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Objective During the start-up and shutdown processes of the natural gas purification unit, the tail gas is directly discharged without the SCOT tail gas treatment unit, and it has the characteristics of long time, high emission, complex composition and large fluctuation. During this period, a large amount of SO2 may accumulate. Therefore, it is necessary to take measures to achieve SO2 emission reductions during the start-up and shutdown processes. Method Aiming at SO2 and H2S in tail gas, a desulfurization process by tail gas absorption-adsorption coupling method was proposed. And the research focused on the absorption of SO2 using an alkaline solution and the adsorption of H2S onto a renewable adsorbent. Results The alkaline solution absorption process could ensure that SO2 was almost completely absorbed, and basically did not absorb H2S and CO2, which could avoid the excessive consumption of alkaline solution. 13X molecular sieve had a good adsorption effect on H2S and regenerative effect, which could adsorb circularly. The regenerated H2S can also be recycled once the facility is restarted and operating stably. Conclusions The absorption of SO2 coupled with adsorption of H2S in tail gas can ensure that the SO2 discharge of the natural gas purification plant is greatly reduced during the start-up and shutdown processes, and the process is simple with a high operational flexibility. [ABSTRACT FROM AUTHOR]

This review examines the impact of various aqueous electrolytes on hydrogen absorption and self-corrosion in magnesium (Mg) anodes. The discussion integrates both historical and recent studies to explore the mechanisms behind self-corrosion and anomalous hydrogen evolution (HE) under conditions of the Negative Difference Effect (NDE) and Positive Difference Effect (PDE). The focus is on the formation and oxidation of magnesium hydride in regions of active dissolution under NDE conditions. In the case of PDE, anodic dissolution occurs through the passive MgO-Mg(OH)₂ film, which shields the metal from aqueous electrolytes, thereby reducing hydrogen absorption and abnormal HE. The NDE conditions showed delayed reduction activity at the surface, attributed to a hydride phase within the corrosion product layer. Hydride ions were quantified through their anodic oxidation in an alkaline electrolyte, measured by the electric charge passed. The review also considers the role of de-passivating halide ions, electrolyte acidity buffering, and the addition of ligands that form stable complexes with Mg2⁺ ions, on the rates of hydride formation, self-corrosion, and anodic dissolution of Mg. The study evaluates species that either inhibit or promote hydrogen absorption and self-corrosion. [ABSTRACT FROM AUTHOR]

The main objective of this work is to study the influence of structural changes in ZrO2 ceramics on the resistance to hydrogenation processes arising from testing the performance of ceramics as materials for solid oxide fuel cells. During the conducted studies, it was established that the use of stabilizing additives MgO and CaCO3 to initiate processes of polymorphic transformations in ZrO2 ceramics makes it possible to increase the resistance of ceramics to hydrogen swelling due to the stabilization of the crystal structure, the change of which is associated with polymorphic transformations. Suppression of volumetric swelling processes due to polymorphic transformations caused by the addition of stabilizing additives made it possible to elevate resistance to hydrogen absorption and destabilization of the near-surface layer by preventing hydrogen agglomeration processes in the near-surface layer. It has been determined that the modification of ZrO2 ceramics by initiating processes of polymorphic transformations of the type m-ZrO2 → t - ZrO2 and m-ZrO2 → c-ZrO2 leads not only to an increase in strength indicators, but also to an increase in resistance to embrittlement processes during hydrogenation and high-temperature degradation. [ABSTRACT FROM AUTHOR]

With escalating global regulatory pressure for countries to adhere to emission laws, repurposing existing natural gas pipelines for hydrogen-based commodities stands to be an economical solution. However, the effects of hydrogen embrittlement must be thoroughly considered for this application to avoid the unexpected catastrophic failure of these pipelines. The literature proposes several physicochemical embrittlement models. This paper reports one aspect of hydrogen embrittlement that remains to be quantified: the recovery of ductility (embrittlement) of mild steel specimens subjected to artificially accelerated hydrogen absorption via electrochemical charging as a function of time. The effects of charging duration and particularly the delay period between charging and mechanical tensile testing were investigated. Unsurprisingly, longer charging time shows a greater loss of elongation; however, a more extensive recovery of ductility correlated with longer charging time in the first few days after charging. The data also show that while the uncharged mild steel met all minimum required values for strength and elongation for the specified grade, there was a substantial variability in the elongation to failure. The same trends in variability of elongation translated to the hydrogen-charged specimens. Due to this extensive variability, failure to meet the elongation specification of the grade is reported based on the worst-case scenario obtained for a given set of samples for each exposure condition. These results have practical implications for the monitoring and testing of infrastructure exposed to hydrogen, particularly as this relates to industry planned operational shutdown schedules. [ABSTRACT FROM AUTHOR]

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 - A l 2 O 3 (0001) / α - F e (111) interface on the F e 01 1 ¯ 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. [ABSTRACT FROM AUTHOR]

Hydrogen holds the advantages of high energy density, great natural abundance and zero emission, making it suitable for large scale and long term energy storage, while its safe and efficient storage is still challenging. Among various solid state hydrogen storage materials, MgH2 is promising for industrial applications due to its high gravimetric and volumetric hydrogen densities and the abundance of Mg on earth. However, the practical application of MgH2 has been limited by its stable thermodynamics and slow hydrogen desorption kinetics. Nanocatalysis is considered as a promising approach for improving the hydrogen storage performance of MgH2 and bringing it closer to the requirements of commercial applications. It is worth mentioning that the recently emerging two-dimensional material, MXene, has showcased exceptional catalytic abilities in modifying the hydrogen storage properties of MgH2. Besides, MXene possesses a high surface area, excellent chemical/physical stability, and negatively charged terminating groups, making it an ideal support for the "nanoconfinement" of MgH2 or highly active catalysts. Herein, we endeavor to provide a comprehensive overview of recent investigations on MXene-based catalysts and MXene supports for improving the hydrogen sorption properties of Mg/MgH2. The mechanisms of hydrogen sorption involved in Mg-MXene based composites are highlighted with special emphases on thermodynamics, kinetics, and catalytic behaviors. The aim of this work is to provide a comprehensive and objective review of researches on the development of high-performance catalysts/supports to improve hydrogen storage performances of Mg/MgH2 and to identify the opportunities and challenges for future applications. [ABSTRACT FROM AUTHOR]

