Liquid Phase-Made\nAluminum Nanoparticles and Their\nHydrogen Sorption as Aluminum/LiH Composite

Aluminum nanoparticles, Al(0), are prepared in toluene\nat room\ntemperature (25 °C) by reduction of AlH<sub>3</sub> with dilithium\nnaphthalenide ([Li<sub>2</sub>Naph]). To dissolve the starting materials\nin toluene, AlH<sub>3</sub> and [Li<sub>2</sub>Naph] are coordinated\nby <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylendiamin (TMEDA). The as-prepared\nAl(0) nanoparticles are monocrystalline and exhibit a uniform size\nof 11 ± 3 nm with narrow size distribution. They are highly reactive,\nas indicated by reaction in air and even with nitrogen. Besides the\nformation of Al(0) nanoparticles, the [Li<sub>2</sub>Naph]-driven\nreduction of AlH<sub>3</sub> results in the formation of LiAlH<sub>4</sub> as a side phase, which can be removed but is difficult to\nremove due to its low solubility in solvents that do not react with\nthe Al(0) nanoparticles (e.g., toluene, THF). The presence of LiAlH<sub>4</sub> and the formation of a Al(0) nanoparticle/LiAlH<sub>4</sub> composite, however, turned out to be advantageous in regard to H<sub>2</sub> sorption. After thermal transition of LiAlH<sub>4</sub> to\nLiH (250 °C, vacuum), the resulting Al(0) nanoparticle/LiH composite\nshows promising H<sub>2</sub> sorption and H<sub>2</sub> uptake at\n250 °C and 100 bar of H<sub>2</sub> with a gravimetric capacity\nof 3.8%. After modification of the Al(0) nanoparticles with 1 wt %\nPd for activation, the H<sub>2</sub> uptake occurs at even a reduced\ntemperature of 150 °C.