Hydrogen Retention Research Articles

Enhanced retention of surface-adsorbed atomic hydrogen through sulfidation of nano zerovalent iron for water decontamination

Enhanced retention of surface-adsorbed atomic hydrogen through sulfidation of nano zerovalent iron for water decontamination

A correlation between hydroxyl vibrations under compression and anharmonicity: glaucophane as a test case

The infrared hydroxyl bands and first hydroxyl combination bands of glaucophane are characterized under pressure. In this weakly hydrogen-bonded mineral, the anharmonicity parameter, as determined from the difference between combinations and the fundamentals, is nearly constant with pressure to 15 GPa, indicating that the ambient pressure value of hydroxyl-bond anharmonicity closely reflects its value at high pressures. Given this near-constancy, the Grüneisen parameters of the hydroxyl stretching vibrations of a wide range of minerals, as derived from the pressure dependence of their O–H stretching frequencies, are correlated with the anharmonic parameter of each vibration, as determined from the ambient pressure offset of the summed frequencies of the fundamental n = 0 to 1 transitions and the frequency of the hydroxyl combination or overtone band corresponding to the n = 0 to 2 transition. This correlation is motivated by (1) the anharmonic origin of the Grüneisen parameter; and (2) the grossly similar form of the interatomic potential governing weak- and medium-strength hydrogen bonding in many minerals. This possible correlation provides a means through which the likely pressure-induced hydroxyl mode shifts of phases might be estimated from ambient pressure near-infrared measurements and emphasizes the importance of near-infrared combination/overtone band measurements. In this context, the combination/overtone bands of high-pressure hydrous phases are almost completely uncharacterized, and thus one probe of their anharmonicity has been neglected. Such information directly constrains the nature of hydrogen bonding in these phases, and hence provides possible insights into both their retention of hydrogen and its mobility. Deviations from the anharmonicity-Grüneisen parameter correlation, when observed (as may be the case in prehnite), could provide insights into anomalous effects on the hydroxyl potential well induced by bifurcated H-bonds, pressure-dependent Davydov splitting, or the influence of neighboring cations.

Application of modified olivine to a two-stage gasification process to evaluate the effects on hydrogen generation and retention of heavy metals

An environmentally-friendly and efficient waste-to-energy and heavy metal retention system was successfully developed in this study. The natural resource-olivine was applied to be the bed material of second-stage gasifier, and the effects of second-stage gasifier temperature, and steam/biomass ratio on the hydrogen (H2) production ratio of syngas and heavy metal retention were discussed in detail. The optimal hydrogen production ratio (30.3%) was achieved when second-stage temperature, steam/biomass ratio (S/B ratio) were respectively controlled at 900 °C, and 0.25. The characterization analysis results evidenced that the Fe and Mg from pristine olivine and calcined olivine can facilitate the waste-to-hydrogen during the gasification reaction. Moreover, the NiO and Ni loaded on the surface of the calcine olivine could not only facilitate the water–gas shift reaction for H2 production, but also provide strong binding sites for the linkage of ether and cleavage of the C–O bond, leading to formation of CH4. The formed CH4 would be further dissociated over the metallic Ni/olivine, resulting in a significantly improved H2 production efficiency. In general, the order based on the H2 ratio of the syngas at the second-stage was calcined Ni-loaded olivine > calcined olivine > olivine; the heavy metal retention efficiency of three bed materials was in the order of Cu > Pb > Zn.

