First-Principles Study of LiBH₄ Nanoclusters and Their Hydrogen Storage Properties

Recent experimental studies suggest faster desorption kinetics, improved reversibility, and more favorable thermodynamics for confined LiBH₄ nanoparticles as compared to bulk. We study the structures, total energies, and decomposition reactions of LiBH₄ nanoparticles using density functional theory calculations. We find that the reaction energies of nanoclusters with a diameter ≳2 nm are very close to that of bulk LiBH₄. Only very small clusters with a diameter <1 nm are significantly destabilized relative to the bulk. The thermodynamics of such small clusters is unfavorable, however, and leads to dehydrogenation temperatures that are higher than that of the bulk. Although small (LiBH₄)_<i>n</i> nanoclusters exhibit a number of different geometries, they show only little variation in the total energy per formula unit. Of all possible decomposition reactions of (LiBH₄)_<i>n</i>, the reaction where diborane is released, is unfavorable for most cluster sizes, whereas the hydrogen desorption reaction to Li₂H₁₂B₁₂ is most favorable. This suggests that the experimentally observed improvement of the (de)­hydrogenation properties of LiBH₄ can be attributed to an improvement of the kinetics of the latter reaction