First-principles study of hydrogen storage on Si atoms decorated C60

Hydrogen storage capacity of Si_nC₆₀ is studied via first-principles theory based on DFT and Canonical Monte Carlo Simulation (CMCS). It is shown that Si atoms strongly prefer D-site rather than other sites and in these structures maximum number of hydrogen molecule onto any Si atom is one. Each Si atom adsorbs one hydrogen molecule in molecular form and with proper binding energies when Si atom is placed in any D-site of C₆₀. Si atoms enhance remarkably hydrogen storage capability in fullerene.     

Grand canonical Monte Carlo simulation of hydrogen physisorption in single-walled boron nitride nanotubes

The properties of hydrogen physisorption in single-walled boron nitride nanotubes (SWBNNTs) and single-walled carbon nanotubes (SWCNTs) are investigated in detail by the grand canonical Monte Carlo simulations. A great deal of our computational results show that the hydrogen storage capacity of SWBNNTs is slightly larger than the capacity of SWCNTs at any time when their diameters were equal and in the same conditions, and indicate that the hydrogen storage capacity of SWBNNTs at 293 K and 10 MPa with a diameter of more than 30 nm or at 293 K and 15 MPa with a diameter of more than 25 nm could exceed the 2010 goal of 6 wt%, which is presented by the U.S. Department of Energy. In addition, these results are discussed in theory.     

Grand Canonical Monte Carlo simulations of the hydrogen storage capacities of slit-shaped pores,nanotubes and torusenes

Grand Canonical Monte Carlo, GCMC, simulations are used to study the gravimetric and volumetric hydrogen storage capacities of different carbon nanopores shapes: Slit-shaped, nanotubes and torusenes at room temperature, 298.15 K, and at pressures between 0.1 and 35 MPa, and for pore diameter or width between 4 and 15 Å. The influence of the pore shape or curvature on the storage capacities as a function of pressure, temperature and pore diameter is investigated and analyzed. A large curvature of the pores means, in general, an increase of the storage capacities of the pores. While torusenes and nanotubes have surfaces with more curvature than the slit-shaped planar pores, their capacities are lower than those of the slit-shaped pores, according to the present GCMC simulations. Torusene, a less studied carbon nanostructure, has two radii or curvatures, but their storage capacities are similar or lower than those of nanotubes, which have only one radius or curvature. The goal is to obtain qualitative and quantitative relationships between the structure of porous materials and the hydrogen storage capacities, in particular or especially the relationship between shape and width of the pores and the hydrogen storage capacities of carbon-based porous materials.     

Adsorption of hydrogen molecule on alkali metal-decorated hydrogen boride nanotubes: A DFT study

Adsorption of Li, Na, and K atom on surfaces of armchair (5,5) and zigzag (10,0) hydrogen boride nanotubes (HBNTs) was investigated using the periodic-DFT method. It was found that the average diameter (5,5) HBNT is shorter than the (10,0) HBNT by 1.246 Å and the (5,5) HBNT is more stable than the (10,0) HBNT by 0.991 eV. Adsorption strength of the (5,5) HBNT on alkali metals was found to be higher than the (10,0) HBNT. Adsorption abilities of H₂ on the (5,5) HBNT and (5,5) HBNT are in the same order: Li > Na > K. The adsorption energies of H₂ on Li-, Na-, and K-(5,5) HBNTs are −0.242, −0.165, and −0.121 eV, respectively, and on Li-, Na-, and K-(10,0) HBNTs are −0.277, −0.168, and −0.094 eV, respectively. The Li-HBNTs, Li-(5,5) HBNT, and (10,0) HBNT are the highest adsorption abilities on H₂ adsorption and the most significant change of metal charges. Therefore, the Li-(5,5) HBNT and (10,0) HBNT used as H₂ storage materials were suggested.     

Prospects of green hydrogen in Poland: A techno-economic analysis using a Monte Carlo approach

The European Commission's plan to decarbonize the economy using innovative energy carriers has brought into question whether the national targets for developing electrolysis technologies are sufficiently ambitious to establish a local hydrogen production industry. While several research works have explored the economic viability of individual green hydrogen production and storage facilities in the Western European Member States, only a few studies have examined the prospects of large-scale green hydrogen production units in Poland. In this study, a Monte Carlo-based model is proposed and developed to investigate the underlying economic and technical factors that may impact the success of the Polish green hydrogen strategy. Moreover, it analyzes the economics of renewable hydrogen at different stages of technological development and market adoption. This is achieved by characterizing the local meteorological conditions of Polish NUTS-2 regions and comparing the levelized cost of hydrogen in such regions in 2020, 2030, and 2050. The results show the geographical locations where the deployment of large-scale hydrogen production units will be most cost effective.     

