Microstructures and hydrogen storage properties of Mg/Cu super-laminates were compared to clarify the effect of initial activation. The initial activation change micro/nano-structures of Mg/Cu super-laminates into Mg2Cu with layered structure in fine grain size of about 1μm and pores highly dispersed between layers in sub-micrometer size. Large surface area, dense defects and short diffusion distance for the reaction enable Mg/Cu super-laminates to absorb hydrogen very quickly.

Our study focused on the formation of Ti40Zr40Ni20 and Ti45Zr35Ni17Cu3 icosahedral (i-phase) quasicrystals directly from the melt and their subsequent characterization and high-pressure hydrogenation. The samples were produced in an inert-gas melt-spinning device from a series of arc-melted precursors. By varying the wheel speeds we were able to produce a range of crystallographic structures, from amorphous, through quasicrystalline, to crystalline. The ribbon thickness showed the expected reduction with wheel speed, from 120 microns to 30 microns, while the Ms exhibited a surprisingly modest change with wheel speed. The XRD analysis showed that depending on the cooling rate it was possible to freeze the icosahedral phase directly from the melt, without any subsequent heat-treatment. Using the same procedure to test the range of formation wheel speeds for a comparable system we also produced samples containing up to 3 atomic % copper. Using transmission electron microscopy we have confirmed that the ribbons contain nanosized particles of Ti40Zr40Ni20 icosahedral phase imbedded in an amorphous matrix with the same composition. The average particle size of the i-phase was approximately 20 nm. The 5-fold symmetry was confirmed by selected-area electron diffraction and high-resolution TEM having the crystallite oriented close to the symmetry axis. Both our X-ray diffraction measurements and the TEM observations have provided direct evidence for the quasicrystalline ordering of Ti40Zr40Ni20 by rapid quenching from the melt. To test the hydrogen-absorption properties of the icosahedral phase we crushed ribbons into finer particles to provide fresh, new surfaces to aid hydrogen dissociation at the metal surface. The uptake of hydrogen was found to be critically dependent on the surface state of the Ni–Ti–Zr ribbons; even modest exposure to the atmosphere produced a protective layer of oxide on the surface that practically prevented any hydrogen being taken up by the icosahedral phase. The concentration of hydrogen in the i-phase was determined from the shift in the XRD peaks. The calculated expansion of aq was 6% and the corresponding [H]/[M] value was 1.5.

Palladium (Pd)-coated magnesium-cobalt (Mg-Co) films were prepared by co-sputtering at various ratios of the sputtering power of Mg to that of Co (PMg/PCo). The elemental composition of the films varies coherently with PMg/PCo. Films of higher Mg contents are of stronger interest. Their structures are more disordered even when just a relatively small amount of Co is added. The respective elemental contents are not uniform along depth, but more Mg aggregate near the surface region. A substantial volume fraction of Mg oxide is present. Though of structural complications, a Mg-rich film shows stronger and faster resistivity (ρ) response when reacting with hydrogen. Soaking an as-deposited Mg-rich film in 15% H2 (in argon) gives a huge change of ρ by 40 times, but it is mainly due to some irreversible structural change when a freshly prepared sample is first brought into contact with H2. The change of ρ in subsequent hydridation-dehydridation cycles is about 50%, while the drift of the baseline is less severe. Co-rich films give much weaker resistivity response to H2.

Nanoporous carbon has been considered an interesting and potentially useful material for storing hydrogen. Using nanoporous carbon periodic supercells with 216 atoms and 50 % porosity, constructed with a novel ab initio approach devised by us, the dangling bonds of the carbon atoms were first saturated with hydrogen, then relaxed and its total energy calculated with and without hydrogen. Next the same number of hydrogen atoms, in molecular form, was randomly placed within the pore of the pure carbon supercell, then the sample relaxed, and finally its total energy calculated, also with and without hydrogens. From these results the average energy per hydrogen atom is obtained for both cases. For the molecular hydrogen sample the binding energy found per hydrogen atom is 343.89 meV, which compares favourably with values reported in the literature, 300-400 meV/molecule.

Three 100 nm-thick Mgx(TM)1-x (TM = Ni and Ti) composition spread thin films having compositional variation 0.4<x<0.95 and capped with a 5 nm-thick Pd layer were deposited in combinatorial electron-beam (e-beam) deposition chamber. Crystallinity of the films was characterized by scanning x-ray diffraction (XRD) and cross-sectional transmission electron microscopy (TEM). Hydrogen absorption and desorption of the films were monitored with an infrared (IR) camera that could image a full area of the films. The observed changes in IR intensity due to hydrogen absorption/desorption demonstrated sensitivity of the method to the differences in compostion, microstructure and type of TM.

Crystal orientation (texture) is an important parameter in the hydrogen absorption and desorption properties of various materials. In this study, we investigate the formation of magnesium nanorod arrays with crystal orientations that are not normally observed in conventional Mg thin films. Mg nanorods are produced using an oblique angle deposition technique through a physical self-assembly process. In this study sputtering and thermal evaporation systems are utilized for the growth of Mg nanorods and thin films on silicon wafer pieces. We present a detailed X-ray diffraction and scanning electron microscopy analysis. It is discussed that under oblique incidence, evolution of crystal orientations with lower adatom mobility are promoted due to the shadowing effect.