At present, there is limited research on the application of fuel cell power generation system technology using solid hydrogen storage materials, especially in hydrogen-assisted two-wheelers. Considering the disadvantages of low hydrogen storage capacity and poor kinetics of hydrogen storage materials, our primary focus is to achieve smooth hydrogen ab-/desorption over a wide temperature range to meet the requirements of fuel cells and their integrated power generation systems. In this paper, the Ti0.9Zr0.1Mn1.45V0.4Fe0.15 hydrogen storage alloy was successfully prepared by arc melting. The maximum hydrogen storage capacity reaches 1.89 wt% at 318 K. The alloy has the capability to absorb 90% of hydrogen storage capacity within 50 s at 7 MPa and release 90% of hydrogen within 220 s. Comsol Multiphysics 6.0 software was used to simulate the hydrogen ab-/desorption processes of the tank. The flow rate of cooling water during hydrogen absorption varied in a gradient of (0.02 + x) m s-1 (x = 0, 0.02, 0.04, 0.06, 0.08, 0.1, 0.12). Cooling water flow rate is positively correlated with the hydrogen absorption rate but negatively correlated with the cost. When the cooling rate is 0.06 m s-1, both simulation and experimentation have shown that the hydrogen storage tank is capable of steady hydrogen desorption for over 6 h at a flow rate of 2 L min-1. Based on the above conclusions, we have successfully developed a hydrogen-assisted two-wheeler with a range of 80 km and achieved regional demonstration operations in Changzhou and Shaoguan. This paper highlights the achievements of our team in the technological development of fuel cell power generation systems using solid hydrogen storage materials as hydrogen storage carriers and their application in two-wheelers in recent years. [ABSTRACT FROM AUTHOR]

Alkaline hydrogen evolution reaction (HER) is suppressed by the water dissociation, leading to more sluggish kinetics than acidic HER. Developing multifunction catalysts via constructing heterogeneous interfaces is a feasible tactic to accelerate the alkaline HER. Herein, NiO coupled with Ni and MoxN (NMN) nanorods were prepared via a hydro-thermal synthesis combined with a thermal decomposition under ammonia atmosphere. The low crystalline NMN nanorods are rich in heterointerfaces, and have sufficient high active sites for HER. The synergistic effect between NiO and Ni-MoxN promotes the water dissociation the hydrogen adsorption, and the charge transfer, contributing to excellent alkaline HER activity. The overpotential on NMN is only 36 and 150 mV for the current density of 10 and 300 mA cm−2, respectively, and the Tafel slope is 48 mV/dec, demonstrating a superior performance for alkaline HER, which is even comparable to the commercial electrocatalysts. [ABSTRACT FROM AUTHOR]

Hydrogen (H2) is known for its clean energy characteristics. Its separation and purification to produce high-purity H2 is becoming essential to promoting a H2 economy. There are several technologies, such as pressure swing adsorption, membrane, and cryogenic, which can be adopted to produce high-purity H2; however, each standalone technology has its own pros and cons. Unlike standalone technology, the integration of technologies has shown significant potential for achieving high purity with a high recovery. In this study, a membrane–cryogenic process was integrated to separate H2 via the desublimation of carbon dioxide. The proposed process was designed, simulated, and optimized in Aspen Hysys. The results showed that the H2 was separated with a 99.99% purity. The energy analysis revealed a net-specific energy consumption of 2.37 kWh/kg. The exergy analysis showed that the membranes and multi-stream heat exchangers were major contributors to the exergy destruction. Furthermore, the calculated total capital investment of the proposed process was 816.2 m$. This proposed process could be beneficial for the development of a H2 economy. [ABSTRACT FROM AUTHOR]

In this study, various chemical treatments were performed on clay-rich media to investigate their effects on hydrogen adsorption performance. We unequivocally demonstrated that acid-treated samples exhibited significant structural changes compared with those treated with alkali solutions. Gas adsorption isotherms and powder X-ray diffraction analyses clearly revealed that the acid treatment of clayey materials not only increased their surface area, but also enhanced hydrogen sorption uptake, increased interstratification, and reduced particle size. Most importantly, we succeeded in rationalizing the improvement in hydrogen uptake by sequentially applying purification, followed by acid treatment. [ABSTRACT FROM AUTHOR]

The capability of carbon nanotubes (CNTs) and boron-nitride nanotubes (BNNTs) to absorb hydrogen atoms might indicate if these materials can be used to develop an efficient and fast hydrogen nanosensor device. In this work, we carry out a theoretical study of the hydrogen adsorption mechanism by carbon and boron-nitride nanotubes irradiated by atomic hydrogen in the impact energy range of 0.25–100 eV. Hydrogen adsorption, reflection, and transmission probabilities are reported. The collision dynamics is calculated by performing quantum-classical molecular dynamics simulations within the self-consistent-charge density-functional tight-binding method. We include fitting curves for the angular distribution of reflected and transmitted H atoms by using a modified Yamamura formula. Results for CNTs follow a cosine-like law, while the majority of the projectiles tend to be scattered at angles lower than 60 ° for BNNTs. Based on previous studies for spherical and planar carbon-based configurations, we analyse the effect of the system's curvature on the hydrogen adsorption on CNTs. We find that for collision energies below 5 eV, the scattering process depends on the carbon system curvature; meanwhile, the adsorption is independent for collision energies below 0.5 eV. Our results for the hydrogen adsorption rates for both types of nanotubes suggest that these materials can be used in hydrogen detector devices in a wide impact energy range. [ABSTRACT FROM AUTHOR]

The effect of Mo content of 1400 MPa-grade high-strength bolt steel on hydrogen diffusion behavior and the hydrogen evolution reaction were studied using a hydrogen permeation experiment, potentiodynamic polarization tests, thermal desorption spectroscopy, and the first-principle calculation. Two 1400 MPa-grade high-strength bolt steels with different Mo content were used. Based on the potentiodynamic polarization tests, both steels' electrochemical behavior was similar in the test range. The hydrogen permeation experiment showed that the process of hydrogen adsorption and absorption was significantly promoted, and hydrogen desorption and recombination were slightly promoted, with the Mo content increasing from 0.70 to 1.09 wt%. The thermal desorption spectroscopy showed the overall reaction of hydrogen permeation and evolution. The increasing Mo content facilitated hydrogen entry behavior and increased the hydrogen content. According to the first-principle calculation and the density functional theory, this phenomenon is induced by the stronger bonding ability of Mo-H than Fe-H. This work could guide the design of 1400 MPa-grade high-strength bolt steel. [ABSTRACT FROM AUTHOR]

In this work, the phenomenon of long-term heat generation from Pd-Ni-Zr (PNZ) alloy samples in hydrogen was investigated using differential scanning calorimetry (DSC). As a result, we succeeded in observing sustained heat generation when the PNZ sample was maintained at temperatures in the 300-500℃ range. The fact that the DSC confirmed sustained heat generation over a short period of time is very significant. This is because repeated measurements over a short period of time provide more information about sustained heat generation. The relationship between sustained heat generation and hydrogen absorption behavior was examined in detail. No sustained heat generation occurred at temperatures at which the hydrogen was absorbed, while sustained heat generation occurred at the temperatures at which hydrogen was desorbed. The output of sustained heat generation decreased as the hydrogen pressure was increased. These results indicate that sustained heat generation is different from the heat of hydrogen storage. It was also found that sustained heat generation can be observed when the temperature is kept constant in the temperature range where hydrogen is being desorbed. In addition, the results of the alloy phase changes of PNZs when heat-treated in hydrogen suggested that the contribution of the alloy phase transition heat to sustained heat generation was small. Thus, it became clear that sustained heat generation in PNZs was not due to the heat of hydrogen storage, and it was suggested that the contribution of the alloy phase transition heat was small. [ABSTRACT FROM AUTHOR]

