Catalytical Synthesis and In Situ Doping of Sodium Aluminum Hydride from Elements

Sodium aluminum hydride (NaAlH4) is a prominent hydrogen storage material and a cost-effective substitute for LiAlH4. For industrial application as a hydrogen store in the medium-temperature range, efficient preparation methods for NaAlH4 are required. We report here a feasible approach to prepare pure and in situ doped NaAlH4 from its constituent elements, namely Na, Al, and H2. Formation of NaAlH4 was realized by ball milling sodium lumps and aluminum powders of commercial grade in tetrahydrofuran followed by hydrogenation under moderate conditions in an autoclave. Metal chlorides CeCl3 and TiCl4 as well as a zero-valent Ti prepared in this work were used as catalysts for the synthesis of NaAlH4. The removal of the solvent after hydrogenation resulted in in situ doped NaAlH4 for hydrogen storage utilization, which exhibits excellent storage properties, whereas pure NaAlH4 was obtained by separation of the catalysts through filtration

Additive Effects of LiBH₄ and ZrCoH₃ on the Hydrogen Sorption of the Li-Mg-N‑H Hydrogen Storage System

LiBH₄ is an effective catalyst for the hydrogen sorption of the Li-Mg-N-H storage system. A combination of LiBH₄ with ZrCoH₃ was reported to be catalytically more effective. In this work, materials doped with LiBH₄ or ZrCoH₃ or a combination of ZrCoH₃ and LiBH₄ were characterized both in the as-prepared and in the cycled states. A comparison of the metathesis conversion, thermal behavior, kinetics, and phase evolution induced by H₂ cycling suggests that the two components function additively. While LiBH₄ facilitates the metathesis conversion in the first cycle and enhances kinetics during H₂ cycling by forming a quaternary complex hydride, ZrCoH₃ has at least a pulverizing effect in the material. The chemical environment and near order of the individual atoms of Zr and Co as well as the structural parameters of ZrCoH₃ were investigated by X-ray absorption and found to be unchanged during H₂ cycling