Atomic and Molecular Hydrogen Interaction with Ti-Doped Al (100): Hydrogen Dissociation and Surface Alane Formation

A comprehensive research effort on the atomistic mechanisms underlying hydrogen storage in Ti-doped NaAlH$_{4}$ is aimed at deriving a knowledge base for the rational optimization of this and other related complex hydride materials. Our investigation focuses on the role of the Ti dopants in promoting reversible hydrogenation, a key requirement for any practical hydrogen storage material. The re-hydrogenation reaction proceeds from the crucial initial step of dissociative adsorption of molecular hydrogen on Al or NaH. A specific Al:Ti complex was recently predicted as an active site for H$_{2}$ dissociation on extended Al(100) surfaces [1]. Combining high-resolution surface imaging experiments (scanning tunneling microscopy, low-energy electron microscopy) with density functional theory, we are investigating the dissociative adsorption of H$_{2}$ on Ti-doped Al(100) prepared in ultrahigh vacuum. We will discuss our progress toward identifying catalytically active sites for H2 dissociation on this surface, as well as pathways toward the formation of mobile Al-species. [1] S. Chaudhuri and J.T. Muckerman, J. Phys. Chem. B 109, 6952 (2005).