Introduction: It has not been experimentally proven whether hydrogen gas (H2) is absorbed into the body through the skin by hydrogen-rich hot-water bathing. Material and methods: In this study, Hairless mini pigs, whose skin closely resembles that of humans, were bathed in hydrogen (H2)-rich hot water to assess the absorption of H2 through the skin. An H2-rich water generation line was developed to maintain a high concentration of H2 via the circulation of hot water in an 80-litre bathtub. Two hairless mini pigs (14.2 ±1.4 kg, 60 days old, 1 male and 1 female) were first placed in the H2-dissolved bath. After a washout period, one pig was bathed in an H2-dissolved bath and the other in a bath containing no H2 for 20 min. During the experiment, blood was collected from the pigs' jugular vein, carotid artery, inferior vena cava (IVCs), and portal vein to measure the blood H2 concentration. Results: The H2 concentration at the IVC of the pig in the H2-dissolved bath increased from 0.733 ±0.636 ppb (w/w) to 16.9 ±4.46 ppb (w/w) after 2 min, 37.2 ±13.8 ppb (w/w) after 10 min, and 45.7 ±7.73 ppb (w/w) (H2 saturation level: 3%) after 20 min. The blood H2 concentration levels of the pig in the non-H2 bath remained below the detection limit of 0.3 ppb. Conclusions: Bathing in water with a high concentration of dissolved hydrogen was considered an effective means of supplying H2 to skin tissues and beyond. [ABSTRACT FROM AUTHOR]

Hydrogen adsorption on Pt(111) has been actively studied using semilocal approximations within the density functional theory featuring simultaneous adsorption of hydrogen on multiple sites, i.e., fcc, atop, and hcp. Considering the accuracy needed to detail the feature, we revisit this problem with the help of higher level of theory, the adiabatic connection fluctuation dissipation theorem within the random phase approximation. Our simulation emphasizes important roles played by the equilibrium lattice parameter of the surface, mass of the hydrogen isotope, and hydrogen coverage. The insight acquired in this study provides a way to consistently interpret electrochemical and spectroscopic data. [ABSTRACT FROM AUTHOR]

To understand the enhanced effects and new hydrogen absorption properties of metal nanoparticles, we theoretically investigated the hydrogen absorption in Pd nanoparticles, adopting the Pd405 model of ca. 2.5 nm by using density functional theory. Pd405 showed inhomogeneous geometric features, especially near the surface region. The hydrogen absorptions in octahedral (O) and tetrahedral (T) sites near the core region were stable and unstable, respectively, similar to the Pd bulk. We clearly demonstrated the possibility of hydrogen absorption in T sites near the surface of Pd405. The flexible volume change and the difference in hydrogen position relative to the center of mass of the T site that we observed are important factors for stable hydrogen absorption in T sites of Pd nanoparticles. In addition, we discuss the differences in hydrogen diffusion mechanisms in the core and near surface regions, based on the stability of hydrogen absorption in O and T sites. [ABSTRACT FROM AUTHOR]

[Display omitted] • The role of C, C + H, CH and CH + H in hydrogen permeation was determined. • Minimum energy pathways for hydrogen diffusion were explored by CI-NEB method. • C atom in carbon-containing species controls inhibitory effect. • Substrate relaxation greatly reduce hydrogen diffusion barrier. This paper investigates the role of carbon-containing impurities (i.e. C, C + H, CH, and CH + H) playing in hydrogen diffusion into Pd(1 0 0) subsurface. Energetics and structures for adsorptions and absorptions of hydrogen were explored with variational coverages and locations of adsorbates by density functional theory, and then minimum energy pathways were cautiously searched out by climbing image nudged elastic band method. Surface relaxation and reconstruction effects were also concerned. Quantum simulations reveal that C and CH strongly bond to hollow site and lead to charge density redistribution and structural change of Pd(1 0 0) surface, and thus predominantly affect hydrogen penetration behavior. [ABSTRACT FROM AUTHOR]

Metal vanadium (V) has a high hydrogen penetration rate, but the problem of hydrogen embrittlement limits its practical application in hydrogen separation/purification. Elemental doping is an effective means to improve metal hydrogen embrittlement. In this paper, the influence of (Pd, Al) doping on the structure and hydrogen permeability of V-based solid solution is studied. A series of V100-xPdx and V100-xPdx/2Alx/2 (x=3.125, 6.25) alloy samples were prepared by arc induction melting. The structure and composition of the alloy samples were characterized by XRD, EDS. The PCT hydrogen absorption curve test was used to analyze the hydrogen solubility of the alloy samples. The electrochemical step method was used to test and analyze the hydrogen diffusion coefficient of the alloy samples. Studies have confirmed that the V100-xPdx and V100-xPdx/2Alx/2 alloy samples are single-phase V-based solid solutions (V-bcc structure). Compared with pure V, the doped solid solution has obvious cell distortion, and the V93.75Pd3.125Al3.125 solid solution has the largest lattice parameter change rate (0.257%). Doping reduces the hydrogen solubility of metal V to varying degrees and increases the enthalpy of hydride formation, which is beneficial to improve the hydrogen embrittlement resistance of metal vanadium. The double-doped V96.875Pd1.5625Al1.5625 alloy has a high hydrogen diffusion coefficient (5.03×10-10 cm²/s), which is more than 4 times that of the single-doped V93.75Pd6.25 alloy. At the same time, the alloy sample also maintains good mechanical ductility, and its Vickers hardness is 185.64 HV. This study shows that, compared with metal vanadium, the hydrogen penetration and hydrogen embrittlement resistance of vanadium-based solid solution alloys prepared by element doping are effectively improved. [ABSTRACT FROM AUTHOR]

Significant attention has been paid to metal hydrides (MH) as an environmentally friendly and safe way to store hydrogen. This technology has considerable potential for the application of embedded hydrogen storage in fuel cell electric vehicles, but its widespread application faces a major problem in terms of estimating the remaining hydrogen amount in the tank. In this work, a new method is proposed for estimating the state of charge (SoC) of the hydrogen hydride tank (HHT) by application of piezoelectric material. The idea is to cover the entire inner wall of the metal-hydride tank with a layer of piezoelectric material. During the process of hydrogen absorption, the pressure inside the tank increases, resulting in an increase in the mechanical stress applied to the piezoelectric layer, thus generating a voltage. This effect can therefore be used as an effective means of estimating the amount of hydrogen absorbed. The COMSOL Multiphysics software was used to implement the model and solve the differential equation of energy, mass, and moment. The simulation results showed that the voltage evolution as a function of hydrogen concentration follows the same behavior as the variation of the Pressure Concentration Isotherm (PCI). [ABSTRACT FROM AUTHOR]

