reaction enthalpy and entropy. Hence, we instead calculated the standard enthalpy and entropy below the melting temperature using the values above the melting temperature and the standard enthalpy and entropy of fusion of the mixture. The values thus obtained, -49 +/- 3 kJ (mol H-2)(-1) and -95 +/- 5 J K (mol H-2)(-1), respectively, are significantly different from those previously reported. Here, the differences are discussed from the standpoint of the difficulty in measuring the hydrogen pressure-composition isotherms at lower temperatures as well as the validity of the method.

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The effect of Al addition on the reversibility of a MgH2+2LiBH4 hydrogen storage mixture was examined in order to improve the mixture’s requirement for a hydrogen atmosphere even in dehydrogenation. The experiments using high pressure differential scanning calorimetry and X-ray powder diffraction confirmed that a MgH2+Al+4LiBH4 mixture can reversibly dehydrogenate and rehydrogenate below 773K under mild conditions of 0.1 MPa H2 for dehydrogenation and 4.0 MPa H2 for rehydrogenation. Moreover, thermogravimetry tests revealed that this mixture starts hydrogen desorption at about 530 K, which is 80K lower than the corresponding temperature for the MgH2+2LiBH4 mixture, and desorbs 9.5 mass% of hydrogen below 773 K. Thus, the addition of Al improves not only the reversibility of the reaction but also dehydrogenation kinetics. The hydrogen desorption of the mixture occurs by three steps, which includes the formation of Mg-Al alloys by the reaction of MgH2 and metallic Al followed by the formation of Mg1-xAlxB2 by the reaction of the Mg-Al alloys and LiBH4. Al in this mixture suppresses the formation of metallic Mg and accelerates the formation of Mg1-xAlxB2 from B produced by dehydrogenation of LiBH4. Mg1-xAlxB2 is derived from partial substitution of Al for Mg in MgB2, which contributes to reversible hydrogenation and dehydrogenation of MgH2+2LiBH4.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ROYAL SOC CHEMISTRY  

Combined thermodynamical and structural studies have confirmed the occurrence of multimode hydriding/dehydriding reactions of CaPd that vary depending on temperature, and that these reactions proceed via hydrogen solution/dissolution in the temperature range 273-523 K and via phase decomposition/recombination in the temperature range 523-773 K.

DOI： 10.1039/c0cc02626c

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A broad sextet signal in the 1HNMR spectrum of Li[AlH 4] in THF-d 8, centered at 2.75 ppm with J/Hz = 176, was assigned to the signal from [AlH4] 1. Also investigated were the reactions of Li[AlH 4] with TiCl 3 or Ti(OBu) 4 in THF. © 2009 The Chemical Society of Japan.

DOI： 10.1246/bcsj.82.709

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

We investigated by differential scanning calorimetry the effect of ball milling on the hydrogenation properties of Mg2Cu, a hydrogen storage alloy, prepared by two methods: One is mechanically alloyed Mg2Cu using Mg and Cu powders as starting materials. Eight hours (= 28.8 ks) of ball milling transformed the Mg : Cu = 2 : I mixture into Mg2Cu single phase which reacts reversibly with hydrogen. The other is prepared by ball milling a cast Mg2Cu alloy. While the as-cast Mg2Cu undergoes neither hydrogenation nor dehydrogenation under 3 MPa of hydrogen in the temperature range of 300-773 K, just an hour of ball milling activates the inert Mg2Cu to react with hydrogen reversibly. Examining the milling period dependency of the particle size, crystallite size, activation energy and the apparent heat of dehydrogenation which reflects the fraction of activated part in a specimen, we found that the ball milling firstly influenced the particle size and the activated fraction of the sample, and then followed the effect on the crystallite size and kinetic properties. We also found that a trace amount of oxygen could significantly spoil the benefits brought by the ball milling for longer period of milling. [doi: 10.2320/matertrans.MRA2008183]

DOI： 10.2320/matertrans.MRA2008183

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：PERGAMON-ELSEVIER SCIENCE LTD  

We investigated at 423K in vacuo the hydrogen desorption kinetics of Ti-doped sodium aluminum hydride (NaAlH4) prepared with using different Ti precursors and procedures. Initial distinction in kinetics among specimens vanishes through several cycles of dehydrogenation at 473K in uacuo and rehydrogenation at 423K under 10 MPa of H-2. Considering that the temperature of dehydrogenation cycle is above the melting point of NaAlH4, we can assume that the difference in physical nature of the materials, such as particle size, phase distribution and so on, disappears through cycling. The present study tells that the chemical nature of the Ti related species which enhances the reaction kinetics of alanate becomes identical whatever Ti presursor is used and, however, the material is prepared. (C) 2007 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijhydene.2007.10.002

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DOI： 10.1016/j.jallcom.2006.04.060

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

It is known that a certain titanium species enhances the dehydro.-enation of alanate, MAlH4 (M = Li and Na), in solid state. We carried out the dehydrogenation in solution in order to examine if the titanium species enhances the reaction under homogeneous condition as in solid state. The results show that the titanium species enhances the reaction in solution as well and that the titanium species interacts not only with hydride anions but also with counter cations. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.04.211

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The effect of melting of LiAlH4 on its dehydrogenation properties was examined using Differential Scanning Calorimetry (DSC). LiAlH4 samples purified in advance were examined on their hydrogen desorption behaviors in the various heating conditions in which some of them were melted and the others not. Some of the as-received samples were mechanically ground in an Ar atmosphere for a short time of period using a ball milling machine and then Supplied to DSC measurements. The color of the sample after milling changes from g-ray-beige to grey. probably due to contamination of metal elements such as iron and chromium from hardened steel vessel and balls during grinding. The rapid hydrogen desorption was observed for the samples melted by heating, whereas the insignificant hydrogen desorption was observed for the ones which were not melted by heating, in spite that heating and cooling were repeated three times. The time from melting to decomposition of LiAlH4 accompanied by hydrogen desorption was 90 +/- 30 s. independent of hydrogen desorption temperature. The samples milled in hardened steel vessel using a planetary-type ball milling machine exhibited about 2 K lower melting temperature and 15 K lower hydrogen desorption temperature than the as-purified samples. These changes can be considered to happen because contamination metal elements contributed to lowering a melting temperature and worked as a catalyst to decrease the activation energy for decomposition of liquefied LiAlH4. These results indicate that metal elements such as iron and chromium certainly contribute to improve hydrogen desorption temperatures of alanates, as reported in many papers, but it is more important to lower their melting temperatures in order to improve their hydrogen desorption kinetics.

