Mechanism Of Hydrogen Adsorption Research Articles

Highly efficient separation of CO2/N2 and CO2/CH4 via metal-ion regulation in ultra-microporous metal-organic frameworks

Efficient separation of CO2 from CH4 and N2 is crucial for industrial processes. This study presents a novel approach to enhance CO2/N2 and CO2/CH4 separation using metal-ion regulation in ultra-microporous metal–organic frameworks (MOFs). Specifically, we synthesized ZSTU-8-M (M=Cd, Zn) by coordinating norfloxacin ligands with different metal ions, achieving precise modulation of the pore structure. Ideal adsorption solution theory (IAST) calculations demonstrated that ZSTU-8-Cd exhibited superior selectivity for CO2/N2 (952) and CO2/CH4 (369) mixtures compared to ZSTU-8-Zn. Grand canonical Monte Carlo (GCMC) simulations and in situ single-crystal X-ray diffraction (SCXRD) confirmed the presence of specific CO2 binding sites within the pore channels. The CO2 molecule shows a unique strong adsorption mechanism of hydrogen bonding sites in this structure, and thus achieves high adsorption capacity at low pressure. Dynamic breakthrough experiments further validated the practical separation efficiency of ZSTU-8-Cd, with high retention times and saturated adsorption capacities for CO2. These findings highlight the ability of metal-ion modulation to achieve simultaneous improvement in adsorption capacity and selectivity, demonstrating the potential of MOFs for advanced gas separation applications.

Molecular dynamics simulation of hydrogen adsorption and diffusion characteristics in graphene pores

Carbon structures have been shown to be potentially efficient hydrogen storage media, but the micro adsorption/diffusion kinetic properties of hydrogen storage are still unclear. We investigated the adsorption of H2 in carbonaceous nanoporous by molecular dynamics simulations. It was found that the hydrogen molecules were completely adsorbed when the pore size was 1 nm, and existed in both adsorbed and free forms when the pore size was 2–6 nm, and the adsorption was in a saturated state, with the absolute adsorption amount keeping constant. Modification of functional groups on the inner side of graphene pores reduces the hydrogen storage capacity, and this effect becomes more and more obvious with decreasing pore size, especially for 1 nm pores. The total adsorption amount of H2 in 1 nm graphene pores was 0.01315 × 10−3 mol/m2, which was 3.8846 times that of graphene oxide pore. The hydrogen adsorption effect on different surfaces is: G > GO(-O-) > GO(-OH) > GO(-O-/OH). The results of this study are helpful to further understand the physical adsorption mechanism of molecular hydrogen on carbonaceous materials.

Improving hydrogen evolution catalytic activity of 2D carbon allotrope biphenylene with B, N, P doping: Density functional theory investigations

Using a first principles approach, we studied the hydrogen evolution reaction activity of newly synthesized biphenylene and B, N, P decorated biphenylene sheet. Hydrogen evolution reaction activity of pristine biphenylene sheet is not encouraging, as it is similar to pristine graphene. The Gibbs free energy and overpotential of P(N) doped on biphenylene sheet are 0.022 (−0.092) eV and 22 (92) mV, respectively. The reported Gibbs free energy and overpotential of Pt are 0.9 eV and 90 mV. Hence doping of P(N) atom on top of biphenylene sheet improves hydrogen evolution reaction activity much better (near to) Pt metal. We analyzed the adsorption mechanism of dopants (B, N, P) and hydrogen with Bader charge analysis and density of states analysis. P and N-decoration on biphenylene sheet change its electronic structure so that one obtains improved hydrogen evolution reaction activity for P and N-doped biphenylene sheet. Furthermore, the stability of N, P decorated biphenylene at room temperature with ab-initio molecular dynamics and formation energy near that of biphenylene indicate experimental feasibility. We have compared all our best hydrogen evolution reaction activity results in the reaction coordinate and volcano plots of pristine, B, N, and P-doped BPh sheets. They indicate that P-doped biphenylene is a metal-free, powerful catalyst for hydrogen evolution reaction activities.

