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 novel lithium decorated N-doped 4,6,8-biphenylene for reversible hydrogen storage: Insights from density functional theory

Two-dimensional (2D) carbon-based (C-based) and carbon-nitrogen (C–N) materials have great potential in the energy harvest and storage fields. We investigate a novel carbon biphenylene (C468) consisting of four-, six- and eight-membered rings of sp² carbon atoms (Fan et al., Science, 372:852-6 (2021)) for hydrogen storage. Using first-principles based Density functional theory calculations, we study the geometrical and electronic properties of C468 and N-doped C468. Lithium (Li) atoms were symmetrically adsorbed on both sides of the substrate, and their adsorption positions were determined. The maximum gravimetric density of hydrogen (H₂) adsorbed symmetrically on both sides of Li atom was studied within the scope of physical adsorption process (−0.2 eV/H₂ ∼ −0.6 eV/H₂). Li-decorated C468 can adsorb 8 upper hydrogen molecules and 8 lower hydrogen molecules, and Li-decorated N-doped C468 can adsorb 9 upper hydrogen molecules and 9 lower hydrogen molecules. The gravimetric densities of Li-decorated C468 and Li-decorated N-doped C468 can reach 9.581 wt% and 10.588 wt%, respectively. Our findings suggest significant insights for using Li-decorated C468 and Li-decorated N-doped C468 as hydrogen storage candidates and effectively expand the application scope of C-based materials and C–N materials.     

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.     

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.     

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.     

Li-decorated B2O as potential candidates for hydrogen storage: A DFT simulations study

Two-dimensional (2D) B₂O monolayer is considered as a potential hydrogen storage material owing to its lower mass density and high surface-to-volume ratio. The binding between H₂ molecules and B₂O monolayer proceeds through physisorption and the interaction is very weak, it is important to improve it through appropriate materials design. In this work, based on density functional theory (DFT) calculations, we have investigated the hydrogen storage properties of Lithium (Li) functionalized B₂O monolayer. The B₂O monolayer decorated by Li atoms can effectively improve the hydrogen storage capacity. It is found that each Li atom on B₂O monolayer can adsorb up to four H₂ molecules with a desirable average adsorption energy (E_ave) of 0.18 eV/H₂. In the case of fully loaded, forming B₃₂O₁₆Li₉H₇₂ compound, the hydrogen storage density is up to 9.8 wt%. Additionally, ab initio molecular dynamics (AIMD) calculations results show that Li-decorated B₂O monolayer has good reversible adsorption performance for H₂ molecules. Furthermore, the Bader charge and density of states (DOS) analysis demonstrate H₂ molecules are physically absorbed on the Li atoms via the electrostatic interactions. This study suggests that Li-decorated B₂O monolayer can be a promising hydrogen storage material.     

Complex interaction of hydrogen with the monolayer TiS2 decorated with Li and Li2O clusters: an ab initio random structure searching approach

We have applied ab initio random structure searching to study the structure, stability and hydrogen storage properties of monolayer TiS₂ coated with Li and small Li₂O clusters. For the low Li covered system we found a complex adsorption mechanism: some hydrogen molecules were adsorbed due to polarization with Li, others due to polarization with S near the surface of TiS₂. The peculiarities of the interaction of the H₂ molecules with each other and the preferred adsorption sites allowed us to formulate a series of recommendations that can be useful when selecting the material for the most effective support. Moreover, the findings also show that the storage capacity of this system can reach up to 9.63 wt%, presenting a good potential as hydrogen storage material. As for the Li₂O clusters supported on TiS₂, we found that the polarization of the Li–O bond increases upon the adsorption of the Li₂O nanocluster. Moreover, the polarized Li–S bonds appear in addition to the already existing Li–O bonds. All this is possible due to the extraction of 1.46 electrons from the S atom of the substrate by O atom of the cluster, and should contribute to an increase in both the adsorption energy and the maximum capacity. The adsorption energies of H₂ for the systems studied here are within 0.11–0.16 eV/H₂ which is a recommended range for reversible hydrogen physisorption under standard test conditions. This study may stimulate experimental efforts to check the claims of high-capacity, stable and reversible hydrogen adsorption reported here.     

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.     

Li-decorated graphyne as high-capacity hydrogen storage media: First-principles plane wave calculations

Taking into account the van der Waals correction, the characteristics of the Li-decorated graphyne as the hydrogen storage medium have been explored using first-principles plane wave calculations. We find that Li atom can be adsorbed not only over the center of large hexagon (H_L site) but also over the center of small hexagon (H_S site). For double-side Li decorations, there are 14H₂ molecules can be adsorbed on Li-decorated graphyne primitive cell with the adsorption energy of 0.19 eV/H₂. As a result, the hydrogen storage capacity of 13.0 wt% can be obtained. This suggests that the Li-decorated graphyne system can serve as a high-capacity hydrogen storage medium.     

