The effects of nanoscale geometry and spillover on room temperature storage of hydrogen on silica nanosprings

Silica nanosprings (NSs) consisting of multiple nanowires intertwined were demonstrated to reversibly store 0.85 wt% hydrogen at 20 bar and room temperature. X-ray photoelectron spectroscopy indicates a mixed 3+-4+ ionization state of the silicon atoms and partially explains the enhanced surface adsorption of H2 relative to other forms of silica. Theoretical modeling and simulation using a Lennard-Jones potential demonstrated that interstitial sites between the silica nanowires forming the NS are energetically more favorable adsorption sites relative to single nanowires. The addition of Pd nanoparticles to the surface of the silica NSs was demonstrated to increase the hydrogen storage capacity to 3.5 wt% at 66 bar and room temperature. Palladium-nanoparticle-induced hydrogen spillover is attributed to the enhanced storage capacity relative to bare silica NSs.