Probing the catalytic activity of first-row transition metal doped C20 fullerene as remarkable HER electrocatalysts: A DFT study

Hydrogen evolution reaction (HER) has captivated the interest of researchers due to ever increasing demand for future sources of energy. With the advancement in renewable energy resources, electrocatalytic production of hydrogen has been considered as the most suitable way for hydrogen production for fuel cells and combustion engines. Herein, we studied HER activity of transition metal doped C20 fullerene (M@C20) by means of adsorption energy, Gibbs free energy and electronic density calculations. Ni@C20 and Cu@C20 complexes provide the best HER activity with Gibbs free energy of −0.09 eV for each. Furthermore, electronic properties such as the density of states (DOS) and frontier molecular orbital analyses are performed which indicate that transition metal doping significantly alters the electronic properties of studied M@C20 complexes. Whereas the adsorption of hydrogen does not affect the electronic parameters much. The basic understanding of hydrogen adsorption mechanism together with analyses of electronic parameters is crucial for the synthesis of highly efficient electrocatalysts for hydrogen energy applications. The critical findings of this study declares that both Ni@C20 and Cu@C20 complexes can act as promising electrocatalysts for hydrogen evolution reaction with low overpotential.

Comparative analysis of hydrogen sorption in large-sized single-walled carbon nanotubes and multi-walled carbon nanotubes: A molecular dynamics study

Recent nanomaterial advancements have resulted in a breakthrough in energy storage and hydrogen carrier technologies. The hydrogen adsorption metrics of single-walled carbon nanotubes (SWCNT) and multi-walled carbon nanotubes (MWCNT) at temperatures of 77 and 300 K are thoroughly investigated using molecular dynamics simulations. This study sheds light on the hydrogen adsorption mechanism of large-sized CNTs at pressures ranging from 0.1 to 10 MPa. Furthermore, the effect of interwall spacing in MWCNT has been analysed and discussed using adsorption isotherms to highlight key features. At 77 K and 10 MPa, SWCNT can store molecular hydrogen with a maximum gravimetric density of 8.33 wt%, compared to 6.56, 4.55, and 3.18 wt% for MWCNT, whereas the storage capacity is less than one wt.% at 300 K. Moreover, the interlayer spacing in MWCNT is found to have a significant influence on the system gravimetric capacity, and the larger the interior space, the greater the adsorption. However, increasing the number of interlayers in MWCNT, on the other hand, reduces storage capacity. As a result, our findings suggest that SWCNT and MWCNT have a promising potential for hydrogen storage applications and, with structural modifications, could meet the US Department of Energy's benchmark.

The elemental weakening & aggregation effect on the hydrogen adsorption on FeCrAl (110) surface

FeCrAl alloys are promising candidates for Accident Tolerant Fuel cladding in Light Water Reactors. Understanding the adsorption mechanism of hydrogen is important for understanding the hydrogen embrittlement of FeCrAl alloys. In our previous work, we find that the adsorption site can significantly influence the H adsorption energy (Eads.). However, the widely adopted Special Quasi-random Structure (SQS) method for constructing FeCrAl structure hinders comprehensive investigations on all the possible H adsorption sites. In this work, a manually created surface structure is used to systematically study all the possible H adsorption sites. It is found that when Cr/Al atoms are dispersed on the surface, the HCr/Al bonding can be weakened. The weaker HCr/Al interactions are attributed to the charge deficit of Cr/Al caused by their relatively higher electronegativity than Fe. In contrast, when Cr/Al atoms aggregate on the surface, the HCr/Al bonding can be reinforced. The reinforcement comes from the increased charge density of Cr/Al due to aggregation.

Interfacial Interaction of Monolayer Black Phosphorus/g‐C3N4 Van Der Waals Heterojunction for Efficient Photocatalytic Hydrogen Evolution

The 2D/2D van der Waals heterojunctions have promising photocatalytic applications. However, their interfacial interaction and photocatalytic mechanism are still unclear. Herein, monolayer black phosphorus (BP)/graphitic carbon nitride (GCN) heterojunction photocatalytic hydrogen evolution is systematically investigated using the density‐functional theory method. It is indicated in the results that BP/GCN heterojunction structure distortion and interface interaction change its electronic structure and photocatalytic performance. The hydrogen‐adsorption free energy of BP/GCN heterojunction is −0.28 eV, indicating that the BP/GCN heterojunction has a high catalytic activity for hydrogen production. Calculated Bader charge and Fermi energy level show that a built‐in electric field from BP to GCN forms in its interface. The energy barrier and built‐in electric field promote the recombination of photogenerated electrons in GCN conduction band and photogenerated holes in BP valence band; electrons on the BP conduction band and holes on the GCN valence band are effectively separated in space; and more electrons and holes can participate in redox reactions on the surface. The BP/GCN heterojunction is a type Z heterojunction. Significant improvement in photocatalytic reaction efficiency is attributed to the type Z photocatalytic mechanism and small free energy of hydrogen adsorption. Herein, it is aimed to offer insights into the photocatalytic mechanism of 2D/2D heterojunctions.

