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

TL;DR

This study uses time-resolved neutron backscattering to observe the molecular motions and decomposition kinetics of sodium alanate, revealing surface autocatalysis effects in its hydrogen release process.

Contribution

It provides new insights into the molecular dynamics and reaction mechanisms of sodium alanate during hydrogen release, using advanced neutron scattering techniques.

Findings

Intra-molecular motion in Na3AlH6 causes a Lorentzian spectrum at 180°C.

Decomposition of NaAlH4 to Na3AlH6 and NaH is monitored in real-time.

Reaction steps are accelerated by autocatalysis at crystallite surfaces.

Abstract

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.