Search

Graphical abstract Highlights • Li prefers to adsorb on the Mg-Mg bridge site of the Mg 17 Al 12 (1 0 0) surface. • Adsorption energies of hydrogen on the surfaces with adding Li are enhanced. • Barrier energy of H 2 dissociation on Li-adsorbed surfaces is reduced evidently. • Formation of Li-H bonds in the hydrogenation of the Li-containing surfaces. Abstract The adsorption and dissociation properties of hydrogen on the Li-adsorbed and -substituted Mg 17 Al 12 (1 0 0) surfaces are investigated by using the first principle calculations. Compared with the clean (1 0 0) surface, the adsorption energies of H and H 2 on the Mg 17 Al 12 (1 0 0) surfaces with a small amount of Li are evidently improved. Moreover, the barrier energy of H 2 dissociation on the Li-adsorbed Mg 17 Al 12 (1 0 0) system is notably reduced 0.51 eV. The catalytic effects of Li on the enhanced hydrogenation properties of the Mg 17 Al 12 surfaces are discussed. [ABSTRACT FROM AUTHOR]

Abstract The long-term hydrogen storage performance of a CaCu 5 -type LaNi 4 Co alloy is studied by detailed analysis of its P-C-T curves and structural changes within 1000 cycles. The alloy shows one absorption plateau (α→β phase transition) and two desorption plateaus (γ→β and β→α phase transitions). With increasing cycle number, the plateau pressures for both α→β and β→α phase transitions decrease due to the increase in cell volumes. The increased crystal cells also provide more space to accommodate the simultaneous occupations of 12° and 6 m sites, and thus β→α and β→γ desorption plateaus become less distinguishable. During cycling, partial phase decomposition, crystal grain destruction and surface oxidation occur, resulting in the loss of hydrogen storage capacity. In addition, due to the increase in the atomic disorder and internal microstrains and defects, the average slope factors (SF / H %) of the hydrogen absorption/desorption plateaus are increased. Particularly, the SF / H % value of the γ→β plateau is always higher than those of the α→β and β→α plateaus, and it also increases faster with cycling, reaching about 4 times of the other two plateaus at the 1000th cycle. It is considered that the improvement of the γ→β phase transition process is significant to promote the cycling behavior and practical applications of this alloy system. Graphical abstract Image 1 Highlights • Hydrogen storage properties of the LaNi 4 Co alloy within 1000 cycles are studied. • Changes in PCT curves with double desorption plateaus are investigated in detail. • Phase decomposition, lattice expansion, crystal damage and surface oxidation occur. [ABSTRACT FROM AUTHOR]

Abstract The paper presents the results of experimental investigations on hydrogen absorption and desorption in the metal hydride reactor RS-1 containing 81 kg of La 0.5 Nd 0.5 Al 0.1 Fe 0.4 Co 0.2 Ni 4.3 intermetallic compound at 60 °C isothermal conditions. During the reactor-scale measurements of pressure-composition isotherms we observe pressure artifacts; pressures for absorption are higher and for desorption are lower than equilibrium pressures obtained after cooling down and reheating of the reactor. This thermal relaxation procedure removes the pressure artifacts. The observed effect is similar to the large aliquot effect, and mostly affects the desorption isotherm. The highest measured pressure difference is 0.7 bar (11%). Highlights • MH reactors can be operated in isothermal conditions. • Pressure artifacts similar to the large aliquot effect are observed. • Equilibrium pressure increases for absorption and decreases for desorption. • The effect mostly affect desorption isotherm. • Cooling down and reheating of the reactor remove the pressure artifacts. [ABSTRACT FROM AUTHOR]

