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

Abstract

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.