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Hydrogen storage in Li functionalized [2,2,2]paracyclophane at cryogenic to room temperatures: A computational quest

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.