The sulphide stress cracking of high strength low alloy (HSLA) carbon steel C110 is related to the hydrogen absorption process. The objective of this research is to evaluate the effect of adsorbed H2S and Cl− on hydrogen permeation in C110, by studying the responses of hydrogen permeation current and characteristic inductance under environment with different H2S activities and NaCl concentrations using electrochemical methods, including hydrogen permeation method and electrochemical impedance spectroscopy (EIS). The hydrogen permeation current measured in Devanathan–Stachurski cell suggests that the enhance effect of the adsorbed H2S on the hydrogen absorption follows an adsorption isotherm behaviour as a function of H2S activity in solution. The inductive response of EIS under different H2S activities shows consistency with hydrogen permeation results. The EIS results also indicate that the coverage of H2S was suppressed by Cl−. A good correlation about the effect of adsorbed Cl− is found between inductive response and hydrogen permeation current. [ABSTRACT FROM AUTHOR]

A simple integrated hydrogen sensor using Pd-Au alloy/air based one dimensional photonic crystal with an air defect layer is theoretically modeled. Structural parameters of the photonic crystal are delicately scaled to generate photonic band gap frequencies in a visible spectral regime. An optimized defect thickness permits a localized defect mode operating at a frequency within the photonic band gap region. Hydrogen absorption causes modification in the band gap characteristics due to variation of refractive index and lattice parameters of the alloy. As a result, the transmission peak appeared due to the resonant defect state gets shifted. This peak shifting is utilized to detect sparse amount of hydrogen present in the surrounding environment. A theoretical framework is built to calculate the refractive index profile of hydrogen loaded alloy using density functional theory and Bruggeman's effective medium approximation. The calculated refractive index variation of Pd3Au alloy film due to hydrogen loading is verified experimentally by measuring the reflectance characteristics. Lattice expansion properties of the alloy are studied through X-ray diffraction analyses. The proposed structure shows about 3 nm red shift of the transmission peak for a rise of 1% atomic hydrogen concentration in the alloy. [ABSTRACT FROM AUTHOR]

The hydrogen storage property of Li-coated B12C6N6 is investigated by density functional theory calculations. B12C6N6 is an electron deficient fullerene. Li atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The binding energy (-2.90 eV) is much larger than the cohesive energy (1.63 eV) of bulk Li, and it prevents the Li atoms from aggregation. The coated Li atoms have large positive charges and the adsorbed hydrogen molecules can be moderately polarized by the Li+ ions. The computation shows that each Li atom coated on B12C6N6 can hold 2-3 H2 molecules with adsorption energies in the range of 0.21-0.24 eV/H2. The B12C6N6Li8 can adsorb 16 H2 and achieve a gravimetric hydrogen density of 8.63 wt. %. The present results indicate that alkali-metal atoms coated on electron deficient fullerenes can serve as hydrogen storage materials that can operate at ambient temperatures with high recycling storage capacity. [ABSTRACT FROM AUTHOR]

The hydrogen storage property of Li-coated B12C6N6 is investigated by density functional theory calculations. B12C6N6 is an electron deficient fullerene. Li atoms can be strongly bound to this cage by donating their valance electrons to the virtual 2p orbitals of carbon in the cluster. The binding energy (-2.90 eV) is much larger than the cohesive energy (1.63 eV) of bulk Li, and it prevents the Li atoms from aggregation. The coated Li atoms have large positive charges and the adsorbed hydrogen molecules can be moderately polarized by the Li+ ions. The computation shows that each Li atom coated on B12C6N6 can hold 2-3 H2 molecules with adsorption energies in the range of 0.21-0.24 eV/H2. The B12C6N6Li8 can adsorb 16 H2 and achieve a gravimetric hydrogen density of 8.63 wt. %. The present results indicate that alkali-metal atoms coated on electron deficient fullerenes can serve as hydrogen storage materials that can operate at ambient temperatures with high recycling storage capacity. [ABSTRACT FROM AUTHOR]

A multilevel hierarchical ab initio protocol for calculating adsorption on non-conducting surfaces is presented. It employs fully periodic treatment, which reaches local Møller-Plesset perturbation theory of second order (MP2) with correction for the basis set incompleteness via the local F12 technique. Post-MP2 corrections are calculated using finite clusters. That includes the coupled cluster treatment in the local and canonical frameworks (up to perturbative quadruples) and correlated core (with MP2). Using this protocol, the potential surface of hydrogen molecules adsorbed on graphane was computed. According to the calculations, hydrogen molecules are adsorbed on graphane in a perpendicular to the surface orientation with the minimum of the potential surface of around -3.6 kJ/mol located at the distance of 3.85 Å between the bond center of the hydrogen molecule and the mid-plane of graphane. The adsorption sites along the path from the downward-pointing carbon to the ring center of the graphane are energetically virtually equally preferable, which can enable nearly free translations of hydrogen molecules along these paths. Consequently, the hydrogen molecules on graphane most likely form a non-commensurate monolayer. The analysis of the remaining errors reveals a very high accuracy of the computed potential surface with an error bar of a few tenths of a kJ/mol. The obtained results are a high-precision benchmark for further theoretical and experimental studies of hydrogen molecules interacting with graphane. [ABSTRACT FROM AUTHOR]

While hydrogen pipelines have attracted increased attention, safety of the pipelines has been a concern in terms of hydrogen embrittlement (HE) occurring upon hydrogen atom (H) generation and permeation in the steels. In this work, thermodynamic analyses regarding H generation and adsorption on pipeline steels by two potential mechanisms, i.e., spontaneous dissociation and dissociative adsorption, were conducted through theoretical calculations based on Gibbs free energy change of the H generation reactions. Moreover, H adsorption free energy and configurations were determined based on density functional theory (DFT) calculations. Effects of H adsorption site, H coverage and hydrostatic stress on H adsorption and absorption were discussed. Spontaneous dissociation of hydrogen gas molecules to generate hydrogen atoms is thermodynamically impossible. Dissociative adsorption is thermodynamically feasible at wide temperature and pressure ranges. Particularly, an increased hydrogen gas partial pressure and elevated temperature favor the dissociative adsorption of hydrogen. Hydrogen atoms generated by dissociative adsorption mechanism can adsorb stably at On-Top (OT) and 2-fold (2F) Cross-Bridge sites of Fe (100), while hydrogen adsorption at 2F site is more stable due to a higher electron density and a stronger electronic hybridization between Fe and H. The influence of H atom coverage on dissociative adsorption occurs at low coverages only, i.e., 0.25–1.00 ML as determined in this work. External stresses make dissociative adsorption more difficult to occur compared with a fully relaxed steel. Both tetrahedral sites (TS) and octahedral sites (OS) can potentially host absorbed H atoms at subsurface of the steel. Absorbed H atoms will be predominantly trapped at TS due to a low energy path and exothermic feature. Diffusion of H atoms from steel surface to the subsurface is more difficult compared with the dissociative adsorption. • Determined the thermodynamic infeasibility of spontaneous dissociation of hydrogen gas molecules in pipelines. • Demonstrated the thermodynamic possibility of dissociative adsorption of hydrogen gas on pipelines. • Determined the charge transfer pattern and formation of hybridization in hydrogen adsorption and absorption processes. [ABSTRACT FROM AUTHOR]