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Hf7Ni10 has the same crystal structure as Zr7Ni10, which shows several unusual hydrogenation properties such as reversible hydrogenation by irreversible phase transformation and structural change caused by hydrogenation followed by dehydrogenation, and its hydrogenation properties have been unknown. The phase relation and hydrogenation properties of HfxZr7-xNi10 alloys were investigated in the compositional range from Zr7Ni10 (x = 0) to Hf7Ni10 (x = 7). All the samples were obtained by arc melting followed by heat treatment in vacuum. The constituent phase was identified by the combination of X-ray diffraction and microscopic analysis and hydrogenation properties were examined by differential scanning calorimetry and Sieverts' method. No structural change from orthorhombic Cmca type to another one such as tetragonal I4/mmm type and orthorhombic Pbca type was observed for the addition of Hf and Hf was substituted for Zr in Zr7Ni10 in all the compositional range we examined. The lattice constant of the aimed phase decreased with an increase in Hf content. The measurements using differential scanning calorimetry indicated that the Hf-substituted alloys showed the same phase transformation as Zr7Ni10 in hydrogenation, that is the unusual phase transformation that an inter-mediate hydride phase appears only in dehydrogenation but not in hydrogenation. The transformation temperature decreased with an increase in Hf content. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.02.080

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We have investigated the hydrogenation and dehydrogenation properties of binary RNi5 (R: La, Pr, Nd, Sm, Gd, Th and Dy) intermetallic compounds in the pressure range of 0.1-35 MPa and temperature range of 223-298 K. Pressure-composition isotherms demonstrated that as the atomic number of R increased in RNi5-H systems, the single pressure plateau (LaNi5) split into two plateaux (PrNi5, NdNi5, SmNi5 and GdNi5), and then into three plateaux (TbNi5 and DyNi5), indicating the presence of two hydrides (beta(2) and gamma(2) phases) and then three hydrides (beta(3), gamma(3) and delta(3) phases). The beta(3)-gamma(3) and gamma(3)-delta(3) phase transitions in the TbNi5-H system corresponded, respectively, to the alpha(2)-beta(2) and beta(2)-gamma(2) transitions in the RNi5-H (R: Pr, Nd, Sm and Gd) systems having two plateaux. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2004.11.112

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Complementary studies by neutron and X-ray diffraction were performed to elucidate the location of deuterium atoms in nano-crystalline FeTiDx. Remarkable rearrangement of the metal atoms due to the deuterium absorption was observed in the pair distribution functions, g(r), obtained by X-ray diffraction. The result indicates that disordered grain boundary is developed through the deuterium absorption. The g(r) function obtained by neutron diffraction indicates the occurrence of two types of deuterium sites located inside the grains and in the grain boundaries, respectively. The deuterium atoms in the grain boundaries occupy tetrahedral sites consisting mainly of Ti atoms. (c) 2005 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2005.01.122

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The stability and electronic structure of perovskite hydrides ABH(3) were investigated by means of first-principles density functional calculations. Two types of perovskite hydrides are distinguished: (1) When A and B are alkali and alkaline earth metals, the hydrides are ionic compounds with calculated band gaps of around 2 eV and higher. Their stability trend follows basically the concept of Goldschmidt's tolerance factor. (2) When A is one of the heavier alkaline earth metals (Ca, Sr, Ba) and B a transition metal, stable compounds ABH(3) result only when B is from the Fe, Co, or Ni groups. This stability trend is basically determined by effects associated with d band filling of both the transition metal and the hydride. In contrast to group (1) perovskites, the transition metal-containing compounds are metals. The synthesis of CaNiH3 and its structure determination from CaNiD3 is reported. This compound is a type (2) perovskite hydride with a fully occupied hydrogen position (CaNiD3: a = 3.551(4) angstrom, d(Ni-D) = 1.776(2) angstrom). Its stability is discussed with respect to transition metal hydrides with complex anions (e.g., Mg2NiH4, Na2PdH2, Sr2PdH4). (c) 2005 Elsevier Inc. All rights reserved.

DOI： 10.1016/j.jssc.2005.08.026

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We have investigated the hydrogenation and dehydrogenation properties of DyNi5 binary intermetallic compound in the pressure range from 0.1 to 35 MPa. After initial activation, DyNi5 compound absorbs hydrogen to reach H/DyNi5 = 3.8 at 248 K. By evaluating the pressure-composition (P-C) isotherm part by part in detail, we found the P-C isotherm for DyNi5-H system comprises three steps of phase transitions during hydrogenation and dehydrogenation processes due to the presence of one solid solution (alpha) and three kinds of hydride (beta, gamma and delta). Below H/DyNi5 = 1.0, the first alpha-beta phase transition appears with large hysteresis, whereas the second beta-gamma and third gamma-delta phase transitions are superposed upon each other around H/DyNi5 = 2.3. Consequently, the P-C isotherm apparently shows two pressure plateaux during both hydrogenation and dehydrogenation. Between these plateaux during dehydrogenation, the hydrogen pressure decreases logarithmically with decreasing hydrogen content or log P alpha H/DyNi5. This complex behavior of P-C isotherm is reversible. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.jallcom.2004.05.087

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We investigated the hydrogen storage properties in a HoNi5-H system combined with TbNi5-H and DyNi5-H systems. pressure-composition (P-C) isotherms in the HoNi5-H system show one reversible pressure plateau during hydrogen absorption and desorption with a hysteretic phase transition. The maximum hydrogen storage capacity was found to be H/HoNi5 = ca. 2, and no second plateau similar to that observed in other RNi5-H (R: rare earth) systems was observed, even at 196 K. Two pressure plateaux found in light rare earth-based RLNi5-H (R-L = La, Pr, Nd, Sm and Gd) systems tend to disappear in TbNi5-H and DyNi5-H systems and are scarcely present in HoNi5-H system. On the other hand, a novel pressure plateau appears at low hydrogen content in these systems due to the presence of a new hydride phase, and the plateau region extends from TbNi5-H and DyNi5-H to HoNi5-H systems. Contrary to the other plateaux, the pressures of the novel plateau during both hydrogen absorption and desorption decrease with decreasing unit cell volume of RNi5 compounds or with increasing atomic number of the R element in RNi5-H systems. To clarify the effect of 4f electrons in the R element in RNi5-H systems on the novel plateau, we have evaluated the hydrogen storage properties in an YNi5-H system. Our results show that YNi5 compound with lattice constants similar to those of TbNi5 and DyNi5 compounds has a similar P-C isotherm, suggesting that 4f electrons has no direct influence on the appearance of the novel plateau.

