Reaction stoichiometry between TiCl 3 and NaAlH 4 in Ti-doped alanate for hydrogen storage: The fate of the titanium species

Abstract

In order to understand the final state of the TiCl 3 dopant during the dehydrogenation and rehydrogenation cycles of NaAlH 4, we determined the reaction stoichiometry between TiCl 3 and NaAlH 4 by measuring the amount of hydrogen evolution from NaAlH 4 with the varying TiCl 3 -load. We found that: (i) TiCl 3 reacted with 3 M equivalents of NaAlH 4 during the doping process of ball-milling, (ii) the Ti dopant continued to react with NaAlH 4 during the first dehydrogenation process until total six equivalents of NaAlH 4 were consumed, and (iii) Ti fixed Al, not NaH, so that Al became insufficient during the rehydrogenation process. These findings lead to the conclusion that the reaction stoichiometry between Ti and Al is 1:6, which probably yields TiAl 6 and plays a catalytic role in the hydrogen storage reactions of Ti-doped NaAlH 4.