Adsorption Of Hydrogen Molecules Research Articles

Hydrogen adsorption, desorption, sensor and storage properties of Cu doped / decorated boron nitride nanocone materials: A density functional theory and molecular dynamic study

The hydrogen storage and sensor properties of Cu-modified boron nitride nanocone (BNNC) structure were comprehensively investigated using the density functional theory method (DFT). By replacing nitrogen atoms with copper atoms on the BNNC structure, the hydrogen molecule's adsorption enthalpy and Gibbs free energy values were calculated as −48.6 and −16.9 kJ/mol, respectively. 4 Cu-doped BNNC structure achieved a notable hydrogen storage capacity of 5.38 wt%. The molecular dynamics calculations demonstrate that the structure modified with four Cu atoms maintains its dynamic stability. Furthermore, this study reveals that the desorption temperatures tend to rise with an increase in the number of adsorbed hydrogen molecules, and the average desorption temperature under 1 atm pressure is determined to be 332 K. The changes of work function values after hydrogen adsorption point out that the Cu-modified BNNC has Φ-sensor feature. Overall, Cu-modified BNNC structures show promising potential as hydrogen storage materials in ambient conditions.

Hydrogen storage in M(BDC)(TED)0.5 metal-organic framework: physical insights and capacities.

Finding renewable energy sources to replace fossil energy has been an essential demand in recent years. Hydrogen gas has been becoming a research hotspot for its clean and free-carbon energy. However, hydrogen storage technology is challenging for mobile and automotive applications. Metal-organic frameworks (MOFs) have emerged as one of the most advanced materials for hydrogen storage due to their exceptionally high surface area, ultra-large and tuneable pore size. Recently, computer simulations allowed the designing of new MOF structures with significant hydrogen storage capacity. However, no studies are available to elucidate the hydrogen storage in M(BDC)(TED)0.5, where M = metal, BDC = 1,4-benzene dicarboxylate, and TED = triethylenediamine. In this report, we used van der Waals-dispersion corrected density functional theory and grand canonical Monte Carlo methods to explore the electronic structure properties, adsorption energies, and gravimetric and volumetric hydrogen loadings in M(BDC)(TED)0.5 (M = Mg, V, Co, Ni, and Cu). Our results showed that the most favourable adsorption site of H2 in M(BDC)(TED)0.5 is the metal cluster-TED intersection region, in which Ni offers the strongest binding strength with the adsorption energy of -16.9 kJ mol-1. Besides, the H2@M(BDC)(TED)0.5 interaction is physisorption, which mainly stems from the contribution of the d orbitals of the metal atoms for M = Ni, V, Cu, and Co and the p orbitals of the O, C, N atoms for M = Mg interacting with the σ* state of the adsorbed hydrogen molecule. Noticeably, the alkaline-earth metal Mg strongly enhanced the specific surface area and pore size of the M(BDC)(TED)0.5 MOF, leading to an enormous increase in hydrogen storage with the highest absolute (excess) gravimetric and volumetric uptakes of 1.05 (0.36) wt% and 7.47 (2.59) g L-1 at 298 K and 7.42 (5.80) wt% and 52.77 (41.26) g L-1 at 77 K, respectively. The results are comparable to the other MOFs found in the literature.

Tailoring the electronic structure of Ni2P/Al2O3 by Pt introduction to boost the ultradeep hydrodesulfurization performance

The catalytic performances of conventional Ni(Co)Mo(W)/Al2O3 catalysts for hydrodesulfurization (HDS) of fuel are far from meeting the near zero emission standards. Therefore, the development of more efficient ultradeep HDS catalyst is highly desirable. Herein, a novel Pt-Ni2P/Al2O3 catalyst with 0.5 wt% Pt loading was prepared, and its catalytic performance for HDS of 4,6-dimethyldibenzothiophene (4,6-DMDBT) was investigated. The introduction of Pt considerably promoted the reducibility and hydrogen atoms produced by the dissociated adsorbed hydrogen molecules on the Pt surface overflowing to the Ni2P because of the lower electronegativity of Pt than that of Ni, thereby increasing the number of stronger Lewis and Brønsted acid sites, and thereafter greatly boosting the direct desulfurization and isomerization pathways. As a result, Pt-Ni2P/Al2O3 catalyst achieved the ultradeep HDS of 4,6-DMDBT, with 100% conversion at 340 °C, remarkably higher than that of Ni2P/Al2O3 (49.8%) and NiMo/Al2O3 (62.0%) counterparts.