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Hydrogen would be ideal as a synthetic fuel, but some problems remain for hydrogen storage. We discussed the possibility of the phase transition between alloy and hydride at high hydrogen pressure from the viewpoint of the hydrogen storage properties in RNi5-H systems. Between La and Gd in RNi5-H systems, pressure-composition isotherms show two well-separated pressure plateaux, indicating two kinds of RNi5 hydrides (beta and gamma) with one RNi5 hydrogen solid solution (alpha). From Tb to Ho in RNi5-H systems, on the other hand, two pressures disappear gradually, whereas novel plateau appears at low hydrogen content, suggesting the presence of another hydride (beta'). Due to the lanthanide contraction, the plateau pressures for both alpha-beta and beta-gamma phase transitions increase with increasing atomic number of R element in RNi5-H systems in contract to the pressure for alpha-beta transitions. Regardless of the RNi5 composition, the entropy change for alpha-beta transition corresponds to the entropy of H-2 gas while that for beta-gamma transition is due to the configrational factor of the hydrogen atoms in the unit cell. The plateau pressure depends mainly on the enthalpy due to the constancy of the entropy. The phase transition to form hydride occurs below several GPa at 298 K.

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In order to obtain information about the hydrogenation properties of Zr-rich Zr7Ni10 with orthorhombic Pbca symmetry, which can help to understand the mechanism of the unusual hydrogenation properties of stoichiometric Zr7Ni10 with orthorhombic Cmca symmetry, the synthesis of the Zr-rich compound was attempted by applying four alloying procedures: (1) alloying and cooling on water-cooled copper hearth in an arc melting furnace, (2) heat treatment at 1273 K in a vacuum for 86.2 ks for the as-cast samples prepared by arc melting, (3) remelting of as-cast alloys followed by quenching on copper wheel rotating at 4000 rpm in an argon atmosphere, and (4) heat treatment of quenched samples at 973 K or 1073 K under pressurized argon atmosphere for 7.2 ks. The target phase was not obtained by these four methods and, through the examinations, it was found that the single-phase region of Zr7Ni10 was quite narrow compared with the solubility range published in a binary phase diagram and the Zr7Ni10 compound with the tetragonal structure, which can also be obtained by hydrogenation to form the corresponding hydride Zr7Ni10H17 followed by dehydrogenation, was formed in the quenched samples prepared by procedure 3. The solubility of Zr7Ni10 and its phase stability are discussed. (C) 2004 Published by Elsevier B.V.

DOI： 10.1016/j.jallcom.2004.01.064

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Orimo et al. reported that nanostructured graphite, prepared by using the mechanical grinding under hydrogen atmosphere, contained more than 7 mass% of hydrogen whose thermal desorption spectrum (TDS) showed characteristic two peaks; one is at around 700 K and the other around 1000 K [Appl. Phys. Lett. 75 (1999) 3093; Appl. Phys. A72 (2001) 167; J. Appl. Phys. 90 (2001) 1545]. We confirmed this claim; namely, c.a. 4.5 mass% of hydrogen was detected by TDS in the desorbed gas from graphite powder mechanically ground under hydrogen in a Cr/Ni steel mortar. Yet the mechanism of hydrogenation and the physico-chemical state of adsorbed hydrogen are not known well. We found that the amount of contained hydrogen depends significantly on the grinding mortar. When a Cr steel mortar was used, we obtained 2 mass%; and when an agate mortar was used, only a trace amount of hydrogen was detected. The transmission electron microscopy and the X-ray powder diffractometry indicated that the nanostructured graphite ground in steel mortars contained a large quantity of cementite, Fe3C, to which the iron element was supplied by wearing out of mortar walls during the grinding. We examined the influence of metal particles by intentionally adding iron and nickel powder into graphite during the grinding in the metal-free agate mortar. Although in the agate mortar with metallic additives the hydrogenation did not proceed as much as in the steel mortar, the TDS spectrum showed characteristic features. The presence of catalytic metal particles seems to be a prerequisite for the hydrogenation of graphite under hydrogen by mechanical grinding. (C) 2003 Elsevier B.V All rights reserved.

DOI： 10.1016/j.mseb.2003.10.093

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We investigated the pressure-composition (P-C) isotherms of several binary RNi5 (R = La, Ce, Pr, Nd, Sm and Gd) intermetallic compounds to clarify the correlation of the hydrogen storage properties between multi-plateaux. It was found that all RNi5 compounds have similar P-C isotherms with two well-separated plateaux except for CeNi5, indicating that two hydrides with compositions of RNi5H3-4 and RNi5H6-7 are formed. With increasing the atomic number of R element in the RNi5 compounds, the unit cell volume decreases due to the decrease of the radius of the R element. This influences the absolute enthalpies of dehydrogenation \DeltaH\ of both hydrides (beta and gamma) to decrease, which consequently leads to the increase of the second plateau pressure as well as the first plateau. Contrary to LaNi5-H-2 system, the \DeltaH\ of gamma hydride is smaller than that of \DeltaH\ of beta hydride for the other systems, which indicates that the pressure gap between two plateau pressures expands with decreasing temperature. The second plateau tends to disappear with large atomic number of R element because the JAHJ value approaches to zero. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2003.10.055

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The C14 intermetallic TiCr1.9 compound was prepared by arc melting, annealed at 1623 K in helium atmosphere for 8 h, and then quenched in water. The X-ray diffraction profiles showed that the crystal structure transformed from C14 to bcc after mechanical grinding for 18 h. The hydrogenation properties of the sample were examined by pressure-composition isotherm measurements. This sample with bcc structure reacted with hydrogen by maintaining the bcc structure. The maximum hydrogen content was found to be about 0.5 H/M at 273 K and 10 MPa, where H/M means the atomic ratio of hydrogen to metal. This hydrogen content was smaller than that of other bcc structure alloys. The sample prepared by MG consists of nanosized grains of polycrystalline TiCr1.9 and amorphous-like structure regions, judging from the bright field image and the corresponding selected area diffraction pattern. The hydrogen storage capacity is reduced due to the amorphous-like structure. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.mseb.2003.10.057

