Effects of Nano-confinement in Mesoporous Silica on Hydrogen Dynamics in TiCl₃-Doped NaAlH₄ Studied using Quasi-Elastic Neutron Scattering

The dynamics of hydrogen in 4 mol % TiCl₃-doped NaAlH₄ which was then confined within the mesoporous SBA15 was studied using quasi-elastic neutron scattering (QENS) technique. Results show that a higher fraction of hydrogen is mobile within the nanoconfined systems relative to bulk TiCl₃-doped NaAlH₄. However, the overall motion of hydrogen was localized and the nanostructured Ti-doped NaAlH₄ exhibited mobility than the bulk (not nanostructured) materials of the same composition. Data were collected on the Disc Chopper Spectrometer and the High Flux Backscattering Spectrometer. Approximately 70% of hydrogen atoms are mobile at 400K while participating in short-range dynamics which could be described by the rotation of a AlH₄ tetrahedra. However, less than 10% hydrogen was mobile at higher temperatures of 420K and 450K, possibly because the higher temperatures lead the formation of hydride phases.