High-pressure hydrogen adsorption in clay minerals: Insights on natural hydrogen exploration

Natural hydrogen has been widely detected in many environments. However, up to date, the knowledge about the occurrence of hydrogen in the geological formation is very limited. Clay minerals with large adsorption capacities due to their huge specific surface area are widely distributed in the subsurface. In order to find whether the hydrogen can be adsorbed on the clay minerals, 6 types of clay minerals (montmorillonite, chlorite, sepiolite, palygorskite, kaolinite and illite) were used for the hydrogen adsorption analysis at various temperatures (0, 25, 45, and 75 °C) and pressures (up to 18 MPa). In addition, multi-scale simulations via density functional theory (DFT) and grand canonical Monte Carlo (GCMC) were carried out to further explore the hydrogen adsorption mechanism of clay minerals in bulk phase. The results show that the excess adsorption capacities of sepiolite and palygorskite are much higher than those of montmorillonite and chlorite, and the excess adsorption capacities of illite and kaolinite are very low, nearly reaching the detection limit. The variation of hydrogen adsorption capacity (HAC) in different clays is attributed to the difference in their pore structures (i.e., specific surface area). A more complex pore structure and a larger specific surface area could provide more sorption sites for hydrogen molecules. HAC increases with pressure and decreases with temperature irrespective of the clay mineral types. This study highlights the features of hydrogen adsorption in clay minerals, contributes to a better understanding of natural hydrogen occurrence and storage in the subsurface, providing the potential application for geological hydrogen exploration.

Effect of Elemental Doping on the Adsorption Behavior and the Mechanism of Hydrogen Adsorption on the Zirconium Surface

This study used the Monte Carlo (MC) and density functional theory (DFT) methods to simulate the adsorption process of a H atom on element (vacancy, Cr, Sn, and Fe)-doped Zr(0001) surfaces and further analyzed the adsorption site distribution, adsorption energy, charge transfer, and electronic structure, etc. of the doped zirconium surface model. Simulated results indicated that (i) although the doping of vacancy, Cr, Sn, and Fe had a significant effect on the adsorption site distributions of the H atom on the Zr(0001) surface, they showed completely different distribution patterns. (ii) Vacancy doping promoted the adsorption of the H atom on the Zr(0001) surface. The H atom would penetrate the zirconium matrix along the vacancy and then occupy the octahedral gap stably. On the contrary, the doping of Cr, Sn, and Fe inhibited Zr(0001) surface hydrogen uptake in the order of Fe > Cr > Sn, where the effect of Sn could be negligible. (iii) Fe doping had the greatest effect on the chemical reaction mechanism of H adsorption on the Zr(0001) surface, which significantly converted the chemical reaction from Zr–H- to Fe–H-dominated, while Cr doping caused the formation of the Cr–H and Zr–H coaction mechanism, and Sn doping had almost no effect on the mechanism of H adsorption on the Zr(0001) surface.

Molecular Dynamics Investigation into the Hydrogen Adsorption Mechanism of the Magnesium-Based Material 2Mg–Fe Mixture

Molecular Dynamics Investigation into the Hydrogen Adsorption Mechanism of the Magnesium-Based Material 2Mg–Fe Mixture

Hydrogen storage metal-organic framework classification models based on crystal graph convolutional neural networks