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We systematically investigated the hydrogenation and dehydrogenation properties for heavy rare earth-based binary RHNi5 (RH = Gd, Tb and Dy) intermetallic compounds and evaluated the correlations between crystallographic and thermodynamic properties. XRD analysis shows that all RHNi5 compounds crystallize in the hexagonal CaCu5 -type crystal structure. In analogy to the light rare earth-based RLNi5 (R-L = La, Pr, Nd and Sm) compounds both lattice constants of RHNi5 compounds decrease with increasing the atomic number of R-H element due to the lanthanide contraction. On the pressure-composition (P-C) isotherms, GdNi5-H-2 system shows two well-separated pressure plateaux qualitatively similar to RLNi5-H-2 systems. Looking over from Gd to Dy in the RHNi5 compounds, we find three specific dehydrogenation properties on the P-C isotherms: 1. The first plateau pressure (pp,) increases in this order (at around H/RHNi5 = 2.5) due to less stability of hydrogen in the unit cell by the lanthanide contraction. Linear correlations are also observed between log(PP1), and the unit cell volume (V) which fall onto the same lines extrapolated from those observed in case of the RLNi5 compounds. 2. The second plateau (P2) tends to disappear because the P-C isotherm goes beyond the critical point of the phase transition. 3. Fairly flat first plateau separates into two parts in which a new plateau (PN) appears at low hydrogen content (H/RHNi5 less than or equal to 2) with hysteretic phase transition. So long as the first plateau of dehydrogenation is concerned, from LaNi5 to DyNi5 we can predict the first plateau pressure from the unit cell volume of compounds and temperature.

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Dehydrogenation process of Ti and Zr doped alanates was studied by means of the thermal gravimetry-differential thermal analysis (TC-DTA) and isothermal dehydrogenation kinetics measurement. With using transmission electron microscope (TEM) equipped with an electron energy loss spectrometer (EELS), we observed the distribution of Ti element on a particle of the Ti doped material. The kinetic measurement showed that: (i) Dehydrogenation of Na3AlH6 proceeds much slower than that of NaAlH4, when the former is observed as a second step of the two step consecutive dehydrogenation of Ti doped NaAlH4. (ii) But if Na3AlH6 is doped directly with Ti, the dehydrogenation rate matches that of NaAlH4. (iii) The activation enthalpies of both Ti doped NaAlH4 and Na3AlH6 are 100 kJ(.)mol(-1), and those of both Zr doped NaAlH4 and Na3AlH6 are 135 kJ(.)mol(-1). These findings imply that the rate determinig step is not related to the cleavage of Al-H bonding, which must be sensitive to whether the species involved is [AlH4](-) or [AlH6](3-), but to a long range phenomenon, such as the diffusion of the atom in the particle. The TEM-EELS observation showed that the Ti element was distributed on the surface of the particle of doped material.

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Potential of a novel hydrogen storage vessel, "hybrid hydrogen storage vessel", combining an aluminum-carbon fiber reinforced plastic (Al-CFRP) composite vessel and hydrogen storage alloy, is reported through calculation of the weight and volume of the hydrogen storage system for 5 kg of hydrogen. Evaluation of this system showed that the concept of the hybrid hydrogen storage vessel allowed us to realize a hydrogen storage system advantageous in both gravimetric and volumetric hydrogen density compared with conventional hydrogen storage techniques. The hybrid vessel requires a hydrogen storage alloy with a higher volumetric hydrogen density as well as a higher gravimetric density, and with a higher equilibrium hydrogen pressure than the hydrogen storage alloys which have been used for conventional hydrogen storage vessels. (C) 2003 International Association for Hydrogen Energy. Published by Elsevier Science Ltd. All rights reserved.

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Zr7Ni10 has three hydrogen occlusion phases, alpha, beta and gamma, and the following unusual features are known for the phase transitions in the Zr7Ni10-H-2 system: (1) The intermediate hydride phase (beta) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase (alpha) exhibits a much higher hydrogen solubility during hydrogenation than during dehydrogenation. In order to clarify the mechanism about the difference in the hydrogen solubility of the alpha phase, the relation between the pressure-composition isotherms and corresponding structural change has been examined by a conventional volumetric method and X-ray diffraction. Through the examination, we discovered that the crystal structure of the alpha phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated a phase changes from an orthorhombic structure to a tetragonal structure. The conditions causing the structural change were then examined, and it has been found that the a phase maintains its original orthorhombic structure as long as it is hydrogenated so as not to absorb enough hydrogen to change it to the hydride with a higher hydrogen content (gamma). The phenomenon can be understood as one of the hydrogen-assisted phase transitions such as hydrogen-induced amorphization (HIA) in the sense that the phase transition requires hydrogenation under special conditions. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0925-8388(03)00358-X

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Some hydrogen storage materials with the hexagonal CaCu5-type crystal structure have two pressure plateaux during hydrogen absorption and desorption processes. To clarify the correlation of hydrogenation proper-ties between two plateaux, we investigated the pressure-composition isotherms of several binary RNi5 (R = La, Ce, Pr, Nd and Sm) intermetallic compounds at pressures up to 35 MPa and at temperatures ranging from 196 to 423 K by use of a modified Sieverts' method. We also determined the unit cell volume of the compounds to correlate the hydrogenation properties with the crystal structure. It was found that RNi5 compounds had qualitatively similar hydrogenation properties in that two well-separated plateaux indicated the existence of two hydrides with the compositions of RNi5H3-4 (beta phase) and RNi5H6-7 (gamma phase) except CeNi5. Similar to the lower plateau pressure, the higher plateau pressure increases with increasing the atomic number of R element or with decreasing the unit cell volume of these compounds. For LaNi5-H-2 system, the pressure gap between two plateaux expands with increasing temperature. indicating that the absolute value of enthalpy of dehydrogenation (\DeltaH\) of beta hydride is smaller than that of gamma hydride or \DeltaH(beta)\ < \DeltaH(gamma)\. On the other hand, for other RNi5-H-2 systems the pressure gap expands with decreasing temperature; that is, the \DeltaH\ values of both hydrides show the opposite tendency or \DeltaH(beta)\ > \DeltaH(gamma)\. The maximum hydrogen content of each RNi5 compound exceeds six hydrogen atoms per formula unit and some compounds absorb the hydrogen to reach the hydride composition of RNi5H7 without new plateau.

