Geometry, Electronic Properties, and Hydrogen Adsorption Properties of Li₃N-Based Nanostructures

Recent studies of hydrogen storage have focused on lithium metal atoms as dopants in a variety of substrates as Li is the lightest metallic element in the periodic table. In this work, we have explored the role of Li 3 N nanostructures in hydrogen storage as they possess Li atoms with varying degrees of coordination. We have performed detailed calculations of geometries, electronic structures, and hydrogen adsorption properties of free (Li 3 N) n ( n = 1−7) clusters and those supported on BN nanoribbons by using density functional theory and generalized gradient approximation for the exchange and correlation potential. We found general motifs of (Li 3 N) n clusters where N sites form polygons for n ≤ 4 and polyhedrons n ≥ 5. The binding energies per formula unit increase with size, whereas the HOMO−LUMO gaps decrease. The HOMO is mainly contributed by Li and the LUMO by N. The bonding between Li and N has both ionic and covalent character. Lithium sites with low coordination are found to have a stronger adsorption energy for hydrogen molecules, which varies in the range of 0.08−0.11 eV/H 2 . When deposited on a BN nanoribbon, the Li 3 N molecules show stronger adsorption of hydrogen due to the changes in charge distribution. This suggests that Li 3 N molecules or small clusters can be introduced in porous substrates for enhancing hydrogen storage.