Liquid Phase-Made Aluminum Nanoparticles and Their Hydrogen Sorption as Aluminum/LiH Composite

Aluminum nanoparticles, Al(0), are prepared in toluene at room temperature (25 °C) by reduction of AlH3 with dilithium naphthalenide ([Li2Naph]). To dissolve the starting materials in toluene, AlH3 and [Li2Naph] are coordinated by N,N,N′,N′-tetramethylethylendiamin (TMEDA). The as-prepared Al(0) nanoparticles are monocrystalline and exhibit a uniform size of 11 ± 3 nm with narrow size distribution. They are highly reactive, as indicated by reaction in air and even with nitrogen. Besides the formation of Al(0) nanoparticles, the [Li2Naph]-driven reduction of AlH3 results in the formation of LiAlH4 as a side phase, which can be removed but is difficult to remove due to its low solubility in solvents that do not react with the Al(0) nanoparticles (e.g., toluene, THF). The presence of LiAlH4 and the formation of a Al(0) nanoparticle/LiAlH4 composite, however, turned out to be advantageous in regard to H2 sorption. After thermal transition of LiAlH4 to LiH (250 °C, vacuum), the resulting Al(0) nanoparticle/LiH composite shows promising H2 sorption and H2 uptake at 250 °C and 100 bar of H2 with a gravimetric capacity of 3.8%. After modification of the Al(0) nanoparticles with 1 wt % Pd for activation, the H2 uptake occurs at even a reduced temperature of 150 °C.