Work function, photoemission yield, and Auger electron spectra were measured on (001) p-type GaAs during negative electron affinity (NEA) surface preparation, surface degradation, and heating processes. The emission current sensitively depends on work function change and its dependence allows us to determine that the shape of the vacuum barrier was close to double triangular. Regarding the NEA surface degradation during photoemission, we discuss the importance of residual gas components the oxygen and hydrogen. We also found that gentle annealing (≤100°C) of aged photocathodes results in a lower work function and may offer a patch to reverse the performance degradation. [ABSTRACT FROM AUTHOR]

Obtaining quantitative agreement between theory and experiment for dissociative adsorption of hydrogen on and associative desorption of hydrogen from Cu(111) remains challenging. Particularly troubling is the fact that theory gives values for the high energy limit to the dissociative adsorption probability that is as much as two times larger than experiment. In the present work we approach this discrepancy in three ways. First, we carry out a new analysis of the raw experimental data for D2 associatively desorbing from Cu(111). We also perform new ab initio molecular dynamics (AIMD) calculations that include effects of surface atom motion. Finally, we simulate time-of-flight (TOF) spectra from the theoretical reaction probability curves and we directly compare them to the raw experimental data. The results show that the use of more flexible functional forms for fitting the raw TOF spectra gives fits that are in slightly better agreement with the raw data and in considerably better agreement with theory, even though the theoretical reaction probabilities still achieve higher values at high energies. The mean absolute error (MAE) for the energy E0 at which the reaction probability equals half the experimental saturation value is now lower than 1 kcal/mol, the limit that defines chemical accuracy, while a MAE of 1.5 kcal/mol was previously obtained. The new AIMD results are only slightly different from the previous static surface results and in slightly better agreement with experiment. [ABSTRACT FROM AUTHOR]

First-principles calculations are performed to investigate the adsorption of hydrogen onto Lidecorated hybrid boron nitride and graphene domains of (BN)xC1-x complexes with x = 1, 0.25, 0.5, 0.75, 0, and B0.125C0.875. The most stable adsorption sites for the nth hydrogen molecule in the lithium-decorated (BN)xC1-x complexes are systematically discussed. The most stable adsorption sites were affected by the charge localization, and the hydrogen molecules were favorably located above the C-C bonds beside the Li atom. The results show that the nitrogen atoms in the substrate planes could increase the hybridization between the 2p orbitals of Li and the orbitals of H2. The results revealed that the (BN)xC1-x complexes not only have good thermal stability but they also exhibit a high hydrogen storage of 8.7% because of their dehydrogenation ability. [ABSTRACT FROM AUTHOR]

The role of nuclear quantum effects on the adsorption of molecular hydrogen in metal-organic frameworks (MOFs) has been investigated on grounds of Grand-Canonical Quantized Liquid Density- Functional Theory (GC-QLDFT) calculations. For this purpose, we have carefully validated classical H2-host interaction potentials that are obtained by fitting Born-Oppenheimer ab initio reference data. The hydrogen adsorption has first been assessed classically using Liquid Density-Functional Theory and the Grand-Canonical Monte Carlo methods. The results have been compared against the semi-classical treatment of quantum effects by applying the Feynman-Hibbs correction to the Born-Oppenheimer-derived potentials, and by explicit treatment within the GC-QLDFT. The results are compared with experimental data and indicate pronounced quantum and possibly many-particle effects. After validation calculations have been carried out for IRMOF-1 (MOF-5), GC-QLDFT is applied to study the adsorption of H2 in a series of MOFs, including IRMOF-4, -6, -8, -9, -10, -12, -14, - 16,-18, and MOF-177. Finally, we discuss the evolution of the H2 quantum fluid with increasing pressure and lowering temperature. [ABSTRACT FROM AUTHOR]

The dissociation of H2 molecule is the first step for chemical storage of hydrogen, and the energy barrier of the dissociation is the key factor to decide the kinetics of the regeneration of the storage material. As a light element, aluminum is an important candidate component for storage materials with high gravimetric density. This paper investigates the adsorption and dissociation of H2 on carbon doping aluminum cluster Al6C. The study shows that doping carbon into aluminum cluster can significantly change the electronic structure and increase the stability. Al6C has a few stable isomers with close energies and their structures are quite flexible. The molecular adsorption of H2 on Al6C is very weak, but the H2 molecule can be dissociated easily on this cluster. The stable product of the dissociated adsorption is searched and the different paths for the dissociation are investigated. During the dissociation of H2, the structure of the cluster adjusts accordingly, and strong orbital interaction between the hydrogen and the cluster occurs. The calculated energy barrier for the dissociation is only 0.30 eV, which means the dissociation can take place at moderate temperatures. [ABSTRACT FROM AUTHOR]

Physisorption of molecular hydrogen on single-walled carbon nanotubes (SWCNTs) is important for its engineering applications and hydrogen energy storage. Using molecular dynamics simulation, we study the physisorption of molecular hydrogen on a SWCNT with a vacant defect, focusing on the effect of the vacant defect size and external parameters such as temperature and pressure. We find that hydrogen can be physisorbed inside a SWCNT through a vacant defect when the defect size is above a threshold. By controlling the size of the defects, we are able to extract hydrogen molecules from a gas mixture and store them inside the SWCNT. We also find that external parameters, such as low temperature and high pressure, enhance the physisorption of hydrogen molecules inside the SWCNT. In addition, the storage efficiency can be improved by introducing more defects, i.e., reducing the number of carbon atoms on the SWCNT. [ABSTRACT FROM AUTHOR]

The microscopic mechanism of low-temperature (80 K < T < 160 K) hydrogen (H) ingress into the H2 (<2.66 × 10−3 Pa) exposed Pd(110) surface is explored by H depth profiling with 15N nuclear reaction analysis (NRA) and thermal desorption spectroscopy (TDS) with isotope (H, D) labeled surface hydrogen. NRA and TDS reveal two types of absorbed hydrogen states of distinctly different depth distributions. Between 80 K and ∼145 K a near-surface hydride phase evolving as the TDS α1 feature at 160 K forms, which initially extends only several nanometers into depth. On the other hand, a bulk-absorbed hydrogen state develops between 80 K and ∼160 K which gives rise to a characteristic α3 TDS feature above 190 K. These two absorbed states are populated at spatially separated surface entrance channels. The near-surface hydride is populated through rapid penetration at minority sites (presumably defects) while the bulk-absorbed state forms at regular terraces with much lower probability per site. In both cases, absorption of gas phase hydrogen transfers pre-adsorbed hydrogen atoms below the surface and replaces them at the chemisorption sites by post-dosed hydrogen in a process that requires much less activation energy (<100 meV) than monatomic diffusion of chemisorbed H atoms into subsurface sites. This small energy barrier suggests that the rate-determining step of the absorption process is either H2 dissociation on the Hsaturated Pd surface or a concerted penetration mechanism, where excess H atoms weakly bound to energetically less favorable adsorption sites stabilize themselves in the chemisorption wells while pre-chemisorbed H atoms simultaneously transit into the subsurface. The peculiarity of absorption at regular Pd(110) terraces in comparison to Pd(111) and Pd(100) is discussed. [ABSTRACT FROM AUTHOR]