Hydrogen molecule adsorption on the MoSe2 and selected-elements (Ru, Os, Rh, Ir, N and P)-doped MoSe2 monolayers as hydrogen storage materials

Adsorption of hydrogen molecules onto the pristine MoSe2 monolayer and N-, P-, Ru-, Rh-, Os- and Ir-doped MoSe2 monolayer surfaces was investigated using periodic DFT method. Adsorption abilities of the pristine and MoSe2 doping derivatives on hydrogen molecule adsorptions are in order: Os–MoSe2 (ΔEads = −2.19 eV) > Ru–MoSe2 (ΔEads = −1.54 eV) > Ir–MoSe2 (ΔEads = −1.08 eV) > Rh–MoSe2 (ΔEads = −0.63 eV) > N–MoSe2 (ΔEads = −0.22 eV) > P–MoSe2 (ΔEads = −0.15 eV) > pristine MoSe2 (ΔEads = −0.06 eV). The adsorption energy of hydrogen onto the Os–MoSe2 surface, which is the most active derivative, stronger than the second most active, the Ru–MoSe2 by 0.65 eV (42%) was found. Nevertheless, all the MoSe2 doping derivatives utilized as hydrogen storage for energy storage purposes were suggested.

Evaluation of hydrogen storage capacity of two-dimensional Sc2N MXene: A DFT study

In this work, the efficiency of hydrogen storage on Sc2N MXenes monolayer is systematically investigated using first-principles calculations. After determining the structural stability of designed monolayer, adsorption sites for the storage of hydrogen atoms (H) and molecules (H2) are identified. The calculated binding energies have indicated that the hydrogen atoms have favorable adsorption at the center or H site of the Sc atoms and hydrogen molecules are found to be the most stable when adsorbed on the top/T site of Sc atoms. The binding energy assessment identified the chemisorption for hydrogen atoms and Kubas-type interactions for H2. To further ascertain the suitability of the Sc2N monolayer for hydrogen storage various analyses including binding energy, partial density of states (PDOS), electron localization function (ELF), Mullikan charge analysis and Hirshfeld charge analysis are conducted. In order to determine the thermal stability of the Sc2N monolayer, desorption temperature with respect to pressure and molecular dynamics study has also been conducted and found the monolayer thermally stable. Desorption isotherms condition with increasing pressure confirms the gravimetric storage uptake. The obtained results have revealed that the hydrogen storage capacity considered monolayer has reached up to 10.8 wt%, which is reasonably high. Hence, the obtained results of hydrogen atom and molecules adsorption have clearly established that Sc2N monolayer is as an exemplary, stable, reliable and efficient medium for hydrogen storage applications.

Dissociative Adsorption of Hydrogen Molecules at Al2O3 Inclusions in Steels and Its Implications for Gaseous Hydrogen Embrittlement of Pipelines