Interaction of 1/2〈111〉 interstitial dislocation loop with hydrogen and helium in tungsten: molecular dynamics simulation

The interaction of hydrogen and helium atoms with 1/2 〈111〉 interstitial dislocation loop in tungsten is investigated by molecular dynamics simulation. The binding energies of hydrogen and helium atoms around dislocation loop are calculated by molecular statics method. The results show that the outer region of the loop is attractive to the two atoms and the inner region is repulsive. Notably, the maximum binding energies are located in the core region of the dislocation loop. We have also studied the influence factors of the interaction between the dislocation loop and two atoms: free volume, lattice distortion degree, the radius and shape of the dislocation loop. The results show that large free volume benefits the retention of hydrogen and helium atoms, especially for helium. The less lattice distortion caused by the impurity atom, the more favorable for the dislocation loop to trap it. In addition, the larger dislocation loop with higher defect concentration results in stronger capture ability for the hydrogen and helium atoms. The different dislocation loop shapes lead to different binding energy distribution patterns. And the hydrogen and helium atoms tend to occupy the groove region of the concave dislocation loop. Finally, we employ the nudged elastic band theory and dynamics method to investigate the diffusion pattern of the hydrogen atom in the dislocation loop and find that the hydrogen atom tends to migrate spirally around dislocation line. Based on the obtained results, a reasonable interpretation of the interaction behaviors between the dislocation loop with hydrogen and helium atoms are discussed, which can provide essential parameters for mesoscopic scale simulations.

Investigation of desorption of hydrogen gas from polymer matrix using thermal desorption analysis and finite element modeling

Polymer materials are used widely as sealing materials and liners in hydrogen storage and transportation infrastructure. During operating conditions, polymers are exposed to high pressure hydrogen gas periodically. When in contact, the hydrogen gas diffuses through the polymer material with ease due to its smaller sized molecules compared to the polymer molecules. In the event of rapid decompression of outside hydrogen gas, the hydrogen molecules within the polymer diffuse out. This process is known as the desorption of polymer and can cause blisters or cracking causing permanent damage to the polymer. Here, we used a combined experimental and modeling approach to investigate the desorption of the hydrogen gas in the polymer. Thermal desorption analysis (TDA) experiments were performed on the polymer sample exposed to the high-pressure hydrogen gas to measure the diffusion coefficient and equilibrium hydrogen concentration. Experiments also provided the quantity of hydrogen within the polymer during the desorption process which followed Fick’s law. However, for higher pressurization values, some anomaly was observed in the quantity of hydrogen remaining in the polymer sample. A continuum mechanics based coupled diffusion–deformation-damage model was deployed to simulate the gas desorption process in the material using the finite element method to understand its effect on the material. It was found that the anomaly in TDA results were due to the blister formation on the polymer surface which resulted in longer hydrogen retention. Simulations also showed that blister formation can be affected by multiple parameters such as the addition of filler particles, and pre-existing cavity size.

Ultrasonic assisted highly porous PPy/JSAC/IMO [PJ-IMO] nanocomposite for hydrogen fuel cell and asymmetric supercapacitor (PJ-IMO||JSAC) applications

Environmental pollution due to irrepressible consumption of fossil fuel and thereby chaotic global temperature enforce the scientific community to search for alternative clean and green energy sources. Hydrogen is considered as a clean, green and alternative energy carrier that has the potential to overcome various environmental issues including the energy crisis. Hence, the present work focuses on the preparation of novel nanocomposite [PPy/JSAC/IMO (PJ-IMO)] comprise of conducting polymer namely polypyrrole (PPy), activated carbon from jack fruit seed (JSAC) and natural clay imogolite (IMO) nanotube where a facile ultrasonic method was adopted for the preparation of PJ-IMO nanocomposite. The structural, morphological and elemental composition of the prepared PJ-IMO nanocomposite reveals that the PPy and IMO were anchored at the surface of JSAC. A drastic increment in the specific surface area of PJ-IMO nanocomposite (1354 m2 g−1) was observed compared to PPy/JSAC (PJ) nanocomposite (892 m2 g−1) and pristine PPy (39 m2 g−1). The prepared PJ-IMO exhibits 7.4 wt% hydrogen storage capacity at 50 °C, desorption of stored hydrogen at 104 °C and very good cyclic stability even after 34 cycles. The calculated binding energy (0.33–0.50 eV) of stored hydrogen falls in the recommended range of US Department of Energy (DOE-2025) targets. The electrochemical hydrogenation studies show that a maximum hydrogen discharge capacity of 3820 mAh/g at 42nd cycle, columbic efficiency of 93.1 %, hydrogen retention rate of 73.8 % and corrosion resistance of 26.3 mA/cm2 respectively. The as-fabricated PJ-IMO||JSAC asymmetric supercapacitor (ASC) has an energy density of 203 Wh kg−1 at 0.5 Ag−1 and power density of 2398 W kg−1 at 2 A g−1. The prepared ASC could able to power blue LEDs for 10 min and motor fan for 7 min. Hence, these excellent characteristics proved that the prepared PJ-IMO nanocomposite may serve as an excellent weakly chemisorbed hydrogen storage material and electrode for electrochemical energy storage applications in the near future.

