Reversible hydrogen storage via titanium-catalyzed LiAlH4 and Li3AlH6

A vibrating-mill technique, which can activate the reaction system by bring ing the reagents into very close contact at the preparative scale and by pr oviding extra mechanical energy, much more effectively than the well-known ball-milling method, was used to prepare titanium(III) chloride (TiCl(3)(.) 1/3AlCl(3))-doped lithium tetrahydridoaluminate (LiAlH4) and lithium hexahy dridoaluminate (Li3AlH6) powders with nanocrystallites. The phase structure and dehydriding/rehydriding properties were characterized by using X-ray d iffraction (XRD), scanning electron microscopy (SEM), thermogravimetry (TG) , and differential scanning calorimetry (DSC). The mechanism of reversible dehydrogenation and rehydrogenation was examined by means of X-ray photoele ctron spectroscopy (XPS). Thermodynamic and kinetic measurements showed a d istinct change for the dehydriding/rehydriding reactions over the temperatu re range 25-250 degreesC. From the Arrhenius plot of hydrogen desorption ki netics, apparent activation energies were found to be 42.6 and 54.8 kJ/mol H-2 for the hydride decompositions of LiAlH4 and Li3AlH6, respectively. The results based on the properties of reversible hydrogen storage and catalys is function indicate that both the homogeneous distribution of Ti-catalyzed nanocrystalline complex hydrides and the Ti-catalyst with a Ti-0 double le ft right arrow Ti3+ (Ti-0/Ti2+/Ti3+) defect site play important roles in op timizing the reversible hydrogen storage.