Li decorated heteroborospherene C4B32 as high capacity and reversible hydrogen storage media: A DFT study

In this work, adsorption of H₂ molecules on heteroborospherene C_2v C₄B₃₂ decorated by alkali atoms (Li) is studied by density functional theory calculations. The interaction between Li atoms and C₄B₃₂ is found to be strong, so that it prevents agglomeration of the former. An introduced hydrogen molecule tilts toward the Li atoms and is stably adsorbed on C₄B₃₂. It is obtained that Li₄C₄B₃₂ can store up to 12H₂ molecules with hydrogen uptake capacity of 5.425 wt% and average adsorption energy of ?0.240 eV per H₂. Dynamics simulation results show that 6H₂ molecules can be successfully released at 300 K. Obtained results demonstrate that Li decorated C₄B₃₂ is a promising material for reversible hydrogen storage.     

Computational insights of alkali metal (Li / Na / K) atom decorated buckled bismuthene for hydrogen storage

The mechanism of hydrogen molecule adsorption on 2D buckled bismuthene (b-Bi) monolayer decorated with alkali metal atoms was studied using density functional theory based first principles calculations. The decorated atoms Li, Na and K exhibited distribution on surface of b-Bi monolayer with increasing binding energy of 2.6 eV, 2.9 eV and 3.6 eV respectively. The adsorption of H₂ molecule on the slabs appeared stable which was further improved upon inclusion of van der Waals interactions. The adsorption behaviour of H₂ molecules on the decorated slabs is physisorption whereas the slabs were able to bind up to five H₂ molecules. The average adsorption energy per H₂ molecules are in range of 0.1–0.2 eV which is good for practical applications. The molecular dynamics simulation also confirmed the thermodynamic stabilities of five H₂ molecules adsorbed on the decorated slabs. The storage capacity values are found 2.24 wt %, 2.1 wt %, and 2 wt %, for respective cases of Li, Na and K atoms decorated b-Bi. The analysis of the adsorbed cases pointed to electrostatic interaction of Li and H₂ molecule. The adsorption energies, binding energies, charge analysis, structural stability, density of states, and hydrogen adsorption percentage specifies that the decorated b-Bi may serve as an efficient hydrogen storage material and could be an effective medium to interact with hydrogen molecules at room temperature.     

Hydrogen trapping efficiency of Li decorated porous boron fullerene B38: The first-principles study

The demand for clean renewable energy is urgent in current. The hydrogen application is difficult mainly due to the ratively low capacity in the storage medium. In this work, the adsorption and desorption of the hydrogen molecules by the Li atoms decorated B₃₈ cage are studied by the density functional theory. The calculated largest binding energy of one Li atom (2.68 eV and 2.58 eV) is upon the hexagonal hole of the B₃₈ cage, which is much larger than the experimental cohesive energy of bulk Li (1.63 eV). Each Li atom in the outside of the B₃₈ cage can adsorb up to four H₂ molecules. The E_ad of B₃₈(Li-nH₂)₄ decreases from the 0.22 eV for n = 1 to the 0.11 eV for n = 4. The B₃₈(Li–4H₂)₄ structure achieves the 6.85 wt% hydrogen gravimetric density, which is higher than the goal of 5.5 wt% before 2017 set by the United States Department of Energy. The almost the same partial density of states for the fifth H₂ molecule as that of the isolated H₂ molecule, the longer 4.5 Å distance between the fifth H₂ molecule and the Li atom, together with the small NBO charges all reveal the weak electronic field around the Li⁺, which can interpret the weak H₂ adsorption mechanism. Finally, the B₃₈Li₄ structure can easily release 9H₂ molecules at 373 K known from the molecular dynamic simulation and practically trap about 1.08H₂ molecules at 373 K/3 atom condition calculated by the grand partition function. Thus, its reversible practical HGD of B₃₈Li₄-14.34H₂ is 6.18 wt%, which is almost the same value as the theoretical 6.85 wt% for B₃₈(Li–4H₂)₄. Our studies will be the strong theory basis for the future application in hydrogen storage material development.     

Lithium clusters on graphene surface and their ability to adsorb hydrogen molecules

This research describes the theoretical study of the adsorption of lithium clusters on graphene and the ability to capture hydrogen molecules. The results of the studied structures showed that the [Li₁C₅₄H₁₈]⁺ system is capable of accepting three hydrogen molecules showing adsorption energies of 0.12 eV. On the other hand, it is important to note that in [Li_nC₅₄H₁₈] n = 2–6 systems, the lithium atoms that do not interact with the graphene surface, they can adsorb up to four hydrogen molecules. The [Li₆C₅₄H₁₈]4H₂ system presented a higher adsorption energy value of 0.31 eV. Finally, the Li–H₂ interactions were characterized by a NBO analysis, which showed that hydrogen atoms are the donors and lithium atoms are the acceptors.     

