Hydrogen cycling behavior of zirconium and titanium-zirconium-doped sodium aluminum hydride

The dehydrogenation kinetics of NaAlH4 are significantly enhanced upon doping with zirconium through homogenization with 2 mol% Zr(OPr)(4). TPD measurements show that zirconium is inferior to titanium as a catalyst for the dehydriding of NaAlH4 to Na3AlH6 and Al but a superior catalyst for the dehydriding of Na3AlH6 to NaH and Al. The benefit of both catalytic effects can be realized in materials containing a combination of both titanium and zirconium catalysts. After the initial dehydriding/rehydriding cycle, NaAlH4 which is doped with titanium and/or zirconium is stabilized with a greater than 4 wt% cyclable hydrogen capacity. The onset of rapid dehydriding occurs in the titanium containing materials at temperatures below 100 degrees C. (C) 1999 Elsevier Science S.A. All rights reserved.