Abstract The hydrogen physisorption properties of diverse examples of Ti-decorated six-membered carbocycles have been established and intensively investigated. However, fewer investigations have been devoted to the chemical reactions occurring during the process of hydrogen storage. Herein, for the first time, a variety of plausible hydrogenation intermediates and physisorption complexes involving multiple H 2 molecules on the complex TiC 6 H 6 has been investigated simultaneously. The relative Gibbs free energies of TiC 6 H 6 -nH 2 (n = 1–4) isomers and the minimum-energy pathways of the successive hydrogenation steps show that the overall reactions to give the hydrogenation product TiC 6 H 11 -3H is exothermic by 11.07 kcal/mol in terms of ΔG (298.15 K). It indicates that a facile switch of hydrogen addition and release with superior capacity of 6.02 wt % can be quickly achieved with simply regulated by increasing/decreasing the hydrogen pressure, which is consistent with the recent experiment on hydrogen adsorption in TiC 6 H 6 at room temperature. The physisorption processes show that three H 2 molecules can be efficiently trapped below 210 K and desorbed completely at 935 K. More importantly, chemisorption and physisorption will convert in certain circumstances, which indicates that the mechanism of the bonding of H 2 molecules on TiC 6 H 6 is an unusual combination of chemisorption and physisorption. Graphical abstract Image 1 Highlights • Chemisorption capacity of 6.02 wt % for TiC 6 H 6 can be achieved at room temperature. • Three H 2 molecules are trapped under 210 K and desorbed completely at 935 K. • Chemisorption explains the experimental results perfectly rather than physisorption. • Chemisorption and physisorption will convert in certain circumstances. • CH 2 groups in hydrogenation intermediates tend to connect adjacently. [ABSTRACT FROM AUTHOR]

The thermodynamic state of H2 adsorbed on Pt in the aqueous phase was determined by kinetic analysis of H2 reacting with D2O to HDO, HD, and D2, and by DFT‐based ab initio molecular dynamics simulations of H2 adsorption on Pt(111), Pt(110), and Pt nanoparticles. Dissociative adsorption of H2 on Pt is significantly weakened in the aqueous phase compared to adsorption at gas–solid interfaces. Water destabilizes the adsorbed H atoms, decreasing the heat of adsorption by 19–22 kJ molH2-1 while inducing an additional entropy loss of 50–70 J molH2-1  K−1. Upon dissociative adsorption of H2, the average distance of water from the Pt surface increases and the liquid adopts a structure that is more ordered than before close to the Pt surface, which limits the translation mobility of the adsorbed H atoms. The presence of hydrated hydronium ions next to the Pt surface further lowers the H−Pt bond strength. The thermodynamic state of H2 adsorbed on Pt in the aqueous phase was determined via kinetic analysis of H2 reacting with D2O and by DFT‐based ab initio molecular dynamics simulations of H2 adsorption on Pt(111). Compared to the gas–solid interface, the presence of liquid water weakens the dissociative adsorption by decreasing the heat of adsorption and inducing a larger loss of entropy. [ABSTRACT FROM AUTHOR]

Abstract In this study, clinoptilolite (CLN), mordenite (MOR) and chabazite (CHA) from Turkey and those of H+-, Na+-, K+-, Li+-, Ca2+- and Mg2+- exchanged forms were investigated for hydrogen storage at 77 K using volumetric apparatus up to 100 kPa. Cation exchange procedures were carried out using 1.0 M HCI, KNO 3 , LiNO 3, NaNO 3 , Mg(NO 3) 2 and Ca(NO 3) 2 solutions at 90 °C for 5 h. Structural characteristics of these zeolite samples were investigated using XRD, XRF and N 2 adsorption techniques. Experimental results showed that the chabazite samples (0.474–1.082 wt %) had a higher hydrogen adsorption capacity than mordenite (0.224–0.337 wt %) and clinoptilolite (0.065–0.555 wt %) samples. The variations in the level of hydrogen adsorption of original and cation exchanged natural zeolites were discussed in terms of the induced differences in their structural properties. Highlights • Investigation of hydrogen storage at 77 K on clinoptilolite (CLN), mordenite (MOR) and chabazite (CHA). • Structural characteristics of zeolite samples investigated with XRD, XRF and N 2 adsorption techniques. • Na-CHA sample showed highest hydrogen adsorption capacity (1.082%). [ABSTRACT FROM AUTHOR]

Highlights • Sintered Nd-Fe-B strip casting flakes (SC) and waste sintered magnets (SM) show the approximate HD process, which accelerates with increasing pressure. • The surface activation process accelerates with increasing pressure, and almost disappears when the initial hydrogen pressure reaches to 6 MPa. • The hydrogen content of SM is lower than SC, and increases with increasing pressure. • For the SM, blasting power of HD process decreases with the increase of the initial hydrogen pressure. Abstract Hydrogen treatment technology is developed to recycle the waste Nd-Fe-B sintered magnets in the way of short route, low cost, and high efficiency. In present study, effect of hydrogen pressure on hydrogen decrepitation (HD) process of sintered Nd-Fe-B strip casting flakes (SC) and waste sintered magnets (SM) was systematically studied. Both SC and SM show the approximate HD process, which accelerates with increasing pressure. The surface activation process accelerates with increasing pressure, and almost disappears when the initial hydrogen pressure reaches to 6 MPa. The hydrogen content of SM is lower than SC, and increases with increasing pressure. For the SM, blasting power of HD process decreases with the increase of the initial hydrogen pressure. It provides beneficial reference for recycling waste Nd-Fe-B sintered magnets. [ABSTRACT FROM AUTHOR]

