Hydrogen Release from Sodium Alanate Observed by Time-resolved Neutron Backscattering

Innermolecular motion in Na3AlH6 gives rise to a Lorentzian spectrum with a wavenumber-independent width of about 1 micro-eV at 180 deg C, which is probably due to rotation of AlH6 tetrahedra. There is no such quasielastic line in NaAlH4 or NaH. Based on this finding, time-resolved measurements on the neutron backscattering spectrometer SPHERES were used to monitor the decomposition kinetics of sodium alanate, NaAlH4 to Na3AlH6 to NaH. Both reaction steps were found to be accelerated by autocatalysis, most likely at the surfaces of Na3AlH6 and NaH crystallites.