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.