The suitability of the solid NHxBHx (x = 1-4) compounds for hydrogen storage has recently been evaluated. The amine boranes have excellent weight percent storage for H2 with BH3NH3 having 19% if 3 molecules of H2 are produced and the salt (NH4)(BH4) having 24% if 4 molecules of H2 are produced. In both cases, the final product would be BN. Thus, the NHxBHx series of compounds (x = 1-4) are attractive targets for chemical H2 storage materials. The properties of molecular complexes (AB)2, diammoniate (DADB), [BH3-NH2-BH3]- NH4+ (DBDA) were characterized based on the results of electronic structure calculations. The thermodynamically unfavorable step of formation of ionic pairs was compensated to a large extent by a more favorable intermolecular interaction term. The DADB and DBDA complexes differed not only in the distribution of the positive and negative electrostatic poles, but they also had different symmetries and geometries. Their dipole moments differed significantly: 6.8 and 5.6 D for DADB and DBDA, respectively, in consequence of the differences in interatomic distances. The ammonia borane dimer was more stable than molecular DADB and DBDA ionic pairs by > 10 kcal/mole. This is an abstract of a paper presented at the ACS Fuel Chemistry Meeting (Washington, DC Fall 2005).
|Number of pages||3|
|Journal||ACS Division of Fuel Chemistry, Preprints|
|Publication status||Published - Dec 1 2005|
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