Direct formation of Na3AlH6 by mechanical milling NaH∕Al with TiF3

Na 3 Al H 6 can be directly formed by mechanical milling NaH∕Al with TiF3 under hydrogen atmosphere. The hydrogenation fraction of NaH increases with increasing the milling time, and reaches up to 0.61 after 20h milling. Thus-formed Na3AlH6 exhibits unexpected polymorphic transformation and decomposition behaviors. This, together with the unusual hydrogen storage performance of the mechanically prepared materials, provides us a suggestive perspective to probe the favorable modification of the thermodynamics of Na3AlH6 and nature of active Ti-species in Ti-doped NaAlH4.