Metal-organic frameworks (MOFs) have been considered as promising physical adsorbents for hydrogen storage due to their high porosity and structural tunability. We selected 7643 real MOFs from the computation-ready MOF 2019 database to screen high-performance materials for hydrogen storage based on the grand canonical Monte Carlo (GCMC) simulations. Based on the obtained data set, we proposed a deep learning classification model powered by the crystal graph convolutional neural networks (CGCNN) for the discovery of the optimal hydrogen storage MOFs. It is demonstrated that our classification model based on CGCNN algorithms exhibits a high prediction accuracy with the area under the ROC-plot curve (AUC) of 0.9208 for hydrogen storage performance of volumetric deliverable capacity (VDC). Compared with the classification models based on other machine learning algorithms such as random forest, our CGCNN model demonstrates the advantages of fast prediction with no feature extraction and little accuracy loss. When the trained CGCNN model was used to predict the classification of the unfamiliar samples (the randomly selected 1000 MOFs from the 137,953 hypothetical MOF database), we also obtain high accuracy with AUC > 0.81, indicating that this model exhibits reliable transferability for other types of MOFs. Meanwhile, we also elucidated the relationship between structure and performance of MOFs for hydrogen storage using the decision tree algorithms and quantitative structure–property analysis. Furthermore, the hydrogen adsorption performance and mechanism of top-performance MOFs were analyzed by adsorption isotherms, radial distribution functions, and mass center density distribution of equilibrium configurations. All those insights from atomic simulations and machine learnings can accelerate the discovery of new nanoporous materials not only for gas adsorption in MOFs but also for gas separation in other types of porous materials.

Cycling stability and adsorption mechanism at room temperature of the upscaled Ni-doped hierarchical carbon scaffold

Hydrogen adsorption performance and mechanism upon cycling of the upscaled Ni-doped hierarchical carbon scaffold (HCS) are investigated. Upon 22 hydrogen ad/desorption cycles (T = 25–50 °C and p (H2) = 1–50 bar), the upscaled Ni-doped HCS shows excellent cycling stability with gravimetric capacity of up to 1.51 wt % H2. This is due to mechanical stability of HCS and good distribution of Ni nanoparticles. Hydrogen adsorption mechanism of Ni-doped HCS upon cycling is experimentally and theoretically characterized. Besides dissociative adsorption onto the surface, hydrogen diffusion into the lattice structure of Ni is observed. The latter enhances with the number of ad/desorption cycles and alters the electron sharing mechanisms between Ni and H during adsorption.

Hydrogen storage by spillover on Ni4 cluster embedded in three vacancy graphene. A DFT and dynamics study

An ab initio dynamics study was performed with the aim of understanding better the hydrogen adsorption mechanism, stability and capacity with the temperature on Ni4 cluster embedded in a three vacancy graphene substrate. Additionally, the hydrogen migration to the substrate was analyzed observing an outstanding improvement for the activation energy compared with the systems without vacancies. Moreover, a suitable reduction in the hydrogen migration energy barriers was achieved with the subsequent hydrogen adsorption of more molecules on the cluster. Consequently, in the light of these new insights hydrogen spillover on Ni4 can be highly influenced by both, vacancy defects and the saturation with hydrogen molecules.

Hydrogen adsorption process in nanocrystalline nuclear graphite

Kinetics and mechanism of hydrogen adsorption in as-obtained and ground nuclear graphite Wendelstein 7-X are examined. In the first time interval the adsorption process is determined by dissociation of the hydrogen molecule, occurring at the outer surface and in open micropores of nuclear graphite particles. However, in the second time interval, the slowest step in the hydrogen adsorption is inter-granular and inter-crystallite diffusion in nanopores of graphite. The X-ray analysis shows, that grinding of as-obtained nuclear graphite results in finer particles with finer nanocrystals and larger density of opened pores and carbon reactive sites. The capacity and rate of adsorption increase with comminution of nuclear graphite particles and adsorbed hydrogen does not substantially alter the microstructure of nuclear graphite.

Microscopic Mechanism of Hydrogen Adsorption on Rutile Titanium Dioxide Surface and Its Optical Properties

Microscopic Mechanism of Hydrogen Adsorption on Rutile Titanium Dioxide Surface and Its Optical Properties

Study on the Electron Action Mechanism of Hydrogen Adsorption and Activation on Platinum Clusters with the help of Computer Software

Cyclic aromatic hydrocarbons occupy a certain proportion in the high boiling point fractions of petroleum and are difficult to convert. Hydrocracking to lighten polycyclic aromatic hydrocarbons is currently an effective way of conversion. As the first step of catalytic reaction, the adsorption of polycyclic aromatic hydrocarbons (PAHs) on the surface of catalytic materials is of great significance to the subsequent reaction process. In this paper, molecular dynamics and density functional theory (DFT) were used as research tools, and Nano-sized PT clusters were selected as adsorption models [1-3]. Firstly, the adsorption mode of H2 on Pt clusters was analyzed from the frontier orbital point of view, and the changes of electron distribution of H2 on Pt clusters from physical adsorption to chemical adsorption were compared with the help of computer software.

