2009 Annual Meeting

(594f) First Principles Study of Dehydrogenation Reaction Intermediates of Complex Metal Borbohydrides

Authors

Karl Johnson - Presenter, University of Pittsburgh
Anant Kulkarni - Presenter, University of Pittsburgh
David S. Sholl - Presenter, Georgia Institute of Technology
Duane D. Johnson - Presenter, University of Illinois
Lin-Lin Wang - Presenter, University of Illinois


Complex metal borohydrides are the promising materials for onboard reversible hydrogen storage. In particular, materials of the form M(BH4)2, where M= Ca or Mg have received considerable attention due to its high gravimetric capacity > 11 wt % H. The experiments have shown that the first step in the dehydrogenation is

6M(BH4)2 -> 5MH2+MB12H12+13H2,

which involves formation of an intermediate phase, MB12H12, M= Mg and Ca. It should be noted that this intermediate is amorphous in nature and has not been properly understood.

Using the first-principles study we propose that MB12H12 has a wealth of nearly isoenergetic states that are structurally distinct. The predicted polymorphs are characterized by different orientations of the closo-borane groups and location of the cations. The results of our study are used to shed light on the nature of the intermediate phase MB12H12 with special reference to the energetics, the reactions they undergo, thermodynamics and the XRD-pattern.