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Deterioration behavior of an electrode made of V4TiNi0.65Co0.05Nb0.047Cr0.058 was studied by means of impedance spectroscopy, scanning electron microscopy (SEM) and impedance spectroscopy. The reaction resistance related to the lowest frequency semi-circle increased considerably and dischargeability became worse with cycling. The double layer capacitance for the same semi-circle became smaller after 50 cycles. The SEM observation of the cross-section of the cycled electrodes indicated that voids were formed around alloy particles embedded in a matrix of Cu powder, and crack formation and dissolution of the TiNi second phase proceeded with cycling. These phenomena indicate that dissolution of the second phase caused loss of reaction sites and TiNi networks as a current collector. (C) 2003 Elsevier B.V. All rights reserved.

DOI： 10.1016/S0925-8388(03)00163-4

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The effect of mechanical grinding on phase transformation in Ti - Cr alloys with nominal compositions of TiCr2-x (x = 0, 0.2 and 0.5) was studied on phase transformation by mechanical grinding (MG). An X-ray diffraction (XRD) technique was applied for the identification of the constituent phases in the samples ground for various periods ranging from 0 to 12 h. The results indicated that the constituent phases changed from the mixture of a C15 and C14 Laves phases stable at ambient temperatures to a bcc phase stable at high temperatures such as 1643 K with an increase in grinding time. It was also found that, after 12 h of grinding, we could obtain samples composed of only a bcc phase within the detection ability of the X-ray diffraction apparatus. (C) 2002 Elsevier Science B.V. All rights reserved.

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An evaluation of the substitution of a third element for the constituent elements (Ca, Ni) in the compound was conducted in order to obtain information about stabilization of the CaNi compound which does not exist as a stable phase. Prior to the experimental study of the substitution, the candidates for the third element were investigated using Miedema's semi-empirical model, from the standpoint of formation enthalpy, and as a result, Pd was chosen as the element to stabilize the compound. The samples with the nominal compositions of CaN1-xPdx (0.1less than or equal toxless than or equal to1) were prepared by sintering and high frequency heating, and the constituent phases and hydrogenation properties were examined. New ternary phases such as Ca-1(Ni, Pd)(1) were not obtained under the present conditions; however, some pieces of new information such as the substitution of Ni for Pd in CaPd2 and reversible hydrogenation of CaPd at 373 K were obtained through the studies. (C) 2002 Elsevier Science B.V. All rights reserved.

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The C15 and C14 intermetallic TiCr2-x (x = 0, 0.2 and 0.5) compounds were subjected to grinding in a high-energy ball mill. The X-ray diffraction profiles showed that the crystal structure transformed from C 15 and C 14 to bcc after mechanical grinding for 57.6 ks. The hydrogenation properties of the TiCr2-x (X = 0, 0.2 and 0.5) samples were examined by differential thermal analysis and pressure-composition isotherm measurements. The sample reacted with hydrogen at 5 MPa and 523 K by maintaining the bcc structure. An higher hydrogen content was observed for the sample with the higher Ti content. The maximum hydrogen content of TiCr2.0, TiCr1.8 and TiCr1.5 was found to be about 0.32, 0.36 and 0.47 H/M at 313 K, respectively, at 8 MPa.

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X-ray diffraction patterns of NaAlH4 doped with up to 10 mol.% of either titanium or zirconium do not contain Bragg peaks for the bulk metals or their aluminum alloys. Instead the hydride lattice parameters a and c undergo significant contraction upon 2 mol.% doping and then expand as the doping level increases from 2 to 5 mol.%. These results are explained by a model that entails substitution of sodium cations by variable valence transition metal cations and the creation of Na+ vacancies in the bulk hydride lattice. (C) 2002 Elsevier Science B.V. All rights reserved.

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Electrical resistance of the Mg2Ni and Mg2NiH4 powders was measured under compressing up to 6 gigapascals (GPa), using the four-point probe method at 20°C. Effects induced by the high-pressure treatment and heating at 400°C with or without hydrogen source LiAlH4 were also studied. The structure and hydrogenation properties of the samples recovered after quenching from high pressure and high temperature were investigated employing the techniques of X-ray diffraction and thermal analyses such as differential scanning calorimetry, thermogravimetry and differential thermal analysis. Decreased absorption/desorption temperatures were observed for the treated samples owing to the changes of microstructure and kinetic factor. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0925-8388(01)01478-5

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We studied reproducibility of discharge capacity, dischargeability, activation behavior, activity and porosity for charge-discharge reaction of a pellet-type electrode consisting of one part by weight of Ti0.5Zr0.5Ni1.3V0.7 Mn0.1Cr0.1 and three parts of the copper powder. We examined electrodes immediately after preparation and electrodes stored for 1 month under the following conditions: vacuum, dry air and humid air. Electrolyte impregnation in vacuo was found to be very effective in improving the reproducibility of electrochemical measurements, reducing measuring effects due to the storage conditions of the electrodes. © 2002 Elsevier Science B.V. All rights reserved.

DOI： 10.1016/S0925-8388(01)01433-5

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A volumetric apparatus for gas phase hydrogen/helium adsorption and desorption measurement aimed at carbon materials was constructed. The performance of the apparatus was assessed using activated carbons and vapor grown carbon nanofibers, and was proved to be applicable for these materials of low apparent densities with sufficient accuracy. Materials used in this study did not show a significant storage capacity of hydrogen. The obtained result, however, will provide reference data for future study to develop the carbon material for hydrogen storage. (C) 2002 Elsevier Science B.V. All rights reserved.

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Ternary Ti4Ni2X (X=O, N, C) compounds and a binary Ti2Ni compound were compared based on their hydrogen pressure-composition-temperature (PCT) relations. It was demonstrated that the ternary compounds desorbed most of the absorbed hydrogen under moderate conditions such as room temperature and atmospheric pressure. The hydrogen desorption pressures of the Ti4Ni2X compounds were more than two orders of magnitude higher than the desorption pressure of the binary compound. In spite of the significant increase in the hydrogen desorption pressure, the slope of the PCT curve of each ternary compound was not large compared with that of the Ti2Ni one. These four Ti2Ni-based compounds and their corresponding hydrogen occlusion ones were discussed in terms of their relative thermal stability. (C) 2002 Elsevier Science B.V. All rights reserved.