Grand canonical Monte Carlo and molecular dynamics simulations of the structural properties,diffusion and adsorption of hydrogen molecules through poly(benzimidazoles)/nanoparticle oxides composites

Comprehensive structural/molecular simulations have been undertaken to study the poly(benzimidazoles) (PBI) membrane combined with four different nano-oxide materials (ZnO, Al₂O₃, SiO₂ and TiO₂) for purification and production of hydrogen from natural gases. Composite membranes were built with different amounts of nano-oxide materials to investigate the influence of nano-oxide content on the PBI membrane performance. Several structural characterizations such as FFV, WAXD and also a thermal one (glass transition temperature) were done to study the structural properties of all simulated membrane cells. Moreover, MSD and adsorption isotherms tasks were used to estimate the diffusivity and solubility of hydrogen molecules through the latter mixed matrix membranes (MMMs), respectively. Permeability and permselectivity of H₂ penetrate molecules were also carefully calculated using the aforementioned penetrating factors (diffusivity and solubility). Results show a significant improvement in structural and transport properties by increasing the nanomaterials content, which could be due to the growth of penetration pathways through the membranes. Furthermore, membranes with SiO₂ yield the best results compared to other three nano-oxide fillers. H₂ gas yields the best results that help the storage and separation of this precious gas from other gas molecules, which present in natural gases. Compared to the previous studies and literature results, the current results are accurate and reliable to describe the structural and transport properties of PBI/nano-oxides composites.     

Structural optimization of arranged carbon nanotubes for hydrogen storage by grand canonical Monte Carlo simulation

We revealed the arrangement of single-wall carbon nanotube (SWNT) which is suitable for the adsorption of hydrogen by means of grand canonical Monte Carlo (GCMC) simulation with simple cylindrical model. Here, we calculated the amount of adsorbed hydrogen with triangular lattice (TL) and square lattice (SL) model for the bundle structure with various kinds of tube diameters (D) and inter-axis distances (R_a). Our results indicate that any arrangements having smaller R_a are not suitable for the storage of hydrogen and the adsorption amount of hydrogen can be achieved the target value (6 wt.% and 45 kg m⁻³) proposed by Department of Energy (DOE) in United States by SWNTs having larger R_a at 77 K and 1 MPa. Furthermore, these results show that the best arrangement of SWNTs for the adsorption of hydrogen at this condition is TL structure having R_a = 2.159 nm and D = 1.227 nm.     

Grand Canonical Monte Carlo simulations of hydrogen adsorption on aluminophosphate molecular sieves

The hydrogen adsorption simulations were carried for several model AlPOs (VPI-5, AlPO-5, AlPO-11 and AlPO-25) employing the Grand Canonical Monte Carlo (GCMC) simulations at 77 K to investigate the effect of pore size and the pore volume on the hydrogen uptake. The adsorption capacity showed no relationship with the pore size, surface area and micropore volume of AlPOs. However, the adsorption capacity per unit micropore volume increased as the pore size decreases. The heat of adsorption also increased as the pore size decreases. For all model AlPOs, the hydrogen exists homogeneously near the oxygen atoms in the framework.     

A DFT study of hydrogen adsorption on Pt modified carbon nanocone structures: Effects of modification and inclination of angles

The adsorption of hydrogen molecule on Pt modified carbon nanocone (CNC) structures was investigated by density functional method. Pt atom was modified by both doping and decorating on the structures with 180⁰, 240⁰ and 300⁰ inclination angles of the CNC. The interactions of the hydrogen molecule on the ring and top sites of these modified structures were explored. Effect of doping and decorating of Pt atom on CNC structures has been also investigated. The adsorption enthalpy and Gibbs free energy values of the structure formed by doping the Pt atom at the ring are −118.4 and −85.3 kJ/mol, respectively. With the increase of the angle of inclination, the hydrogen interaction decreased at the ring and increased at the top. According to the results of this study, it is predicted that CNCs modified with Pt atom can be a promising hydrogen storage material under ambient conditions.     

