M. Latroche

Hydrogen adsorption in the nanoporous metal-benzenedicarboxylate M(OH)(O2C–C6H4–CO2)(M = Al3+, Cr3+), MIL-53

Hydrogen adsorption has been studied in the nanoporous metal-benzenedicarboxylate M(OH)(O2C-C6H4-CO2) (M = Al3+, Cr3+); these solids show a hydrogen storage capacity of 3.8 and 3.1 wt.% respectively when loaded at 77 K under 1.6 MPa.

The Kagomé Topology of the Gallium and Indium Metal-Organic Framework Types with a MIL-68 Structure: Synthesis, XRD, Solid-State NMR Characterizations, and Hydrogen Adsorption

The vanadium-based terephthalate analogs of MIL-68 have been obtained with gallium and indium (network composition: M(OH)(O(2)C-C(6)H(4)-CO(2)), M = Ga or In) by using a solvothermal synthesis technique using N,N-dimethylformamide as a solvent (10 and 48 h, for Ga and In, respectively, at 100 degrees C). They have been characterized by X-ray diffraction analysis; vibrational spectroscopy; and solid-state (1)H and (1)H-(1)H radio-frequency-driven dipolar recoupling (RFDR), (1)H-(1)H double quantum correlation (DQ), and (13)C{(1)H} cross polarization magic angle spinning (CPMAS) NMR spectroscopy. The three-dimensional network with a Kagomé-like lattice is built up from the connection of infinite trans-connected chains of octahedral units MO(4)(OH)(2) (M = Ga or In), linked to each other through the terephthalate ligands in order to generate triangular and hexagonal one-dimensional channels. The presence of DMF molecules with strong interactions within the channels as well as their departure upon calcination (150 degrees C under a primary vacuum) of the materials has been confirmed by subjecting MIL-68 (Ga) to solid-state (1)H MAS NMR. The (1)H-(1)H RFDR and (1)H-(1)H DQ spectra revealed important information on the spatial arrangement of the guest species with respect to the hybrid organic-inorganic network. (13)C{(1)H} CPMAS NMR of activated samples provided crystallographically independent sites in agreement with X-ray diffraction structure determination. Brunauer-Emmett-Teller surface areas are 1117(24) and 746(31) m(2) g(-1) for MIL-98 (Ga) and MIL-68 (In), respectively. Hydrogen adsorption isotherms have been measured at 77 K, and the storage capacities are found to be 2.46 and 1.98 wt % under a saturated pressure of 4 MPa for MIL-68 (Ga) and MIL-68 (In), respectively. For comparison, the hydrogen uptake for the aluminum trimesate MIL-110, which has an open framework with 16 A channels, is 3 wt % under 4 MPa.

Size-Dependent Hydrogen Sorption in Ultrasmall Pd Clusters Embedded in a Mesoporous Carbon Template

Hydrogen sorption properties of ultrasmall Pd nanoparticles (2.5 nm) embedded in a mesoporous carbon template have been determined and compared to those of the bulk system. Downsizing the Pd particle size introduces significant modifications of the hydrogen sorption properties. The total amount of stored hydrogen is decreased compared to bulk Pd. The hydrogenation of Pd nanoparticles induces a phase transformation from fcc to icosahedral structure, as proven by in situ XRD and EXAFS measurements. This phase transition is not encountered in bulk because the 5-fold symmetry is nontranslational. The kinetics of desorption from hydrogenated Pd nanoparticles is faster than that of bulk, as demonstrated by TDS investigations. Moreover, the presence of Pd nanoparticles embedded in CT strongly affects the desorption from physisorbed hydrogen, which occurs at higher temperature in the hybrid material compared to the pristine carbon template.

Anisotropic diffraction peak broadening and dislocation substructure in hydrogen-cycled LaNi5 and substitutional derivatives

An erroneous equation and some consequently underestimated values of dislocation densities in the paper by Cerný et al. [J. Appl. Cryst. (2000), 33, 997–1005] are corrected.

Hydrogen cycling induced degradation in LaNi5-type materials

Defect generation in hydrogen cycled LaNi5 and substituted derivatives was studied in previous work by analysis of the X-ray line broadening. In the present work, the pulverization in the same samples is analyzed by granulometric measurements and scanning electron microscopy. Both phenomena correspond to irreversible degradation of the initial intermetallic compounds, as confirmed by first cycle hysteresis presence in pressure composition isotherms. They are analyzed in terms of the lattice expansion occurring at the discrete phase transition between α and β phases and measured by X-ray diffraction. This study shows that, in addition to this latter parameter, the limit of elasticity and the resistance to rupture must be considered.

