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LiNiO2 with Ni defects in the 3b sites (named “Ni defected” LiNiO2) was prepared and characterized using electrochemical calorimetry. Different from conventionally prepared “Standard” LiNiO2, “Ni defected” LiNiO2 exhibited high reversibility. The 1st coulombic efficiency was recorded to be 101% due to minimization from the Ni ion substitution at the Li 3a sites. The reversible capacity was 212 mAh g−1 in the 1st cycle with 87% capacity retention after 80 cycles because Li+ ordering and Jahn-Teller distortion during the charge and discharge cycle were suppressed by introducing the Ni defect 3b sites. The proposed simple defect design concept introduced the development of a high capacity and highly reversible LiNiO2 material without metal substitutions and without increasing the charge cut-off voltage.

The hydrides of zirconium based pseudobinary alloys Zr(Co1-xTx)2, (T = Fe, V or Cr) and Zr1-xRxCo2 (R = Y, La, Pr) were synthesized under 1.2 GPa of hydrogen pressure. It was revealed that partial substitution of cobalt by V, Cr or Fe increases hydrogen absorption capacity and stability of derived hydrides. Especially, it was found that ZrCo1:8V0:2 alloy exposed to high hydrogen pressure can absorb 50% more hydrogen than pure ZrCo2 and the hydride ZrCo1:8V0:2Hy has surprisingly high stability. Substitution of zirconium by Y, La or Pr in ZrCo2 alloys improved hydrogen absorption but hydrides derived from La and Pr substituted alloys were less stable than ZrCo2H2. Only for Zr0:7Y0:3Co0:2Hy the hydrogen absorption was higher and desorption rate markedly smaller comparing ZrCo2H2.

This chapter introduces the near miss reports at Kyushu University submitted from 2007 to 2013 in terms of system- or organization-related problems due to machine functions and safety measures and human errors due to unconscious behavior, impulsive behavior, incomplete recognition and knowledge, and disregard of rules.

A powder mixture of MgH2:VH2:NaH = 6:1:n is treated under 8 GPa at 873 K using an eight-anvil apparatus in order to investigate the influence of NaH addition to Mg6VHy, a Ca7Ge-type FCC hydride. Synchrotron radiation X-ray diffraction (SR-XRD) of the obtained sample reveals that Na occupies the vacant 4b site in Mg6VHy to form Mg6VNaxHy (0 ≤ x ≤ 1) as the main product while retaining its Ca7Ge-type structure. The Rietveld analysis of the SR-XRD data suggests that the bond lengths between hydrogen and magnesium remain constant through the Na addition. All the samples reversibly desorb and absorb hydrogen at 620–630 and 590–600 K, respectively, under 0.5 MPa (H2). These temperatures are, respectively, about 70 and 120 K lower than those of MgH2. The hydrogen capacity of the main product phase, Mg6VNaxHy, is estimated to be 5–6 mass% from the pressure-composition isotherms (PCIs) by taking its content rate in the specimen into account. The reaction enthalpies calculated from the van’t Hoff relation of the PCIs do not significantly differ from that of MgH2. The bond lengths and energies between hydrogen and magnesium are not affected by the perturbation by the NaH addition in the lattice in Mg6VNaxHy.

This study is intended to determine if the capacitive properties are improved when a specific amount of crystalline ruthenium oxide (c-RuO 2 ) is added to an amorphous hydrous ruthenium oxide (a-RuO 2 ) electrode fabricated by the spark plasma sintering technique. For at the cyclic voltammetry scan rates higher than 10 mV s −1 , the capacitance of a highly pseudo-capacitive, but less electron-conductive a-RuO 2 electrode is augmented by adding 5–20 wt.% of c-RuO 2 which is less capacitive, but more electron-conductive than a-RuO 2 . The capacitance fades when more than 20 wt.% of c-RuO 2 is added because the less capacitive nature of c-RuO 2 prevails. The proximate cause of this phenomenon is the electronic conductivity, σ , of the composite electrode as we observe a maximum in σ at around a 5–20 wt.% c-RuO 2 content. The fact that c-RuO 2 is composed of smaller particles than a-RuO 2 seems to be related to the maximum σ value for a certain c-RuO 2 content of the composite electrode.

