The hydrogen storage property of Li-coated BCN is investigated by density functional theory calculations. BCN is an electron deficient fullerene. Li atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The binding energy (-2.90 eV) is much larger than the cohesive energy (1.63 eV) of bulk Li, and it prevents the Li atoms from aggregation. The coated Li atoms have large positive charges and the adsorbed hydrogen molecules can be moderately polarized by the Li ions. The computation shows that each Li atom coated on BCN can hold 2-3 H molecules with adsorption energies in the range of 0.21-0.24 eV/H. The BCNLi can adsorb 16 H and achieve a gravimetric hydrogen density of 8.63 wt. %. The present results indicate that alkali-metal atoms coated on electron deficient fullerenes can serve as hydrogen storage materials that can operate at ambient temperatures with high recycling storage capacity.
The hydrogen adsorption on Ca-decorated C 48 B 12 clusters is studied using density functional theory. The favorable binding site for Ca atom is the hexagonal C 4 B 2 rings. The strong interaction between Ca atoms and C 48 B 12 cluster hinders the aggregation of Ca atoms on the cluster surface. C 48 B 12 is an electron deficient system with a large electron affinity of 2.952 eV. The decorated Ca atoms transfer their electrons to the cluster easily. The net charges on the Ca atoms are in the range of
By considering the contribution of the higher order term representing the lowest approximation of beyond mean field correction and taking Roser-Zener tunneling as the underling process, we study the nonlinear Rosen-Zener transition of Fermi superfluid gas in a two-level system. We find that the nonlinearity can affect the quantun trasition in the fast scan limit and the adiabatic limit. We also derive the analytical expression for the of rectangular oscillation period dependent on nonlinear parameter. This provides a theoretical basis for a deeper understanding of the basis properties of Fermi gases.
In the mean-field theory and two-mode approximation, we study the self-trapping of superfluid Fermi gases in the BEC regime and in unitarity by observing the evolution of the population imbalance with time and the variation of the average of population imbalance with several non-linear interaction parameters. The high-frequency modulations of both the symmetric double-well potential and the potential well are studied. The boundary conditions of the self-trapping and non-self-trapping are given. We find that high-frequency modulation in a certain range of modulation can make the self-trapping phenomenon easier to achieve. Finally, we study the influence of the initial value on self-trapping, and find that the increase of the absolute of the initial value can make the self-trapping more conducive to the realization.
By using the analysis of phase, fixed point and tunneling rate between two wells, we study the nonlinear Landau-Zener transition of Fermi superfluid gases in a two-mode system. We find that the interaction between fermi pairs can affect the quantum transition. We also find that when the interaction parameter c is less than the critical value c*, in the adiabatic limit, the quantum adiabatic transition theorem is still satisfied, but when the interaction parameter c is greater than this critical value, the quantum adiabatic transition theorem will not be satisfied. Finally, we obtain the relationship between the tunneling rate and the scan rate by comparing with the linear case.
Hydrogen is considered as a potentially ideal substitution for fossil fuels in the future sustainable energy system because it is an abundant, clean and renewable energy carrier. A safe, efficient and economic storage method is the crucial prerequistite and the biggest challenge for the wide scale use of hydrogen. The nanomaterial is one of the most promising hydrogen storage materials because of its high surface to volume ratio, unique electronic structure and novel chemical and physical properties. It has been demonstrated that pristine nanostructures are not suitable for hydrogen storage, since they interact weakly with hydrogen molecule and their hydrogen storage density is very low. However, the hydrogen storage capacity of the nanostructures can be significantly enhanced through substitutional doping or decoration by metal atoms. Using density functional theory, we investigate the properties of hydrogen adsorption on Li-decorated C24clusters. Results show that the preferred binding site for Li atom is the pentagonal rings. The interaction of Li atoms with the clusters is stronger than that among Li atoms, thus hindering effectively aggregation of Li atoms on the surface of the cluster. The decorated Li atoms are positively charged due to electron transfer from Li to C atoms. When H2 molecules approach Li atoms, they are moderately polarized under the electric field, and adsorbed around the Li atoms in molecular form. Each Li atom in the Li-decorated C24 complexes can adsorb two to three H2 molecules. The H-H bond lengths of the adsorbed H2 molecules are slightly stretched. The average adsorption energies are in the range of 0.08 to 0.13 eV/H2, which are intermediate between physisorption and chemisorption. C24Li6 can hold up to 12 H2 molecules, corresponding to a hydrogen uptake density of 6.8 wt%. This value exceeds the 2020 hydrogen storage target of 5.5 wt% proposed by the U. S. Department of Energy.
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