The chemisorption of hydrogen on graphene or graphite is studied within a quantum formalism involving a subsystem coupled to a phonon bath. The subsystem includes the hydrogen atom approaching the surface perpendicularly right on top of a carbon atom which puckers out of the surface. The bath includes the acoustic and optical phonon modes vibrating perpendicularly to the surface. Couplings between subsystem and bath are obtained with a periodic density functional theory calculation. Trapping probabilities are obtained as a function of the hydrogen atom kinetic energy. These results are discussed in the light of the experimental hydrogenation studies performed on graphite by Zecho et al. [J. Chem. Phys. 117, 8486 (2002)] and on graphene by Haberer et al. [Adv. Mater. 23, 4497 (2011)]. [ABSTRACT FROM AUTHOR]

The adsorption, diffusion, and molecular dissociation of hydrogen on the biaxially strained Mg (0001) surface have been systematically investigated by the first principle calculations based on density functional theory. When the strain changes from the compressive to tensile state, the adsorption energy of H atom linearly increases while its diffusion barrier linearly decreases oppositely. The dissociation barrier of H2 molecule linearly reduces in the tensile strain region. Through the chemical bonding analysis including the charge density difference, the projected density of states and the Mulliken population, the mechanism of the strain effect on the adsorption of H atom and the dissociation of H2 molecule has been elucidated by an s-p charge transfer model. With the reduction of the orbital overlap between the surface Mg atoms upon the lattice expansion, the charge transfers from p to s states of Mg atoms, which enhances the hybridization of H s and Mg s orbitals. Therefore, the bonding interaction of H with Mg surface is strengthened and then the atomic diffusion and molecular dissociation barriers of hydrogen decrease accordingly. Our works will be helpful to understand and to estimate the influence of the lattice deformation on the performance of Mg-containing hydrogen storage materials. [ABSTRACT FROM AUTHOR]

The kinetics of molecular hydrogen reactions at the Si (100) surface has been studied by simulation to extract the physics underlying two unexpected experimental observations: apparently first-order desorption kinetics and an increase in sticking probability with hydrogen coverage. At a partially H-terminated Si(100) surface, each Si dimer assumes an unoccupied dimer (UOD), singly occupied dimer (SOD), or doubly occupied dimer (DOD) structure. In our hydrogen reaction model based on an inter-dimer mechanism, a site consisting of an adjacent pair of a DOD and a UOD (DOD/UOD) is a key component for the desorption and adsorption kinetics of hydrogen at the Si(100) surface. To simulate reaction kinetics of both reactions, DU (D: DOD, U: UOD) and SS (S: SOD) pathways are proposed: DU pathway claims that the adsorption as well as desorption of hydrogen takes place at common sites having a cis-configured SOD/SOD pair that is transformed transiently from a DOD/UOD pair by H(D) diffusion. Thus the adsorption obeys the so-called 4H mechanism, but the desorption obeys the 2H mechanism. SS pathway claims that the adsorption occurs at sites having a UOD/UOD pair, and the desorption occurs at sites having a cis-configured SOD/SOD pair that is generated by diffusion of isolated SODs. To simulate temperature-programmed-desorption spectra and sticking probability vs coverage curves, thermo-statistics for a lattice-gas system characterized with parameters for hydrogen pairing and dimer clustering is used to evaluate equilibrium populations of DOD/UOD pairs and isolated SODs. The model simulation based on the above reaction model successfully reproduces all of the complicated, coverage dependent adsorption and desorption reactions of hydrogen at Si(100) surfaces. Specifically, at high coverage above 0.1 ML majority of the adsorption and desorption proceed along the DU pathway. Hence, it is suggested that the adsorption and desorption in the high coverage regime are not microscopically reversible. On the other hand, at low coverages below 0.1 ML, the simulation shows up that the majority of adsorption proceeds along the SS pathway, and the desorption by the DU pathway. Since both reactions obey the 2H mechanism, it is suggested that the desorption and adsorption in the low coverage regime are microscopically reversible. [ABSTRACT FROM AUTHOR]

Titanium‐Iron alloy is a well‐known material for hydrogen storage applications at room temperature. The limitations of TiFe alloy is its low hydrogen storage capacity, higher activation temperature, and pressure. In order to improve the hydrogen adsorption of TiFe alloy, TiFe clusters with Zr atom as a dopant are investigated using first‐principle calculations. The structure of the Zr‐substituted and unsubstituted clusters was optimized and it is found that the binding energy of the Zr‐substituted TiFe clusters is higher than TiFe clusters, thus, the doping Zr atom stabilizes the TiFe clusters. Hydrogen adsorption over Zr doped TiFe cluster is investigated, where, Zr is revealed to be an active site for hydrogen adsorption except Ti3Zr1Fe4 cluster. Hence, Zr substitution stabilizes the TiFe clusters and hydrogen storage properties were tuned by the introduction of the Zr atom. [ABSTRACT FROM AUTHOR]

The stress variations during polarization of iron thin film electrode in pH 8.4 borate buffer solution have been measured by a cantilever bending method to investigate the correlation between stress evolution and electrochemical reaction of the iron electrode. The stress variations toward compressive direction during active dissolution of iron result from the relaxation of the residual tensile stress due to the decrease in thickness of the iron electrode. The stress variations toward tensile direction in the pre-passive region are brought by the anodic deposition of ferrous ions once dissolved into solution. The successive potential steps for each interval of 1 h in the passive region between 0.20 and 0.90 V induce the stress variations toward compressive direction at potentials more positive than 0.30 V in connection with the growth of the inner (barrier) layer in the passive film. The electrostriction stress in the inner layer of the passive film formed on iron at 0.90 V has been estimated from the stress relaxation in the cathodic potential sweep after 1-h passivation at 0.90 V. In addition, the stress variations toward compressive direction during cathodic reduction of the passive film are attributed to the volume expansion due to the formation of iron (II) hydroxide at the intermediate step of the cathodic reduction at pH 8.4. Furthermore, the rapid stress variations toward compressive direction during hydrogen evolution at potentials more negative than 0.52 V are caused by the volume expansion in near the surface region of the iron thin film electrode due to hydrogen adsorption or absorption. [ABSTRACT FROM AUTHOR]

Ab initio first-principles calculations were carried out to investigate Li-decorated boron nitride atomic chains (BNACs) for their applications as hydrogen storage materials. We have shown that the interaction between hydrogen molecules and the pristine chains is too weak to be used at room temperature, and the hydrogen adsorption energies and storage capacities can be obviously increased by decorating Li atoms on the ends of the BNACs. Moreover, the bonding energy between Li and BNAC is much greater than the cohesive energy of bulk Li so that the clustering of Li atoms will not occur once Li is bonded with BNAC. Our studies also revealed that the van der Waals interaction plays an important role in the adsorption of the H2 molecules. Therefore, with two Li atoms binding to each end of the BNACs, the hydrogen storage capacity can reach up to 29.2 wt % theoretically. [ABSTRACT FROM AUTHOR]

