Transportation of hydrogen atom and molecule through X12Y12 nano-cages

Hydrogen technology provides efficient, clean and environment friendly alternative to fossil fuel. A major challenge in use of hydrogen fuel is effective storage and release of hydrogen. Therefore, information regarding the barrier for encapsulation and decapsulation are very vital for understanding the phenomenon. A number of reports describe exo(endo)hedral binding of H-2 to inorganic X12Y22 fullerenes; however, the information regarding the barrier for en(de)capsulation are very scarce. In this study, the barriers for encapsulation and release of hydrogen atom and hydrogen molecule through X12Y12 nano cages (where X = Al, B, Y = N, P) are studied. The translation of H/H-2 through the surface of nano-cages (permeability) is studied through density functional theory calculations with MO5-2X method. The kinetic barriers for en(de)capsulation are obtained through scanning potential energy surface along the motion through hexagon of the nano-cage. The size of the nano-cage plays significant role in determining the barrier for en(de)capsulation. The relative stability of exohedral and endohedral complexes of H-2/H with X12Y12 nano-cages is obtained through binding energy calculations. Distortion energies are also calculated and the results show that encapsulation of H-2/H does not distort the nano-cage. Moreover, important minima along PES are also fully characterized. Electronic structures of nano cages including HOMO-LUMO gap, TDOS, PDOS and excitation energies are analyzed. The H-L gap analysis shows that exohedral complexes have minimal effect on the electronic nature of the nano-cage whereas the endohedral complexes have marked effect on the H-L gap. (C) 2017 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.