Stabilized Li-decoration and enhanced hydrogen storage on reduced graphene oxides

Hydrogen storage properties of Li-decorated graphene oxides containing epoxy and hydroxyl groups are studied by using density functional theory. The Li atoms form Li₄O/Li₃OH clusters and are anchored strongly on the graphene surface with binding energies of −3.20 and −2.84 eV. The clusters transfer electrons to the graphene substrate, and the Li atoms exist as Li⁺ cations with strong adsorption ability for H₂ molecules. Each Li atom can adsorb at least 2H₂ molecules with adsorption energies greater than −0.20 eV/H₂. The hydrogen storage properties of Li-decorated graphene at different oxidation degrees are studied. The computations show that the adsorption energy of H₂ is −0.22 eV/H₂ and the hydrogen storage capacity is 6.04 wt% at the oxidation ratio O/C = 1/16. When the O/C ratio is 1:8, the storage capacity reaches 10.26 wt% and the adsorption energy is −0.15 eV/H₂. These results suggest that reversible hydrogen storage with high recycling capacities at ambient temperature can be realized through light-metal decoration on reduced graphene oxides.     

Hydrogen adsorption on Li decorated graphyne-like carbon nanosheet: A density functional theory study

Motivated by novel graphyne-like carbon nanostructure C₆₈-GY, spin-polarized DFT calculations with dispersion-correction were performed to investigate the hydrogen adsorption capacity of Li decorated C₆₈-GY nanosheet. The binding energy between Li and C₆₈-GY was larger than the cohesive energy of bulk metal, indicating Li atoms would prefer to separately attached on C₆₈-GY. The ab initio molecular dynamics simulation has been performed to confirm the stability of Li/C complex. When five Li atoms decorated on C₆₈-GY, 14H₂ molecules were captured. The maximum hydrogen storage density was 8.04 wt% with an average hydrogen adsorption energy of −0.227 eV per H₂. The positively charged Li atoms aroused electrostatic field and induced the polarization of H₂. It was notable to observe strong hybridization between the main peak of H-1s orbitals with Li below Fermi level, which was responsible for the enhancement of hydrogen binding energy, indicating its potential application on hydrogen storage.     

Electronic structure and hydrogen storage properties of Li–decorated single layer blue phosphorus

Single layer blue phosphorus (SLBP) is a promising two–dimensional material for nanoelectronic devices, but the electronic structure and hydrogen storage property of modified SLBP received little attention. Li atoms can be strongly bonded on SLBP in a 1:1 Li/P ratio with a binding energy larger than the cohesive energy of bulk Li. The geometric structure of SLBP suggests the 3s3p orbitals of the P atom hybridize in sp³ manner. But our analyses show that the 3s and 3p orbitals form bonding and antibonding orbitals respectively. The 3s orbitals are fully occupied as they have much lower energies, and the bonding orbitals formed by P 3p are occupied in pure SLBP. The decorated Li atoms transfer their 2s electrons to the antibonding orbital formed by P 3p. The Li atoms exist as +1 cations and they are ionically bonded on SLBP. H₂ molecules adsorbed on the Li⁺ cations are strongly polarized and form strong adsorption. When two H₂ are adsorbed on each Li atom decorated at the 1:1 Li/P ratio, the hydrogen storage capacity reaches 9.52 wt% but the H₂ molecules are arranged in two layers with the adsorption energy ?0.168 eV/H₂. When the Li atoms are decorated alternatively on the two sides of the P₆ rings with a Li/P ratio of 1:2, each Li atom can absorb two H₂ molecules in a single–layer; the hydrogen storage capacity is 5.48 wt% and the adsorption energy reaches ?0.227 eV/H₂. These results mean the Li–decorated SLBP can work at ambient temperature with high reversible hydrogen storage capacity.     

Li decorated penta-silicene as a high capacity hydrogen storage material: A density functional theory study

The H₂ adsorption characteristics of Li decorated single-sided and double-sided penta-silicene are predicted via density functional theory (DFT). The orbital hybridization results in Li atom strongly bind onto the surface of the penta-silicene with a large binding energy and it keeps the decorated Li atoms from aggregation. Moreover, Li decorated double-sided penta-silicene can store up to 12H₂ molecules with the average hydrogen adsorption energy of ?0.220 eV/H₂ and hydrogen uptake capacity of 6.42 wt%, respectively. The ab initio molecular dynamics (AIMD) simulations demonstrate the H₂ molecules are released gradually from the substrate material with the increasing simulation time and the calculated desorption temperature T_D is 281 K in the suitable operating temperature range. Our explorations confirm that Li decorated penta-silicene can be regarded as a promising hydrogen storage candidate for hydrogen storage applications.     

