First-Principles Prediction of Intermediate Products in the Decomposition of Metal Amidoboranes

Abstract

The nonvolatile products remaining after the thermal decomposition of metal amidoboranes (MAB, M = metal) are amorphous and incompletely characterized, increasing the complexity of devising regeneration strategies for these potential hydrogen storage materials. Utilizing the combined prototype electrostatic ground state search and density-functional theory (PEGS+DFT), we find that potential reaction products ([NHBH2]−, [NBH]−, [N3H2B3H3]−, and polymer-M[NHBH2] anion groups) in the decomposition of LiAB and CaAB are calculated to be significantly endothermic, in contrast to the experimentally measured nearly thermoneutral values [∼−4 kJ/(mol H2) in LiAB and 3.5 kJ/(mol H2) in CaAB], suggesting that there are alternative products formed. The dianion group [NHBHNHBH3]2– has recently been suggested to form in the decomposition of a calcium amidoborane complex in solution. In LiAB and CaAB, we use PEGS+DFT to predict intermediate metal–dianion compounds, and the static H2 release enthalpy is 27.4 and 27.3 kJ/(...