Quasi-Elastic Neutron Scattering Studies of Hydrogen Dynamics for Nanoconfined NaAlH4

The hydrogen dynamics of nanoconfined sodium Alanate (NaAlH4) has been studied using quasi-elastic neutron scattering (QENS). Results indicate thermodynamic destabilization is responsible for reduced desorption temperatures of NaAlH4 upon confinement within the nanopores of a metal organic framework (MOF). The quasi-elastic broadening in the nano-NaAlH4 indicates that there are two dynamic states of hydrogen, which can be tracked by fitting the QENS signal to Lorentzian functions. The fastest hydrogen dynamics show some limited amount and range of long-range diffusion (i.e., not spatially confined motion) as indicated by a weakly varying Q-dependent fwhm on the broad Lorentzian quasi-elastic broadening data. These data trend toward zero at Q = 0 A–1. Slower hydrogen dynamics, described by a narrow Lorentzian function, are present in the nanoconfined sample and can be attributed to reorientation and localized motion of H around AlHx tetrahedra. Both the as-purchased NaAlH4 (hereafter called “bulk” or “micr...