The solubility of H in the solid solution phase of the Ti35Cr47V18 alloy has been investigated at high and low temperature. The Sieverts law has been found to hold for 808 K≤T≤1204 K and fail for 302 K≤T≤335 K. For H contents nH ≤0.07 (nH=H/Me) the partial molar enthalpy and partial non-configurational entropy at high temperature are:

On heating the material under H2 gas pressures lower than 0.1 MPa H absorption only occurs above 700 K. Below this temperature, surface oxide films prevent H uptake. Thermal decomposition spectroscopy of the α phase carried out for nH≤0.24 exhibits a single peak whose temperature increases with decreasing nH owing to selective occupancy by H of energetically non-degenerate interstitial sites.

Efficient storage of hydrogen for use in fuel cell-powered vehicles is a challenge that is being addressed in different ways, including adsorptive, compressive, and liquid storage approaches. In this paper we report on adsorptive storage in nanoporous carbon fibers in which palladium is incorporated prior to spinning and carbonization/activation of the fibers. Nanoparticles of Pd, when dispersed in activated carbon fibers (ACF), enhance the hydrogen storage capacity of ACF. The adsorption capacity of Pd-ACF increases with increasing temperature below 0.4 bar, and the trend reverses when the pressure increases. To understand the cause for such behavior, hydrogen uptake properties of Pd with different degrees of Pd-carbon contact (Pd deposited on carbon surface and Pd embedded in carbon matrix) are compared with Pd-sponge using in situ XRD under various hydrogen partial pressures (<10 bar).

Rietveld refinement and profile analysis of diffraction patterns does not show any significant changes in carbon structure even under 10 bar H2. Pd forms β PdH0.67 under 10 bar H2, which transforms to α PdH0.02 as the hydrogen partial pressure is decreased. However, the equilibrium pressure of transition (corresponding to a 1:1 ratio of α and β phases) increases with increasing the extent of Pd-carbon contact. This pressure is higher for Pd embedded in carbon than for Pd deposited on carbon surface. Both these Pd-carbon materials have higher H2 desorption pressure than pure Pd, indicating that carbon “pumps out” hydrogen from PdHx and the pumping power depends on the extent of Pd-carbon contact. These results support the spillover mechanism (dissociative adsorption of H2 followed by surface diffusion of atomic H).

It was indicated that H2 is generated by the reaction of LiH and NH3. After H2 generation, the byproduct LiNH2 was recycled back to LiH under H2 flow condition at 500K.

In an effort to develop reversible metallic borohydrides with high hydrogen storage capacities and low dehydriding temperature, modifications to LiBH4 with metal halides TiCl3 have been conducted. Adding TiCl3 to LiBH4 effectively reduced the dehydriding temperature through an ion exchange interaction by producing instable transition metal borohydrides and lithium salts. The material LiBH4+0.1TiCl3 desorbed 3.5wt% and 8.5wt% hydrogen at 150°C and 450°C respectively. Subsequent re-absorption of 6wt% hydrogen at 500°C and 70 bars was observed. The XRD analysis of the rehydrided samples confirmed the partial reformation of LiBH4. However, adding more TiCl3 made material more volatile and irreversible. TGA-RGA analyses indicated diborane evolution during dehydrogenation resulting in unrecoverable capacity loss and irreversibility. TiCl3 reduced LiBH4 stability and also made material irreversible.

We present the effect of thermal treatments on the transduction behaviors of HCl-doped polyaniline (PANI) nanofibers integrated in conductometric devices upon exposure to 1% H2 (carried by N2). After drying in N2 at 25ºC for 12 hours, devices showed a ∼10% decrease in electrical resistance upon exposure to 1% H2. However, devices subject to 12-hour drying in N2 at 25ºC followed by further thermal treatments in N2 at 100ºC, 164ºC or 200ºC for 30 minutes showed different transduction behaviors. Specifically, devices subject to thermal treatments at 100ºC and 164ºC showed a decrease in electrical resistance by ∼7% and <0.5%, respectively. More interestingly, the device subject to thermal treatment at 200ºC showed a transduction behavior with opposite polarity, i.e. a ∼5% increase in electrical resistance upon exposure to 1% H2. SEM, FTIR and TGA were employed to investigate the effect of thermal treatments on the morphology and chemical characteristics of HCl-doped polyaniline nanofibers. The results indicated that the change in the devices' interesting transduction behaviors might be related to the thermal treatment effects on the HCl-doped PANI nanofibers in (i) removal of adsorbed water, and (ii) crosslinking and/or degradation of polymer backbones.