Impact of Soret effect on hydrogen and helium retention in PFC tungsten under ELM-like conditions

In our previous work, we have demonstrated using nonequilibrium molecular-dynamics simulations that the fluxes of helium and self-interstitial atoms in the presence of a thermal gradient in tungsten are directed opposite to the heat flux, indicating that species transport is governed by a Soret effect, namely, thermal-gradient-driven diffusion, characterized by a negative heat of transport that drives species transport uphill, i.e. from the cooler to the hot regions of the tungsten sample. In this work, the findings of our thermal and species transport analysis have been implemented in our cluster-dynamics code, Xolotl, which has been used to compute temperature and species profiles over spatiotemporal scales representative of plasma-facing component (PFC) tungsten under typical reactor operating conditions, including extreme heat loads at the plasma-facing surface characteristic of plasma instabilities that induce edge localized modes (ELMs). We demonstrate that the steady-state species profiles, when properly accounting for the Soret effect, vary significantly from those where temperature-gradient-driven transport is not accounted for and discuss the implications of such a Soret effect on the response to plasma exposure of plasma-facing tungsten. Although our cluster-dynamics simulations do not yet include self-clustering of helium or hydrogen blister formation, our simulation results show that the Soret effect substantially reduces helium and hydrogenic species retention inside PFC tungsten.

Hydrogen retention and affecting factors in rolled tungsten: Thermal desorption spectra and molecular dynamics simulations

Hydrogen isotope retention of tungsten in nuclear fusion reactors is one of the hot research issues all along. In this paper, tungsten samples in different rolled surfaces were polished by mechanical processing, subsequently subjected to D2+ irradiation and thermal desorption. To better understand the experimental observations, this study also performed molecular dynamics (MD) simulation and investigated the effects of temperature, grain number, grain boundary density, and crystal orientation on hydrogen retention. It is found that the grain number and grain boundary density of rolled tungsten increase successively in RD/TD, RD/ND, and TD/ND surfaces. The RD/ND surface exhibits the best hydrogen radiation resistance, whereas the TD/ND surface is unsatisfactory. MD simulations further indicate that hydrogen retention is more obvious with the increase of grain density in tungsten, and hydrogen atoms are more easily enriched at the grain boundaries. With the increase in temperature, the retention of hydrogen atoms in monocrystalline/polycrystalline tungsten decreases significantly. The average implantation depth of H atoms is deepest along the <111> and <112> crystalline directions, which reveals that hydrogen retention is dependent on the crystal orientations. The good agreement between the experimental data and simulation results reveals that grain boundaries play an important role in hydrogen retention.

Upper limits of water contents in olivine and orthopyroxene of equilibrated chondrites and several achondrites

