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Published on: April 28, 2022
Hydrogen release from sodium alanate observed by time-resolved neutron backscattering
1Karlsruhe Institute of Technology, Institute of Nanotechnology, Hermann-von-Helmholtz-Platz, Eggenstein-Leopoldshafen, Germany. aline.leon@kit.edu
Innermolecular motion in sodium alanate (Na3AlH6) was observed via neutron backscattering. Decomposition kinetics revealed autocatalysis, likely on Na3AlH6 and NaH surfaces, accelerating the reaction.
Area of Science:
- Materials Science
- Solid-State Chemistry
- Chemical Kinetics
Background:
- Sodium alanates are hydrogen storage materials.
- Understanding their decomposition pathways is crucial for practical applications.
- Previous studies lacked detailed kinetic insights into the decomposition process.
Purpose of the Study:
- To investigate the innermolecular dynamics of sodium alanate (Na3AlH6).
- To monitor the decomposition kinetics of sodium alanate using time-resolved neutron backscattering.
- To elucidate the role of autocatalysis in the decomposition of sodium alanate.
Main Methods:
- Neutron backscattering spectroscopy (SPHERES) was employed to study Na3AlH6 at 180°C.
- Time-resolved measurements were conducted to track decomposition kinetics.
- Comparative analysis was performed on NaAlH4 and NaH to identify unique spectral features.
Main Results:
- A Lorentzian spectrum, indicative of AlH6 tetrahedra rotation, was observed in Na3AlH6.
- No similar quasielastic line was detected in NaAlH4 or NaH.
- Autocatalysis was identified as a key factor accelerating both steps of sodium alanate decomposition, particularly on Na3AlH6 and NaH crystallite surfaces.
Conclusions:
- Innermolecular motion, specifically AlH6 tetrahedra rotation, is a characteristic feature of Na3AlH6.
- The decomposition of sodium alanate is an autocatalytic process.
- Surface effects on Na3AlH6 and NaH crystallites play a significant role in accelerating the decomposition kinetics.
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