Hydrogen-storage materials dispersed into nanoporous substrates studied through incoherent inelastic neutron scattering

Incoherent inelastic neutron scattering measurements on four impregnated/infiltrated composites of hydrides (namely, NaAlH_4,NH_3BH_3, LiBH_4 + Mg(BH_4)_2, and MgH_2) plus nanoporous scaffolds (active carbon fibers or silica-based MCM41) have been performed at low temperature. After a careful data analysis, the present experimental results have been compared to the corresponding spectroscopic data of bulk hydrides. Evident signatures induced by infiltration process on the NaAlH_4 phonon bands have been detected, showing up as a strong peak broadening and smoothing together with, in some cases, an energy shift. Less pronounced phonon spectrum modifications have been found in MgH_2 and NH_3BH_3, mainly concentrated in the low-energy acoustic region. Finally, no relevant effect has been observed for LiBH_4 + Mg(BH_4)_2.