Theoretical study on the structure and stability of aluminum hydride (Al n H 3n ) clusters
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Theoretical study on the structure and stability of aluminum hydride (AlnH3n) clusters Bo Xu • Jiping Liu • Lili Zhao • Lili Yan
Received: 14 July 2012 / Accepted: 28 November 2012 / Published online: 11 December 2012 Ó Springer Science+Business Media New York 2012
Abstract Density functional theory (DFT) calculations have been carried out to study the linear polymeric AlnH3n (n = 1–12) clusters and cage AlnH3n (n = 6, 8, 10, and 12) clusters. In particular, a stable cage-chain (Al12H36)m (m = 2, 3) structure has been predicted for the first time, with the basic unit, cage Al12H36 structure connected by double hydrogen-bridged bonds (i.e., Al–2H–Al). The stability of these clusters has been confirmed by the large binding energies and substantial energy gaps between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, and the cage-chain structure is more stable than the corresponding chain and cage forms. Furthermore, with the cluster size increasing, the aluminum hydride clusters tend to exist with the cage structure compared with the chain structure, even though the formation of the chain structure is much easier than others. Also, the heats of formation for some clusters have been calculated by the atomization reaction method based on the results from DFT calculations, and it is revealed that the
B. Xu (&) J. Liu (&) L. Yan School of Material Science and Engineering, Beijing Institute of Technology, 5 South Zhongguancun Street, Beijing 100081, People’s Republic of China e-mail: [email protected] J. Liu e-mail: [email protected] B. Xu J. Liu L. Yan State Key Laboratory of Explosion Science and Technology, Beijing Institute of Technology, 5 South Zhongguancun Street, Beijing 100081, People’s Republic of China L. Zhao College of Chemistry and Chemical Engineering, Graduate University of the Chinese Academy of Sciences, 19A Yuquanlu Road, Beijing 100049, People’s Republic of China
cage and cage-chain clusters can store more energy and, especially the latter, is more promising as a kind of energetic material.
Introduction Hydrogen storage has become a growing interest for both academic and industrial fields over the years, which is mainly due to the limitation of hydrogen (gas under ambient condition). The increasing interest in all types of nanostructured materials, which are needed for implementation of the next generation of the technological systems, is based on the current high demand for energetic resources. Herein, solid media (e.g., complex hydrides, metal organic frameworks) are one of several promising candidates [1–5]. Among these hydrogen storage solid materials, aluminum hydride (i.e., alane) has attracted much attention during the past decade [5–11]. The well-known AlH3, alane, is a metastable, crystalline solid at room temperature that has a volumetric hydrogen density (148 g H2/L) greater than twice that of liquid hydrogen, and a gravimetric hydrogen density that exceeds 10 wt%, which is much higher than that of most of the known metal hydrides [12]. Such high
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