Location of Ti Catalyst in the Reversible AlH3 Adduct of Triethylenediamine

AlH3, a metastable binary hydride with a hydrogen content of 10.1 wt % hydrogen and a density of 1.48 g/mL, is a potential lightweight hydrogen storage system for transportation applications. A key component to understanding the discharge and uptake of hydrogen is the role of the Ti dopant in these processes. Here, the morphological and compositional changes caused by the synthesis and dehydriding of the AlH3 adduct of triethylenediamine was determined by using a combination of scanning electron and scanning transmission electron microscopy as well as X-ray energy dispersive spectroscopy. It is shown that there is significant loss of the added Ti at each step in the synthesis; the Ti agglomerates in the Al particles, causing enrichment, and the amount of Ti needed to catalyze the activity is on the order of 0.4 at.%, which amounts to approximately a 90% reduction from the amount added.