A magnesium amide-based hydrogen storage material, 3 Mg(NH2)2 + 8LiH, was subjected to cycling tests of dehydrogenation and hydrogenation, in which the cyclic trend in the hydrogen storage capacity as well as the amount of the ammonia by-product contained in the desorbed hydrogen gas were recorded. After 300 cycles at 473 K, the initial hydrogen capacity of 4.2 mass% dropped to 3.6 mass%, corresponding to the decay rate of 0.0004 per cycle. The average ammonia concentration through the 300 cycles was determined to be 0.05 ± 0.01 mol%(NH3/H2) which is entirely responsible for the hydrogen capacity decay because the ammonia emission leads to the loss of elemental nitrogen from the system. When the dehydrogenation temperature was raised to 573 K, the hydrogen capacity decay became more significant and the ammonia concentration increased to 0.27 ± 0.06 mol%(NH3/H2). The reaction kinetics also severely deteriorated during cycling at the higher temperature.

It is important to develop the hydrogen storage technology by creating novel metal hydrides. In the present study, the powder mixtures of 6MgH 2 + ZrH 2 + n AH (A = Li, Na; n = 0, 0.3, 0.7, 1.0) were reacted to synthesize quaternary hydrides by use of a high pressure technique. The crystal structures of the new hydrides were refined by the Rietveld method based on the synchrotron XRD data. By reacting 6MgH 2 + ZrH 2 + n LiH, the quaternary hydrides with simple FCC-type structure were formed. In the case of 6MgH 2 + ZrH 2 + n NaH, novel quaternary hydrides with Ca 7 Ge type structure were formed as well as the hydrides with simple FCC structure. The hydrogen storage capacities were around 6 wt.% according to the pressure-composition isotherm measurements. The formation enthalpies of the quaternary hydrides with simple FCC structure were proved to be lower while the enthalpies of the Mg–Zr–Na–H hydrides with Ca 7 Ge type structure were higher, than that of the ternary Mg–Zr–H hydride obtained by reacting the basic system 6MgH 2 + ZrH 2 . The hydrogen releasing temperatures of the quaternary Mg–Zr–A–H hydrides were slightly lower than that of the ternary Mg–Zr–H hydride.

Cobalt clusters–silica nanospheres (15–30 nm) were synthesized using a Co(NH 3 ) 6 Cl 3 template method in a polyoxyethylene-nonylphenyl ether/cyclohexane reversed micelle system followed by in situ reduction in aqueous NaBH 4 /NH 3 BH 3 solutions. The cobalt clusters are located either inside or on the outer surface of the silica nanospheres as shown by the transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The cobalt–silica nanospheres have a high catalytic activity for the hydrolysis of ammonia borane that generates a stoichiometric amount of hydrogen, and can be efficiently cycled and reused 10 times without any significant loss of the catalytic activity.

The mutagenicity of a series of the light element hydrides (containing NaAlH4, Mg(NH2)2, LiBH4, etc.) was examined by evaluating the frequency of mutation in bacterial DNAs. Although some materials were suspected to be slightly mutagenic, their effect was much less malignant than that of well-known potent mutagens. The hydrides exhibited high cytotoxicity, rather than mutagenicity. A Mg(NH2)2-related material was also subjected to a series of toxicity tests on aqueous organisms, i.e., algae, water fleas and fish. The result suggests that the material is as toxic as alkaline metal hydroxides, such as NaOH and KOH.

High hydrogen pressure technique up to 1.2 GPa has been used for synthesis of novel hydrides in RFe 2 Laves phases (R = Gd, Tb, Dy, and Ho) compounds as well as in pseudobinary ZrCo 2 − x Fe x and Y x Dy 1 − x Mn 2 Laves phases. Existence of new orthorhombic hydrides HoFe 2 H 5 , and DyFe 2 H 5 , isostructural with YFe 2 H 5 , was found, whereas GdFe 2 H 5 and TbFe 2 H 5 kept the cubic C15 lattice. Pseudobinary Zr(Fe x Co 1 − x ) 2 D y (2 ≤ y ≤ 4) hydrides were synthesized and their stability was discussed as a function of Fe/Co content. It was revealed that the formation of non-interstitial YMn 2 H 6 -type Fm-3m hydrides is possible in the whole range of pseudobinary (Y x Dy 1 − x )Mn 2 compositions.

