Li center clusters MLi4+ (M = C,Si, Ge) for dihydrogen storage

A density functional study of dihydrogen adsorption and storage capacity of reported stable clusters MLi₄⁺ (M = C, Si, Ge) has been performed at different levels. The cationic systems MLi₄⁺ (M = C, Si, Ge) can adsorb up to 12, 12, and 14 hydrogen molecules respectively with respective H₂ gravimetric uptake capacity of 37.82, 30.22, and 21.94 wt%. The interactions of MLi₄⁺ (M = C, Si, Ge) with H₂ molecules are analyzed by means of the bond critical points (bcp) in the quantum theory of atoms in molecules (QTAIM). The Gibbs free energy corrected adsorption energies indicate that the maximum adsorption of MLi₄⁺ (M = C, Si, Ge) are energetically favorable at low temperature or high pressure. Atom-centered density matrix propagation (ADMP) molecular dynamics simulations are performed at different temperatures. It can be found that MLi₄⁺ (M = C, Si, Ge) can bind 3, 6, and 4 hydrogen molecules with respective gravimetric densities of 13.20, 17.80, and 7.43 wt% at 200 K and 1atm. At room temperature, MLi₄⁺ (M = C, Si, Ge) can adsorb 3, 5, and 3 hydrogen molecules with gravimetric densities of 13.20, 15.29, and 5.68 wt%.     

Strain and defect engineering of graphene for hydrogen storage via atomistic modelling

The adsorption of hydrogen molecules on monolayer graphene is investigated using molecular dynamics simulations (MDS). Interatomic interactions of the graphene layer are described using the well-known AIREBO potential, while the interactions between graphene and hydrogen molecule are described using Lennard-Jones potential. In particular, the effect of strain and different point defects on the hydrogen storage capability of graphene is studied. The strained graphene layer is found to be more active for hydrogen and show 6.28 wt% of H₂ storage at 0.1 strain at 77 K temperature and 10 bar pressure. We also studied the effect of temperature and pressure on the adsorption energy and gravimetric density of H₂ on graphene. We considered different point defects in the graphene layer like monovacancy (MV), Stone Wales (SW), 5-8-5 double vacancy (DV), 555–777 DV, and 5555-6-7777 DV which usually occur during the synthesis of graphene. At 100 bar pressure, graphene with 1% concentration of MV defects leads to 9.3 wt% and 2.208 wt% of H₂ storage at 77 K and 300 K, respectively, which is about 42% higher than the adsorption capacity of pristine graphene. Impact of defects on the critical stress and strain of defected graphene layers is also studied.     

Modeling hydrogen adsorption in the metal organic framework (MOF-5, connector): Zn4O(C8H4O4)3

Density functional theory investigation is performed to understand the underlying mechanism of hydrogen adsorption in the MOF-5 by using for first time the connector structure. The analysis of chemical bonds of the connector's atoms shows a good agreement between experimental and theoretical results. In particular, we show that this material has a desorption temperature of 115 K and an initial hydrogen storage capacity around 1.57 wt% which are close to the experimental values. We consider the coupling-energy mechanism to explore the most stable configurations in multiple adsorption sites namely metallic, carboxylic and cyclic sites. Three orientations which are vertical, horizontal and sloping are taking into account. The results show that the metallic and cyclic sites are more stable for multiple hydrogen molecule storage and the system reaches 4.57 wt% as a gravimetric storage capacity which is located in the interval 4.50–5.20 wt% found experimentally. In addition, the desorption temperature is improved significantly.     