AbstractHydroxyl defects in nominally anhydrous minerals (NAMs) were potential carriers of water in the early Solar System and might have contributed to the accretion of terrestrial water. To better understand this, we have conducted a nanoscale secondary ion mass spectrometry survey of water contents in olivine and orthopyroxene from a set of equilibrated ordinary chondrites of the L and LL groups (Baszkówka, Bensour, Kheneg Ljouâd, and Tuxtuac) and several ultramafic achondrites (Zakłodzie, Dhofar 125, Northwest Africa [NWA] 4969, NWA 6693, and NWA 7317). For calibration, we used terrestrial olivine and orthopyroxene with H2O contents determined by Fourier transform infrared. Our 99.7% (~3SD) detection limits are 3.6–5.4 ppmw H2O for olivine and 7.7–10.9 ppmw H2O for orthopyroxene. None of the meteoritic samples studied consistently shows water contents above the detection limits. A few exceptions slightly above the detection limits are suspected of terrestrial contamination by ferric oxyhydroxides. If the meteorite samples investigated accreted in the presence of small amounts of water ice, the upper limits of water contents provided by our survey suggest that the retention of hydrogen during thermal metamorphism and differentiation was ineffective. We suggest that loss occurred through combinations of low internal pressures, high permeability along grain boundaries, and speciation of hydrogen into reduced compounds such as H2 and methane, which are less soluble in NAMs than in water.

Experimental simulations of hydrogen migration through potential storage rocks

In the framework of future decarbonization of the energy industry, the safe and effective storage of hydrogen is an important approach to add to a climate-friendly energy system. Until the development of sufficiently large electrical storage systems, the storage of hydrogen in the order of GWh to TWh is envisaged in salt caverns or porous geological formations with a gas-tight covering of salt or claystone. In order to calculate gas losses from these H2 storage facilities, the H2 diffusivity of the storage and cap rocks must be known. To determine the hydrogen diffusion rates in these rocks, an experimental set-up was designed, constructed and tested. The set-up comprises two gas chambers, separated by the rock sample under investigation with an exposed area of approximately 7 cm2. The driving force for gas migration through the rock sample from the hydrogen-containing feed gas chamber to the hydrogen-free permeate chamber is the chemical potential (concentration) gradient. With respect to hydrogen migration behaviour, hydrogen breakthrough times and hydrogen diffusion coefficients were determined for dry and wet Bentheimer sandstone, Werra rock salt and Opalinus clay samples. Breakthrough times varied between less than 1 h and 843 h. Based on concentration changes at the permeate side, hydrogen diffusion coefficients were derived ranging from 10−9 to 10−8 m2/s. The differences between the materials and the effect that wetted or water-saturated samples have higher hydrogen retention due to closed pores and microcracks were clearly shown. The experimental set-up proves to be a suitable approach to determine site-specific rock characteristics such as hydrogen diffusion coefficients and breakthrough times for natural geomaterials.

Impact of yttrium hydride formation on multi-isotopic hydrogen retention by a getter trap for the DONES lithium loop

Compliance with imposed hydrogen concentration limits in the lithium loop of the DEMO-Oriented Neutron Source (DONES) requires the installation of an yttrium-based hydrogen trap. To determine an appropriate H-trap design, it is essential to have access to a numerical tool capable of simulating hydrogen transport in the DONES lithium loop connected to an yttrium pebble-bed. In the past, a simplified model was created that allows such calculations when hydrogen concentrations in the lithium are low. However, in certain DONES operating phases, the concentration in the lithium is high and in a range where yttrium dihydride (YH2) formation is likely. Due to the anticipated great impact of YH2 formation on the H-trap performance a new model is developed that includes the mechanism of hydride formation. It is based on a mathematical reproduction of complete pressure-composition isotherms of the Li–H and Y–H systems. Thus, the conditions that trigger YH2 formation are determined and the variation of hydrogen solubility in different yttrium hydride phases is deduced. An approximate concentration-dependent relationship of hydrogen diffusivity in yttrium is derived and incorporated into the model. Simulations are performed to analyze the dynamics of the concentration decrease during purification of the lithium circuit prior to the experimental DONES phase by varying design parameters of the trap. It is found that hydride formation greatly increases the hydrogen gettering capacity of the H-trap and limits the maximum concentration in the lithium. Indeed, YH2 formation may be purposefully triggered to exploit its beneficial properties for DONES. Simulations of the hydrogen purification process during the experimental phase of DONES show that the H-trap must be replaced at least every 28 days to meet tritium limits. This work sets the conditions for the required pebble-bed mass of the H-trap at a given temperature to comply with the DONES safety requirements. Finally, the model is validated by numerical reproduction of experimental results.

