  In this work, we have studied the hydrogen adsorption-desorption properties
and storage capacities of Li functionalized [2,2,2]paracyclophane (PCP222)
using dispersion-corrected density functional theory and molecular dynamic
simulation. The Li atom was found to bond strongly with the benzene ring of
PCP222 via Dewar interaction. Subsequently, the calculation of the diffusion
energy barrier revealed a significantly high energy barrier of 1.38 eV,
preventing the Li clustering on PCP222. The host material, PCP222-3Li adsorbed
up to 15H2 molecules via a charge polarization mechanism with an average
adsorption energy of 0.145 eV/5H2, suggesting a physisorption type of
adsorption. The PCP222 functionalized with three Li atom showed maximum
hydrogen uptake capacity up to 8.32 wt%, which was fairly above the US-DOE
criterion. The practical storage estimation revealed that the PCP222-3Li
desorbed 100% of adsorbed H2 molecules at the temperature range of 260 K-300 K
and pressure range of 1-10 bar. The maximum H2 desorption temperature estimated
by the Vant-Hoff relation was found to be 219 K and 266 K at 1 bar and 5 bar,
respectively. The ADMP molecular dynamics simulations assured the reversibility
of adsorbed H2 and the structural integrity of the host material at
sufficiently above the desorption temperature (300K and 500K). Therefore, the
Li-functionalized PCP222 can be considered as a thermodynamically viable and
potentially reversible H2 storage material below room temperature.
