Structures and thermodynamics of the mixed alkali alanates

Journal Article · Sun May 01 04:00:00 EDT 2005 · Physical Review. B, Condensed Matter and Materials Physics

DOI:https://doi.org/10.1103/PhysRevB.71.184115· OSTI ID:20719004

Graetz, J; Reilly, J J ^[1]; Lee, Y; Park, S; Vogt, T ^[2]

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1. Department of Energy Sciences and Technology, Brookhaven National Laboratory, Upton, New York 11973 (United States)
2. Department of Physics, Brookhaven National Laboratory, Upton, New York 11973 (United States)

The thermodynamics and structural properties of the hexahydride alanates (M{sub 2}M{sup '}AlH{sub 6}) with the elpasolite structure have been investigated. A series of mixed alkali alanates (Na{sub 2}LiAlH{sub 6}, K{sub 2}LiAlH{sub 6}, and K{sub 2}NaAlH{sub 6}) 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% TiCl{sub 3}) and uncatalyzed Na{sub 2}LiAlH{sub 6} 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 Fm3m space group with the smaller ion (M{sup '}) 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.

• OSTI ID: 20719004
• Journal Information: Physical Review. B, Condensed Matter and Materials Physics, Journal Name: Physical Review. B, Condensed Matter and Materials Physics Journal Issue: 18 Vol. 71; ISSN 1098-0121
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
75 CONDENSED MATTER PHYSICS
SUPERCONDUCTIVITY AND SUPERFLUIDITY
ABSORPTION
ALUMINIUM HYDRIDES
CATALYSIS
CATALYSTS
CATIONS
DENSITY
DESORPTION
FCC LATTICES
HYDROGEN
HYDROGEN STORAGE
ION EXCHANGE
ISOTHERMS
POTASSIUM COMPOUNDS
SODIUM COMPOUNDS
SPACE GROUPS
THERMODYNAMICS
TITANIUM CHLORIDES
X-RAY DIFFRACTION