Aluminum-silicon hydride clusters for prospective hydrogen storage

Abstract

The structures and bonding properties of Al4Si2H2n (n = 0–10) clusters are systematically studied by using the evolutionary algorithm combined with ab initio computations. While the H atoms are bond on the terminal sites of the clusters at low H contents, the Al atoms are combined together by double H-bridges and the Al/Si atoms are tetrahedrally coordinated at high H contents. The Al4Si2H2n clusters break into a few fragments for n = 9,10. Analysis on the bonding natures shows that the Al–H bonds are strongly polarized and the Si atoms balance the charge states of the Al/H atoms according to the hydrogen concentrations. The hydrogen storage capacity in Al4Si2H16 cluster reaches 8.9 wt%, and the estimated strength of the hydrogen bonding is about −0.55 eV per H2, which falls in the ideal window for reversible hydrogen storage at ambient temperatures. The high hydrogen capacity and moderate bonding strength suggest that Al–Si hydrides can be promising candidates for hydrogen storage.