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This article presents the reversible hydrogen storage capacities of Li-decorated Si6C14 and Si8C12 using Density Functional Theory (DFT). The chemical stabilities of the designed Si6C14Li6 and Si8C12Li4 nanocages are investigated using HOMO-LUMO gaps and various global reactivity descriptors such as chemical hardness and electrophilicity index. Our study reveals that each Li atom decorated over the designed Si6C14 and Si8C12 nanocages can hold up to 5H2 molecules with adsorption energy lying in the optimum range of 0.14-0.085 eV, thereby yielding an overall gravimetric density of 13.8% and 9.2% respectively. The interaction between adsorbed H2 molecules and the Li metal sites is found to occur via non-covalent and closed shell type of interaction. The H2 molecules are adsorbed in a quasi-molecular fashion with elongated bond length. The molecular dynamics study reveals that most of the H2 molecules get desorbed from the designed host nanocages at 300K without causing any significant structural changes, which confirms their reversibility. When the adsorption and desorption conditions are set at 100K/60bar and 240K/1bar respectively, the practical storage gravimetric densities of Si6C14Li6 and Si8C12Li4 cages are estimated to be 13.73 wt% and 9.08 wt%, which are relatively high in comparison to the US-DOE target of 5.5 wt% by the year 2020. Hence, the computationally designed Si6C14Li6 and Si8C12Li4 nanocages can be regarded as prospective systems for hydrogen storage applications.

In this work, we studied the hydrogen adsorption-desorption properties and storage capacities of Ti functionalized [2,2,2]paracyclophane (PCP222) using density functional theory and molecular dynamic simulation. The Ti atom was bonded 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 5.97 eV preventing the Ti clustering over PCP222 surface. On adsorption of hydrogen, the first H2 molecule was chemisorbed over PCP222 with a binding energy of 1.79 eV with the Ti metals. Further addition of H2 molecules, however, exhibited their physisorption over PCP222-Ti through the Kubas type H2 interaction. The charge transfer mechanism during the hydrogen adsorption was explored by the Hirshfeld charge analysis and electrostatic potential map, and the PDOS, and Baders topological analysis revealed the nature of the interaction between Ti and H2. The PCP222 functionalized with three Ti atoms showed a maximum hydrogen uptake capacity of up to 7.37 wt%, which was fairly above the US-DOE criterion. The practical H2 storage estimation revealed that at ambient conditions, the gravimetric density of up to 6.06 wt% H2 molecules could be usable, and up to 1.31 wt% of adsorbed H2 molecules were retained with the host. The ADMP molecular dynamics simulations assured the reversibility by desorption of adsorbed H2 and the structural integrity of the host material at sufficiently above the desorption temperature (300K and 500K). Therefore, the Ti-functionalized PCP222 can be considered as a thermodynamically viable and potentially reversible H2 storage material.

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.

This work reports the hydrogen storage, and delivery capacities of Sc and Y functionalized [1,1]paracyclophane using dispersion corrected density functional theory calculations. The Sc and Y atoms are bind strongly with benzene rings of [1,1]paracyclophane. Each Sc and Y atom functionalized over [1,1]paracyclophane adsorb up to 6 H2 molecules via Kubas interaction achieving maximum gravimetric density up to 8.22 wt% and 6.33 wt%, respectively. The calculated average hydrogen adsorption energy (0.36 eV) is lower than the chemisorption but higher than the physisorption process. The kinetic stabilities are verified through the HOMO-LUMO gap and different global reactive descriptors. ADMP molecular dynamics simulations reveal the reversibility of adsorbed H2 molecules at sufficiently above the room temperature and the solidity of host material at 500 K. Average Van't Hoff desorption temperature for Sc and Y decorated system was calculated to be 439 K and 412 K respectively at 1 atm of pressure. The estimated thermodynamically usable hydrogen capacities are found to be 5.92 wt% and 5.87 wt% of hydrogen which fulfil the hydrogen energy criteria (by 2025) of US-DOE. Hence, we believe that Sc and Y functionalized [1,1]paracyclophane can be considered as a thermodynamically viable, and potential reversible hydrogen storage materials at ambient environment.