Long term cycling behavior of titanium doped NaAlH4 prepared through solvent mediated milling of NaH and Al with titanium dopant precursors

A simple and an efficient synthesis route, solvent mediated milling of NaH and Al with 2 mol% of the dopant precursor, Ti(OBu)(4) followed by hydrogenation, has been developed and employed to synthesize Ti-doped NaAlH4. The long-term hydrogenation and dehydrogenation, up to 100 cycles were carried out systematically. Reversibility of about 3.4 wt.% hydrogen release was obtained during the first dehydrogenation (160 degreesC) run after the initial hydrogenation of Ti-doped (NaH + Al) at 150 degreesC; similar to 11.4 MPa H-2 for 12 h. In the subsequent cycles, the storage capacity increased, reaching an optimum of 4.0 wt.%. This capacity was retained for 40 cycles with the dehydrogenation kinetic curves showing remarkable reproducibility. Comparison of the X-ray diffraction profiles of Ti-doped (NaH + Al) from initial and final stages of the cycling study reveals a growing resistance to the hydrogenation of Na3AlH6 to NaAlH4. (C) 2004 Elsevier B.V. All rights reserved.