Direct Pyrolysis Dehydrogenation Mechanism of Ammonia Borane and Alkali Metal Substituted Ammonia Borane

Abstract

As a material with high hydrogen storage density, ammonia borane has attracted the attention of researchers. Ammonia borane can release hydrogen gas through hydrolytic dehydrogenation and pyrolysis dehydrogenation, where hydrolytic dehydrogenation has a low actual hydrogen storage density and is expensive, which is not conducive to practical application. Direct thermal dehydrogenation research shows that improving the dehydrogenation performance of ammonia borane by metal substitution can not only increase the dehydrogenation rate, but also suppress the generation of impurity gases. In this paper, the density functional theory (DFT) is used to calculate the structural parameters, density of states, and HOMO-LUMO energy difference to obtain the dehydrogenation stability of ammonia borane and alkali metal substituted ammonia borane. Subsequently, the reaction energy barriers of the N-H ... H-B path and the M-H ... H-N path are calculated to obtain which dehydrogenation path is easy to occur. The results show that alkali metal substituted ammonia borane MAB(M = Li, Na, K) is easier to dehydrogenate than AB, and MAB is more likely to dehydrogenate by forming M-H ... H-N double hydrogen bonds. Density functional theory calculations can obtain the structural parameters and related thermodynamic information of each stagnation point on the dehydrogenation reaction path, which provides theoretical guidance for the research and improvement of the dehydrogenation performance of ammonia borane.