Influence of dopants Ti and Ni on bonding interactions and dehydrogenation properties of lithium alanate.

We report a study of the influence of Ti and Ni dopants on the stability and bonding interactions of LiAlH(4) using the first-principles method. Both the Ti and the Ni prefer to occupy an interstitial site in the LiAlH(4) owing to lower occupation energies estimated from the total energy calculations. Calculations show that the bonding interactions between the Al and the H atoms within the [AlH(4)] groups were significantly reduced by the dopants, and both the stability and the geometry of the [AlH(4)] group were distorted in the doped LiAlH(4) systems. However, Ti and Ni use different mechanisms to improve the dehydrogenation properties of LiAlH(4). The Ti dopant tends to interact with the Al atom in its neighbouring [AlH(4)] to 'free' the H atoms from these [AlH(4)] groups. The effect of Ni dopant on the stability and the bonding interactions of the LiAlH(4) is due to the induction of the Ni d electrons that could cause a bonding interaction between the Ni and the Al atoms, strengthening the interactions between the Li and the H atoms, and 'freeing' the H atoms from the neighbouring [AlH(4)] groups as well.