High temperature elastic properties of sub-stoichiometric yttrium dihydrides

Yttrium hydrides are considered as candidate materials for neutron moderation applied in microreactors (akin transportable miniaturized nuclear reactors) owing to their superior thermal stability and hydrogen retention. The evolution of elastic properties of these materials at elevated temperatures, needed for predicting the thermomechanical response and performance of the moderator during in-service reactor conditions, however, is lacking. Here, we report the Young’s and shear elastic moduli of three stoichiometries of bulk yttrium hydride (YHx, x = 1.61, 1.82, and 1.84) from room temperature to 1000 °C. In situ temperature-dependent measurements of the longitudinal and shear wave velocities were performed using a laser ultrasonic technique while heating the sample in a vacuum-pumped heating stage. The elastic moduli increased linearly with increasing hydrogen content and decreased by ∼10 % during heating from room temperature to 1000 °C in the three YHx compositions. The linear relationship between the elastic moduli and the hydrogen content in yttrium hydride was verified by atomistic calculations based on density functional theory (DFT). The absence of abrupt changes in the temperature-dependent measurements of elastic modulus of the YHx samples suggested negligible loss of hydrogen at elevated temperatures. Excellent agreement was found between the measured and calculated dependence of the elastic moduli on the stoichiometry, thereby providing a new approach for investigating the effects of fabrication-induced parameters (such as porosity) on the elastic moduli. This study demonstrates the utility of the combined approach involving DFT-based atomistic calculations and measurements of the elastic moduli for the informative development of metal hydrides and can be used as a metric for novel moderator materials investigations for emerging microreactors and beyond.

Molecular Dynamics Simulation on Hydrogen Trapping on Tungsten Vacancy

The effect of hydrogen on the structural change of vacancies in tungsten is analyzed by molecular dynamics in order to clarify the interaction between vacancies and hydrogen in tungsten. Simulations are performed at different temperatures (573, 773, 1073 K) and with different numbers of hydrogen in the vacancies (0, 18, 36, 54). Evaluating (1) isopotential surface for the increase of total potential energy, (2) the root mean square deviation (RMSD) of tungsten atoms, (3) the root mean square fluctuation (RMSF) of tungsten atoms and (4) density distribution in radial direction, we found that the presence of a large number of hydrogen in a vacancy at each temperature caused changes in the structure. This fact partially supports the experimental fact that in the coalescence of two tungsten vacancies, the retention of hydrogen activates them.

Behaviour of helium and hydrogen in vanadium alloys – innovative fusion reactor first wall materials: a review. Part 1. V – Ti and V – Fe alloys

This paper is the first part of a three-part review that looks at the effect of doping elements on the behaviour of helium, the development of gas porosity, as well as at the amount of retained hydrogen introduced into vanadium alloys with Ti, Cr, W and Ta (using different techniques) with a rapid decay of induced radioactivity. The same regularities have been identified regarding how the chemical composition of the alloys impacts the hydrogen entrapment and retention regardless of the way it is introduced: either through pressure saturation without defect formation or through ion implantation with radiation-induced defects entailed. It was established that when vanadium is doped with a chemically active element (V &ndash; Ti alloys), the concentration of the latter has a nonmonotonic effect on the helium porosity and the mass fraction of retained hydrogen. It can be attributed to the way titanium interacts with oxygen and nitrogen in vanadium, which dictates how much titanium hydride will form. The paper demonstrates that pre-irradiation of the alloy with helium ions results in a higher amount of retained hydrogen when it is introduced further, regardless of the temperature.