We have developed a perovskite catalyst, (La0.7Ba0.3)(Fe0.776Nb0.194Pd0.03)O3, applicable to the NOx storage-reduction system. The perovskite catalyst exhibits 47% of NOx conversion rate at 523 K under the 54–6 s alternation of the lean–rich-burning where the lean and rich gases contain 512 ppm NO + 5 vol.% O2 and 512 ppm NO + 4 vol.% CO, respectively. The base perovskite, LaFe0.97Pd0.03O3, was endowed with a NOx adsorbing capability by partially substituting Ba for La in the A-site of ABO3 structure. Partially replacing Fe in the B-site with pentavalent transition metals (Nb, V and Ta) was also required to develop the NOx-reducing ability.

Nickel clusters contained within silica nanospheres (20–30 nm) were synthesized by using a Ni(NH 3 ) 6 Cl 2 crystal template method in a polyoxyethylene–nonylphenyl ether/cyclohexane reversed micelle system followed by an in situ reduction in aqueous NaBH 4 /NH 3 BH 3 solutions. Metallic nickel clusters exist inside the SiO 2 nanospheres prepared by the method while oxidized nickel clusters prepared by the conventional impregnation method were supported on the outer surface of silica as shown in the results of transmission electron microscope (TEM)/energy dispersive X-ray (EDX) and X-ray photoelectron spectroscopy (XPS) measurements. The nickel clusters inside of silica nanospheres show higher catalytic activity for hydrolysis of ammonia borane to generate stoichiometric amount of hydrogen than the supported nickel catalysts.

The spark plasma sintering (SPS) technique was successfully used to mold a hydrous amorphous RuO 2 electrode without any additives and binders. At the cyclic voltammetry (CV) scan rate of 1 mV s −1 , the electrochemical capacitances of the RuO 2 electrodes are 600–700 F g −1 for the entire electrode. An increase in the SPS current during the compaction led to the crystallization and dehydration of RuO 2 , which in turn, resulted in a significant decrease in its capacitance. There is room to improve the rate properties as we observed a steep drop in the capacitance when the CV scan rate was raised.

An amorphous nickel catalyst stabilized by poly(N-vinyl-2-pyrrolidone) (PVP) was synthesized by reduction in an aqueous NaBH4/NH3BH3 solution. Both the bare nickel catalyst and the PVP stabilized nickel catalyst contain grains with an amorphous structure after the reduction. The PVP stabilized nickel catalyst maintains high activity for hydrolysis of NH3BH3 to generate a stoichiometric amount of hydrogen with the cycle number up to 5, while the reaction rate in the presence of the bare nickel catalyst decreases with cycle number. After five cycles, the PVP stabilized nickel catalyst maintains the amorphous structure, while the agglomeration of nickel in the bare nickel catalyst is observed. The results indicate that PVP prevents agglomeration and crystallization of nickel nanoparticles, leading to higher durability than the bare nickel catalyst.

Hydrogen storage materials containing NaAlH 4 , LiNH 2 , Mg(NH 2 ) 2 , LiH and LiBH 4 were subjected to standardized safety tests in order to assess the potential hazards caused by the environmental exposure of these materials. All the materials were judged ‘flammable’, ‘pyrophoric’ and ‘water-reactive’, resulted in being classified as the United Nations Packing Group I, the most stringent category of container regulations in transporting these materials. A small spark energy (1.4 mJ) can trigger an intense dust cloud explosion of the Mg(NH 2 ) 2 + LiH system of which the minimum explosive concentration was determined to be 90 mg dm −3 . Although this value is lower than those of the hydrogen storage alloys, the minimum explosive concentration of complex hydrides can be comparable to the alloys if expressed in terms of the amount of stored hydrogen in the material. Also examined was the eruption test, a non-standard test, in which the sample powder was pushed out of a container into the atmosphere by pressurized H 2 . Despite the pyrophoricity, we observed only one explosion of the Ti-doped NaAlH 4 in dozens of trials using all the materials. A comparison with other materials points to the inevitability of more cautious measures than metal hydrides when handling these complex hydrides.

