High-resolution and “environmental cell” microscopy were applied for surveying the reaction of hydrides in Vanadium and Magnesium based alloys, which are candidate for hydrogen storage materials of advanced hydrogen energy systems. For clarify the hydrogenation process, in-situ experiment was carried out by using 200 kV TEM equipped with a newly developed environmental cell, which is enable to observe transmitted image and electron-diffraction under gas reaction under hydrogen environment of 0.1 MPa at room temperature. In case of Vanadium, bending fringe was created under hydrogen-gas of 0.1 MPa, which means that hydrogen reaction is not so quick in this case, and the local stress due to the hydrogen solution caused the fringes. In case of Magnesium, the gas reacted with the powders and showed the swelling, where the surface steps with several ten nm become to more straight, and also SADP showed the formation of MgH2. In-situ experiment for hydrogenation reaction by using the environmental cell has started recently, therefore the precise studies will be continued, as well as its improvement, especially in the transparence films.

Mg(NH2)2-LiH system which have the properties of reversible hydrogenation and dehydrogenation is one of the promising candidates for new hydrogen storage materials. For understanding of the reversible reaction mechanism, we investigated the crystal structure changes in 3Mg(NH2)2-12LiH system using the pressure-composition (p-c) isotherm measurement and synchrotron X-ray diffraction. The sample was prepared by the hydrogenation of Mg3N2 + 4Li3N. At the several dehydrogenation stages of the p-c isotherm measurement at temperature 523 K, the sample was taken out and X-ray diffraction measurement was performed. By the amount of desorbed hydrogen, the reaction was expressed as the following formula, Mg(NH2)2 + 4LiH → LixMg(NH2)2-x(NH)x + (4-x)LiH + xH2 (x = 0∼2). The crystal structures of LixMg(NH2)2-x(NH)x, similar to CaF2-type one, formed during the dehydrogenation reaction were determined by Rietveld analysis. As a result, it is considered that the dehydrogenation process might relate to the diffusion of Li+ ion in cation sites of Mg(NH2)2.

One of impotent materials issues of Ti-Cr-V based hydrogen storage alloys is to improve cyclic degradation of storage capacity, which has been assumed to be the effect of internal stress. We focused on the sub-micron structure of this material, which can be accumulated during cyclic use. We used 24Ti-36Cr-40V alloy for the specimens, after FZ melting. Powered samples were fabricated by mechanical grinding under Ar environment. Vacuum annealing was carried out for reducing residual stress and lattice defects. PCT properties were tested at 293 K under 4.5 MPa. XRD and TEM were carried out for important samples. In the first cycle, the annealing resulted in the increasing of storage capacity, but in the second cycle the improving was disappeared. Comparing microstructures with and without annealing, complex dislocation structures were observed after cyclic hydrogenation. It is notable that dislocation free structure was some time observed in the fine grains of less than 0.1 micron, which suggests the possibility of fine structure without defect accumulation.

Porous silicon may be an interesting alternative to store hydrogen. Unlike carbon, its bonding multiplicity is limited, and because of this, the probability of having more dangling bonds on the pore surface is larger than in carbon. Using nanoporous silicon periodic supercells with 216 atoms and 50 % porosity, constructed with a novel ab initio approach devised by us, the dangling bonds of the silicon atoms were first saturated with hydrogen, then relaxed and its total energy calculated. Next the same number of hydrogen atoms was placed within the pore in the pure silicon supercell, then the sample relaxed, and finally its total energy calculated, with and without hydrogens. From these results the average energy per hydrogen atom is obtained. We compare our results to SiH bond energies and to previous results for hydrogenated carbon; conclusions are drawn concerning the possibility of using porous silicon as a fuel tank for hydrogen.

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 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, which would contribute to achieve high performance hydrogen storage materials.