IMPLEMENTATION OF THE NEW APPROACHES TO PRODUCTION OF HIGH-QUALITY ROLLED METAL FOR ENAMELING

Consumers of cold-rolled steel for enamelling are standardizing the indicators that exclude the occurrence of the “fish scale” defect in the finished product. In the domestic practice the hydrogen embrittlement index (HEI) is considered to be the index characterizing the tendency of rolled products to formation of the mentioned defect. The threshold values of HEI are determined by the domestic standards and normative documents. The existing method of HEI determination has a number of essential drawbacks, and the values received on its basis do not always objectively reflect the tendency of the rolled metal to form the defect “fish scale”. A new indicator the volume fraction of structurally free cementite, which correlates with a sufficiently high degree of the HEI value, has been proposed. A method allowing establishment of the tendency of the rolled metal to appearance of the “fish scale” defect on enamelled products has been presented. It is shown that the microstructure of the low-carbon steel for enameling with low cementite content significantly influences the mechanism of the “fish scale” defect formation and it is closely connected with the HEI. The presence of a considerable amount of cementite globules allows (all other things being equal) increase in the capture and retention of the surface hydrogen which occurs during the enameling process. It is noted that the testing of the rolled metal corresponds to the normative documents if the volume fraction of the structurally free cementite is 2.7 % and more. The technological modes of the hot rolling were developed for the most widespread steel grade utilized for enameling 08ЮР (Russian Standard), that provides the high values of volume fraction of cementite in microstructure. The temperature of final stage of hot rolling depending on thickness of finished rolled product was in the range of 860‒890 °С; the temperature of coiling was not lower than 740 °С. It was found that apart from the temperature conditions of the process, the significant factor is the speed parameters of rolling and stripping, as well as cooling mode on the diverting roller conveyor of the hot-rolling mill. A new cooling mode on the diverting mill was proposed and adapted to the mill model.

Electronic descriptors for vacancy formation and hydrogen solution in Be-rich intermetallics

The use of an electronic descriptor is a high-throughput approach for predicting the chemical reactivities of various materials that has the potential to significantly facilitate the material design of Be intermetallic neutron multipliers for nuclear fusion applications. However, electronic descriptors for Be intermetallics with the desired properties, including radiation tolerance and reduced hydrogen retention, have been poorly understood. Herein, we perform first-principles calculations on 42 existing binary Be intermetallics to find an effective electronic descriptor. We demonstrate that the occupied Be p band center relative to the Fermi level is a bulk descriptor, correlating with the Be vacancy formation energy; a positive and linear correlation with a coefficient of determination R2 = 0.85 was observed for Be12X (X: transition metal). The upward shift in energy of the occupied Be p states with early or middle transition metals can reduce hydrogen solution energy, which could be attributed to the less filled anti-bonding state of interstitial hydrogen atom. It is confirmed that the bulk descriptor is an experimentally measurable scale, having the strong linearity (R2 = 0.97) with the calculated; therefore, it can accelerate the material development of beryllium intermetallic neutron multipliers.

Influence of carbon on hydrogen retention in molybdenum for nuclear material application: A first-principles investigation

• Systematic DFT simulations for the effect of carbon on the H retention in Mo. • Impurity carbon cannot trap H atoms in perfect Mo. • Impurity carbon has little effect on the H vacancy capturing in Mo. • Mo-carbon layer prevents the H diffusion and permeation in Mo. Mo has been applied to nuclear material, in which H and carbon impurities are unavoidable. In view of this, we have studied the effect of carbon on the H retention in Mo using first-principles simulations. In perfect Mo, there is always repulsion between H and carbon, and impurity carbon cannot capture H atoms. With the appearance of vacancy in Mo, vacancy and carbon-vacancy cluster trap seven and six H atoms, respectively. This means that impurity carbon has little effect on the H vacancy capturing. Finally, we explore the H diffusion by considering the presence of one Mo-carbon layer in Mo. Away from the Mo-carbon layer, H jumps along the optimal route with a diffusion barrier of 0.12 eV. As H moves close and passes through the Mo-carbon layer, the H diffusion barrier is increased to 0.73 eV. Therefore, the repulsive interaction between H and carbon can increase the H energy barrier in the vicinity of the Mo-carbon layer, which prevent the H diffusion and permeation in Mo. The current results can explain the promoting mechanism of bubble formation due to impurity carbon implantation and help us design future Mo-based nuclear material.

