Hydrogen Pressure-composition Research Articles

Hydrogenation and structural properties of Gd2Ni7 with superlattice structure

The crystal structure and hydrogenation properties of Ce2Ni7-type Gd2Ni7 were investigated by X-ray diffraction (XRD) and the hydrogen pressure–composition (P–C) isotherm. Ce2Ni7-type Gd2Ni7 was obtained by annealing at 1523 K for 12 h and quenching in ice water. Two superlattice reflections (002 and 004) of the Ce2Ni7-type were clearly observed at 2θ = 7.3° and 14.6° in the XRD profile. The refined lattice parameters were a = 0.49662(9) nm and c = 2.4255(3) nm, respectively. Two plateaus were clearly observed during the absorption–desorption process in the P–C isotherm. The first and second plateaus were at 0.015 and 0.13 MPa, respectively, in the first desorption. The maximum hydrogen capacity reached was 1.13 H/M. The enthalpy and entropy were calculated as −20 kJ/mol H2 and −80 J/mol H2 K, respectively, from the van’t Hoff plot. After the P–C isotherm, the GdNi5 cell expanded by 2.15%, but the Gd2Ni4 cell shrank by 2.83%.

Nanosize-Induced Hydrogen Storage and Capacity Control in a Non-Hydride-Forming Element: Rhodium

We report the first example of nanosize-induced hydrogen storage in a metal that does not absorb hydrogen in its bulk form. Rhodium particles with diameters of <10 nm were found to exhibit hydrogen-storage capability, while bulk Rh does not absorb hydrogen. Hydrogen storage was confirmed by in situ powder X-ray diffraction, solid-state (2)H NMR, and hydrogen pressure-composition isotherm measurements. The hydrogen absorption capacity could be tuned by controlling the particle size.

Lattice defects introduced into LaNi 5-based alloys during hydrogen absorption/desorption cycling

LaNi 5-based intermetallic compounds before and after hydrogen absorption/desorption cycling were observed by transmission electron microscopy. Both a-type and c-type dislocations, which had respective Burgers vectors of 1 / 3 < 1 1 2 ¯ 0 > and <0 0 0 1> in the { 0 1 1 ¯ 0 } slip plane, were introduced into LaNi 5, LaNi 4.5Cu 0.5 and LaNi 4.5Fe 0.5 after the first absorption/desorption cycle. These alloys exhibited large difference in the equilibrium pressure between the first absorption and first desorption. Dislocations were introduced during hydrogenation in order to accommodate lattice mismatch between the metal-hydrogen solid solution and the metal hydride; furthermore, the interface between the solid solution and hydride was suggested to be the { 0 1 1 ¯ 0 } plane. In contrast, neither dislocations nor stacking faults were observed in LaNi 4.5Si 0.5, LaNi 4.5Al 0.5 and LaNi 4.75Sn 0.75, which showed little or no hysteresis in the hydrogen pressure–composition isotherms. Excess pressure was needed in the absorption process for the formation of misfit dislocations.

Hydrogen Absorption and Desorption in Nanocrystalline LaMg2Ni.

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Formation region and hydrogen storage abilities of perovskite-type hydrides

Abstract Formation region and hydrogen desorption and absorption properties of the perovskite-type structure in Li x Na 1− x MgH 3 with x = 0, 0.17, 0.33, 0.50 and 1.00 were studied in the present work. The experimental results are reasonably explained from the viewpoint of the geometric restrictions of ions that are described by so-called Goldschmidt tolerance factors. In NaMgH 3 ( x = 0), two plateau pressures of about 0.040 and 0.15 MPa were clearly detected by hydrogen pressure–composition ( p – c ) isotherm measurement at 673 K. Moreover, NaMgH 3 can be reversibly formed in 1.0 MPa of hydrogen at 673 K, from the decomposed phase of elemental Na and Mg.

Hydrogen absorption and desorption in nanocrystalline LaMg 2Ni

Hydrogen absorption and desorption properties in LaMg 2Ni compound are presented. Nanostructured phases have been obtained by means of ball milling in order to study the influence of the microstructure on the absorption/desorption properties. The structural and hydriding properties were examined by X-ray diffraction, thermal analysis, hydrogen pressure–composition and thermal desorption measurements. Ball milling of as-cast compound gives a significant refinement of the microstructure. Hydrogenation at 443 K leads to the formation of LaMg 2NiH 7, but at higher temperatures (523 K) LaH 2 is produced. Two hours of ball milling promote the formation of LaH 2 under hydrogenation at 443 K. Thermal desorption up to 983 K of hydrogenated samples leads again to parent LaMg 2Ni phase.

Hydrogenation characteristics of Ti 2Ni and Ti 4Ni 2X (X=O, N, C)

Ternary Ti 4Ni 2X (X=O, N, C) compounds and a binary Ti 2Ni 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 Ti 4Ni 2X 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 Ti 2Ni one. These four Ti 2Ni-based compounds and their corresponding hydrogen occlusion ones were discussed in terms of their relative thermal stability.

Hydrogenation equilibria characteristics of LaNi5−xZnx intermetallics

Abstract A series of metal hydride alloys were prepared based on the LaNi 5 formula, by substituting 0, 5, 10, 15 and 20 at.% of Zn for Ni. The obtained pseudobinary LaNi 5− x Zn x alloys have been characterized by X-ray diffraction patterns and hydrogen pressure–composition–temperature ( PCT ) diagrams at temperatures ranging from 293 to 353 K. The P – C isotherms were used to determine thermodynamic functions (enthalpy and entropy) for the hydrogen desorption process. Increasing Zn substitution causes the unit cell volume to increase and the plateau pressures to decrease. The maximum concentration of hydrogen in the tested La(Ni,Zn) 5 alloys slightly decreases with increasing Zn content.

Structural and hydriding properties of (Mg 1− xAl x)Ni–H(D) with amorphous or CsCl-type cubic structure ( x=0–0.5)

The amorphous phase is formed in (Mg 1− x Al x )Ni with x=0–0.2, while the crystalline phase of a CsCl-type cubic structure is formed with x=0.3–0.5 even in the as-mechanically-alloyed states. The total radial distribution functions for X-ray and neutron diffractions show that deuterium in MgNi, that is, x=0, occupies the interstitial tetrahedral site composed of nearly 2Mg2Ni. Electrochemical P– C (hydrogen pressure–composition) isotherm measurements revealed that there is an obvious miscibility-gap pressure higher than 10 −4 MPa at room temperature even in MgNi, and that the pressure increases by the Al substitution.

Gas-phase H 2 absorption and microstructural properties of LaNi 5− xGe x alloys

Metal hydride alloys were prepared based on the LaNi 5 formula by substituting 0–10 at.% of Ge for Ni. Crystal lattice parameters were obtained from X-ray diffraction patterns of each alloy. Hydrogen pressure–composition–temperature isotherms were measured for these LaNi 5− x Ge x (0≤ x≤0.5) alloys at temperatures ranging 296 to 348 K. These isotherms were used to determine thermodynamic parameters for hydrogen absorption and desorption. The unit cell volumes increase, and the plateau pressures decrease, with increasing Ge substitution. Isotherms and capacities from gas-phase absorption are comparable to those of LaNi 5− x Sn x .