Hydrogen embrittlement (HE) of steel pipelines in high-pressure gaseous environments is a potential threat to the pipeline integrity. The occurrence of gaseous HE is subjected to associative adsorption of hydrogen molecules (H2) at specific “active sites”, such as grain boundaries and dislocations on the steel surface, to generate hydrogen atoms (H). Non-metallic inclusions are another type of metallurgical defect potentially serving as “active sites” to cause the dissociative adsorption of H2. Al2O3 is a common inclusion contained in pipeline steels. In this work, the dissociative adsorption of hydrogen at the α-Al2O3(0001)/α-Fe(111) interface on the Fe011¯ plane was studied by density functional theory calculations. The impact of gas components of O2 and CH4 on the dissociative adsorption of hydrogen was determined. The occurrence of dissociative adsorption of hydrogen at the Al2O3 inclusion/Fe interface is favored under conditions relevant to pipeline operation. Thermodynamic feasibility was observed for Fe and O atoms, but not for Al atoms. H atoms can form more stable adsorption configurations on the Fe side of the interface, while it is less likely for H atoms to adsorb on the Al2O3 side. There is a greater tendency for the occurrence of dissociative adsorption of O2 and CH4 than of H2, due to the more favorable energetics of the former. In particular, the dissociative adsorption of O2 is preferential over that of CH4. The Al-terminated interface exhibits a higher H binding energy compared to the O-terminated interface, indicating a preference for hydrogen accumulation at the Al-terminated interface.

First principles study of hydrogen storage on B-doped SiC monolayers through light transition metal atoms

In this first-principles study, based on Density Functional Theory, we assess the capacity of metal-decorated, boron-doped, graphene-like monolayers of silicon carbide (SiC) to adsorb hydrogen molecules. To enhance the binding of metal adatoms on SiC monolayers, these were substitutionally doped with boron atoms. Alkaline, alkaline-earth, and transition metal adatoms were considered and their hydrogen storage capabilities were compared. The results show that alkaline-earth metal adatoms are not suitable for hydrogen storage. On the other hand, sodium- and potassium-decorated B-doped SiC monolayers adsorb the largest number of H2 molecules per adatom, but their adsorption energies are insufficient for an adequate hydrogen storage. Titanium and scandium adatoms are the most suitable for hydrogen storage since they exhibit good adsorption energies and up to four and five H2 molecules per adatom, respectively. Moreover, the estimated potential barriers for diffusion of these two adatoms on the B-doped SiC monolayers indicate that the probability of clustering is very low. Moreover, within the ideal-gas approximation, it is estimated that hydrogen can be stored in the Ti- and Sc-decorated monolayers at room temperature and atmospheric pressure. Furthermore, if SiC monolayers were doped with boron atoms in concentrations similar to those reported for graphene, it is estimated that the gravimetric capacities could reach 5.1 wt% and 6.3 wt% for Ti-decorated and Sc-decorated monolayers, respectively, which are close to the target hydrogen-storage capacities envisioned for the near future.

Adsorption and evolution of hydrogen molecules on hexagonal boron nitride monolayer: a combined DFT and kinetic monte-carlo simulations study

Density functional theory (DFT) and kinetic Monte-Carlo (kMC) simulation code has been combinedly used to study the adsorption and evolution dynamics of hydrogen molecules over a hexagonal boron nitride (h-BN) monolayer. Maximum adsorption energy from van der Waals curve is predicted to be around 60 to 70 meV using two different DFT functionals. Repulsive lateral interaction between two hydrogen molecules plays a key role in determining the maximum number of adsorptions inside one unit cell of h-BN. Bader charge analysis, electron localization function (ELF), total and partial density of states (DOS) plots have been included to understand the weak interaction going on between the adsorbent and substrate. The input energy parameters from the DFT calculation has been used to perform the kMC simulation for describing the adsorption, desorption and the diffusion pattern of hydrogen molecules with a given time of exposure to an empty h-BN substrate along with the overall surface coverage.