We report further and more detailed results of our recent investigation [W. A. Herrebout, B. J. van der Veken, and A. P. Kouzov, Phys. Rev. Lett. 101, 093001 (2008)] on the collision-induced fundamental absorption by hydrogen dissolved in liquid neon (T ≈ 25 K). The band shapes were studied in a wide range of concentrations (0.003-0.05 mole fractions) as well as for different ortho/para ratios and at much higher level of accuracy and resolution than before. Due to almost unhindered rotation of the hydrogen molecule and low temperature, an unprecedently rich frequency-domain picture produced by different terms of the interaction-induced polarization was observed. While some of them are conspicuous via fast intracell motion of a light guest (H2), others-induced by the electrostatic field of the guest-give rise to lines whose shapes are imprinted by fluctuations of the nearest surrounding. Strong motional narrowing observed on the guest-guest induced lines shows up in their Lorentzian shapes which are signatures of microscopic-scale diffusion. Near-Lorentzian peaks were also detected at the tops of the diffuse lines induced by isolated guests. Their formation may be associated with a long-living defect (vacancy) emerging in the vicinity of the polarization inductor. Altogether, our results give the first unambiguous spectroscopic evidence on the diffusional evolution of isolated binary interactions that emerge in dense chaotic media. [ABSTRACT FROM AUTHOR]

Abstract We investigated mass transports during hydrogen adsorption and absorption processes of PdCu alloys that has advantages of higher hydrogen diffusivity and economically lower-cost than the other Pd-alloys. The research was made with a comparison of the well-known ordered phase of the bcc structure (the B2 phase) and a mixed phase of the fcc and B2 structures. In-situ ultrahigh vacuum X-ray photoelectron spectroscopy (UHV-XPS) and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) using synchrotron radiation were carried out to trace the chemical states of the Pd and Cu atoms as a function of temperatures. It is newly elucidated that the initial adsorption and absorption processes were similar in the two phases, but a hydrogen diffusion rate to the bulk was apparently higher in the ordered phase than in the mixed one. We found the dynamics of the Pd and Cu atoms during the hydrogen adsorption/absorption processes largely depends on temperature. In the hydrogen atmosphere, the Pd atoms segregate at the surface below 373 K and Cu atoms segregate at the surface above 373 K, showing a reversal behavior. The present results agree well with the previous theoretical calculations and, thus, provide appropriate inputs toward developments of the industrial hydrogen permeation materials. Highlights • Hydrogen adsorption/absorption in a PdCu alloy is studied by XPS under the H 2 atmosphere. • The surface segregation becomes inverted at 373 K during hydrogen adsorption. • Hydrogen absorption process strongly depends on phase-structures and temperature. • We revealed the diffusion process during the absorptions in the bulk PdCu phases. [ABSTRACT FROM AUTHOR]

Hydrogen economy has gained pace globally due to the depletion of fossil fuels at an alarming rate. A good number of multidecker transition metal complexes have been studied for their hydrogen storage ability. However, the problem of finding an ideal multidecker system for hydrogen storage applications still remains a challenge. Herein, we report a comparative study on multidecker complexes of VTi(C6H6)3, Sc2(C6H6)3, and Sc2(C5H5)2(C6H6) using density functional theory at PBEPBE functional and 6–31G (d,p) basis set level of theory. The three complexes show hydrogen adsorption capacity in a range of 2.94 to 5.28 wt%, with an average binding energy of 0.65 to 0.92 eV/H2. Trends in adsorption energies, Gibbs free energy changes and energy gaps indicate the adsorption of H2 molecules on these multidecker complexes is thermodynamically and kinetically favorable. [ABSTRACT FROM AUTHOR]

Abstract In order to understand the effects of rare element substitution on activation performance of Laves phase-related BCC solid solution alloys, cerium (Ce) is used to partial substitute for Mn in Ti 33 V 37 Mn 30 alloy. Results show that Ce substitution leads to the formation of Ce/CeO 2 while decreases C14 Laves phase. Ce substituting alloys can absorb hydrogen without being activated at a high temperature, which means the activation performance of Ti 33 V 37 Mn 30 alloys is improved greatly by the Ce/CeO 2 rather than C14 Laves phase. The maximum hydrogen absorption capacity also increases when Ce content increases. The hydrogen absorption capacity and effective hydrogen storage capacity reach the maximum when the composition is Ti 33 V 37 Mn 29.4 Ce 0.6 , with the values of 3.35 wt% at 293 K and 2.25 wt% at 423 K. The dehydriding enthalpy (ΔH) of 0.6 at.%-Ce-substituting alloy is higher than that of Ce-free alloy, which indicates that Ce substitution can increase the stability of hydrides. Highlights • Ce substitution decreases the formation of C14 Laves phase. • The Ce substitution improves the activation performance rather than C14 Laves phase due to the formation of CeH 2.51. • Ce substitution improves the hydrogen storage properties of Ti 33 V 37 Mn 30 alloy. • Ce substitution increases thermal stability of the hydride. [ABSTRACT FROM AUTHOR]

Abstract In this study the activation behavior of hydrogen absorption in a TiZrNbTa high-entropy alloy (HEA) has been investigated. Results showed that the hydrogen absorption temperature of the TiZrNbTa HEA were significantly decreased from 715 K to room temperature, and the hydrogen absorption kinetics were also improved greatly after activation. The X-ray photoelectron tests showed that, after activation, almost all the oxides at the surface of the TiZrNbTa HEA were reduced to suboxides and sub-hydroxides after activation, but only parts of oxides at the surface of pure metals were reduced, in the form of suboxides. Based on these results, a two-step mechanism for the activation of TiZrNbTa HEA was proposed. The positron annihilation lifetime analysis showed that both the size and concentration of vacancy clusters increased significantly in the TiZrNbTa HEA after activation. It could be responsible for the improvement of hydrogen absorption kinetics in TiZrNbTa HEA. Highlights • The hydrogen absorption temperature of TiZrNbTa high entropy alloy decreased to room temperature after activation. • After activation, the transformation from oxides into suboxides and sub-hydroxides in the TiZrNbTa surface was observed. • Both the size and concentration of vacancy clusters increased significantly in the TiZrNbTa alloy after activation. • A two-step activation mechanism of TiZrNbTa alloy was proposed. [ABSTRACT FROM AUTHOR]

