1 research outputs found
First-Principles Study of Intrinsic Defects in Ammonia Borane
Solid
ammonia borane is a promising hydrogen storage material but
suffers from a slow and ill-controlled dehydrogenation process. We
studied intrinsic point defects that might play a role for hydrogen
release by means of first-principles calculations augmented with van
der Waals (vdW) corrections. The vdW corrections proved to be crucial
for structural properties and also for energies in some cases. For
vacancy and interstitial defects of single H as well as of molecular
(NH<sub>3</sub>, BH<sub>3</sub>) type, we determined formation energies
and local lattice structures of the defects in various charge states.
Atomic H-related vacancies and interstitials exist predominantly in
charged states in agreement with their chemical, i.e., protonic or
hydridic, character. For molecular defects, some NH<sub>3</sub>- and
BH<sub>3</sub>-related neutral defects have rather low formation energies,
suggesting that the dehydrogenation of undoped ammonia borane is initiated
by the cleavage of the B–N bond. The relaxation pictures associated
with H-related defects can explain the observation of a variety of
oligomeric products in experiment. Besides, some low-energy defects
are found to form H<sub>2</sub> molecules spontaneously and thus might
catalyze the dehydrogenation reaction of doped ammonia borane