Structures and thermodynamics of the mixed alkali alanates

J. Graetz, Y. Lee, J. J. Reilly, S. Park, T. Vogt

Research output: Contribution to journalArticle

69 Citations (Scopus)

Abstract

The thermodynamics and structural properties of the hexahydride alanates (M2 M′ Al H6) with the elpasolite structure have been investigated. A series of mixed alkali alanates (Na2 LiAl H6, K2 LiAl H6, and K2 NaAl H6) were synthesized and found to reversibly absorb and desorb hydrogen without the need for a catalyst. Pressure-composition isotherms were measured to investigate the thermodynamics of the absorption and desorption reactions with hydrogen. Isotherms for catalyzed (4 mol% Ti Cl3) and uncatalyzed Na2 LiAl H6 exhibited an increase in kinetics, but no change in the bulk thermodynamics with the addition of a dopant. A structural analysis using synchrotron x-ray diffraction showed that these compounds favor the Fm 3̄ m space group with the smaller ion (M′) occupying an octahedral site. These results demonstrate that appropriate cation substitutions can be used to stabilize or destabilize the material and may provide an avenue to improving the unfavorable thermodynamics of a number of materials with promising gravimetric hydrogen densities.

Original languageEnglish
JournalPhysical Review B - Condensed Matter and Materials Physics
Volume71
Issue number18
DOIs
Publication statusPublished - 2005 Dec 1

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Alkalies
Hydrogen
alkalies
Thermodynamics
thermodynamics
Isotherms
isotherms
hydrogen
Synchrotrons
Structural analysis
Cations
Structural properties
Desorption
Substitution reactions
Thermodynamic properties
Diffraction
Positive ions
Doping (additives)
structural analysis
Ions

All Science Journal Classification (ASJC) codes

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics

Cite this

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Structures and thermodynamics of the mixed alkali alanates. / Graetz, J.; Lee, Y.; Reilly, J. J.; Park, S.; Vogt, T.

In: Physical Review B - Condensed Matter and Materials Physics, Vol. 71, No. 18, 01.12.2005.

Research output: Contribution to journalArticle

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