Recent investigations on thermodynamical stabilities of metal borohydrides were reviewed. The first-principles calculations indicated that the heat of formation normalized by the number of BH4 complexs, ΔHboro, show a good correlation with the Pauling electronegativitiese of M, χp, which is represented by the liner relation, ΔHboro = 252.8χp − 396.4 in the unit of kJ/mol BH4. In order to clarify the correlation between the stability of borohydrides and the electronegativity χp of M, M(BH4)n (M = Mg, Ca, Sc, Ti, V, Cr, Mn, Zn, Zr and Al; n = 2-4) were systematically synthesized by mechanical milling. The thermal desorption analyses indicated that Td correlate with χ p of M; Td decrease with increasing the values of χp, in M(BH4)n. Furthermore, the correlation can be reasonably extended to double cation ones, (ZrLin-4)(BH4)n. For single cation, M(BH4)n (M = Mn, Zn and Al; χp ≥ 1.5) desorb borane besides hydrogen, and M(BH4)n (M = Ti, V and Cr; χp ≥ 1.5) desorbe small amount of hydrogen provably due to desorption reaction during milling. Therefore χp is an indicator to approximately estimate the stability of M(BH4)n, and appropriateχp in M(BH4)n is expected to be smaller than 1.5. The enthalpy change for the desorption reaction, ΔHdes, is estimated using our predicted ΔHboro and the reported data for decomposition product, ΔHhyd/borideboro, which shows a good correlation with the observed Td. These results are useful for exploring M(BH4)n with appropriate stability for hydrogen storage applications

The microstructure and hydrogen sorption behaviour of MgH2 based nano-hydrides with different additives prepared by ball milling and inert gas condensation has been investigated by XRD, Differential Scanning Calorimetry and Mechanical Spectroscopy. Preliminary results on materials with similar composition and different nanostructures show that suitable mechanical processing and additive additions induce in the nanostructured composites tailored channels for improved ab/de-sorption kinetics at reduced temperatures.

High throughput, asymmetric carbon membranes derived from pyrolysis of polyfurfuryl alcohol (PFA) have been fabricated on a novel support composed of porous stainless steel filled with nanoparticles. Variation of PFA molecular weight was found to have a significant impact on the single gas permeances of the resultant carbon membranes. High molecular weight precursor material yielded the best results; oxygen permeance values for membranes synthesized from high molecular weight resins were on the order of ∼1×10−8 mol m−2s−1Pa−1 with oxygen over nitrogen ideal selectivities greater than 7. Binary separations of hydrogen from nitrogen and hydrogen from carbon monoxide were carried out using a NPC membrane synthesized from high molecular weight precursor material. For both separations, hydrogen purities of better than 99% by volume were obtained in the permeate stream.

The pressure-temperature phase diagrams of alkali metal alanates and borohydrides are of large current interest, and we have recently studied phase transformations under pressure in several of these materials. We here report Raman studies of KBH4 under pressure at room temperature, showing a phase transition near 6 GPa. Although no structural information is yet available, the similarity between KBH4 and NaBH4 suggests the new structure is orthorhombic. We also report studies on LiBH4 showing that the high pressure phase of this material is metastable to zero pressure below 200 K.

In order to investigate the reason for the higher capacity of the interpenetrating isoreticular metal-organic frameworks (IRMOFs) at lower temperatures, we performed grand canonical Monte Carlo (GCMC) simulations and molecular dynamics simulations at 77 K for a set of the interpenetrating IRMOF-11 and the non-interpenetrating counterpart IRMOF-12. From the GCMC simulations, we found universal force field (UFF) is better for describing the hydrogen adsorption behavior than DREIDING force field. The results from the molecular dynamics simulations showed the density of adsorbed hydrogen molecules was increased in the various pores created by the catenation of IRMOF comparing to that of the pores in IRMOF-12. Moreover, the adsorbed hydrogen molecules in IRMOF-11 have the smaller diffusion coefficients. It means that their dynamic behavior is more restricted because of the complexity of the interpenetrating network of IRMOF-11. These results of molecular simulations show the small pores created by the catenation are important for the increase of hydrogen adsorption on IRMOF-11 at lower temperatures.