Heterofullerene C48B12-impregnated MOF-5 and IRMOF-10 for hydrogen storage: A combined DFT and GCMC simulations study

The H₂ storage properties of isoreticular metal-organic framework materials (IRMOFs), MOF-5 and IRMOF-10, impregnated with different numbers and types of heterogeneous C₄₈B₁₂ molecules were investigated using density functional theory and grand canonical Monte Carlo (GCMC) calculations. The excess hydrogen adsorption isotherms of IRMOFs at 77 K within 20 bar indicate that suitable number and type of C₄₈B₁₂ molecules play a crucial role in improving the H₂ storage properties of IRMOFs. Among the studied pure and nC₄₈B₁₂ (n = 1, 2, 4, 8) in Ci symmetry impregnating into MOF-5, at 77 K under 6 bar, MOF-5-4C₄₈B₁₂ with a 3.5 wt% and 29.9 g/L hydrogen storage density, and at 77 K under 12 bar, the pure MOF-5 with a 4.9 wt% and 31.0 g/L hydrogen storage density has the best hydrogen storage properties. Whereas, among the studied pure and nC₄₈B₁₂ (n = 1, 2, 4, 8) in S6 symmetry impregnating into IRMOF-10, IRMOF-10-8C₄₈B₁₂ always shows the best hydrogen storage properties among the pure and C₄₈B₁₂-impregnated IRMOF-10 at 77 K within 20 bar. IRMOF-10-8C₄₈B₁₂ has a 6.0 wt% and 34.6 g/L hydrogen storage density at 77 K under 6 bar, and has a 7.1 wt% and 41.4 g/L hydrogen storage density at 77 K under 12 bar. The confinement effect of IRMOFs on C₄₈B₁₂ molecules, and steric hindrance effect of C₄₈B₁₂ molecules on IRMOFs mainly affects the H₂ uptake capacity by comparing the absolute H₂ molecules in individual IRMOFs units, C₄₈B₁₂ molecules, and IRMOFs-nC₄₈B₁₂ compounds. The absolute hydrogen adsorption profiles show that eight C₄₈B₁₂ molecules impregnating into MOF-5 can exert obvious steric effects for H₂ adsorption. The saturated gravimetric and volumetric H₂ densities of IRMOF-10-8C₄₈B₁₂ higher than those of MOF-5-8C₄₈B₁₂ due to with larger free volume.     

Hydrogen storage in lithium,sodium and magnesium-decorated on tetragonal silicon carbide

Motivated by the widespread application and fascinating properties of various silicon-carbon nanomaterials, we have extensively investigated the properties of tetragonal silicon carbides (t-SiC) monolayer as a novel 2D material for hydrogen storage.Using calculations of the density functional theory comprising van der Waals interactions of type vdW-DF2-C09_x, the structural stability, electronic properties and hydrogen molecules adsorption energies on the surface of pure t-SiC were investigated.The results show that adsorption energies of H₂ molecules in this system are stronger than that of graphene. We also found that the decoration with alkali (Li, Na) and alkaline-earth (Mg) metals atoms increases the stability of hydrogen compared to the pure system. The studied system decorated with 8 elements of Li/Na/Mg is able to adsorb up 24 molecules of hydrogen and reaches a gravimetric capacity of 6.50, 5.54 and 5.48 wt%, respectively. The desorption temperatures found are significantly high compared to other 2D systems.     

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.     

Superior hydrogen storage capacity of Vanadium decorated biphenylene (Bi+V): A DFT study

Herein, the hydrogen storage competency of vanadium-decorated biphenylene (Bi+V) has been investigated using Density Functional Theory simulations. The metal atom interacts with biphenylene with a binding energy value of −2.49 eV because of charge transfer between V 3d and C 2p orbitals. The structure and electronic properties are studied in terms of adsorption energy values, the spin-polarized partial density of states (PDOS), band structure plots, and charge transfer analysis. The Kubas-type interactions lead to average hydrogen adsorption energy values of −0.51 eV/H₂ which fulfills DOE-US criteria (0.2–0.7 eV/H₂). The diffusion energy barrier value of 1.75 eV lowers the chances of metal clustering. The complex binds 5H₂ on each V-atom resulting in a storage capacity of 7.52 wt% with an average desorption temperature of 595.96 K. The ab-initio molecular dynamics (AIMD) and phonon dispersions validates structural integrity at higher temperatures suggesting the excellent storage properties of this material at room temperature.     

