Metal/graphene nanocomposites synthesized with the aid of supercritical fluid for promoting hydrogen release from complex hydrides

With the aid of supercritical CO₂, Fe-, Ni-, Pd-, and Au-nanoparticle-decorated nanostructured carbon materials (graphene, activated carbon, carbon black, and carbon nanotubes) are synthesized for catalyzing the dehydrogenation of LiAlH₄. The effects of the metal nanoparticle size and distribution, and the type of carbon structure on the hydrogen release properties are investigated. The Fe/graphene nanocomposite, which consists of ∼2 nm Fe particles highly dispersed on graphene nanosheets, exhibits the highest catalytic performance. With this nanocomposite, the initial dehydrogenation temperature can be lowered (from ∼135 °C for pristine LiAlH₄) to ∼40 °C without altering the reaction route (confirmed by in situ X-ray diffraction), and 4.5 wt% H₂ can be released at 100 °C within 6 min, which is faster by more than 135-fold than the time required to release the same amount of H₂ from pristine LiAlH₄.