Nobuhiro Kuriyama

X-ray diffraction studies of titanium and zirconium doped NaAlH4: elucidation of doping induced structural changes and their relationship to enhanced hydrogen storage properties

Abstract 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.

“Hybrid hydrogen storage vessel”, a novel high-pressure hydrogen storage vessel combined with hydrogen storage material

Abstract 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.

Electrochemical Impedance Spectra and Deterioration Mechanism of Metal Hydride Electrodes

Electrochemical impedance spectrum of a metal hydride electrode was interpreted by an equivalent circuit including a reaction resistance on the alloy surface, a contact resistance between the current collector and the pellet, one related to alloy particle‐to‐particle contact, and a Warburg impedance. According to the interpretation, deterioration of a metal hydride electrode using copper‐coated alloy powder was found to be caused by passivation of the alloy surface only. On the other hand, deterioration of an electrode using uncoated alloy was dominated by increase of the contact resistances.

Phase structure of V-based solid solutions containing Ti and Ni and their hydrogen absorption-desorption properties

Abstract Crystal structures and pressure-composition isotherms were investigated for the vanadium rich ternary TiVNi solid solution. The alloy containing more than 85at.% vanadium absorbed hydrogen of 1.6 in H/M ratio that amounted to 3.2 mass% H. The pressure-composition isotherm for Ti 22 V 66 Ni 12 in the hydrogen pressure range of 10 0 to 10 −8 MPa was obtained by the electrochemical method. Two pressure plateaus were found at hydrogen pressures of 10 −2 MPa and 10 −6 MPa. The upper plateau would be ascribed to the reaction from dihydride to monohydride and the lower plateau would be ascribed to the reaction from monohydride to solid solution of the alloy and hydrogen.

Hydrogen Storage Alloys for Nickel — Metal Hydride Battery*

— 2 times higher energy density per unit volume and longer cycle life than Ni —Cd cells with almost comparable rate capability and charge retention. A very unique feature of the hydrogen battery is a self-protective mechanism for overdischarge. The hydrogen produced on the nickel electrode is absorbed on the MH electrode and then oxidized to water, keeping the cell voltage around —0.2 V. No oxidation and degradation of alloy occurs during overdischarge if the recombination reaction is fast enough to keep up with the discharge rate. This good overdischarge protection is very advantageous for the series stacking of many cells, i.e., for high voltage applications such as electric vehicles (EV) [6]. Secondly, AB5 (A = rare earth, Zr, B = Ni, Co, Fe, Mn, Al) and AB2 (A = Ti, Zr, B = Ni, V, Fe, Co, Mn, Al) type alloys do not contain hazardous materials, being safe from the standpoint of environmental and safety regulations [7].

Hydrogen adsorption in carbonaceous materials

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.

The TiV3Ni0.56 hydride electrode: its electrochemical and cycle life characterization

Abstract Charge/discharge cycle tests for the TiV 3 Ni 0.56 electrode were conducted in order to investigate the processes of activation and deterioration. Cracking formation was observed to occur across the alloy grain during the activation process. After a few more cycles following the activation, smaller cracks were observed between the matrix and a secondary phase and also within the secondary phase. In the deterioration process titanium and vanadium were found to dissolve selectively from both phases. When the electrode lost its discharge ability, titanium and vanadium in the secondary phase had almost disappeared, leaving the nickel layer, while the matrix phase still retained the original composition and hydrogen storage ability.

Structure and related properties of (La,Ce,Nd,Pr)Ni5 alloys

Abstract The effects of substitution of La by Ce, Nd and Pr in the LaNi5-based alloys were systematically studied, with the use of factorial analysis. The changes of equilibrium pressure, hydrogen capacity and hysteresis were analyzed in relation to the structure changes of the hexagonal unit cell of (La,Ce,Nd,Pr)Ni5. Both individual effects of each alloy component, and their interaction in the alloy were studied. It has been shown that variations in the basal plane parameter (a) can be used as an indication for the plateau pressure changes resulting from substitution, giving better fits than variations in the unit cell volume. Structural anisotropy is discussed as a possible tool for the prediction of the decrepitation resistance of the alloy. Methods for optimization of the electrode alloys (including reduction of the cobalt content) are proposed.

Hydrogenation characteristics of ternary alloys containing Ti4Ni2X (X=O, N, C)

Abstract Ti 2 Ni-based alloys containing oxygen, nitrogen and carbon were investigated regarding their metallographic structures and hydrogenation characteristics. The alloy samples containing these non-metal elements had multi-phase structures composed of Ti 4 Ni 2 X, TiNi and TiX (X=O, N, C) phases. The ternary alloy samples reversibly absorbed and desorbed hydrogen under moderate conditions such as room temperature and atmospheric pressure. The hydrogenation properties of the alloy samples containing the non-metal elements were compared with those of the binary Ti 2 Ni compound.

Effects of mechanical grinding on the hydrogen storage and electrochemical properties of LaNi5

Abstract LaNi5 powders were mechanically ground under argon atmosphere. After 2 h of milling, a limit particle size of 1.5 μm was obtained. This powder was easily activated under hydrogen atmosphere and the time for a 90% maximum hydrogen uptake was found to be close to that of the unmilled powder. The first hydrogenation cycle of the milled powder shows a strong slope indicating the presence of several hydrides. The hydrogenated ground powder was stabilized with a carbon monoxide surface treatment that markedly slows down the desorption kinetics. From the ball milled and hydrogenated powder, the formation of the intermediate phase LaNi5Hx with x≈3 is observed, contrarily to what is found with hydrogenated but unground powders, such a different behavior was questioned in terms of electrochemical conditions, as milled or unmilled LaNi5 powders are intensively used as the negative electrode of reversible metal hydrogen batteries. The unmilled but activated LaNi5 electrode exhibits the lowest discharge capacity but the best cycle life time (loss of only 5% of the discharge capacity after 50 cycles). The powder milled for only 1 h before activation does not present any intermediate hydride and shows a better discharge capacity. The best performance is obtained for the powder containing the intermediate phase with a discharge capacity of 307 mA h g−1. Nevertheless, the loss in capacity after 50 cycles is large (24%).