Effect of confinement inside CNTs for improving dehydrogenation from MXH4 clusters where M = Na, Li and X = Al, B

Carbon nanomaterials such as fullerenes, CNTs and graphene have been reported as effective catalysts in improving the desorption behavior of complex metal hydrides. In comparison to catalytic effect, nanoconfinement plays... [ view full abstract ]

Carbon nanomaterials such as fullerenes, CNTs and graphene have been reported as effective catalysts in improving the desorption behavior of complex metal hydrides. In comparison to catalytic effect, nanoconfinement plays dominant role in improving the dehydrogenation of LiBH4. We present results of our investigation into the effect of confinement of MXH4, where M = Na, Li and X = Al, B inside carbon nanotubes (CNTs). The calculations have been performed using density functional theory. NaAlH4, NaBH4, LiAlH4 and LiBH4 clusters were confined inside (9,0), (10,0) and (11,0) CNTs diameter of 7.47 Å , 7.87 Å , 8.73 Å respectively. The MXH4 interacts strongly with the surface atoms of CNT and CNT (11,0) is found to be the smallest stable system for confinement of MXH4 clusters. Hydrogen release energy(EHre) of NaAlH4 decreases sharply by 68.3%, w.r.t pure NaAlH4 cluster when confined inside CNT(11,0). Similarly, in CNT (11,0) EHre decreases by 38.1 % for LiAlH4, 12.7 % for NaBH4 and 19.1 % for LiBH4. The results can be interpreted in terms of charge transfer between the CNT and confined MXH4 clusters. Thus, resulting confinement had a profound effect in improving the energetics of complex metal hydrides without catalyst. The results provide an outline for extending the work to larger nanoparticles of metal hydrides inside CNTs of larger diameters and other carbon nanostructures.