The difference in capacitive performance between high and low surface area RuO 2 electrodes, synthesized with and without a mesoporous silica template, respectively, was investigated in aqueous solutions of sulfuric acid and sulfates by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). RuO 2 synthesized with the template was crystalline and the formation of the mesoporous structure with a 6.5 nm diameter was confirmed using a transmission electron microscope and the nitrogen adsorption and desorption isotherm. From the CV at the scan rate of 1 mV s −1 , the specific capacitance of the high surface area electrode in H 2 SO 4 (aq) was determined to be 200 F g −1 . The high surface area RuO 2 has a three times higher BET specific surface area (140 m 2 g −1 ) than the low surface area sample (39 m 2 g −1 ). Introducing the mesoporous structure was proved effective for increasing the capacitance per mass of the RuO 2 , though not all the surface functions as a capacitor. Both the CV and EIS suggest that by increasing the charging rate or frequency, the mesoporous structure of the electrode leads to a lower capacitance decrease (higher capacitance retention) than the low surface area electrode. The EIS also indicates that the response time of the capacitor is hardly influenced by the presence of the mesoporous structure.

Boron- and nitrogen-based chemical hydrides are expected to be potential hydrogen carriers for PEM fuel cells because of their high hydrogen contents. Significant efforts have been devoted to decrease their dehydrogenation and hydrogenation temperatures and enhance the reaction kinetics. This article presents an overview of the boron- and nitrogen-based compounds as hydrogen storage materials.

The electrochemical behavior of ammonia borane on an Au electrode in the absence and presence of thiourea (TU) was detailedly investigated by cyclic voltammetry (CV). In the absence of TU, the feature of the CV is fairly complex affected by both the hydrolysis and the direct oxidation of ammonia borane. With the aid of TU, known as an effective inhibitor for the formation and recombination of adsorbed H radicals associated with ammonia borane hydrolysis, the two peaks at 414 and 0 mV may be attributed to direct electrooxidation of ammonia borane at Au electrode. These two peaks are particularly important for the practical direct ammonia borane fuel cell (DABFC). Additionally, the Tafel slope (b ¼ 0.15 V) and charge transfer coefficient (a ¼ 0.604) were obtained as well as number of electrons exchanged (n ¼ 2) in the ammonia borane oxidation at the Au/solution interface in the presence of TU.

The hydrogen desorption and absorption cycles of the LiNH 2 –LiH system were investigated. We have devised a method to simultaneously measure the hydrogen capacity and the amount of ammonia emitted from the system as a by-product during the hydrogen desorption. The initial hydrogen capacity of ca. 5 mass% exponentially decreased to ca. 2 mass% after 200 cycles at 573 K in which one cycle comprises the hydrogen desorption in vacuo for 3 h and the hydrogen absorption under 3 MPa of pure hydrogen for 2 h. The ammonia concentration in the desorbed hydrogen gradually increased with repeated cycling and abruptly dropped by re-mixing the sample after 100 cycles. By comparing the observed decay rate in hydrogen capacity with the mean ammonia concentration of 0.24 ± 0.05 mol%(NH 3 /H 2 ), we found that about half the decay in hydrogen capacity can be explained by the loss of the constituent nitrogen due to the ammonia emission.

The electrochemical behavior of the novel fuel cell directly using aqueous ammonia borane (NH3BH3 )a s the fuel has been systematically investigated. The cell consists of an oxygen cathode and an ammonia borane solution fed anode, where the catalyst layers are made of Vulcan XC-72 with 46.6 wt.% Pt. An anion exchange membrane is employed as the electrolyte. It is found that the concentrations of NH3BH3 solution and temperatures significantly affect the open circuit potentials of the anode as well as the cell performance. Although the cell voltages decrease with the increase of current densities, the cell is capable of discharging at a current density of 185 mA cm −2 with the cell potential larger than 0.6 V. The obtained high energy densities indicate that the direct ammonia borane fuel cell holds potential applications for portable devices. © 2008 Elsevier B.V. All rights reserved.

Micro/nano-structures and hydrogen storage properties of Mg/Cu super-laminates were investigated. Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473 K. In order to clarify the process of hydrogenation and dehydrogenation at 473 K, we performed TEM observations of micro/nano-structures of the Mg/Cu super-laminates and Mg2Cu powder prepared by conventional casting method. TEM observations revealed that the as-rolled Mg/Cu super-laminates had laminated structures in size of sub-micrometer thickness composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation kept laminated structures and had uniformly distributed pores with a sub-micrometer diameter. On the other hand, the cast Mg2Cu powder after initial activation had pores only beneath the surface oxide layers. It is considered that these micro/nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics, which would contribute to achieve high-performance hydrogen storage materials.