Density functional theory study on hydrogen storage capacity of metal-embedded penta-octa-graphene

H₂ storage capabilities of penta-octa-graphene (POG) adorned by lightweight alkali metals (Li, Na, K), alkali earth metals (Be, Mg, Ca) and transition metals (Sc, Ti, V, Cr, Mn) are studied by density functional theory. Metals considered, with the exception of Be and Mg, can be stably adsorbed to POG, effectively avoiding metal clustering. The average H₂ adsorption energies are calculated in a range from 0.14 to 0.95 eV for Li (Na, K, Ca, Sc, Ti, V, Cr, Mn) decorated POG. Because the H₂ adsorption energies for reversible physical adsorption lie in the range of 0.15–0.60 eV and the desorption temperatures fall in the range of 233–333 K under the delivery pressure, 4Li@POG and 2Ti@POG are found to be the most suitable for H₂ storage at ambient temperature. By polarization and hybridization mechanisms, up to 3 and 5 hydrogen molecules are stably adsorbed around each Li and Ti, respectively. The H₂ gravimetric densities can reach up to 9.9 wt% and 6.5 wt% for Li and Ti decorated POG, respectively. Our findings suggest that, with metal decoration, such a novel two-dimensional carbon-based structure could be a promising medium for H₂ storage.     

Li decorated C9N4 monolayer as a potential material for hydrogen storage

Based on first−principles calculations, we investigate the possibility of the two-dimensional porous C₉N₄ material as for hydrogen storage, and find that the adsorption energy of H₂ molecules on the pristine C₉N₄ is too weak to meet the requirements of hydrogen storage, whereas the adsorption on the Li−decorated sheet is relatively moderate. Each C₉N₄ unit cell can incorporate 6 Li atoms, of which 3 Li atoms are located above the intrinsic hole and the others are below. The unit cell can hold 14 hydrogen molecules with an average adsorption energy of −0.12 eV, which meets the reversible storage condition of hydrogen, and the gravity density reaches 7.04 wt%. Particularly, 6Li@C₉N₄ maintains excellent H₂ storage performance under a tensile strain within 2%. The ab initio MD simulations performed at 300 K show that all 14 H₂ molecules remained on the double sides of 6Li@C₉N₄ in the absence and presence of strain. Therefore, we predict that Li−modified C₉N₄ could be a potential material with excellent ductility for hydrogen storage at room temperature.     

A reversible hydrogen storage material of Li-decorated two-dimensional (2D) C4N monolayer: First principles calculations

Two-dimensional (2D) materials can be regarded as potential hydrogen storage candidates because of their splendid chemical stability and high specific surface area. Recently, a new dumbbell-like carbon nitride (C₄N) monolayer with orbital hybridization of sp³ is reported. Motivated from the above exploration, the hydrogen adsorption properties of Li-decorated C₄N monolayer are comprehensively investigated via first principles calculations based on the density functional theory (DFT). It is found that the Dirac points and Dirac cones exists in the Brillouin zone (BZ) from the calculated electronic structure and indicates the C₄N can be used as an excellent topological material. Also, the calculated phonon spectra demonstrate that the C₄N monolayer owns a strong stability. Moreover, the calculated binding energy of decorated Li atom is bigger than its cohesive energy and results in Li atoms disperse over the surface of C₄N monolayer uniformly without clustering. In addition, the Li₈C₄N complex can capture up to 24H₂ molecules with an optimal hydrogen adsorption energy of −0.281 eV/H₂ and achieves the hydrogen storage density of 8.0 wt%. The ab initio molecular dynamics (AIMD) simulations suggest that the H₂ molecules can be desorbed quickly at 300 K. This study reveals that Li-decorated C₄N monolayer can be served as a promising hydrogen storage material.     

A density functional theory and grand canonical Monte Carlo simulations study the hydrogen storage on the Li-decorated net-τ

To find ideal hydrogen storage media, hydrogen storage performance of Li decorated net-τ has been investigated by first-principles calculations. Maximum 6 Li atoms are adsorbed on net-τ, with the average binding energy of 2.15 eV for per Li atom. Based on 6Li-decorated net-τ, up to twenty H₂ molecules are adsorbed, with a high H₂ storage capacity of 12.52 wt% and an appropriate adsorption energy of 0.21 eV/H₂. Finally, H₂ uptake performance is measured by GCMC simulations. Our results suggest that Li-decorated net-τ may be a promising hydrogen storage medium under realistic conditions.     

