Enhanced Effect of an External Electric Field on NH₃BH₃ Dehydrogenation: an AIMD Study for Thermolysis

How to improve the dehydrogenation properties of ammonia borane (AB, NH₃BH₃) is always a challenge for its practical application in hydrogen storage. In this study, we reveal the enhanced effect of an external electric field (E _ext) on AB dehydrogenation by means of the ab initio molecular dynamics method. The molecular rotation induced by an electrostatic force can facilitate the formation of the H-N···B-H framework, which would aggregate into poly-BN species and further suppress the generation of the volatile byproducts. Meanwhile, the dihydrogen bond (N-H^δ+···^δ-H-B) is favorably formed under E _ext, and the interaction between relevant H atoms is enhanced, leading to a faster H₂ liberation. Correspondingly, the apparent activation energy for AB dissociation is greatly reduced from 18.42 to around 15 kcal·mol^-1 with the application of an electric field, while that for H₂ formation decreases from 20.4 to about 16 kcal·mol^-1. In the whole process, the cleavage of the B-H bond is more favorable than that of the N-H bond, no matter whether the application of E _ext. Our results give a deep insight into a positive effect of an electric field on AB dehydrogenation, which would provide an important inspiration for hydrogen storage in industry applications.