A synergistic effect of NH3BH3 and H2 on their pressurization metallization: An Ab initio molecular dynamics study

Abstract

Ammonia borane (NH3BH3, AB), as a typical hydrogen-rich compound, is expected to be a promising hydrogen source for low-pressure metallization materials. However, its microscopic electronic properties subjected to pressure are not sufficiently understood yet. In this study, we systematically investigate the pressurization process of AB and its complex with H2 to uncover their metallization mechanism, using ab initio molecular dynamics method. As pressure increase, AB first undergoes partial dehydrogenation to liberate some H2 molecules. The metallization progress is effectively promoted via HH⋯HB interaction between new-formed H2 and -BHx group, with the metallization pressure of 450 GPa. As to ABH2 compound, the electron states of AB are first activated through the enhanced interaction of HH⋯HB deriving from the additional H2. In turn, the HH bonds within the corresponding H2 molecules are partially polarized. The special H2-couples are formed through the HH⋯HH interaction, promoting the electron dispersion with each other. The whole electron channel of ABH2 system is threaded together by the synergistic interactions of HH⋯HB and HH⋯HH, which significantly accelerate the pressurization metallization progress, resulting in a really lower metallization pressure of 250 GPa. Our study elucidate the synergistic metallization mechanism of AB and H2 system for the first time, which would provide a great inspiration for low-pressure metallization studies of hydrogen or hydrogen-rich materials.