Study on Adsorption of Diesel Molecules on MoS<sub>2</sub> and NiMoS Catalysts

For deep insight into complex reaction system of diesel hydrotreating, the monolayer adsorption and competitive adsorption of typical reactant molecules (phenanthrene, naphthalene, acridine, quinoline, dibenzothiophene, 4,6-dimethyldibenzothiophene and H2) on MoS2 and NiMoS catalyst models with different structures were investigated. The basal plane is discovered to be the best physical adsorption position for all molecules in MoS2 series catalysts. Following saturation of the basal plane, reactant molecules will be adsorbed at Mo edge first, and Mo edge is more prone to bimolecular or multimolecular adsorption than S-edge, implying that Mo edge active sites play an important role in diesel hydrotreating. Naphthalene has a higher adsorption capacity in the partial pressure system that simulates the actual reaction atmosphere, and it is the most likely reactant molecule to predominately occupy active sites, but 4,6-dimethyl dibenzothiophene still exhibits good competition adsorption performance due to its high adsorption capacity and heat release. Interestingly, after phenanthrene adsorption, the secondary adsorption of hydrogen decreases in all of the catalyst models studied, indicating that phenanthrene is one of the most important molecules influencing hydrogen adsorption. Furthermore, the secondary adsorption of hydrogen after phenanthrene adsorption decreased the most on Tri-S50 catalyst. It shed light on that the activity and stability of Tri-S50 catalyst was most likely to decrease during diesel hydrotreating because of the notable inhibition on adsorption of hydrogen molecules brought by phenanthrene adsorption. It presents a theoretical basis for the design and development of highly efficient diesel hydrotreating catalysts.

Hydrogen storage efficiency of Fe doped carbon nanotubes: molecular simulation study.

Given that adsorption is widely regarded as a favorable technique for hydrogen storage, it is appropriate to pursue the development of suitable adsorbent materials for industrial storage. This study aimed to assess the potential of Fe-doped carbon nanotubes (FeCNT) as a remarkable material for hydrogen storage. The structures of pure and Fe-doped CNTs were optimized based on quantum mechanical calculations using density functional theory (DFT) with the Perdew-Burke-Ernzerhof (PBE) method. To gain a comprehensive understanding of the adsorption behavior, Monte Carlo simulation was employed to investigate the adsorption of hydrogen molecules on FeCNT. The study specifically examined the impact of temperature, pressure, and hydrogen mole percentage on the adsorption capacity of FeCNT. The findings indicated that the uptake of hydrogen increased as the pressure increased, and when the pressure exceeded 5 MPa, FeCNT reached a state of near saturation. At room temperature and pressures of 1 and 5 MPa, the hydrogen capacities of FeCNT were determined to be 1.53 and 6.92 wt%, respectively. The radial distribution function diagrams confirmed the formation of a one-layer adsorption phase at pressures below 5 MPa. A comparison of the temperature dependence of hydrogen adsorption between FeCNT and pure CNT confirmed the effectiveness of Fe doping in hydrogen storage up to room temperature. FeCNT exhibited a greater reduction in initial hydrogen capacity at temperatures above room temperature. To evaluate the safety of the system, the use of N2 as a dilution agent was investigated by examining the hydrogen uptake of FeCNT from pure and H2/N2 mixtures at 300 K. The results showed that the addition of N2 to the environment had no significant effect on FeCNT hydrogen storage at pressures below 4 MPa. Furthermore, the study of H2 selectivity from the H2/N2 mixture indicated that FeCNT demonstrated a preference for adsorbing H2 over a wide range of bulk mole fractions at pressures of 4 and 5 MPa, suggesting that these pressures could be considered optimal. Under these conditions, Fe doping can offer an efficient and selective adsorption surface for hydrogen storage.

Adsorption of Hydrogen Molecules in Nickel Decorated Silicene

First-principles simulations based on density functional theory (DFT) have been used to study the structural, electronic and magnetic properties of pristine and Ni decorated silicene sheets. Generalized Gradient Approximation (GGA) based exchange correlation functionals are used under software package Quantum ESPRESSO (QE), 6.5 versions. We have reconstructed the optimized unit cell of silicene, which has a face centered cubic (fcc) structure with two silicon atoms having lattice parameters a = b = 3.8 Å. The distance between two nearest silicene monolayers is found to be 20.5 Å which is large enough to neglect the interlayer interactions between 4×4 supercells of silicene monolayers. The atoms in the prepared supercell are fully relaxed under Bloyden-Fletcher-Goldfarb-Shanno (BFGS) scheme prior to the self-consistent, band structure and density of state (DoS) calculations. The pristine silicene is semi-metallic in nature possessing a Dirac-cone as in graphene. The h-site adsorption is found to be the most stable adsorption site of nickel in silicene with the binding energy of 4.69 eV. The addition of nickel atom completely distorts the hexagonal structure of silicene destroying the Dirac cone and the system becomes slightly insulating from its semi-metallic nature. We then construct a 4×4 nickel dimer silicene which further destroys the hexagonal silicene structure with further opening of the band gap. The charge transfer analysis in the Ni decorated systems shows the charge transfers of 0.163e and 0.294e in Ni adatom silicene and Ni dimer silicene respectively showing that the nickel atoms are adsorbed by weak van der Waals forces in both of the systems. We then proceed to hydrogen molecule adsorption in these prepared 4×4 silicene systems: pristine, Ni adatom and Ni dimer silicene systems. The adsorption energy of hydrogen in the Ni adatom silicene is found to be the largest making it the most effective system for hydrogen storage.