This paper reports the synthesis and characterization of coherent Boron/Nitrogen –doped –carbon cryogels- ammonia borane nanocomposites for hydrogen storage. Resorcinol formaldehyde derived doped carbon cryogels (CC) were obtained via chemical modification.CC- ammonia-borane nanocomposites were made by incorporation of ammonia borane (AB), in CCs. Nitrogen sorption analysis, scanning electron microscopy, and X-ray photoelectron spectroscopy, are used to investigate the structure and morphology of the modified CCs. Differential scanning calorimetry is used to study the dehydrogenation of coherent doped-CC-AB nanocomposites. Modified CCs show higher mesoporosity, and more homogeneous porous structure compared to undoped CCs. Also, dehydrogenation kinetics of nanocomposites is enhanced as compared to neat AB. Possible nanoscale and catalytic effects of nanocomposites in improved dehydrogenation kinetics are discussed.

High pressure physic-sorption hydrogen tank using high purity and high surface area SWNTs is considered to be one of the most promising hydrogen tank systems

Inert gas condensation was employed to prepare nanoparticles of Mg and MgH2 which morphology, clustering degree and structural stability have been investigated by X-ray diffraction and electron microscopy. Thermodynamic functional properties of the Mg and MgH2 nanostructured samples were investigated by high pressure differential scanning calorimetry. Some specific features of the morphology of the samples prepared by inert gas condensation are compared with powders obtained by ball milling through desorption kinetics behavior.

High-capacity conventional and advanced multicomponent metal hydride alloys were synthesized in this work by two different methods. A set of AB5–type intermetallic compounds, with different Al content, were produced by high-frequency vacuum induction melting method, while AB, A2B and mixed (AB5+Mg)-types composite nanocrystalline-amorphous alloys were obtained mechanochemically by high-energy ball milling in a planetary type mill. The alloys were characterized physically by XRD, SEM and thermodynamically by van't Hoff's plots derived from experimentally obtained PCT isotherms at various temperatures. Different optimized techniques for model electrode preparation from selected metal hydride alloys were also applied. The electrodes were charged-discharged electrochemically in concentrated alkaline solution. In this paper we compare the values for the electrochemical maximum capacity and cycle-life performance of the electrodes prepared by the investigated types of alloys.

The study of sorption reactions of metal hydrides is the subject of numerous researches in connection with the development of a safe technology for hydrogen storage, and MgH2, in particular, is one of the most promising materials. Several efforts have been already carried out in order to understand the kinetic mechanisms involved in the MgH2 decomposition which is at the basis of H2 release. However, the role of additives and induced structural defects on the sorption cycles is not clear yet. With the purpose of supporting the reaction analysis we have developed an experimental protocol for the metallographic examination at high spatial resolution of partially desorbed MgH2 powders. In particular, this procedure allows cross-sectional analysis of powders embedded into conductive matrix, while the observation method produces a different contrast among metallic Mg, MgH2 and additive particles made of heavier materials.

Hydridation of palladium (Pd) is accompanied by a substantial volume expansion. The electrical resistivity (ρ) would rise because the volume fraction of the hydride phase increases. However, if the material structure is porous/defective, hydridation induced volume expansion may lead to the closing of some pores/defects to result in a drop of ρ. We verified that a magnetron sputtered Pd film deposited at a higher argon ambient pressure (ϕ) was more defective, such that the contribution from the latter mechanism was stronger with increasing ϕ, and reached a maximum level for a film deposited at a ϕ of 6 mTorr. However, the film structure was weaker and unstable during the switching cycles, such that the magnitude of the change of ρ was found to increase successively with increasing number of switching cycles. The performances of ρ during initial soaking in H2 and subsequent hydridation and dehydridation switching cycles were different. The observed results are presented and discussed in this paper.

Metal hydrides and amides are potential candidate materials for hydrogen storage. Lithium- and magnesium-based material systems are among the most promising materials owing to their high hydrogen contents. In the present work, we investigated hydrogenation/dehydrogenation reactions of a binary nitride, LiMgN. LiMgN can be formed by a reaction of MgH2 with LiNH2 in 1:1 ratio. The reaction also releases approximately ∼ 8.1 wt% H2 (theoretical value is 8.2 wt%) between 160 and 220 °C. The reaction product LiMgN can be rehydrogenated by reacting with H2 under 2000 psi of hydrogen pressure and 160 °C with small amount of TiCl3 doping. TGA results showed that about 8.0 wt% of hydrogen was stored in TiCl3-doped LiMgN during the hydrogenation process. The reversible hydrogenation and dehydrogenation mechanisms involving LiMgN and H2 are discussed.

Degradation property of aluminum due to hydrogen is studied. Hydrogen is introduced by electrolysis charge in aqueous solution with addition of 0.1 mass % NH4SCN as a hydrogen recombination poison. The amount of hydrogen and its existing state in the material is analyzed by hydrogen desorption curves measured by the thermal desorption spectroscopy. The hydrogen desorption curves of charged aluminum showed two peaks, one at less than 100 °C and the other around 400 °C. The existing state of hydrogen relate to each peaks are identified as weakly trapped solute hydrogen to vacancy and free hydrogen molecule located in cavities that exists in the bulk of the material. Tensile properties are obtained to determine degradation property of the material due to hydrogen. The effect of hydrogen on degradation of charged aluminum is analyzed in terms of interaction between hydrogen and vacancy or dislocation. Solute hydrogen and cavities are found to affect ductility of aluminum, whereas hydrogen molecule in cavities has no effect.