NMR Search for Mobile, Aluminum-bearing Species during Reactions of Sodium Alanate

NaAlH<sub>4<sub> has become the archetypal complex: ionic-covalent) hydrogen storage solid, since the discovery in 1997 that titanium and some other metals catalyze the reaction in both directions. Given that spatially separated NaH and Al under excess H<sub>2<sub> pressure can form NaAlH<sub>4<sub>, we have hypothesized a mobile Al- or Na- bearing intermediate species in the reaction scheme. <super>27<super>Al <italic>in situ<italic> NMR has been used to discover such a new species during dehydriding of NaAlH<sub>4<sub>. Importantly, the new species can also be formed under excess H<sub>2<sub> pressure without net evolution of Al and H<sub>2<sub>; the new species can be returned to ambient for further study. The features of the new species include: a very rapid <super>27<super>Al T<sub>1<sub>, a sharp line: without MAS) at 300 K that broadens by -60<super>o<super>C, an accompanying sharp hydrogen NMR line that is also motionally narrowed, CPMAS evidence of bonded or at least nearby H, and a <super>27<super>Al shift just above NaAlH<sub>4<sub>. The new species appears to be a highly defective form of NaAlH<sub>4<sub>, where the large concentration of vacancies promotes rapid diffusion of Al and H.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Physics

Year dc:date.available

2010

Author dc:creator

• Ivancic, Timothy

Contributors dc:contributor

• Mark Conradi

• Physics
• Condensed Matter
• hydrogen storage
• in situ 27Al NMR
• intermediate species
• mobile species
• sodium alanate
• vacancies

Language dc:language

English (en)

DOI

https://doi.org/10.7936/K7W37TFR

OAI identifier oai:identifier

oai:openscholarship.wustl.edu:etd-1164