Enhanced room-temperature hydrogen storage by CuNi nanoparticles decorated in metal-organic framework UiO-66(Zr)

This study demonstrates the significant effect of incorporating inexpensive transition metal nanoparticles into metal-organic frameworks (MOFs) to improve their room-temperature hydrogen storage properties. Low-cost nanoparticles (Cu, Ni, and CuNi) were incorporated into UiO-66(Zr) via the double-solvent approach (DSA) plus chemical reduction processes. All composites exhibited higher hydrogen storage capacity compared to pure UiO-66 at both room temperature and 60 bar. Notably, the hydrogen spillover efficiency of CuNi nanoparticles loaded in UiO-66 was comparable to that of MOF adsorbents embedded with noble metals such as Pd and Pt. The hydrogen storage capacity of CuNi@UiO-66 was significantly increased from 0.20 wt% to 0.74 wt%. DFT calculations showed that the CuNi alloys facilitated the adsorption and dissociation of hydrogen molecules in comparison to the single metal nanoparticles, thus favoring the hydrogen spillover effect and improving the hydrogen storage performance. This work demonstrates the potential of designing MOF loaded with inexpensive metal nanoparticles for optimized room-temperature hydrogen storage.

Potentially reversible hydrogen storage medium: Calcium-decorated boron-doped blue phosphorene

Developing novel hydrogen storage materials with high capacity and efficient reversibility at ambient conditions is crucial to the extensive use of hydrogen energy. In this study, we have systematically investigated the hydrogen storage performances of Ca-decorated boron-doped blue phosphorene (B@BlueP) monolayers by using first-principles calculations. The results show that substitutional boron doping can enhance the interaction between the Ca atom and BlueP and effectively hinder the formation of Ca clusters on the surface of BlueP. The Ca-decorated B@BlueP can store six hydrogen molecules per Ca atom with average adsorption energies of around 0.17–0.24 eV/H2. Electronic structure analysis confirms that both the polarization of hydrogen molecules under the local electrostatic field and the hybridization of Ca-s/d orbitals with H2-σ orbitals contribute to the adsorption of hydrogen molecules in the surrounding of the Ca atom. The decoration of double-sided Ca atoms can lead to a high theoretical gravimetric hydrogen density of 7.29–7.76 wt%, exceeding the storage goal of 5.50 wt% proposed by US-DOE for applications. Furthermore, the practical hydrogen storage capacity at different pressures and temperatures was also studied through thermodynamic analysis, and the storage capacity is calculated to be around 5.50 wt% in practical circumstances (298 K/30 atm and 358 K/5 atm are used as adsorption and desorption conditions, respectively). Hence, the Ca-decorated B@BlueP monolayers have promising potential as reversible hydrogen storage materials under ambient conditions.