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Electrochemical activation behavior of an AB(2)-Laves-phase type hydrogen storage alloy, Zr0.9Ti0.1Ni1.1Co0.1Mn0.6V0.2, was studied to make clear activation process of pellet-type metal hydride electrodes. An alkaline treatment of the electrodes with heated alkaline solution gave alloy surface enriched with nickel, and the treated electrode was more easily activated. The treated electrode desorbed more hydrogen during the first charge-discharge cycle, and was activated without induction period. A cross sectional view of the activated electrode showed finer pulverization of alloy particles than the annealed alloy, and impedance spectroscopy indicated larger surface area of the electrode using the as-east alloy. Since the as-cast alloy contains inhomogeneities, multi-phase microstructure and stress in the particle, the finer pulverization of alloy particles with hydrogenation are considered to increase surface area in an earlier cycle in the case of the as-cast alloy, which leads larger reaction area and faster activation of the as-cast alloy electrode.

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One method to store hydrogen effectively involves the use of metal complexes such as the alkali-element aluminum hydrides. The hydriding/dehydriding properties of these materials depend on how to prepare them with different structures and microstructures. The present work focused on a high-energy ball milling technique to produce Ti-doped lithium tetrahydridoaluminate (LiAlH4) and lithium hexahydroalanate (Li3AlH6) powders with nanocrystallites. The phase structures and dehydriding/rehydriding characteristic's were investigated by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller measurement, thermogravimetry, and differential scanning calorimetry. The mechanism of dehydrogenation and rehydrogenation was also examined by means of X-ray photoelectron spectroscopy (XPS). The results on the relation between the reversible hydrogen storage and catalysis function of the Ti-doped complex hydride indicate that both the homogenous distribution of Ti+A1 nanoclusters and the Ti-catalyst with Ti-0 <----> Ti3+ (Ti-0/Ti2+/Ti3+) defect sites play important roles in optimizing the reversible hydrogen storage.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

A vibrating-mill technique, which can activate the reaction system by bringing the reagents into very close contact at the preparative scale and by providing extra mechanical energy, much more effectively than the well-known ball-milling method, was used to prepare titanium(III) chloride (TiCl(3)(.)1/3AlCl(3))-doped lithium tetrahydridoaluminate (LiAlH4) and lithium hexahydridoaluminate (Li3AlH6) powders with nanocrystallites. The phase structure and dehydriding/rehydriding properties were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG), and differential scanning calorimetry (DSC). The mechanism of reversible dehydrogenation and rehydrogenation was examined by means of X-ray photoelectron spectroscopy (XPS). Thermodynamic and kinetic measurements showed a distinct change for the dehydriding/rehydriding reactions over the temperature range 25-250 degreesC. From the Arrhenius plot of hydrogen desorption kinetics, apparent activation energies were found to be 42.6 and 54.8 kJ/mol H-2 for the hydride decompositions of LiAlH4 and Li3AlH6, respectively. The results based on the properties of reversible hydrogen storage and catalysis function indicate that both the homogeneous distribution of Ti-catalyzed nanocrystalline complex hydrides and the Ti-catalyst with a Ti-0 double left right arrow Ti3+ (Ti-0/Ti2+/Ti3+) defect site play important roles in optimizing the reversible hydrogen storage.

DOI： 10.1021/jp012127w

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

The performance of a high hydrogen capacity alloy, V-16%Ti-12%Ni-1.4%Nb-0.96%Co-2.8%Ta, is sensitively influenced by dissolved aluminum and oxygen, both of which can be removed from vanadium by a refining process, but the process currently used is too expensive. It is necessary to develop a process to remove these impurities at a reasonable cost. We propose a new method for production of the alloy. A V-15%Ni-1.8%Nb precursor with a low enough level of aluminum was produced by alumino-thermic reduction from a mixture of V2O5, Nb2O5 and nickel. Subsequently, a V-16%Ti-12%Ni-1.4%Nb-0.96%Co-2.8%Ta alloy was obtained by alloying the precursor and the other constituents of titanium, cobalt and tantalum, and by adding mischmetal as a reducing agent to remove oxygen to a low enough level. It was demonstrated that, by the method described here, the vanadium-based alloy could be produced at a reasonable cost.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMER CHEMICAL SOC  

DOI： 10.1021/ja010170r

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KLUWER ACADEMIC PUBL  

The stoichiometric mixture of 2MgH(2) + Co was ball milled under a hydrogen atmosphere to synthesize nanocrystalline metal hydride Mg2CoH5. Upon milling, the mixture was analyzed by X-ray powder diffraction (XRD) and thermal methods employing the techniques of differential scanning calorimetry (DSC), thermogravimetry (TG) and differential thermal analysis (DTA). Hydrogen absorption and desorption measured by pressure-composition-temperature (P-C-T) curves indicated that the capacity loss was small after 20 consecutive cycling tests. The enthalpies associated with hydride formation and decomposition were measured to be -69.5 and -83.2 kJ mol(-1) H-2, respectively. At the temperatures of this study (553 to 653 K), hysteresis decreases with increasing temperature. (C) 2001 Kluwer Academic Publishers.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：KOREAN INST METALS MATERIALS  

The effect of high-pressure (6 gigapascal) and heating (600 degreesC) the hydrogen source of LiAlH4 on the structural and hydrogenation properties of 0.9MgH(2)+0.1Al+0.9Ni+0.1VH(0.9) was investigated. After recovery to ambient conditions, the sample was analyzed using X-ray diffraction, differential scanning calorimetry, thermogravimetry and differential thermal analyses. The results reveal that a nominal hydride phase with the composition of Mg0.90Al0.08Ni0.94V0.08H1.6 can be obtained, in which a maximum H-2-uptake can reach 1.9 wt.%, with hydride decomposition occurring between 160 degreesC and 250 degreesC.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Electrochemical Soc Inc  

A vanadium-based solid-solution-type alloy V4TiNi0.65Co0.05Nb0.047Ta0.047 with a large discharge capacity was obtained using a low-cost precursor of V4Ni0.65Nb0.047 produced by aluminothermic reduction from V2O5, Nb2O5, and Ni. The alloy was deoxidized to a low level by adding mischmetal as a reducing agent when the precursor was alloyed with Ti, Co, and Ta. The alloy showed a hydrogen absorption behavior similar to an alloy prepared from high-purity constituent metals. Moreover, the Mm-Ni-O phase was precipitated as spherical particles along the TiNi network phase in the alloy, remarkably improving the electrode rate capability because of enhanced catalytic ability of the network phase.

