Investigations on the structural, microstructural and dehydrogenation/rehydrogenation behavior of Ti doped sodium aluminum hydride materials

In this paper, we have carried out investigations on Ti doping to increase the desorption kinetics of sodium aluminum hydride (NaAlH4) materials. Ti powder can be directly used for doping in the preparation of Ti doped NaAlH4 materials (Ti:NaAlH4). Out of various materials corresponding to NaAlH4-x mol% Ti (x = 1, 2, 3,4,5,6), we have found that the material with x = 3 mol% is the optimum material. It shows the maximum storage capacity similar to 5.23 wt% for the first two reactions at 150 and 210 degrees C, respectively. The first decomposition reaction of Ti doped NaAlH4 material was found to depend upon milling time. The optimum milling time for Ti doping was 10 min under argon atmosphere at 1500 rpm. The desorption kinetics improved nearly three times for Ti doped materials as compared to the procured materials. Rehydrogenation occurred at 110 degrees C under similar to 10 MPa pressure in hydrogen environment within 8 h. The hydrogen storage capacity of this material was found to gradually decrease to 2.93 wt% after 15th cycles. The structural and microstructural characterizations have been evaluated by X-ray diffraction and scanning electron microscopy. The results of the present investigations will be described and discussed. (C) 2006 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.