Dynamics of bound states of dihydrogen at Cu(I) and Cu(II) species coordinated near one and two zeolite framework aluminium atoms: A combined sorption,INS, IR and DFT study

Ambient conditions sorption isotherms of dihydrogen in a series of various levels of Cu-exchanged ZSM-5 zeolites, with two different Si/Al ratios, namely 11.5 and 25, show the presence of different amount of Cu centres able to strongly bind H₂. Although the isosteric heats of adsorption derived from these isotherms are rather similar, of the order of 30 kJ/mol H₂, Inelastic Neutron Scattering (INS) of adsorbed dihydrogen and Fourier-Transformed Infra-Red (FTIR) spectroscopy measurements of adsorbed CO and NO reveal that copper is encountered in two oxidation states. At least two types of Cu(I) ions are clearly detected as well as some heterogeneity of the Cu(II) species. The number of these Cu species is different in the two investigated ZSM-5 materials and depends on the Cu exchange level. With the aid of DFT model cluster calculations we find that under different coordination environments, determined by the Al distribution, both mono- and divalent Cu ions could bind H₂ with a different strength. Unprecedentedly, we found that Cu-ions compensating two Al atoms, i.e. formally Cu(II) species, relatively far apart from each other, may behave very similarly to the monovalent Cu-species or alternatively viewed – as Cu(I) species that compensate for two framework Al-atoms. Such Cu-species also form stable η² dihydrogen complexes.     

The hydrogen storage properties of Mg-intermetallic-hydrides by ab initio calculations and kinetic Monte Carlo simulations

First-principle calculations and kinetic Monte-Carlo simulations were performed to study the hydrogen storage properties of the intermetallic hydrides MgNiH₃, MgCoH₃ and thier mixture namely MgCo_0.5Ni_0.5H₃.Based on the heat of formation, desoprtion temperature, activation energies computed from DFT calculations and KMC simulations, we show that the MgNiH₃ involves a fast kinetic while it is thermodynamically unstable (−9.96 kJ/mol.H₂; 76.61 K) whereas MgCoH₃ has a high thermodynamic stability (−73.32 kJ/mol.H₂; 560.97 K) which prevents their application for mobile hydrogen storage.On the other hand, the electronic structures show that the Ni weakens the strong CoH bonding of the mixture MgCo_0.5Ni_0.5H₃, which enhances significantly its stability and its desorption temperature (−45.92 kJ/mol.H₂ and 351.33 K) without reducing its high volumetric capacity 133.73 g.H₂/l. Kinetic Monte-Carlo simulations show that MgCo_0.5Ni_0.5H₃ exhibits a fast charging time (only 4.6 min at 400 K and 10 bar).Thermodynamic properties including entropy S, Gibbs free energy G and thermal expansion coefficient are predicted within the quasi-harmonic approximation. It is verified that crystal structure of MgCo_0.5Ni_0.5H₃ is stable.     

The influence of pre-adsorbed Pt on hydrogen adsorption on B2 FeTi(111)

The hydrogen adsorption properties on a Pt covered Fe-terminated B2-FeTi (111) surface are studied using the Density Functional Theory (DFT). The calculations are employed to trace relevant orbital interactions and to discuss the geometric and electronic consequences of incorporating one Pt atom or a Pt monolayer on top of the FeTi surface. The most stable adsorption site is a distorted FCC hollow for one Pt atom and from this location we build the Pt monolayer (ML). The H-adsorption energy is very close among BRIDGE, HCP and FCC hollow sites (∼−0.45 eV) being lower for the TOP site (−0.34 eV) in the case of a Pt(111) fcc surface. In the case of a Pt ML/FeTi, the H more stabilized on a BRIDGE site (∼−1.13 eV) interacting with both a Pt and Fe atom. We also computed the density of states (DOS) and the overlap population density of states (OPDOS) in order to study the evolution of the chemical bonding after adsorption.     

蒙特卡罗方法在锅炉烧干事故预测及分析中的应用

通过建立锅炉缺水烧干事故故障树,提出了一种基于蒙特卡罗的锅炉缺水烧干事故预测仿真分析方法。通过算例详细介绍了此方法的实施过程,仿真结果有助于保证锅炉系统的可靠运行和降低事故发生的可能性,该方法对其他相似系统的事故预防也能起到一定的参考作用。     

DFT simulation of hydrogen storage on manganese phosphorous trisulphide (MnPS3)

Manganese phosphorous trisulphide, MnPS₃, is a solid layered material. The hydrogen gravimetric storage capacities of MnPS₃ powder at 80.15, 173.15 and 298.15 K and at moderate pressures has been recently measured in experiments. The origin of the storage capacities of this material is not well understood. The main hypothesis is that hydrogen is stored in the pores of MnPS₃ powder. The pores are modelled as two parallel MnPS₃ layers separated a certain distance. Density Functional Theory simulations of the interaction of H₂ with the surface of a MnPS₃ layer have been carried out, in order to test that hypothesis. The simulations indicate that the adsorption of hydrogen on the surface of a MnPS₃ layer is energetically favourable, but only through the physisorption mechanism. Calculations of the gravimetric capacities of the pores of MnPS₃ powder have also been carried out, obtaining a reasonable agreement with the experimental results. The comparison of the calculated and experimental gravimetric capacities show that the hydrogen storage on MnPS₃ powder is mainly due to compression in the pores and that the contribution of the physisorption process to the storage is very small.     

