Hydrogen-capped silicon nanoparticles as a potential hydrogen storage material: Synthesis, characterization, and hydrogen release

Chemical hydrides are compounds that can potentially uptake and release hydrogen without the use of hydrogen gas. Nanostructure silicon may have great potential as a chemical hydride. The surface can be capped by hydride and dihydride, and hydrogen can be thermally desorbed from the surface. We have prepared large-scale (1 -2 g) samples of hydrogen-capped silicon nanoparticles with average diameters of 60,10,5, and 4 nm via a low-temperature chemical method to explore the release of hydrogen from the surface as a function of size. The 60- and 10-nm-diameter particles have only hydrogen on the surface. The 60-nm-diameter particles are crystalline, and the 10-nm-diameter particles are amorphous according to powder X-ray diffraction (XRD). The 5- and 4-nm-diameter particles have both hydrogen and solvent capped on the surface. The 4-nm-diameter particles are amorphous and the 5-nm-diameter particles are crystalline by powder XRD. Weight percentages of ∼3.5% at 350 °C are observed for the 10-nm-diameter particles. The largest weight loss is observed for the amorphous 4-nm-diameter particles, which show a weight loss of ∼4.5%, which is attributed primarily to hydrogen. The products have been investigated by powder XRD, scanning electron microscopy (SEM), transmission electron microscopy (TEM), solid-state magic-angle spinning nuclear magnetic resonance (MAS NMR), Fourier transform infrared (FTIR) analysis, thermogravimetry/differential scanning calorimetry (TG/DSC), and thermogravimetry/mass spectroscopy (TG/MS).