Ab initio investigation of ammonia-borane complexes for hydrogen storage

Abstract

The structural, electronic, and thermodynamic properties of ammonia-borane complexes with varying amounts of hydrogen have been characterized by first principles calculations within density functional theory. The calculated structural parameters and thermodynamic functions (free energy, enthalpy and entropy) were found to be in good agreement with experimental and quantum chemistry data for the crystals, dimers, and molecules. The authors find that zero-point energies change several H2 release reactions from endothermic to exothermic. Both the ammonia-borane polymeric and borazine-cyclotriborazane cycles show a strong exothermic decomposition character (approximately -10 kcal/mol), implying that rehydrogenation may be difficult to moderate H2 pressures. Hydrogen bonding in these systems has been characterized and they find the N-H bond to be more covalent than the more ionic B-H bond.

High Influence of Potassium Bromide on Thermal Decomposition of Ammonia Borane†

“…In the case of 3, even a smaller amount of CDAB was observed without a traces of µADB (Table 4). Thus, decomposition of 1 can be satisfactorily modeled by a combined consideration of formation of both cyclic and linear polymers, 12 having in mind that the two mechanistic pathways are not independent, but mutually entangled since the starting species are equal. 4 A complete absence of these species is observed in the case of 3.…”

“…In a recent publication, Kobayashi et al used a combination of 11 B and 15 N NMR spectroscopy to successfuly resolve the species that appear at different temperatures between 100 and 200 • C. 13 Miranda and Ceder considered thermodynamics and vibrational spectra of AB decomposition by DFT on the basis of a simple model of two mechanistic pathways; the first leads toward linear and another toward cyclic polymers. 12 A comparative analysis of AB dehydrogenation in solution and in gas phase, given more recently by the Zimmerman's group, indicates considerably different reaction pathways in considered media. 5 Especially important is their consideration of formation of ionic species diammoniate of diborane (DADB), which is feasible in solution phase, particularly in polar media.…”

High‐Pressure Hydrogen Interactions with Polyaminoborane and Polyiminoborane

“…[12] Herein, we demonstrate reactions of H 2 and D 2 with PAB and PIB in the 2-4 GPa pressure range and temperatures up to 220 8C, in situ in a diamond anvil cell (DAC). [13] Isotopic scrambling of H 2 and D 2 , when thermodynamics prevent reversible reactions, [4,14] is proposed to occur by a mechanism involving "polymeric" FLPs.…”

The Search for Hydrogen Stores on a Large Scale; A Straightforward and Automated Open Database Analysis as a First Sweep for Candidate Materials

“…Many strong hydrogen storage candidates exist among covalent boron-hydrogen compounds such as NH3BH3 [62], NH3B3H7 [63] and H4N2BH3 [64]. The B-N-H combination is not an arbitrary one but defines a distinctive family of complex molecular species that are stabilised by the dative bond between the strong electron-donating Lewis base, nitrogen and the strong electron-accepting Lewis acid, boron [65,66]. The strength of this bonding interaction also provides a rationale as to why in ammonia borane, for example, the respective gaseous components, ammonia and borane are able to exist together as a covalent solid at ambient conditions.…”