Improvement of the electrochemical activity of ZrNiCr Laves phase hydride electrodes by secondary phase precipitation

Abstract Within the framework of research on intermetallic compounds for nickel-hydride batteries, we have studied ternary ZrNiCr alloys. In that system, we have measured both the hydride thermodynamic properties by solid-gas reaction and the electrochemical capacities for ternary Laves phases and binary ZrNi intermetallic compounds. A knowledge of the ternary phase diagram has allowed the synthesis of alloys where these two kinds of phase are in equilibrium, at predetermined rates. Study of the electrochemical capacities of these two-phase alloys has shown that the surface modification induced by the precipitation of ZrNi binaries considerably enhances the electrochemical capacity discharged by the Laves phase.

Hydrogen absorption properties of several intermetallic compounds of the ZrNi system

Abstract This paper deals with the hydrogen absorption properties of four binary compounds of the Zr Ni system: Zr 8.85 Ni 11.15 , Zr 7 Ni 10 , Zr 8 Ni 21 and Zr 2 Ni 7 . Hydrogen capacities, absorption kinetics and pressure-composition isotherms were measured by the volumetric method. We have observed, except for Zr 2 Ni 7 , an increase of both capacity and stability of hydrides as a function of zirconium content in the intermetallic compound.

Crystallographic study of LaNi5−xSnx (0.2≤x≤0.5) compounds and their hydrides

The structural properties of tin substituted LaNi5 compounds and corresponding deuterides have been investigated by single crystal X-ray and neutron powder diffraction. Tin is found to substitute nickel exclusively on site 3g of space group P6/mmm. No other significant disorder occurs in the structure. At tin contents of x=0.4 and x=0.5, the crystal structures of the deuterides do not significantly deviate from those of other metal substituted LaNi5 deuterides. At a tin content of x=0.2, with higher deuterium content, however, a symmetry decrease to non-centrosymmetric space group P6mm is observed due to partial deuterium ordering.

The Influence of Mn on the Crystallography and Electrochemistry of Nonstoichiometric AB 5 -Type Hydride-Forming Compounds

To design Co-free, low-pressure, hydride-forming compounds for application in rechargeable nickel metal hydride batteries, nonstoichiometric ABx materials were investigated. The influence of both the Mn content and the degree of nonstoichiometry on the crystallography, electrochemical cycling stability, and electrode morphology were studied. The investigated composition was in th e range of La(Ni12zMnz)x with 5.0 # x # 6.0 and 0 # xz # 2.0. The annealing temperature was essential in preparing homogeneous compounds. In agreement with geometric considerations, both the a and c axis of the hexagonal unit cell increase with increasing Mn content. In contrast, the a axis decreases with increasing degree of nonstoichiometry. As proved by neutron-diffraction experiments, the introduction of dumbbell pairs of Ni or Mn atoms on the La positions in the crystal lattice is responsible for this behavior. The electrochemical cycling stability is found to be strongly dependent on both the chemical and nonstoichiometric composi tion. Electrochemically stable materials are characterized by the absence of a significant particle-size reduction upon electro de cycling, reducing the overall oxidation rate. Unstable materials suffer from severe mechanical cracking through which the oxidation rate is increased. The improved mechanical stability is attributed to the reduced discrete lattice expansion. The most sta ble compound has a partial hydrogen pressure of only 0.1 bar, which matches well with that desirable in practical NiMH batteries. Neutron-diffraction experiments confirmed the hypothesis that La atoms are replaced by dumbbell pairs of Ni, in the case of the binary LaNi5.4, and by Mn atoms in the case of the Mn-containing nonstoichiometric compounds. Electron-probe microanalyses and density measurements support the dumbbell hypothesis.

Structural studies of LaNi4CoD6.11 and LaNi3.55Mn0.4Al0.3Co0.75D5.57 by means of neutron powder diffraction

Abstract The structural properties of LaNi 4 CoD 6.11 and LaNi 3.55 Mn 0.4 Al 0.3 Co 0.75 D 5.57 deuterides have been investigated by means of powder neutron diffraction analysis. The data analysis of LaNi 4 CoD 6.11 deuteride has been performed using a modified Rietveld procedure in order to take into account the anisotropic broadening of the observed diffraction lines. Distribution of Mn, Al and Co substituting atoms on the nickel sublattice and occupancy rate determination of the occupied deuterium sites have been achieved and are compared with those of other single substituted compounds.