DOI： 10.1149/1.1393628

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELECTROCHEMICAL SOC INC  

A powder sintering method was used to synthesize the intermetallic compounds LaCaMgNi9, CaTiMgNi9, LaCaMgNi6Al3, and LaCaMgNi6Mn3 (PuNi3-type). The microstructure and primary phases were observed by scanning electron microscopy and X-ray diffraction. The pressure-composition isotherms showed that all alloys could reversibly absorb and desorb up to 1.8 wt % hydrogen at 20 degrees C and a hydrogen pressure of 3.3 MPa. The sintered samples were employed as the active materials of metal hydride electrodes. The hydride stability and electrochemical performance, combined with low cost raw materials, make these compounds attractive for metal hydride electrodes. (C) 2000 The Electrochemical Society. S1099-0062(00)01-068-3. All rights reserved.

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Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：JAPAN INST METALS  

A high performance hydrogen storage alloy V-16 mass%Ti-12 mass%Ni-1.4 mass%Nb-0.96 mass%Co-2.8 mass%Ta is sensitively influenced by dissolved aluminum and oxygen, both of which are reduced by unproductive refining process. Then, it was necessary to develop the process of simply removing these impurities at a reasonable cost. Then, we propose a new production technique. A V-15 mass%Ni-1.8 mass%Nb precursor with a low enough level of aluminum was produced by aluminothermic reduction of the mixture V2O5, Nb2O5 and nickel.
When the V-16 mass%Ti-12 mass%Ni-1.4 mass%Nb-0.96 mass%Co-2.8 mass%Ta alloy was obtained by alloying the precursor and the other constituents of titanium, cobalt and tantalum, it was deoxidized to a low enough level by adding mischmetal as a reducing agent.
By the method described here, the vanadium-based alloy can be produced at a reasonable cost.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

The PuNi3-type intermetallic compounds LaNi3, CaNi3, La0.5Ca0.5Ni3, LaCaMgNi9, La0.5Ca1.5MgNi9, CaTiMgNi9, LaCaMgNi6Al3 and LaCaMgNi6Mn3 have been prepared using a powder-metallurgy-sintering method. The hydrogenation behaviour of these materials has been studied through the gas-solid reaction. The as-prepared compounds were easily activated at room temperature under a hydrogen pressure of 3.3 MPa. The pressure-composition-temperature (P-C-T) curves show a single plateau region with the exception of LaNi3-H, which shows no plateau, and La0.5Ca1.5MgNi9-H, which shows two plateaus. All of these alloys can absorb/desorb hydrogen by 1.8 wt.% under the conditions studied. X-ray diffraction (XRD) analysis reveals that LaNi3H4.5 is in the amorphous state, and the other hydrides are accompanied by different expansions of the unit cell volume of the host alloy. (C) 2000 Elsevier Science S.A. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

Alloy samples with a single phase structure of Ti4Cu2O were prepared and their hydrogenation characteristics were investigated. pressure-composition isotherms of hydrogen absorption and desorption at 373, 303 and 313 K for the oxometallic alloys were measured over the range of hydrogen pressure from 0.004 to 2 MPa. The Ti4Cu2O alloys absorbed hydrogen up to 0.47 in the atomic ratio of hydrogen to metal at 273 K and under 2 MPa and reversibly desorbed at 313 K more than half of hydrogen absorbed. No distinct pressure plateau was observed in the isotherms. For all the samples after hydrogenation at temperatures and pressures below 523 K and 3 MPa, no phase other than Ti4Cu2O was observed in the X-ray diffraction profiles. The thermodynamic properties for the hydrogenation of the alloys were discussed. (C) 2000 Elsevier Science S.A. All rights reserved.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：MINERALS, METALS & MATERIALS SOC  

AB(5) type hydrogen storage alloys (A: rare earths, B: transition metals) are extensively applied to a negative electrode of a nickel-metal hydride (Ni-MH) rechargeable battery for portable electric equipments, electric vehicles, hybrid vehicles etc. Performance of a hydrogen storage alloy electrode is affected by various factors, microstructure and surface composition of the alloy and structure of the electrode as well as composition of the alloy. Control of those factors enables us to commercialize the Ni-MH battery in various field.

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Language：English   Publishing type：Research paper (international conference proceedings)   Publisher：ELECTROCHEMICAL SOCIETY INC  

A vanadium-based solid solution type alloy V4TiNi0.65Co0.05Nb0.047Ta0.047 with a very large discharge capacity was obtained using a low cost precursor of V4Ni0.65Nb0.047 produced by alumine-thermic reduction from V2O5, Nb2O5 and nickel. The alloy was deoxidized to a low enough level by adding mischmetal as a reducing agent, when the precursor was alloyed with the other constituents of titanium, cobalt and tantalum. The alloy showed a similar hydrogen absorption behavior to an alloy prepared from high purity constituent metals. Moreover, the Mm-Ni-O phase was precipitated spherically along the TiNi network phase in the obtained alloy, remarkably improving rate capability, because of enhanced catalytic ability of the network phase.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA  

influences of carbon on microstructure and electrode properties were investigated for battery alloy V4TiNi0.65Co0.05Nb0.047Ta0.047. With increasing carbon concentration, the cycle-life of charge/discharge became longer. One of main factors that affected the cycle-life was the expansion and reduction of the (Ti,V)-based solid solution phase. Cracks yielded in TiNi phase more easily than in other phases. V-based battery alloys were more hardly pulverized than AB(5) and AB(2) intermetallic compound type materials. (C) 1999 Published by Elsevier Science S.A. All rights reserved.

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

The influence of the carbon impurity on the microstructure, hydrogen storage, and electrochemical performance of alloy V4TiNi0.65Co0.05Nb0.047Ta 0.047 were investigated by varying the weight percent of added carbon in the range of 0-1%. The hydrogen storage ability and discharge capacity were significantly decreased in the presence of a smaller content carbon. This is ascribed to the solution of carbon into the V-Ti-based main phase. A new TiC phase was clearly observed when the added carbon content was over 0.6 wt%. © 1999 Elsevier Science S.A. All rights reserved.

