|Title||Towards Direct Synthesis of Alane: A Predicted Defect-Mediated Pathway Confirmed Experimentally|
|Publication Type||Journal Article|
|Year of Publication||2016|
|Authors||Wang, LL, Herwadkar, A, Reich, JM, Johnson, DD, House, SD, Pena-Martin, P, Rockett, AA, Robertson, IM, Gupta, S, Pecharsky, VK|
|Type of Article||Article|
|Keywords||al, al(111), alane, aluminum-hydride, ball milling, catalysis, chemistry, density funcitonal theory, desorption, electron-gas, mechanochemical synthesis, reversible hydrogen storage, scanning, surfaces, Technology - Other Topics, total-energy calculations, tunneling microscopy, wave basis-set|
Alane (AlH3) is a unique energetic material that has not found a broad practical use for over 70 years because it is difficult to synthesize directly from its elements. Using density functional theory, we examine the defect-mediated formation of alane monomers on Al(111) in a two-step process: (1)dissociative adsorption of H-2 and (2)alane formation, which are both endothermic on a clean surface. Only with Ti dopant to facilitate H-2 dissociation and vacancies to provide Al adatoms, both processes become exothermic. In agreement, in situ scanning tunneling microscopy showed that during H-2 exposure, alane monomers and clusters form primarily in the vicinity of Al vacancies and Ti atoms. Moreover, ball milling of the Al samples with Ti (providing necessary defects) showed a 10% conversion of Al into AlH3 or closely related species at 344bar H-2, indicating that the predicted pathway may lead to the direct synthesis of alane from elements at pressures much lower than the 10(4)bar expected from bulk thermodynamics.
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