Abstract:
The use of hydrogen as a sustainable clean energy source has several benefits, such as
reduction in dependency on petroleum fuel and emission of green house gases, and
enhanced energy security. The H2 storage properties of Sc grafted calix[4]arene (CX) and
octamethylcalix[4]arene (MCX) are investigated by using density functional theory with
M06/6-311G(d,p) level of theory. It is observed that Sc strongly binds with benzene rings of
CX and MCX through Dewar coordination with average Sc binding energy of 1.09 and
1.25 eV, respectively for CXSc4 and MCXSc4. Each Sc atom adsorbs 4 H2 molecules on both
the Sc grafted systems and H2 molecules are bound by Kubas interaction with H2 interaction energy in the range of 0.2e0.5 eV. The calculated conceptual reactivity index shows
the stability of the systems increases with number of hydrogen molecules. Hirshfeld
charge analysis shows the charge transfer mechanism during H2 adsorption. BornOppenheimer molecular dynamics simulations of CXSc4-16H2 and MCXSc4-16H2 systems,
show that these systems are stable up to 273 K and all the adsorbed H2 releases at 373 K.
The hydrogen storage capacity of Sc grafted CX system is found to be 8.9 wt % and for MCX
system is 9.7 wt %. The energy and storage capacity meets the US Department of Energy
target, which makes them a propitious hydrogen storage material.