Abstract Zr 3 Fe and Ni-substituted Zr 3 Fe alloys with 30 and 50 at.% Ni were synthesized and their hydrogen absorption/desorption characteristics were compared experimentally (pressure–composition isotherms, thermal desorption spectroscopy, in-situ neutron diffraction) and by computational methods (ab-initio molecular dynamics (AMD), nudged elastic band theory (NEB)). All the alloys absorbed hydrogen to a hydrogen-to-metal atomic ratio of about 1.7, but the hydrides formed were stable at room temperature. The Zr 3 Fe 0.5 Ni 0.5 alloy and its hydrided form were multi-phase. The Zr 3 Fe 0.7 Ni 0.3 alloy was single-phase and retained the C m c m structure of the parent intermetallic. In-situ neutron diffraction with D 2 in place of H 2 showed that the hydride formed in the isotherm measurements, Zr 3 Fe 0.7 Ni 0.3 H 6.88 , had the same structure (C m c m) as Zr 3 FeH 7 , while disproportionation was observed in the hydrogenation of Zr 3 Fe. The kinetics of hydride formation was slower in both the Ni-substituted alloys. Thermal desorption spectroscopy showed that substitution of 0.3Ni significantly destabilized the hydride, lowering the temperature of the principal desorption peak by about 300 K relative to Zr 3 Fe–H 2 , without loss of hydrogen capacity, and avoiding disproportionation. Based on the structures determined by neutron diffraction, AMD and NEB calculations were conducted to compare Zr 3 Fe and Zr 3 Fe 0.7 Ni 0.3 and their hydrides. The AMD calculations predicted that H diffusion was slower in Ni-substituted Zr 3 Fe, in agreement with the experimental observation of slower kinetics, implying a higher activation energy for H migration. The NEB calculations also predicted a higher energy barrier for H migration in Ni-substituted Zr 3 Fe. Highlights • New metal hydride introduced. • Desorption temperature lowered by about 300 °C compared to parent intermetallic. • New alloy and its hydride are single-phase. • Disproportionation noted for Zr 3 FeH 7 is avoided. • Experiment and computational modelling combined to explain improved properties. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Minimum energy pathways of hydrogen diffusion into Pd(1 0 0) subsurface with varying coverages of four types of adsorbed gases (H, O, O 2 and OH) were explored by NEB method. • Their effect order on decreasing barriers of hydrogen diffusion into subsurface is as follows: O 2 > O > OH > H. • The substrate relaxation effect is influenced by these adsorbed gases with the variation of coverages. • Hydrogen adsorption would reduce the probability of hydrogen diffusion into subsurface. • Oxygen gas greatly facilitates hydrogen diffusion with an exothermal process at 0.5 ML coverage. Abstract Hydrogen diffusion from metal catalyst surface into subsurface is the key step for the heterogeneous catalysis, hydrogen purification, and hydrogen-induced embrittlement in practical applications. However, it has been scarcely concerned by previous works, especially with distinct types of adsorbates covered on surface. To deeply understand the impact of adsorbates on the microscopic mechanism for hydrogen diffusion into subsurface, four representative types of gases (H, O, O 2 , and OH) were chose to serve as adsorbates with varying coverages, and all possible minimum energy pathways were globally searched out on base of an appropriate Pd(1 0 0) surface by the NEB method. The present calculation results imply that the barriers, the stable adsorption and absorption sites for the forward and inverse diffusion routes are greatly influenced by the main features for adsorbed gases, which include electronic property, spatial structure, the relative adsorption position, and the variation of coverages. The effect ranking for four types of adsorbed gases on lowering the barriers of hydrogen diffusion into subsurface is: O 2 > O > OH > H. One exothermic process at 0.5 ML coverage particularly exhibits the good performance of oxygen gas in facilitating hydrogen diffusion. However, hydrogen is the special one that would increase diffusion barrier for the forward process at hydrogen coverages of 0.25 and 0.75 ML. Additionally, the substrate relaxation effect that plays a significant role in lowering diffusion barrier is also affected by the varying coverages of hydrogen and oxygen atoms. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Strong interaction and charge transform are observed between adsorbed atoms and the nano-sheets. • The adsorbed atoms could effectively modulate the band gap of both GDY and BNdiyne sheets. • Atomic oxygen induced spin polarization is observed in GDY sheet. • Both hydrogenated and oxygenated GDY sheets perform better conductivity than the pristine's. Abstract In this paper, the structural and electronic properties of atomic oxygen and hydrogen adsorption on graphdiyne (GDY) and its BN analog (BNdiyne) has been studied by the first-principles calculations. The calculated results show that the most stable adsorption positions of atomic hydrogen (oxygen) for GDY and BNdiyne monolayer are the top site (T2) and the hollow site (H2), respectively. The strong interaction (chemisorption) between atomic hydrogen and the monolayers leads to a decrease of 0.1 eV in the band gap of GDY, while an increase of 0.15 eV in BNdiyne. The shallow impurity energy level introduced by oxygen enhances the conductivity of GDY which could be indicated from the non-zero transmission coefficient at zero bias as well. In addition, a tiny magnetic has occurred in the oxygenated GDY while it has not occurred in the hydrogenated GDY which is different from the graphyne. [ABSTRACT FROM AUTHOR]

Abstract The semi-empirical model for predicting the hydrogen desorption enthalpy and plateau pressure of AB 2 type-Ti x (CrFeMn) 2 Alloys is established by MATLAB soft in the method of linear-interaction. Through the significance testing analysis, it indicates that the factor order of the influence on the hydrogen desorption plateau pressure is T>δ2 > Z/R>(Δn)2/3 >(ΔX)2. Due to its negative and positive coefficients, the effects of (Δ X)2, δ2, (Δ n)2/3 on the desorption plateau pressure and enthalpy are negative, and Z/R effect is positive. The relative error of ΔH was less than 3.7% in the choose database which is more accuracy than previous model of AB 2. The calculated desorption plateau pressures by the model are agreed with our experimental data very good in the most experiment. The difference of ΔH calculated by the model and fitting experimental data were not more than 4 kJ/(mol H 2). The model can be used to save cost and development time through predicting the hydrogen desorption plateau pressure of different composition alloys. Highlights • Model for hydrogen desorption plateau pressure of Ti x (CrFeMn) 2 Alloys is established. • Factor influence order in the model is confirmed by significance testing analysis. • The prediction pressures by the model are in agreement with experimental data. • The model is more accuracy than previous model for AB 2 alloys and can save cost. [ABSTRACT FROM AUTHOR]

Abstract The intermetallic compounds Zr 2 Pd and ZrPd 2 have been investigated by perturbed angular correlation (PAC) spectroscopy considering anomalies in their hydrogen absorption properties. It is known that both these compounds have same crystal structure, but Zr 2 Pd forms an excellent hydride while ZrPd 2 does not, even at high pressure. From PAC measurement at room temperature in annealed ZrPd 2 sample, this phase is found as a minor component (∼27%) while the dominating phase is identified to be the ZrPd 3 (∼73%). In Zr 2 Pd, this phase has been found to be predominant (∼86%) along with a minor phase (∼14%) due to ZrPd. In ZrPd 2 , unlike Zr 2 Pd, a weak temperature dependence of electric field gradient (EFG) has been found from present PAC measurements. Also, site occupancies for both Zr and Pd atoms by the Ta-probe atoms have been found in ZrPd 2 and ZrPd 3 (formed in ZrPd 2). In ZrPd 3 , Pd site occupancy by the probe is found to be maximum while a small fraction for Zr site occupancy has been found. But, in case of Zr 2 Pd and ZrPd, no Pd site occupancy of the probe is observed. Calculation of electric field gradients at 181Ta impurity atom for different phases have been performed by density functional theory based on the all electron full potential linearized augmented plane wave plus local orbitals (FP-(L)APW + lo) method to assign the different components observed from PAC measurements. Measurements by XRD have also been carried out to confirm the presence of component phases in the samples. [ABSTRACT FROM AUTHOR]