Gas- and plasma-driven hydrogen permeation behavior of stagnant eutectic-solid GaInSn/Fe double-layer structure

Gas-driven permeation (GDP) and plasma-driven permeation (PDP) of hydrogen gas through GaInSn/Fe are systematically investigated in this work. The permeation parameters of hydrogen through GaInSn/Fe, including diffusivity, Sieverts’ constant, permeability, and surface recombination coefficient are obtained. The permeation flux of hydrogen through GaInSn/Fe shows great dependence on external conditions such as temperature, hydrogen pressure, and thickness of liquid GaInSn. Furthermore, the hydrogen permeation behavior through GaInSn/Fe is well consistent with the multi-layer permeation theory. In PDP and GDP experiments, hydrogen through GaInSn/Fe satisfies the diffusion-limited regime. In addition, the permeation flux of PDP is greater than that of GDP. The increase of hydrogen plasma density hardly causes the hydrogen PDP flux to change within the test scope of this work, which is due to the dissolution saturation. These findings provide guidance for a comprehensive and systematic understanding of hydrogen isotope recycling, permeation, and retention in plasma-facing components under actual conditions.

The Role of Cobalt Clusters (Con, n = 1–5) Supported on Defective γ–Graphyne for Efficient Hydrogen Adsorption: A First Principles Study

AbstractIn this theoretical work, density functional theory calculations show the effect of small cobalt clusters (Con, n = 1–5) adsorbed on pristine γ‐graphyne (γ‐GY), and modify N‐doped γ‐GY monolayers (GYNs‐def). Different geometrical configurations are assessed with the adsorption energy, charge transfer, and density of states. The system with vacancy defects shows a large adsorption energy (19.96 eV) for the Co5 cluster. This behavior may be associated to the overlapping of the electronic state contributions between cobalt and carbon atoms in the valence states. This indicates that the Co5 cluster could be deposited on N‐doped γ‐GY monolayers (Con@GYNs‐def). The lowest‐energy systems are evaluated to estimate the strength of the interaction with hydrogen molecules (xH2, where x = 1–5). According to the adsorption energy values, the modified γ‐GY monolayers are allowed to be a suitable support material to capture H2 molecules via the small Con clusters. The hydrogen retention capacity for the supported cobalt atoms corresponding to the lowest‐energy configurations and larger systems are evaluated by using molecular dynamics simulations with the Born–Oppenheimer approximation. The role played by defects in the GYNs‐def monolayers is important, since the Con clusters remain attached to the vacancy with the absence of surface diffusion. This study may represent a guide to tailor novel nanostructures based on small cobalt clusters supported on graphyne monolayers modified to be applied in H2 adsorption.

Effect of uniaxial tensile strain on binding energy of hydrogen atoms to vacancy-carbon-hydrogen complexes in α-iron

• The hydrogen binding energy to vacancies under uniaxial tensile strain was calculated. • The binding energy of hydrogen atoms to vacancies decreased with increasing strain. • The binding energy of hydrogen to vacancy-C complexes increased with increasing strain. • The hydrogen retention was estimated under uniaxial tensile strain. The hydrogen binding energy to vacancies or vacancy-carbon complexes in α -Fe under uniaxial tensile strain was calculated using the density functional theory. The solution energies of hydrogen and carbon decreased with an increase in the uniaxial tensile strain. With increasing strain, the binding energy of hydrogen atoms to vacancies also decreases; however, the binding energy of the vacancy-carbon complexes increases. The hydrogen retention was estimated under exposure to hydrogen gas. In the strained area, both the hydrogen concentration of the interstitial hydrogen atoms and the number of hydrogen atoms trapped in the vacancies increased. Therefore, hydrogen retention increased with increasing strain; however, the change in the hydrogen binding energy did not have a strong impact on the hydrogen retention. The presence of vacancies affects hydrogen retention more strongly. Although the binding energy of hydrogen atoms to vacancy-carbon complexes increased, the hydrogen retention in the Fe-C alloy was lower than that in pure Fe.