Potential main group amine borane-based chemical hydrogen storage molecular systems

Abstract

The thermodynamics as a function of the temperature for the decomposition of the substituted amine boranes X(NH2BH3)3 and X(BH2NH3)3 for X = N and P and E(NH2BH3)4 and E(BH2NH3)4 for E = C and Si were predicted using composite correlated molecular orbital G3(MP2) theory. The relative stabilities of isomers were explained using bond dissociation energies. Equilibrium concentrations of products with respect to temperature were determined using Gibbs free energy minimization. The activation energy for loss of the first H2 was calculated at the G3(MP2)B3 level and is larger than the respective bond dissociation energy to lose terminal BH3 or NH3 via dative bond cleavage. Dipole moments and polarizabilities were calculated at the DFT/B3LYP level and boiling points were calculated at the DFT/BP/COSMO-RS level. Planar fits were developed for the boiling points of N(BH2NH3)3, P(BH2NH3)3, C(BH2NH3)4, and Si(BH2NH3)4 dehydrogenation products using dipole moment, polarizability, and solvent cavity surface area.