Electronic and structural properties of hydrogen adsorption on γ-Graphyne and γ-BNyne

While the study of one-dimensional materials such as carbon nanotubes and boron-nitrogen structures have attracted technological interest, the appearance of new two-dimensional materials has expanded the spectrum with new potential applications. The most recent report published in 2022 on the synthesis of γ-graphyne has sparked scientific interest in describing the properties that this material and its analogs may exhibit under different physical and chemical conditions. In this study, the effect of hydrogen molecule adsorption on γ-BNyne surface is presented for the first time and compared with the properties reported for γ-graphyne, these calculations have been carried out through first-principles calculations using Density Functional Theory with DFT-D3 Grimme’s correction. The results showed that molecular hydrogen adsorption on these two-dimensional surfaces does not significantly alter their pristine structural and electronic properties, demonstrating their stability under molecular hydrogen adsorption conditions. The results presented here contribute to the promotion of these two-dimensional materials as potential candidates for technological applications such as nanosensors, nanomedicine, and hydrogen storage, among others.

Impact of Alloy Elements on the Adsorption and Dissociation of Gaseous Hydrogen on Surfaces of Ni–Cr–Mo Steel

In this study, the effect of alloying elements on the adsorption and dissociation behaviors of hydrogen molecules on the bcc-Fe (001) surface has been investigated using first-principles calculations. H2 molecules can easily dissociate on the hollow site, and the dissociated hydrogen atoms bond with the surrounding metal atoms. Doping Cr and Mo atoms on the surface would reduce the H2 molecule adsorption energy, which promotes the H2 molecule adsorption and dissociation. When only one or two Ni atoms doping on the surface, it improves the adsorption energies, which in turn can hinder the H2 molecule adsorption and dissociation. However, three or four Ni atoms doping on the surface is beneficial to the H2 molecule adsorption and dissociation. Thus, the nickel content in Ni–Cr–Mo steel should be reasonably controlled to improve the hydrogen embrittlement resistance of the steel.

An ab-initio analysis of the hydrogen storage behaviour of V doped Si2BN nanotube

Within the context of density functional theory (DFT), the investigation of the functionalization of vanadium (V) on Si2BN nanotube and process of hydrogen molecule adsorption upon V-doped Si2BN nanotube were conducted. It investigated optimized configurations and charge transfer, including interactions with H2 molecules According to our findings, the energy after adsorption of the single V-functionalized Si2BN nanotube is −6.67 eV (PBE) and −7.43 eV (vdW). V-functionalized Si2BN nanotube binds H2 more strongly (−0.78 eV PBE, −0.76 eV vdW) than reported studies. Our results show that the V-doped Si2BN nanotube are highly responsive to the existence of H2 molecules. We studied H2 adsorption on V-doped Si2BN nanotubes, revealing a maximum capacity of five molecules. V-doped Si2BN nanotubes hold potential for hydrogen storage intermediate. The storage capacity of the complex is an impressive 3.02 wt%, achieved through the adsorption of 5H2 molecules on each V-atom. Our findings reveal Si2BN nanotubes with V atoms hold promise for efficient hydrogen storage as an intermediate application.

Hydrogen storage in MXenes: Controlled adjustment of sorption by interlayer distance and transition metal elements

MXene is an attractive solid-state material for high-capacity, secure hydrogen storage under ambient conditions. Controlled adjustment of hydrogen sorption in MXene is essential to improve the storage capability and reversibility at room temperature. This study employed first-principles calculations to investigate the hydrogen sorption properties of multilayered MXenes at the electron level. The strong physical adsorption (Kubas type) of hydrogen was observed in MXene. The interlayer distance and the transition metal elements of MXenes allowed adjustment of the sorption energy of hydrogen. The narrow interlayer space benefited the adsorption of hydrogen molecules, instead of hydrogen atoms. Group 4B elements enhanced the chemical absorption, while Hf2C and Ta2C MXenes possessed relatively strong physical adsorption of hydrogen molecules. Furthermore, the density of states, d-band center, and electron density difference were used to reveal the electronic properties of MXene-hydrogen system.

First-principles study of Li-doped planar g-C3N5 as reversible H2 storage material.

