Abstract:
Hydrogen is the most promising candidate for a
sustainable energy source in the transport sector. However, the
storage of hydrogen is a major problem. Calix[4]arene (CX) is
functionalized with Ti and Li metals on the delocalized π
electrons of benzene rings, and the metal-functionalized
system is studied for hydrogen storage efficiency by applying
density functional theory using the M06 hybrid functional and
6-311G(d,p) basis set. The calculated binding energy indicates
Ti coordinates with CX strongly while Li coordinates weakly
and the binding of CX and metal is through Dewar
mechanism. On saturation with hydrogen, each Ti atom
traps four H2 molecules while each Li atom traps three H2 molecules on CX. Hydrogen molecules are adsorbed on the metal
atoms by Kubas−Niu−Rao−Jena interaction. The global reactivity index obtained for the system obeys the maximum hardness
and minimum electrophilicity principle. Molecular dynamics simulations are performed using spin-polarized generalized gradient
approximation with the Perdew−Burke−Ernzerhof functional including Grimme diffusion parameter on H2 saturated systems.
The dissociation of H2 molecules in the Ti-functionalized CX system begins from 273 K, while all the H2 molecules are desorbed
by 473 K. The storage capacity is found to be 8.7 wt % for Ti and 10.1 wt % for Li-functionalized CX. When the Ti atom is
intercalated between the two CX moieties, the storage capacity does not reduce significantly. This study reveals that the Tifunctionalized CX is a potential reversible hydrogen storage material.
