Confinement effects on structural, electronic properties and dehydrogenation thermodynamics of LiBH4

Confinement effect on the structural, electronic and thermodynamic properties of LiBH4 is investigated by density functional theory. The thermodynamically and dynamically stable confinement structure is testified to be γ-LiBH4@C31Ti according to the adsorption energy and vibrational frequency calculations. The tridentate structure formed by [BH4]− and Li+ in the unconfined LiBH4 changes into bidentate structure in γ-LiBH4@C31Ti. We observe that both the occupied and unoccupied states of H 1s, B 2s, B 2p, Li 2s, and Li 2p orbitals in the partial DOSs of γ-LiBH4@C31Ti shift to high energy level and the splits of DOS peaks occur at the states of H 1s, B 2p, and Li 2p orbitals. Different from the first-step decomposition reaction of LiBH4, the one for γ-LiBH4@C31Ti changes into 2LiBH4@C31Ti → 2LiH + 2B@C31Ti + 3H2. Moreover, the reaction enthalpy for the first-step decomposition reaction of γ-LiBH4@C31Ti decreases to 5.864 eV, which is smaller than that (17.204 eV) of LiBH4. According to the hydrogen removal energy calculations, we observe that the confinement effects make the removal of the first and second hydrogen atoms in γ-LiBH4@C31Ti easy.