Under the background of energy crisis, hydrogen owns the advantage of high combustion and shows considerable environment friendliness; however, to fully utilize this novel resource, the major hurdle lies in its delivery and storage. The development of the in-depth yet systematical methodology for two-dimensional (2D) storage media evaluation still remains to be challenging for computational scientists. In this study, we tried our proposed evaluation protocol on a 2D material, g-C3N5, and its hydrogen storage performance was characterized; and with addition of Li atoms, the changes of its electronical and structural properties were detected. First-principles simulations were conducted to verify its thermodynamics stability; and, its hydrogen adsorption capacity was investigated qualitatively. We found that the charges of the added Li atoms were transferred to the adjacent nitrogen atoms from g-C3N5, with the formation of chemical interactions. Thus, the isolated metallic sites tend to show considerable electropositivity, and can easily polarize the adsorbed hydrogen molecules, and the electrostatic interactions can be enhanced correspondingly. The maximum storage capacity of each primitive cell can be as high as 20 hydrogen molecules with a gravimetric capacity of 8.65wt%, which surpasses the 5.5wt% target set by the U.S. Department of Energy. The average adsorption energy is ranged from -0.22 to -0.13eV. We conclude that the complex 2D material, Li-decorated g-C3N5 (Li@C3N5), can serve as a promising media for hydrogen storage. This methodology provided in this study is fundamental yet instructive for future 2D hydrogen storage materials development.

Metallofullerenes as Robust Single-Atom Catalysts for Adsorption and Dissociation of Hydrogen Molecules: A Density Functional Study.

Hydrogen is currently considered as the best alternative for traditional fuels due to its sustainable and ecofriendly nature. Additionally, hydrogen dissociation is a critical step in almost all hydrogenation reactions, which is crucial in industrial chemical production. A cost-effective and efficient catalyst with favorable activity for this step is highly desirable. Herein, transition-metal-doped fullerene (TM@C60) complexes are designed and investigated as single-atom catalysts for the hydrogen splitting process. Interaction energy analysis (Eint) is also carried out to demonstrate the stability of designed TM@C60 metallofullerenes, which reveals that all the designed complexes have higher thermodynamic stability. Furthermore, among all the studied metallofullerenes, the best catalytic efficiency for hydrogen dissociation is seen for the Sc@C60 catalyst Ea = 0.13 eV followed by the V@C60 catalyst Ea = 0.19 eV. The hydrogen activation and dissociation processes over TM@C60 metallofullerenes is further elaborated by analyzing charge transfer via the natural bond orbital and electron density difference analyses. Additionally, quantum theory of atoms in molecule analysis is carried out to investigate the nature of interatomic interactions between hydrogen molecules and TMs@C60 metallofullerenes. Overall, results of the current study declare that the Sc@C60 catalyst can act as a low cost, highly efficient, and noble metal-free single-atom catalyst to efficiently catalyze hydrogen dissociation reaction.

DFT study of Hydrogen storage capacity on Hf doped graphene

We explored the molecular hydrogen storage capacity of complex system with Hafnium doped graphene (Gr-Hf) using the Density Functional Theory (DFT) method. We efficiently adsorbed molecular six hydrogens on the Hf doped graphene surface. The quantum chemically calculated adsorption energy is found negatively in the range of - 344.433 Ry to -333.836 Ry this implies as increasing the adsorbed hydrogen molecule on hafnium doped graphene (Gr-Hf) sheet the adsorption energy decreases continuously. The binding energy of after adsorbing second hydrogen molecule too much larger than the next adsorbed H2 molecules i.e., the binding energy per hydrogen molecule highly decreases when we increase adsorbed atom (2.197 Ry in 2H2 to 1.048 Ry in 3H2) then small decreases for next adsorbed H2 molecules. The extracted binding energy found in the range 2.197 Ry to 2.120 Ry, fermi energy found minimum for 1H2 shows the minimum electron occupancy at the different energy levels. The fermi energy increases accordingly, the electron occupancy also increases and evaluates higher electron occupancy with fermi energy 2.850 eV for 6H2 and density of states (DOS) confirm the weak interaction between σ bonding electrons of H2 molecule with Hf doped graphene complex system. The proposed system opens a new insight for hydrogen storage-based devices.