A DFT-D3 investigation on Li,Na, and K decorated C6O6Li6 cluster as a new promising hydrogen storage system

Because of the increasing demand for energy sources, searching for reversible and high-capacity hydrogen storage materials plays a vital role in the extensively utilizing of hydrogen as a clean energy source. In this study, dispersion-corrected density functional theory (DFT-D3) calculations are utilized to examine the possibility of storing H₂ molecules on Li, Na, and K alkali metals decorated C₆O₆Li₆ cluster. To evaluate H₂ adsorption capability, the adsorption energies, electron density difference iso-surfaces, and charge-transfers are calculated and discussed. The results indicate that a hydrogen molecule is physisorbed on the Li@C₆O₆Li₆, Na@C₆O₆Li₆, and K@C₆O₆Li₆ with average adsorption energies of −0.264, −0.150, and −0.109 eV, respectively. Double-sided alkali metal atoms decoration can lead to the maximum gravimetric density of 15.68, 14.49, and 13.79 wt% for 2Li@C₆O₆Li₆–8H₂, 2Na@C₆O₆Li₆–10H₂, and 2K@C₆O₆Li₆–12H₂ complexes, respectively. Finally, desorption temperatures reveal that the systems can operate as reversible hydrogen storage materials.     

High-capacity hydrogen storage in Li-decorated (AlN)n (n = 12, 24, 36) nanocages

The capability of Li-decorated (AlN)_n (n = 12, 24, 36) nanocages for hydrogen storage has been studied by using density functional theory (DFT) with the generalized gradient approximation (GGA). It is found that each Al atom is capable of binding one H₂ molecule up to a gravimetric density of hydrogen storage of 4.7 wt% with an average binding energy of 0.189, 0.154, and 0.144 eV/H₂ in the pristine (AlN)_n (n = 12, 24, 36) nanocages, respectively. Further, we find that Li atoms can be preferentially decorated on the top of N atoms in (AlN)_n (n = 12, 24, 36) nanocages without clustering, and up to two H₂ molecules can bind to each Li atom with an average binding energy of 0.145, 0.154, 0.102 eV/H₂ in the Li_n(AlN)_n (n = 12, 24, 36) nanocages, respectively. Both the polarization of the H₂ molecules and the hybridization of the Li-2p orbitals with the H-s orbitals contribute to the H₂ adsorption on the Li atoms. Thus, the Li-decorated (AlN)_n (n = 12, 24, 36) nanocages can store hydrogen up to 7.7 wt%, approaching the U.S. Department of Energy (DOE) target of 9 wt% by the year 2015, and the average binding energies of H₂ molecules lying in the range of 0.1–0.2 eV/H₂ are favorable for the reversible hydrogen adsorption/desorption at ambient conditions. It is also pointed out that when allowed to interact with each other, the agglomeration of Li-decorated (AlN)_n nanocages would lower the hydrogen storage capacity.     

Hydrogen storage in lithium-decorated benzene complexes

Based on first-principles calculations, we find Li-decorated benzene complexes are promising materials for high-capacity hydrogen storage. Lithium atoms in the complexes are always positively charged, and each one can bind at most four H₂ molecules by a polarization mechanism. Therefore, a hydrogen uptake of 8.6 wt% and 14.8 wt% can be achieved in isolated C₆H₆–Li and Li–C₆H₆–Li complexes, respectively. The binding energy in the two cases is 0.22 eV/H₂ and 0.29 eV/H₂, respectively, suitable for reversible hydrogen storage. Various dimers may form, but the hydrogen storage capacity remains high or uninfluenced. This study provides not only a promising hydrogen storage medium but also comprehensions to other hydrogen storage materials containing six-carbon rings.     

Hydrogen storage properties of Li-decorated B2S monolayers: A DFT study

Hydrogen storage properties of Li functionalized B₂S honeycomb monolayers are studied using density functional theory calculations. The binding of H₂ molecules to the clean B₂S sheet proceeds through physisorption. Dispersed Li atoms on the monolayer surface increase both the hydrogen binding energies and the hydrogen storage capacities significantly. Additionally, ab initio molecular dynamics calculations show that there is no kinetic barrier during H₂ desorption from lithiated B₂S. Among the studied B₈S₄Li_x (x = 1, 2, 4, and 12) compounds, the B₈S₄Li₄ is found to be the most promising candidate for hydrogen storage purposes; with a 9.1 wt% H₂ content and 0.14 eV/H₂ average hydrogen binding energy. Furthermore, a detailed analysis of the electronic properties of the B₈S₄Li₄ compound before and after H₂ molecule adsorption confirms that the interactions between Li and H₂ molecules are of electrostatic nature.     