Mesoporous and worm-like In2O3 catalysts have been prepared using KIT-6 and MCM-41 silicas as templates, which show low crystallinities and high surface areas. Compared with commercial In2O3 catalyst with low surface area, these two nano-structured In2O3 catalysts exhibit higher catalytic activity for steam reforming of ethyl alcohol at low temperature to produce hydrogen containing no detectable CO impurity, presenting an advantage in comparison with the previous reported catalysts.

We investigated at 423 K in vacuo the hydrogen desorption kinetics of Ti-doped sodium aluminum hydride ( NaAlH 4 ) prepared with using different Ti precursors and procedures. Initial distinction in kinetics among specimens vanishes through several cycles of dehydrogenation at 473 K in vacuo and rehydrogenation at 423 K under 10 MPa of H 2 . Considering that the temperature of dehydrogenation cycle is above the melting point of NaAlH 4 , 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.

In order to improve the hydrogenation property of Mg/Ti laminate composite, Ni was added as a third element. Hydrogen storage properties of the laminated Mg/Ti/Ni alloy films were studied. Laminated Mg/Ti/Ni multilayer alloy films were prepared by cold rolling of stacked Mg, Ti and Ni under ambient conditions. The stacked foils were subjected to repetition of rolling and stacking, resulting in super-laminated foils with the thickness less than 0.3mm, containing more than 15000 layers. Microstructures of the super-laminates were studied by scanning electron microscopy and X-ray diffractometry. Their hydrogenation behaviors were investigated by use of a Sieverts type apparatus. The hydrogen storage capacity (H/M) of the laminate with composition Mg/Ti/Ni=9.0/0.9/0.1 amounted H/M=1.6 at 573K, 0.4MPa. Initial activation property was improved by controlling the amount of Ni appropreately.

Ti-Cr-V alloys with body-centered cubic (BCC) structure were investigated on hydrogen absorbing-desorbing cyclic durability by using H2 without and with several concentrations of CO (Hereafter, they are described as pure H2 and n ppm CO, respectively.). The alloy which offers the excellent durability except the early stages of cyclic absorption-desorption under pure H2 atmosphere gave good durability also in a flow of low concentration of CO. However, capacities’ degradation curves under high CO concentration reflected that duration and concentration effects competed with each other. The results suggests to be able to express each degradation by intrinsic and extrinsic factors as an aggregation of several prime functions.

Mg-based laminate composites prepared by a repetitive-rolling method have a large hydrogen capacity as well as good kinetics and reversibility for hydrogen reaction. Mg/Pd laminate composite (Mg/Pd=6) can absorb a large amount of hydrogen up to 1.47 H/M (4 mass%), and desorb hydrogen reversibly at 573K. In this study, we investigated the mechanism of phase transition of the Mg/Pd laminate composites during hydrogenation/dehydrogenation by means of in-situ XRD measurements. In Mg/Pd laminate composite (Mg/Pd=6), the XRD profile of as-rolled sample indicated the existence of Mg and Pd within the detection ability of our XRD equipment. Mg6Pd intermetallic compound are formed during initial activation process. The Mg6Pd intermetallic compound can store hydrogen reversibly through the disproportionation and recombination processes.

Microstructures and hydrogen storage properties of Mg-Al super laminate composite alloys were investigated. The laminated sample was made by alternately stacking Mg films and Al films. The laminate was subjected to repetition of stacking and cold-rolling under an ambient condition (super lamination technique), combined with final heat treatment under an argon gas atmosphere. The number of films and thickness was nearly 15000 layers and about 50μm, respectivery. Their microstructures and hydrogen storage properties were studied by scanning electron microscopy, X-ray diffractometry and volumetric method by use of a Sieverts-type apparatus. In heat treatment process at 673K, Mg17Al12 intermetallic compound was formed by interdiffusion. This compound absorbed and desorbed hydrogen reversibly through the disproportionation and recombination react at 673K.

Super-laminates have been attracting attention since co-authors Ueda et al. reported that Mg/Cu super-laminates showed reversible hydrogenation and dehydrogenation at 473K. The Mg/Cu super-laminates were prepared by a repetitive fold and roll method. Initial activation at 573 K led the super-laminates to absorb hydrogen at 473K. TEM observations of micro/nano-structures in the super-laminates and Mg2Cu powder were performed in order to clarify the process of hydrogenation and dehydrogenation at 473K. The as-rolled Mg/Cu super-laminates have laminated structures in size of sub-micrometer thickness composed of Mg and Cu layers with dense lattice defects. The super-laminates after initial activation keep laminated structure and have uniformly distributed pores with a sub-micrometer diameter. It is considered that these micro/nano-structures of Mg/Cu super-laminates lead to lower dehydrogenation temperature and better kinetics.