Catalytic methane activation over La1−xSrxScO3−α proton-conducting oxide surface: A comprehensive study

The detailed investigation of the influence of strontium on the methane activation over the state-of-the-art proton-conducting oxide catalyst La1−xSrxScO3−α was carried out using a combination of the novel H/D isotopic exchange method, Raman Spectroscopy, 1H NMR and DFT studies in the temperature range 673 – 973 K, at 10 mbar of CH4 + H2 (95%+5%) mixture. It was found that methane activation occurs via the four parallel channels of the hydrogen adsorption and incorporation mechanism, followed by the formation of methane intermediates with different hydrogen content (CHx species). The dominant type of adsorbed intermediate is governed by the temperature and the surface defect structure, which is in close correlation with the strontium content. The increase of strontium content in La1−xSrxScO3−α drastically increases the catalytic activity due to the surface modification with oxygen deficiencies in the ScO6 octahedron, and stabilisation of the CHx species with a low amount of hydrogen.

DFT study of the hydrogen adsorption and storage on Ni4 cluster embedded in multivacancy graphene

Hydrogen adsorption stability, geometry, electronic structure and mechanism has been investigated on Ni4 cluster embedded in graphene with three, four and six vacancies by density functional theory (DFT) calculations. An energetic analysis of hydrogen adsorption by addition of one to four H2 molecules was performed for each system in order to determine their hydrogen storage capacity. Dispersion force contribution to the adsorption energy is quantitative evaluated to know whether H2 molecules adsorption behavior is dominated by chemical or van der Waals interactions. A further analysis of this type of interactions is also addressed by total and partial density of states. Bonding and charge transfer characteristics for the different steps involved in the adsorption mechanism are also included. Special attention is given to the effects caused by this new Ni/graphene interface to the hydrogen adsorption behavior.

Mechanisms of hydrogen atom interactions with MoS2 monolayer

The mechanisms of H atoms interactions with single-layer MoS2, a two-dimensional transition metal dichalcogenide, are studied by static and dynamic DFT (density functional theory) modeling. Adsorption energies for H atoms on MoS2, barriers for H atoms migration and recombination on hydrogenated MoS2 surface and effects of H atoms adsorptions on MoS2 electronic properties and sulfur vacancy production were obtained by the static DFT calculations. The dynamic DFT calculations give insight into the dynamics of reactive interactions of incident H atoms with hydrogenated MoS2 at H atoms energies in the range of 0.05–1 eV and elucidate the competitive mechanism of hydrogen adsorption and recombination that limits hydrogen surface coverage at the level of 30%. Various pathways of S-vacancies production and H atoms losses on MoS2 are calculated and the effects of MoS2 temperature on these processes are estimated and discussed.

Synthesis and characteristics of CMK-3 modified with magnetite nanoparticles for application in hydrogen storage

In this work, we report the synthesis and characterization of iron oxide nanoparticles supported in nanostructured carbon (CMK-3). This material is promising in the application of hydrogen adsorption for energy storage. The material with iron oxide nanoparticles (Fe-CMK-3) was successfully synthesized and characterized by X-ray diffraction, textural properties analysis, transmission and scanning electron microscopy, X-ray photoelectron spectroscopy, and magnetization studies. A large amount of the iron incorporated as iron oxide nanoparticles was in the magnetite phase. The incorporation of magnetite on the CMK-3 carbon surface significantly improved the storage capacity of hydrogen (4.45 wt% at 77 K and 10 bar) compared with the CMK-3 framework alone (2.20 wt% at 77 K and 10 bar). The synthesized material is promising for hydrogen adsorption by weak bond forces (physisorption). A hydrogen adsorption mechanism was proposed in which the nanoparticles of magnetite have an important role.