Li-decorated double vacancy graphene for hydrogen storage application: A first principles study

Lithium decoration is an effective strategy for improving the hydrogen adsorption binding energy and the storage capacity in carbon nanostructures. Here, it is shown that Li-decorated double carbon vacancy graphene (DVG) can be used as an efficient hydrogen storage medium by means of Density Functional Theory (DFT) based calculations. The Li binding energy in DVG is 4.04 eV, which is much higher than that of pristine graphene. A maximum of four hydrogen molecules adsorb on Li decorated on one side of DVG and this leads to a gravimetric storage capacity of 3.89 wt% with an average adsorption binding energy of 0.23 eV/H₂. When Li is decorated on both sides of DVG, the gravimetric storage capacity reaches 7.26 wt% with a binding energy of 0.26 eV/H₂ which shows that desorption would take place at ambient conditions.     

A comparative study of the reversible hydrogen storage behavior in several metal decorated graphyne

In virtue of the first-principle calculations, the hydrogen storage behavior in several metal decorated graphyne was investigated. It is found that the hydrogen storage capacity can be as large as 18.6, 10.5, 9.9 and 9.5 wt% with average adsorption energy of about −0.27, −0.36, −0.76 and −0.70 eV/H₂ for Li, Ca, Sc, Ti decorated graphyne, respectively. The results suggest potential candidates for hydrogen storage at ambient condition. The adsorption mechanism for H₂ on metal coated graphyne was mainly attributed to the polarization induced by electrostatic field of metal atoms on graphyne and the hybridization between the metal atoms and hydrogen molecules. Furthermore, the formation of super-molecules of hydrogen can enhance the adsorption energy.     

Superalkali NLi4 decorated graphene: A promising hydrogen storage material with high reversible capacity at ambient temperature

This paper investigates the decoration of superalkali NLi₄ on graphene and the hydrogen storage properties by using first principles calculations. The results show that the NLi₄ units can be stably anchored on graphene while the Li atoms are strongly bound together in the superalkali clusters. Decoration using the superalkali clusters not only solve the aggregation of metal atoms, it also provide more adsorption sites for hydrogen. Each NLi₄ unit can adsorb up to 10 H₂ molecules, and the NLi₄ decorated graphene can reach a hydrogen storage capacity 10.75 wt% with an average adsorption energy ?0.21 eV/H₂. We also compute the zero-point energies and the entropy change upon adsorption based on the harmonic frequencies. After considering the entropy effect, the adsorption strengths fall in the ideal window for reversible hydrogen storage at ambient temperatures. So NLi₄ decorated graphene can be promising hydrogen storage material with high reversible storage capacities.     

The enhancement of hydrogen storage capacity in Li,Na and Mg-decorated BC3 graphene by CLICH and RICH algorithms

New hydrogen adsorption states on Li, Na, and Mg-decorated graphene-type BC₃ sheet have been investigated by first-principles calculations. The structural, electronic and binding properties, metal binding and nH₂ (n = 1–10) adsorption states of these systems are studied in detail with the Mulliken analysis, charge density differences, and partial density of states. To enhance the number of the adsorbed H₂ molecules per metal atom, and also to generate the better initial coordinates for reducing the simulation time, we present two masthematical algorithms (CLICH and RICH). The tested results on BC₃ sheet and boron-doped graphene (C₃₀B₂) show that these algorithms can increase the number of adsorbed hydrogen molecules by minimizing the computational time. It is seen that nH₂ (n = 1–10) adsorbed Li,/Na and/Mg-decorated BC₃ single- and double-sided systems are industrial materials for hydrogen storage technology, their adsorption energies fall into the acceptable adsorption energy range (0.20–0.60 eV/H₂). It is concluded from the optimized geometries and charge density differences for the higher number of H₂ adsorbed systems that not only decorated metal atom but also the sheet plays an important role in hydrogen storage process, because the boron atoms in the sheet expand the induced electric field between the adatoms and BC₃ sheet. From Mulliken analysis, there is a charge transfer mechanism between H₂ molecules and metal atoms. Moreover, the resonant peaks for the sheet, metal atoms and H₂ molecules in partial density of states curves indicate the possible hybridizations. Additionally, these adsorption processes are supported by charge density difference plots.