From both the experimental and theoretical aspects we have investigated the cycle durability against CO and degradation mechanism of the LaNi5 hydrogen storage alloy with CO-containing H2. Temperature-programmed desorption (TPD) measurements on the pristine alloy and the corresponding one after hydrogen absorption–desorption cycles exhibit that: (1) the molecular CO can be adsorbed on the clean alloy surface, and thus decrease the hydrogen storage ability of the alloy; (2) with the increase of the cycle number the partial decomposition of the CO and the subsequent adsorption of C atom and O atom on the surface is deleterious to the hydrogen storage competence of alloy. From the results of first-principle calculations, it is found that the adsorption of the molecular CO prefers the on-top and bridging sites on the Ni atoms. Moreover, the latter one is more stable than the former one.

Ammonia-borane (NH 3 BH 3 ), as a source of protide (H − ), is initially proposed to release its energy through a fuel cell (direct ammonia-borane fuel cell, DABFC). Cell performance has been elucidated in a 25 cm 2 laboratory cell constructed with an oxygen cathode and an ammonia-borane solution fed anode, where the catalyst layers are made of Vulcan XC-72 with 30 wt.% Pt. The potential is 0.6 V at the current density of 24 mA cm −2 , corresponding to power density >14 mW cm −2 at room temperature. The direct electron transfer from protide (H − ) in NH 3 BH 3 to proton (H + ) has been further proved by the open circuit potential and the cyclic voltammetry results, which show the possibility of improvement in the performance of DABFC by, for example, exploring new electrode materials.

The adsorption and dissociation of H2 on the Na2O (110) surface have been studied with the first-principles molecular dynamics method. It is found that the adsorption configuration is energetically...

We present electrochemical properties of lithium alanate (LiAlH4) dissolved in aprotic ethers – diethyl ether (Et2O) and tetrahydrofuran (THF) – under an Ar atmosphere of 1 atm at 298 K. Specific conductivities of both LiAlH4–THF and LiAlH4–Et2O solutions are measured by AC four-terminal method. Cyclic voltammetry is performed with using a beaker-type electrochemical cell consisted of a Ni wire, Ni mesh and Li wire as a working, counter and reference electrode, respectively. In order to clarify the electrochemical behavior, anodic polarization of LiAlH4–THF solution is measured. The current density of 1.0 M LiAlH4–THF solution reaches to 1 A cm−2, which is higher than the LiAlH4–Et2O solution. Quantitative analysis of H2 gas generated on the working electrode during the potentiostatic electrolysis tells that the number of electrons involved in the anodic reaction at the limiting current is one in case of the LiAlH4–THF solution. We propose conceivable electrochemical reactions of LiAlH4 in the non-aqueous ethereal solutions.

In this article, we propose a novel hydrogen storage system which has both lightness and compactness a combination of a lightweight high pressure vessel and hydrogen storage alloy. The system is expected as a promising formation to improve the properties of hydrogen storage techniques in weight and volume other than the conventional techniques using compressed hydrogen or hydrogen storage alloy individually. The novel system requires a hydrogen storage alloy with higher volumetric hydrogen density as well as higher gravimetric density, and with higher equilibrium dissociation pressure than the hydrogen storage alloys which have ever been used for hydrogen storage systems.

The reaction of cadmium(II) perchlorate with urocanic acid under different conditions created three novel coordination compounds: [Cd2(L2)2-(L3)2(H2O)8] (1), {[Cd(L)(L2)](H2O)(1/2)}n (2), and {[Cd(L3)2](H2O)(3/2)(EtOH)}n (3), in which L, L2, and L3 are three urocanate tautomers. Complex 1 consists of two separate mononuclear units with different urocanate tautomers, which self-assemble into a 3D hydrogen-bonding network constructed by alternating 2D layers, whereas complexes 2 and 3 self-assemble into 3D alpha-polonium and four-fold interpenetrated diamondoid networks, respectively. The tautomerism of the urocanate ligands and the enormous structural diversity of their complexes are present in this system, which illustrates that the reaction temperature, pressure, and the metal ions themselves act cooperatively to tune the tautomerism of the ligands and the frameworks of their metal coordination compounds. The fluorescence-emission and nitrogen-adsorption properties of these complexes are also investigated.

