Role of charge in destabilizing AlH4 and BH4 complex anions for hydrogen storage applications: Ab initio density functional calculations

Du, A. J,, Smith, Sean C. and Lu, G. Q. (2006) Role of charge in destabilizing AlH4 and BH4 complex anions for hydrogen storage applications: Ab initio density functional calculations. Physical Review B, 74 19: 193405-1-193405-4. doi:10.1103/PhysRevB.74.193405

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Author Du, A. J,
Smith, Sean C.
Lu, G. Q.
Title Role of charge in destabilizing AlH4 and BH4 complex anions for hydrogen storage applications: Ab initio density functional calculations
Journal name Physical Review B   Check publisher's open access policy
ISSN 1098-0121
Publication date 2006-11-15
Sub-type Article (original research)
DOI 10.1103/PhysRevB.74.193405
Open Access Status File (Publisher version)
Volume 74
Issue 19
Start page 193405-1
End page 193405-4
Total pages 4
Editor P. D. Adams
Place of publication College Pk
Publisher American Physical Society
Language eng
Subject 670799 Other
291804 Nanotechnology
C1
CX
Abstract NaAlH4 and LiBH4 are potential candidate materials for mobile hydrogen storage applications, yet they have the drawback of being highly stable and desorbing hydrogen only at elevated temperatures. In this letter, ab initio density functional theory calculations reveal how the stabilities of the AlH4 and BH4 complex anions will be affected by reducing net anionic charge. Tetrahedral AlH4 and BH4 complexes are found to be distorted with the decrease of negative charge. One H-H distance becomes smaller and the charge density will overlap between them at a small anion charge. The activation energies to release of H-2 from AlH4 and BH4 complexes are thus greatly decreased. We demonstrate that point defects such as neutral Na vacancies or substitution of a Na atom with Ti on the NaAlH4(001) surface can potentially cause strong distortion of neighboring AlH4 complexes and even induce spontaneous dehydrogenation. Our results help to rationalize the conjecture that the suppression of charge transfer to AlH4 and BH4 anion as a consequence of surface defects should be very effective for improving the recycling performance of H-2 in NaAlH4 and LiBH4. The understanding gained here will aid in the rational design and development of hydrogen storage materials based on these two systems.
Keyword Physics, Condensed Matter
Total-energy Calculations
Augmented-wave Method
Aluminum Hydrides
Doped Naalh4
Basis-set
Libh4
Approximation
Diffraction
Q-Index Code C1

 
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Created: Thu, 18 Oct 2007, 01:25:03 EST