Hydrogen adsorption and storage behaviors of Li-decorated PdS2 monolayer: An extended tight-binding study based on DFT

The hydrogen adsorption and storage of the lithium-decorated PdS₂ monolayer at nano-size has been investigated by using extended tight-binding (GFN1-xTB) based on density functional theory (DFT). The calculation results demonstrate that the average adsorption energies of 1–5H₂ change in 0.47–0.20 eV/H₂ range which decreases with increasing of adsorbed hydrogen molecule number. The gravimetric density for hydrogen storage adsorption with 12Li atom and 60H₂ molecules of Li-decorated PdS₂ monolayer is about 6.98 wt% considered as possible application in hydrogen storage. The examination of the hydrogen store mechanism between the monolayer and hydrogen molecules is presented by polarization between Pd and H₂, which can be effect on the adsorption behavior.     

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.     

An investigation of Li-decorated N-doped penta-graphene for hydrogen storage

By making use of first principles calculations, lithium-decorated (Li-decorated) and nitrogen-doped (N-doped) penta-graphene (PG) was investigated as a potential material for hydrogen storage. The geometric and electronic structures of two types of N-doped PG were studied, and the band gaps were 1.86 eV and 2.06 eV, respectively, depending on the positions of the substitution. The probable adsorption sites for Li atoms on topside and downside were calculated. Hydrogen molecules were added one by one to Li-decorated N-doped PG to research the maximum hydrogen gravimetric density. It is found that up to 5 hydrogen molecules on topside and 8 hydrogen molecules on downside can be adsorbed around a Li atom, and the average adsorption energies are in the range of physical adsorption processes (0.1–0.4 eV). The gravimetric densities can reach 7.88 wt% for N-doped PG with Li decoration. Our results suggest that Li-decorated N-doped PG is a significantly promising material for hydrogen storage.     

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.     

Light and stable LinB14(n=1–5) clusters for high capacity hydrogen storage at room temperature: A DFT study

In this article, we have explored the hydrogen (H₂) storage capacity of the Li doped B clusters Li_nB₁₄(n = 1–5) using density functional theory (DFT). The geometrical and Bader's topological parameters indicate that the clusters adsorb H₂ in the molecular form. The Li atom polarises the H₂ molecules for their effective adsorption on the clusters. The Li_nB₁₄ (n = 1–5) clusters are found to be stable even after H₂ adsorption at room temperature. The average adsorption energy is found to be in the range of 0.12–0.14 eV/H₂. Among the various clusters, the Li₅B₁₄ shows maximum H₂ storage capacity (13.89 wt%) at room temperature. The ADMP simulation reveals that within few femtoseconds (fs), the H₂ molecules begin to move away from the clusters and within 400 fs most of the H₂ molecules moved away from the clusters.     

Density functional theory study of reversible hydrogen storage in monolayer beryllium hydride by decoration with boron and lithium

The hydrogen storage capacity of M-decorated (M = Li and B) 2D beryllium hydride is investigated using first-principles calculations based on density functional theory. The Li and B atoms were calculated to be successfully and chemically decorated on the Surface of the α-BeH₂ monolayer with a large binding energy of 2.41 and 4.45eV/atom. The absolute value was higher than the cohesive energy of Li and B bulk (1.68, 5.81eV/atom). Hence, the Li and B atoms are strongly bound on the beryllium hydride monolayer without clustering. Our findings show that the hydrogen molecule interacted weakly with B/α-BeH₂(B-decorated beryllium hydride monolayer) with a low adsorption energy of only 0.0226 eV/H₂ but was strongly adsorbed on the introduced active site of the Li atom in the decorated BeH₂ with an improved adsorption energy of 0.472 eV/H₂. Based on density functional theory, the gravimetric density of 28H₂/8li/α-BeH₂) could reach 14.5 wt.% higher than DOE's target of 6.5 wt. % (the criteria of the United States Department of Energy). Therefore, our research indicates that the Li-decorated beryllium hydride monolayer could be a candidate for further investigation as an alternative material for hydrogen storage.     

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.     

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.     

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.     

A study on the hydrogen storage performance of graphene–Pd(T)–graphene structure

The 1–6 H₂ molecule adsorption energy and electronic properties of sandwich graphene–Pd(T)–Graphene (G–Pd(T)–G) structure were studied by the first-principle analysis. The binding energies, adsorption energies, and adsorption distances of Pd atoms-modified single-layer graphene and bilayer graphene with H₂ molecules at B, H, T adsorption sites were calculated. In bilayer graphene, the adsorption properties at T sites were found to be more stable than those at B and H sites. The binding energy of Pd atoms (4.16 eV) on bilayer graphene was higher than the experimental cohesion energy of Pd atoms (3.89 eV), and this phenomenon eliminated the impact of metal clusters on adsorption properties. It was found that three H₂ molecules were stably adsorbed on the G–Pd(T)–G structure with an average adsorption energy of 0.22 eV. Therefore, it can be speculated that G–Pd(T)–G is an excellent hydrogen storage material.     

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.