Sodium oxide, Na2O, reversibly absorbs hydrogen, H2, to form sodium hydride, NaH, and sodium hydroxide, NaOH, which possesses a potential to find its application to reversible hydrogen storage. X-ray diffraction measurements illustrate reversible phase and composition changes during the hydrogen absorption and desorption in the Na–O–H system. Pressure–composition (P–C) isotherm and thermogravimetric (TG) measurements exhibit a hydrogen capacity up to 3.0 wt.%. Temperature-programmed desorption (TPD) measurements demonstrate that mixing NaOH to NaH significantly shifts the hydrogen desorption of NaH towards lower temperature, to which TiCl3 and SiO2 show catalytic activity. A reaction intermediate, Na H δ − ⋯ H δ ′ + ONa , involving dihydrogen bonding between the negatively charged hydrogen atom bonded to sodium and the positively charged hydrogen atom bonded to oxygen is proposed for the reaction mechanism.

It is known that a certain titanium species enhances the dehydrogenation 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.

We have investigated the hydrogenation and dehydrogenation properties of binary RNi5 (R: La, Pr, Nd, Sm, Gd, Tb 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 ( β 2 and γ 2 phases) and then three hydrides ( β 3 , γ 3 and δ 3 phases). The β 3 – γ 3 and γ 3 – δ 3 phase transitions in the TbNi5–H system corresponded, respectively, to the α 2 – β 2 and β 2 – γ 2 transitions in the RNi5–H (R: Pr, Nd, Sm and Gd) systems having two plateaux.

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 (α) and three kinds of hydride (β, γ and δ). Below H/DyNi5 = 1.0, the first α–β phase transition appears with large hysteresis, whereas the second β–γ and third γ–δ 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 ∝ H/DyNi5. This complex behavior of P–C isotherm is reversible.

V- and Ti-Cr-based solid solutions with body-centered cubic (BCC) type structure were investigated on hydrogen absorbing-desorbing cycle durability by using H2 without and with 10ppm CO (Hereafter they are expressed as H2 and CO/H2, respectively.). The solid solutions showed excellent cycle durability even after 1,000 cycles of hydrogen absorption and desorption under H2 atmosphere. On the other hand, the capacities decreased rapidly during hydrogen absorbing-desorbing cycles in the beginning of the tests under CO/H2 one. The solutions were not disproportionate though the stable monohydride phase increased, that is, stored hydrogen increased gradually. It was observed that not only microscopic pulverization but also nanoscopically fine-grained crystallization occurred in degraded particles. It is considered that the impurity CO influences bulk structure as an intrinsic factor as well as surface area as an extrinsic factor as regarded as ever. This causes the degradation of the cycle capacities.

In order to obtain information about the hydrogenation properties of Zr-rich Zr 7 Ni 10 with orthorhombic Pbca symmetry, which can help to understand the mechanism of the unusual hydrogenation properties of stoichiometric Zr 7 Ni 10 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 Zr 7 Ni 10 was quite narrow compared with the solubility range published in a binary phase diagram and the Zr 7 Ni 10 compound with the tetragonal structure, which can also be obtained by hydrogenation to form the corresponding hydride Zr 7 Ni 10 H 17 followed by dehydrogenation, was formed in the quenched samples prepared by procedure 3. The solubility of Zr 7 Ni 10 and its phase stability are discussed.

The C14 intermetallic TiCr 1.9 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 TiCr 1.9 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.

We investigated the pressure–composition ( P – C ) isotherms of several binary RNi 5 (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 RNi 5 compounds have similar P – C isotherms with two well-separated plateaux except for CeNi 5 , indicating that two hydrides with compositions of RNi 5 H 3–4 and RNi 5 H 6–7 are formed. With increasing the atomic number of R element in the RNi 5 compounds, the unit cell volume decreases due to the decrease of the radius of the R element. This influences the absolute enthalpies of dehydrogenation |Δ H | of both hydrides (β and γ) to decrease, which consequently leads to the increase of the second plateau pressure as well as the first plateau. Contrary to LaNi 5 –H 2 system, the |Δ H | of γ hydride is smaller than that of |Δ H | of β 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 |Δ H | value approaches to zero.