DFT study of hydrogen storage on the metallic decoration of boron substitution on zeolite templated carbon vacancy

This work reports DFT calculations for the assessment of metallic decoration of boron substitution Zeolite Templated Carbon vacancy for hydrogen adsorption. The boron substitution on Zeolite Templated Carbon vacancy is characterized by the formation of pentagonal and heptagonal rings. Moreover, the boron substitution can be considered as a promising way for hydrogen storage, this way boron substitution is used on Zeolite Templated Carbon vacancy in order to create an active site for metallic decoration. Once that we develop a Boron substitution on Zeolite Templated Carbon vacancy, the decoration with Lithium, Sodium, and Calcium atoms is also carried out. The analysis reveals that the Na decoration has the best performance for hydrogen storage. The results show that boron substitution on Zeolite Templated Carbon vacancy decorated with 3 Sodium atoms can adsorb up to fifteen hydrogen molecules (5 hydrogen molecules per Sodium atom), this gives a gravimetric storage capacity of 6.55 % wt., which is enough for meeting DOE gravimetric targets. In addition, the average binding energies and adsorption energies are calculated in the range 0.2298–0.2144 eV/H₂, which constitute desirable energies for hydrogen adsorption. Besides, the hydrogen adsorption process is carried out by electrostatic interaction between the Na cation and the induced H₂ dipole. The calculation performed in this work reveals that the boron substitution on Zeolite Templated Carbon vacancy decorated with Na atoms is a good candidate as a medium for hydrogen storage.     

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.     

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.     

Enhanced thermodynamic properties of ZrNiH3 by substitution with transition metals (V,Ti, Fe,Mn and Cr)

First-principles calculations based on Plane-Wave Self-Consistent Field (PWSCF) method, implemented in quantum espresso program, have been performed on ZrNiH₃ substituted with transition metals (V, Ti, Fe, Mn, and Cr). The study aims to investigate the heat of formation in terms of material stability and desorption temperature. It is found that the substitution by transition metals, results in a significant enhancement in the thermodynamic properties accompanied by an increase of the volumetric and gravimetric hydrogen storage capacities. In addition, the obtained values of heat of formation and desorption temperature corroborate with that required by the U.S. Department of Energy (DOE) for stability and volumetric capacity criteria. Moreover, Mn and Fe elements are found to present the lowest substituting content (34%) to obtain optimum hydrogen storage characteristics (enthalpy of formation of - 40 kJ/mol.H₂, decomposition temperature of 300 K and volumetric capacity of 134 g.H₂/l), without affecting the electronic structure and the metallic character of ZrNiH₃.     

Computer-aided prediction of structure and hydrogen storage properties of tetrakis(4-aminophenyl)silsesquioxane based covalent-organic frameworks

With the aid of computer simulation, we have designed four covalent-organic frameworks based on tetrakis(4-aminophenyl)silsesquioxane (taps-COFs) and their hydrogen storage properties were predicted with grand canonical Monte Carlo (GCMC) simulation. The structural parameters and physical properties were investigated after the geometrical optimization. The accessible surface for H₂ molecule (5564.68–6754.78 m²/g) were estimated using the numerical Monte Carlo integration and the pore volume (4.06–10.74 cm³/g) was evaluated by the amounts of the containable nonadsorbing helium molecules at low pressures and room temperature. GCMC simulation reveals that at 77 K, tapsCOF1 has the highest gravimetric H₂ adsorption capacity of 51.43 wt% and tapsCOF3 possesses the highest volumetric H₂ adsorption capacity of 58.51 g/L. Excitedly, at room temperature of 298 K, the gravimetric hydrogen adsorption capacities of tapsCOF1 (8.58 wt%) and tapsCOF2 (8.20 wt%) have exceeded the target (5.5 wt%) of onboard hydrogen storage system for 2025 set by the U.S Department of Energy.     

