NaAlH₄ is among lightweight metal hydrides being investigated as a means of storing hydrogen, e.g. for fuel cell applications. Decomposition occurs in three steps upon heating:

(a) Calculate the H content of NaAlH₄ as a wt %. 

(b) Step (3) occurs above 670K and this limits the practical dehydrogenation steps to (1) and (2). What is the hydrogen storage capacity (in wt %) of NaAlH₄ if only steps (1) and (2) are considered? 

(c) Unfortunately, the kinetics of the dehydrogenation of NaAlH₄ militate against practical applications as a hydrogen storage material, but doping the material with Ti improves the kinetics both of dehydrogenation and rehydrogenation. Comment on this statement in terms of the role of the dopant, and the need for both dehydrogenation and rehydrogenation to be viable processes.

Transcribed Image Text:

3NaAlH4 → Na3AlH6 +2A1+ 3H₂ Na3AlH63NaH+Al+ 1.5H₂ 3NaH3Na + 1.5H₂ (1) (2) (3)