Effect of transition metal (Cu and Pt) doping/ co-doping on hydrogen gas sensing capability of graphene: A DFT study

Carbon nano-materials are found to demonstrate good hydrogen gas sensing capability and researchers are trying their modified derivatives for enhanced sensitivity. Studies have confirmed improvement in sensing performance of graphene when doped with N or Si or Sb. However, effect of the doping of graphene with transition metals of comparable size on its hydrogen sensing properties has not yet been studied. In the present study, we investigated the sensitivity of pristine graphene, Pt-doped graphene; Cu-doped graphene and Pt–Cu co-doped graphene surface towards hydrogen molecule adsorption utilizing density functional theory (DFT) by ab initio method. The adsorption energies for the optimized geometries have been calculated to probe the suitability and effectiveness of the modified graphene structures for Hydrogen sensing. In addition, the electronic properties for instance charge transfer analysis, band gap and density of states have also been taken into consideration. The reactivity of graphene surface for hydrogen adsorption was found to be greatly enhanced with Pt–Cu co-doped graphene surface as demonstrated by the adsorption energies and electronic properties.     

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.     

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.     

Toward hydrogen storage material in fluorinated zirconium metal-organic framework (MOF-801): A periodic density functional theory (DFT) study of fluorination and adsorption

In this study, the structural properties and hydrogen adsorption energy of the fluorinated metal-organic framework (MOF)-801 were evaluated using density functional theory (DFT). We calculated the Zr–F bond distance to be approximately 0.225 nm, which is longer than the bond distance in zirconium fluoride compounds. Due to the electronegativity of F, this site was considered as an adsorption site for hydrogen. We determined the adsorption energy to be ?5 kcal/mol per hydrogen (H₂) molecule, which is higher than that of H₂ in pristine MOF. This value is also slightly lower than the adsorption energy in a metal-decorated MOF. The introduction of F atoms is determined to enhance the binding capacity of MOF-801.     

O-assisted and pristine Au-Pt(100) surfaces: A platform for adsorption and decomposition of H2O

Adsorption and decomposition of water (H₂O) over pristine and oxygen (O) assisted Au-Pt(100) surfaces were systematically explored using ab initio calculations based on density functional theory (DFT). To consider the long-range interaction, semi-empirical dispersion correction (D2) was included in all calculations. The most preferable adsorption sites for H₂O and its fragments such as OH, O, and H, over clean and O-assisted Au-Pt(100) surfaces were determined by examining adsorption energy with different configurations. Our calculations showed that the H₂O prefers top site over Au atom while OH, O, and H prefer to be adsorbed over bridge position. In present study, we determine the best possible co-adsorption sets for considered adsorbates. We further investigated the transition states, dehydrogenation process, and activation energies for extracting H from adsorbed H₂O over both pristine and O-aided Au–Pt(100) surfaces. It was found that the O promotes H₂O dissociation significantly by diminishing the barrier energy. The decisive role played by O in decomposing H₂O molecule is revealed in this work. Our study will further assist experimentalists in designing and synthesizing novel catalysts for dehydrogenation of H₂O in hydrogen production.     

Density functional theory based molecular dynamics study on hydrogen storage capacity of C24, B12N12, Al12 N12, Be12O12, Mg12O12, and Zn12O12 nanocages

In the current study, the density functional theory calculations (DFT) were employed to determine the hydrogen storage properties of some nanoclusters including C₂₄, B₁₂N₁₂, Al₁₂ N₁₂, Be₁₂O₁₂, Mg₁₂O₁₂, and Zn₁₂O₁₂. After full geometrical optimization of all nanocages under the DFT framework, we found that C₂₄ and B₁₂N₁₂ were unstable structures even in case of incorporating only one hydrogen molecule to them due to positive obtained formation energy magnitudes while Al₁₂N₁₂ and Be₁₂O₁₂ were able to adsorb one hydrogen molecules and became thermodynamically unstable for more than one hydrogen molecule. Also, Mg₁₂O₁₂ and Zn₁₂O₁₂ were capable of storing up to 4 hydrogen molecules according to negative achieved formation energies. Also, calculated bulk modulus revealed that when all studied structures stored H₂ molecules the bulk modulus decreased compared to pristine nanoclusters. The highest reduction in bulk modulus was 10% which occurred in C₂₄ while storing 5H_2. Furthermore, the adsorption properties of these nanocages were considered using DFT and the results showed that Zn₁₂O₁₂ was a stronger adsorbent for H₂ in comparison to the rest of the studied nanocages.