C7N6 monolayer as high capacity and reversible hydrogen storage media: A DFT study

Searching advanced materials with high capacity and efficient reversibility for hydrogen storage is a key issue for the development of hydrogen energy. In this work, we studied systematically the hydrogen storage properties of the pure C₇N₆ monolayer using density functional theory methods. Our results demonstrate that H₂ molecules are spontaneously adsorbed on the C₇N₆ monolayer with the average adsorption energy in the range of 0.187–0.202 eV. The interactions between H₂ molecules and C₇N₆ monolayer are of electrostatic nature. The gravimetric and volumetric hydrogen storage capacities of the C₇N₆ monolayer are found to be 11.1 wt% and 169 g/L, respectively. High hardness and low electrophilicity provides the stabilities of H₂–C₇N₆ systems. The hydrogenation/dehydrogenation (desorption) temperature is predicted to be 239 K. The desorption temperatures and desorption capacity of H₂ under practical conditions further reveal that the C₇N₆ monolayer could operate as reversible hydrogen storage media. Our results thus indicate that the C₇N₆ monolayer is a promising material with efficient, reversible, and high capacity for H₂ storage under realistic conditions.     

The effect of functional groups (O,F, or OH) on reversible hydrogen storage properties of Ti2X (X=C or N) monolayer

The effect of functional groups (O, F, or OH) on the hydrogen storage properties of Ti₂X (X = C or N) monolayer was systematically investigated by first-principles calculations. The results show that the reversible hydrogen storage capacity of Ti₂X(OH)₂ monolayer is approximately 2.7 wt%, which is larger than that of Ti₂XO₂ and Ti₂XF₂ monolayers. The binding energy of the OH group at the F site is stronger than H atom. Thus, H₂ molecules will not be dissociated on Ti₂X(OH)₂ monolayer. At this time, the loss of 1.8 wt% hydrogen storage capacity is not produced in Ti₂X(OH)₂ monolayer. Furthermore, the PDOS, the population analysis, and the electron density difference explore that electron transfer appears between Ti and the second layer H₂ molecules on Ti₂X(OH)₂ monolayer, and a Dewar-Kubas interaction lies between second layer H₂ molecules and Ti₂X(OH)₂ monolayer. For Ti₂X(OH)₂ monolayer, the molecular dynamic simulation indicates that the H₂ molecules by Dewar-Kubas interaction sable adsorption at 300 K, and desorption at 400 K. Therefore, Ti₂X(OH)₂ is appropriate for reversible hydrogen sorbent storage materials under ambient 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.     

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.     

Hydrogenation properties of MgH2- x wt% AC (x=0, 5, 10, 15) nanocomposites

Magnesium is considered as a promising candidate for hydrogen storage due to its high storage capacity (theoretical value ~ 7.6 wt%). Nanocomposites of Magnesium hydride and activated charcoal (AC) were prepared using ball milling method. These nanocomposites were characterized by XRD, TGA, DSC and SEM techniques. The TGA analysis show that the MgH₂-5 wt% AC nanocomposite exhibits dehydrogenation capacity of 7.45 wt% (which is very close to the storage capacity of MgH₂) and starts release of hydrogen at 140 °C temperature. The results from the Kissinger plot from DSC result showed that the activation energy for hydrogen desorption of MgH₂ with 5 wt% AC was reduced compared to those of as-received.     

C2H2M (M = Ti,Li) complex: A possible hydrogen storage material

The hydrogen storage capacity of Ti-acetylene (C₂H₂Ti) and Li-acetylene (C₂H₂Li) complex has been tested using second order Møller Plesset method with different basis sets. Single Ti(Li) decorated acetylene complex can adsorb maximum of five(four) hydrogen molecules, which corresponds to the gravimetric hydrogen storage capacity of 12(19.65) wt % and it meets the target of 9 wt % by 2015 specified by US Department of Energy. The hydrogen adsorption energies with zero point energy and Gibbs free energy correction show that hydrogen adsorption on C₂H₂Ti is energetically favourable for a wide range of temperature and that is unfavourable on C₂H₂Li complex even at a very low temperature. Atom centered density matrix propagation molecular dynamics simulations reveal that four H₂ molecules remain adsorbed on C₂H₂Ti complex at 300 K. Though H₂ uptake capacity of C₂H₂Li complex is higher than that of C₂H₂Ti complex, the thermochemistry results favour to C₂H₂Ti complex over C₂H₂Li complex as a possible hydrogen storage media.