Abstract: Initiation of the HYDRO-STAR (Advanced Fundamental Research Hydrogen Storage Materials) Project itself and what have happened throughout the course of the project are introduced. This project aimed for fundamental research on hydrogen storage materials but the situation around the project dramatically changed during the project.

As modern technologically important materials become increasingly disordered, in addition to the long range structural information yielded by the traditional crystallographic analysis on Bragg intensities, the short and intermediate range structural information is highly demanded. Here we present how we applied the atomic pair distribution function analysis technique to unravel the important local structural features of crystallographically challenged metal hydrides which strongly link to their hydrogen storage properties. The systems of interest are mechanically alloyed Mg_xCo_100-x and V-based bcc alloys.

It is quite important to understand the reaction mechanism in nano-scale for tailoring much superior hydrogen storage materials. So far we have investigated the reaction mechanism of various hydrogen storage materials with high hydrogen capacity by in-situ Transmission Electron Microscopy (TEM) with Environmental Cell (EC). For example, absorption and desorption reactions of Mg/MgH₂ catalyzed by Nb₂O₅ have been observed in nano-scale. From the results, we proposed the reaction model during hydrogen absorption at the interface between Mg and catalyst. The model shows Mg forms at the interface of MgH₂ and catalyst with hydrogen diffusion through Mg phase. Moreover, we discussed the reaction mechanism of the other systems, such as NaH + NH₃, Li₂NH, NaAlH₄, NH₃BH₃, and AlH₃, in this report.

Hydrogenation reaction of aluminum was achieved using cubic-type multi-anvils apparatus. The reaction was investigated by in-situ synchrotron radiation x-ray diffraction measurement. The reaction pressure-temperature diagram was obtained by the measurements and was confirmed to agree with thermodynamical calculation. Aluminum-based alloy hydrides have been explored using the technique because it allows hydrogenation reaction of the alloys with chemically stable surface oxide layer.

The study on the hydrogen storage capability of large diameter SWCNT(10, 10), graphene and C₆₀ functionalized with borane in shown. The SWCNT (10, 10) -BH₃ is able to adsorb 6.12wt.% of hydrogen with optimum binding energy. While, both graphene and C6o functionalized with borane are found not to be suitable for hydrogen storage materials. The planar structure of graphene is not conducive for the functionalization with borane and hydrogen storage. While, the interaction between BH₃ and C₆₀ is such that the borane molecule is dissociatively absorbed. But, the interaction with hydrogen molecules is found to be repulsive and hence C₆₀-BH₃ is not eligible for hydrogen storage. The interaction between BHs and the carbon nanostructures strongly depends on the curvature of C-C bonds in these systems.

Abstract: It is common and fundamental technique for developments of hydrogen storage materials to investigate atomic arrangements of hydrogen during the absorption and desorption process. Since neutron is sensitive probe against hydrogen, the structural environment of hydrogen in atomic scale is clarified by neutron scattering method. High intensity total diffractometer, NOVA, was constructed in the pulsed neutron facility of Japan Proton Accelerator Research Complex (J-PARC). The most characteristic feature of NOVA is that it covers a wide scale of atomic distance from nearest neighbor to several ten nano meters by wide-Q (momentum transfer) measurement in short-time. By Fourier transformation of the obtained wide-Q diffraction data, Pair Distribution Function (PDF) useful for the analysis of disordered structures can be derived with high real-space resolution. On NOVA, both the wide-d space crystal structure analysis (Rietveld analysis) and the high-resolution PDF analysis can be performed. This means that various structures of crystals, amorphous and liquids for hydrogen storage materials are elucidated with NOVA. Aluminum hydride, Lanthanum hydride under GPa pressure and so on have been analyzed. Furthermore, time-transient measurement during hydrogen absorption and desorption process under hydrogen gas atmosphere (max 10 MPa) have been equipped on NOVA. It is expecting that structural analysis with NOVA will accelerate developments of hydrogen storage materials by industries.

Abstract: As one of the promising H₂ storage materials, porous coordination polymers (PCPs), also known as metal-organic frameworks (MOFs), have been extensively studied for the past decade. PCPs are crystalline materials constructed by metal ions and organic linkers to have micropores. We overview PCPs that have been developed for H₂ storage materials to summarize their structures, organic linkers, and physical properties. The big issue is the gap of H₂ storage capacity between at cryogenic temperature and room temperature. Furthermore, we describe the prospects of PCPs as H₂ storage material.

Energy storage is facing an impressive growth mainly coming from renewable energy sources. Sun and wind do not always provide electricity when it is needed the most (peak periods). Electricity has then to wait for its consumption. Transforming the excess of electricity into hydrogen makes electricity easy to store for both long and short term period. McPhy has decided to focus on this opportunity and comes up on the market with a highly innovative energy storage system. On the other hand, hydrogen consumers need safe hydrogen storage, 300 bar pressure vessels and liquid hydrogen are in most cases issues. Metal hydrides allow low-pressure storage and are a solution for industries, which require safety hydrogen storage. While coupling hydrogen produce with water electrolysis from renewable energy and McPhy storage system, it brings today on the market breakthrough “green” hydrogen. Thus C0₂ emissions from hydrogen production can be heavily lowered.

Promising hydrogen storage materials have been picked up from latest publications mainly relating to the disclosed presentations of DOE’s Basic Energy Research, and have been classified to be comparatively evaluated. Composites and nanoconfined materials would particularly play important roles in the near future.

Abstract: Ni-MH battery have been commercialized for hybrid vehicle since 1997. In order to realize sustainable mobility, novel metal hydrides will be used not only for anode material of Ni-MH battery but also for innovative batteries such as materials for all solid state battery, metal-air battery, or multi-cation battery