The cycle durability of Ca–Mg–Ni hydrogen storage alloys, which are investigated in the Japanese national project (International Clean Energy Network), WE-NET, was examined using pure H2 (99.99999%). The tested alloys were Ca0.25Mg0.66Y0.09Ni1.86 (cubic MgCu2-type structure), Ca0.55Mg0.45Ni3 (rhombohedral PuNi3-type) and Ca0.5Mg0.5Ni2 (MgCu2-type). Although initially the ‘dynamic’ hydrogen storage capacities were H/M ∼0.7, they decreased steeply within a few cycles, and then they declined gradually. At around 400th cycle, they decreased to nearly half of the maximum capacities regardless of crystal structures and compositions of the tested alloys. However, their ‘equilibrium’ capacities did not decrease as the ‘dynamic’ ones with progress of hydrogen sorption. As for the bulk, not serious disproportionation but pulverization and lattice expansion were observed by X-ray diffractometry (XRD) and microscopic analyses. The expansion indicated that some amounts of hydrogen remained in the lattice cells. It was considered that pulverization of the alloy particles and amorphous shell formed on the surface prevented the alloys from smooth hydrogen sorption, and which led to the decrease of the ‘dynamic’ hydrogen storage capacities without that of the ‘equilibrium’ ones in the cycle tests.

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, Fe 3 C, 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.

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 (RL = La, Pr, Nd and Sm) compounds both lattice constants of RHNi5 compounds decrease with increasing the atomic number of RH element due to the lanthanide contraction. On the pressure-composition (P-C) isotherms, GdNi5-H2 system shows two well-separated pressure plateaux qualitatively similar to RLNi5-H2 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 (pP1) 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 � 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.

Pressure-composition (P-C) isotherms of RNi5-H (R = Pr, Nd, Sm and Gd) systems show two hydrogen pressure plateaux during hydrogen absorption and desorption. These correspond to the transitions among three phases: one hydrogen solid solution (� phase; RNi5H� 0:5) and two hydrides (� phase; RNi5H3� 4 andphase; RNi5H5� 7). To explore the mechanism of the phase transitions, we investigated the structural changes in RNi5-H systems with ex-situ XRD. During hydrogen desorption, the ex-situ XRD profiles show that the crystal structures in RNi5-H systems change from hexagonal (� phase) through monoclinic (� phase) to hexagonal (� phase). The temporary decrease in structural symmetry may be due to hydrogen occupation except in the basal plane of the crystal structure. Lattice expansion between theandphases normalized in the monoclinic structure decreases slightly with the increasing atomic number of R in RNi5-H systems. Similarly to the correlation between the first plateau pressure and the unit cell volume of thephase, the second plateau pressure is logarithmically related to the unit cell volume of the � phase. As far as the RNi5-H (R: from La to Gd except Ce) system is concerned, we can empirically predict the second plateau pressure as well as the first plateau pressure from the unit cell volume of the alloys.

Zr7Ni10 has three hydrogen occlusion phases, α, β and γ, and the following unusual features are known for the phase transitions in the Zr7Ni10–H2 system: (1) The intermediate hydride phase (β) appears only during dehydrogenation but not during hydrogenation, and (2) The continuous hydrogen solid solution phase (α) 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 α 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 α phase, which undergoes hydrogenation followed by dehydrogenation, is different from that of its pure metal phase, where the crystal structure of the dehydrogenated α 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 α 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 (γ). 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.

NaAlH4 is considered as a promising material for onboard storage of hydrogen. It is generally thought that high temperature (>120 °C) and high pressure (>15 MPa) are needed for rehydrogenation of dehydrogenated NaAlH4. However, for practical application, reducing the rehydrogenation temperature and pressure as much as possible would be highly desirable. We have found that the dehydrogenated NaAlH4, in either the undoped or titanium-doped state, can be rehydrogenated at temperatures of 25−120 °C and pressures of 2−12 MPa. This finding is confirmed by the subsequent dehydrogenation at 160 °C. In addition to that, after rehydrogenation under the same conditions, the amount of evolved hydrogen from the titanium-doped NaAlH4 was much higher than that of the undoped NaAlH4. This clearly indicates that the addition of titanium species enhances kinetically not only the dehydrogenation, but also the reverse process, the rehydrogenation reaction of the dehydrogenated NaAlH4.

Deterioration behavior of an electrode made of V 4 TiNi 0.65 Co 0.05 Nb 0.047 Cr 0.058 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.

The effect of mechanical grinding on phase transformation in Ti–Cr alloys with nominal compositions of TiCr 2− 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.