Effects of Titanium-Containing Additives on the Dehydrogenation Properties of LiAlH4: A Computational and Experimental Study

Abstract

Metal hydrides are attractive materials for use in thermal storage systems to manage excessive transient heat loads and for hydrogen storage applications. This paper presents a combined computational and experimental investigation of the influence of Ti, TiO2, and TiCl3 additives on the dehydrogenation properties of milled LiAlH4. Density functional theory (DFT) is used to predict the effect of Ti-containing additives on the electronic structure of the region surrounding the additive after its adsorption on the LiAlH4 (010) surface. The electron distribution and charge transfer within the LiAlH4/additive system is evaluated. Electronic structure calculations predict covalent-like bonding between the Ti atom of the adsorbate and surrounding H atoms. The hydrogen (H) binding energy associated with the removal of the first H from the modified LiAlH4 surface is calculated and compared with experimental dehydration activation energies. It is seen that the weaker H binding corresponds to the larger amount of charge transferred from the Ti atom to adjacent H atoms. A reduction in charge transfer between the Al atom and surrounding H atoms is also observed when compared to charge transfer in the unmodified LiAlH4 surface. This reduction in charge transfer between Al-H weakens the covalent bond within the [AlH4](-) tetrahedron, which in turn reduces the dehydrogenation temperature exhibited by LiAlH4 when Ti-containing additives are used.

Keywords

REVERSIBLE HYDROGEN STORAGE; METAL-HYDRIDES; CRYSTAL-STRUCTURES; ALUMINUM-HYDRIDE; COMPLEX HYDRIDES; CHEMICAL-BOND; TI; DECOMPOSITION; ALANATE; LITHIUM

DOI

10.1021/jp3050109

Citation

J. Phys. Chem. C, 2012, 116 (42), pp 22327–22335

Date of this Version

10-25-2012

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