DOI： 10.1016/S0925-8388(99)00210-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：Elsevier BV  

Pseudobinary TiFe1 - xPdx (0.05≤x≤0.30) alloys have been investigated on their crystal structure and hydriding behavior. The lattice constant increased with an increase in the substituted amount of Pd with maintaining the CsCl type crystal structure. The partial substitution by Pd with superior catalytic and hydriding natures were effective for mitigation of their activation conditions to a considerable extent. The substitution resulted in lowering the plateau pressures ascribed to formation of the monohydride in the PCT diagrams.

DOI： 10.1016/S0925-8388(96)02925-8

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Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE SA LAUSANNE  

Enhancement of the electrochemical activity of a LaNi4.7Al0.3 electrode was observed subsequent to some charge-discharge cycles in a KOH solution containing hydrogen peroxide. Metallic nickel is enriched at the alloy surface after the treatment, and the concentration of lanthanum decreased during the treatment. The change in the distribution of elements at the alloy surface is expected to lead to a different dispersion state of nickel particles in the region, resulting in improvement of the catalytic activity for the charge-transfer process on the alloy surface.

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Language：Japanese   Publisher：The Japan Institute of Metals and Materials  

DOI： 10.2320/materia.33.356

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Language：Japanese   Publisher：日本金属学会  

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Language：Japanese   Publisher：The Japan Institute of Metals and Materials  

 Mg is hydrogenated as core-shell type hydride in which the surface is covered with MgH<sub>2</sub> (shell) and unreacted Mg remains at the internal side (core). Therefore, increase of absorption capacity to the theoretical hydrogen capacity is still one of the most important issues for the hydrogen storage materials, although several treatments were proposed to enhance their absorption capacity. In this study, the procedure of the core-shell structure as well as effect of Al concentration in Mg on the growth MgH<sub>2</sub> in Mg were investigated using pure Mg and Mg-(3-9)mass%Al-1 mass%Zn alloys (AZ). MgH<sub>2</sub> was formed on the surface as well as inside of unreacted Mg core which was apart from both gaseous H<sub>2</sub> and the surface MgH<sub>2</sub> layer. The inside MgH<sub>2</sub> was formed in a granular form on Mg grain boundary and its size increased by applying plastic deformation. Thickness of the surface MgH<sub>2</sub> and size of the internal MgH<sub>2</sub> increased with an increase in hydrogenation time until the hydride surface was completely covered with MgH<sub>2</sub>. However, the growth of the surface and internal MgH<sub>2</sub> came to a halt after the surface was covered with MgH<sub>2</sub>. The increase in Al concertation in AZ lead to decrease in thickness of the surface MgH<sub>2</sub>, prolongation of the halt time and increase in the internal MgH<sub>2</sub> grain size. From these results, supplying H from metal side was dominantly contributed for growth of the surface and internal MgH<sub>2</sub> because diffusion rate of H in Mg was much higher than that in MgH<sub>2</sub>. In addition, the growth of internal MgH<sub>2</sub> as well as control of surface MgH<sub>2</sub> can contribute to the promotion of the complete hydrogenation of Mg based hydrogen storage materials.<br>

DOI： 10.2320/jinstmet.JD201603

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Language：English   Publisher：ELSEVIER SCIENCE BV  

It is reported that nanostructured graphite, ball-milled under hydrogen atmosphere, desorbs 7.4mass% of hydrogen gas (H-2) during the temperature programmed desorption (TPD). Two remarkable peaks are observed in TPD spectrum at around 750K (peak1) and around 1000K (peak2). The mechanism how such a significant amount of hydrogen is contained in graphite is not known. We have observed that iron particles, which are introduced as impurity during ball-milling, played a significant role in the formation of hydrogenated graphite. The feature of hydrogen desorption at peak2 is similar to that of iron phthalocyanine.

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Ca-Ni based alloys were investigated on structures, hydrogenation properties and the effect of additive elements on hydrogenation properties. CaNi 3 samples were decomposed to form a new hydride with a CsCl-type structure on the constituent metal atoms at high temperatures such as 673K in a hydrogen atmosphere. The candidate of the third element which was added to stabilize the original compound was investigated by using the Miedema's semi-empirical model and, as a result, Pd was chosen. The hydrogenation of CaPd was conducted with a Sieverts' type apparatus and the synthesis of Ca-Ni-Pd ternary alloys was performed by high frequency heating.

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Language：English   Publishing type：Rapid communication, short report, research note, etc. (scientific journal)  

DOI： 10.1021/ja017121z

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Venue：Kyoto TERRSA, Kyoto, Japan  

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It was reported by Orimo and Fukunaga that mechanical grinding under hydrogen atmosphere significantly enhanced hydrogen storage capacity of graphite [1]. In order to clarify the mechanism, the effect of materials of mill pots and balls on the hydrogenation properties of graphite was investigated. Two kinds of pots and balls were used for the milling of graphite under hydrogen atmosphere of 0.6MPa; the one was made of Cr steel and the other was made of agate. The graphite prepared in Cr steel pot exhibited the hydrogen storage capacity of 2.2 mass%, indicating the enhancement of hydrogen storage capacity of graphite by ball milling, although the value was smaller than that reported (7.4 mass%) [1], whereas, interestingly, the graphite milled with agate balls in the agate pot exhibited very small hydrogen storage capacity (0.1 to 0.2 mass%). Further experiments were performed to clarify the effect of particle size and metal impurity on the hydrogen storage capacity of nano-structured graphite. The results will be reported in the Poster session in details. [1]S. Orimo, T. Matsushima, H. Fujii, T. Fukunaga, G. Majer, J. Appl. Phys., 90 (2001), 1545.

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１．水素吸蔵合金による水素の貯蔵法 (1)水素吸蔵合金の種類と特徴 ①希土類系水素吸蔵合金 ②ラーベス相水素吸蔵合金 ③BCC系水素吸蔵合金 ④その他 (2)水素吸蔵合金の技術課題と対応のポイント ①水素吸収特性に及ぼす要素 ②水素密度、安全性２．水素吸蔵合金による水素貯蔵技術の応用のポイント (1)燃料電池自動車 (2)水素ステーション (3)その他

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