Hydrogen desorption reactions of the mixtures of (i) lithium amide and lithium hydride (LiNH2/LiH), and (ii) magnesium amide and lithium hydride (Mg(NH2)2/4LiH) were studied. Titanium compounds and nano-particles including fullerene (C60), were doped to those hydrogen storage mixtures respectively. The hydrogen desorption reactions were monitored by means of temperature programmed desorption (TPD) technique under an Ar atmosphere. The reaction of LiNH2/LiH was accelerated by adding either 1 mol% of Ti species or 0.2 mol% of fullerene (C60), while those additives did not show significant acceleration effects on the reaction of Mg(NH2)2/4LiH. Kinetic studies revealed the enhanced hydrogen desorption reaction rate constant for TiCl3 doped LiNH2/LiH, k = 3.1 × 10−4 s−1 at 493 K, and the prolonged ball-milling further improved reaction rate, k = 1.1 × 10−3 s−1 at the same temperature. For the dehydrogenation reaction of TiCl3 doped LiNH2/LiH, the activation energies estimated by Kissinger plot (95 kJ mol−1) and Arrhenius plot (110 kJ mol−1) were in reasonable agreement each other. The LiNH2/LiH mixture without additive exhibited slower hydrogen desorption process and the kinetic traces deviated from single exponential behavior. The results indicated the Ti(III) additives change the hydrogen desorption reaction mechanism of LiNH2/LiH.

Mg2-xSnxNi (x=0, 0.05, 0.1, 0.15, 0.2) hydrogen storage alloys were prepared and the effects of substitution of Sn for Mg on hydrogen storage performances of the alloys were investigated. In the alloys, Mg2Ni is main phase and the amorphous degree increases gradually with amount of Sn content increasing. Partial substitution of Sn for Mg can change the temperature of hydrogen absorption reaction effectively. The Mg1.85Sn0.15Ni alloy absorbs hydrogen at about 330K which is about 80K lower than that of Mg2Ni alloy. Discharge capacity increases quickly with amount of substitution Sn for Mg increasing. Suitable amount of substitution of Sn for Mg and amorphous can improve the thermodynamic and electrochemical characteristics of hydrogen absorption reaction for Mg2Ni-based alloy.

It is hardly achieved to prepare highly pure MgH2 by the conventional method of solid-gas reaction between solid magnesium and hydrogen; therefore, we proposed and succeeded to synthesize MgH2 by Hydriding Chemical Vapor Deposition (HCVD). Very interestingly, the HCVDed MgH2 was made of single crystals with fibrous figures; however, further detail of the HCVDed product had not been studied. Therefore the aim of this study was to examine the HCVDed MgH2 in hydrogen storage and to observe the microstructure of the HCVDed MgH2 after the hydrogen desorption and absorption.

As the results of Pressure-Composition-Isotherm (PCT) measurement, the HCVDed MgH2 reversibly absorbed and desorbed 7.6 mass% hydrogen, as much as the theoretical maximum hydrogen capacity of magnesium, without any activation treatment. The equilibrium pressure was slightly lower than the reported value. Before and after the PCT measurement, the HCVDed MgH2 did not showed noticeable difference in figure; however, MgHx, which was prepared dehydriding the HCVDed MgH2 in the PCT, showed significant difference in figure: It had zebra stripes in the SEM observation. This observation showed that the hydrogen storage and release went in the radious direction and the hydrogen diffusion was no more rate-limiting. The phase boundaries of Mg and MgH2 involving strain should affected on the plateau pressure in PCT.

A kind of low-cost hydrogen storage alloy containing B has been prepared by near rapid solidification strip casting. And computer optimization has been carried out with MASTER software through mode identification and neuro-network. The alloy microstructure, the alloy performance and the battery performance have been evaluated through optical microscope, TEM and X-ray diffraction. The results indicate that the alloy microstructure is fine columnar crystal and there exists the second phase of CeCo4B on the crystal interface, which increases the diffusion channels for hydrogen atoms and improves the alloy activation. The MmNi3.9Co0.37Mn0.4Al0.3B alloy has excellent performance at room, high and low temperatures prepared by strip casting.