Abstract We use the first principles methods based on density functional theory to study the hydrogen storage capacity of Na-decorated two dimensional (2D) boron monolayer (BM). The result shows the favorable position for Na to adsorb is on the top of hexagon of BM with the highest binding energy of −2.087 eV. Moreover, the single-sided Na-decorated BM can store up to seven H 2 molecules with average adsorption energy of −0.145 eV/H 2. For double-sided Na-decorated BM, the 28 H 2 molecules are captured around 4Na/BM complex with average adsorption energy of −0.152 eV/H 2 and the hydrogen storage capacity of 8.28 wt.%. In addition, first principles molecular dynamics simulations indicate H 2 molecules are quickly released from 28H 2 /4Na/BM structure at room temperature and the metal clusters are avoided at the same time. Finally, the linear periodic [(Na 7H 2) 2 BM] n polymer is considered as a promising hydrogen storage candidate for industrial applications. Graphical abstract The isosurface of electrostatic field for 1H 2 /Na/BM configuration, the red and blue denote the positive and negative region, respectively. Image 1 Highlights • The Na-decorated two-dimensional boron monolayer can serve as a promising hydrogen storage candidate. • The storage density reaches up to 8.28 wt.% with the desirable adsorption energy of −0.152 eV/H 2. • The metal clusters are avoided for the dispersed Na atoms onto boron monolayer. [ABSTRACT FROM AUTHOR]

Abstract In recent years, nanoporous materials with high specific surface areas and porosity have been developed to meet the commercial demands of hydrogen storage systems. Subnanometer micropores of less than 1 nm are known for their excellent performances in hydrogen physisorption, but their exact contribution and temperature-dependent adsorption performance are still ambiguous. In this work, we have prepared microporous carbons using Ketjenblack with various micropore size portions via chemical activation. In addition, we propose a new density functional theory (DFT) pore volume-based model to determine the contribution of pore size to gas adsorption. The values of the contribution factor (k) derived from the proposed model indicate the effect on the physical adsorption by pore size and are indicated to be inversely proportional to temperature. The proposed model and k values can be used for an important method for ambiguous physical adsorption studies. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Abstract Hydrogen adsorption over silicon carbide of different nature was investigated. High specific hydrogen adsorption (up to 15 μmol/m2), nontypical for silicon carbide was obtained for the materials prepared by the template method. A more perfect truly "carbide" structure (with a higher content of Si–C bonds in the form of carbide) in this type of materials contributes to an increase of the specific hydrogen adsorption. However, some non-stoichiometricity manifested in the presence of carbon in other (non-carbide) bonds (graphite or terminal and sp3 hybridized C) is required for exceptionally high specific hydrogen adsorption. The influence of the adsorbate nature for several gases (Н 2 , N 2 , CO) was found to be less prominent for SiC compared to carbon and silica materials. This feature inherent only to silicon carbide exhibiting an increased level of specific hydrogen adsorption, is due to cooperative adsorption, accompanied by an abnormally high loading of the adsorbent surface in the supercritical region. Highlights • High specific H 2 adsorption was observed for SiC prepared by the template method. • Some non-stoichiometricity is required for exceptionally high specific H 2 adsorption. • The adsorbate nature (Н 2 , N 2 , CO) has not a large influence on adsorption over SiC. • An increased level of specific H 2 loading over SiC is due to cooperative adsorption. • The experimental adsorption data were modeled using the Sips equation. [ABSTRACT FROM AUTHOR]

Abstract Mg-based materials have been widely researched for hydrogen storage development due to the low price of Mg, abundant resources of Mg element in the earth's crust and the high hydrogen capacity (ca. 7.7 mass% for MgH 2). However, the challenges of poor kinetics, unsuitable thermodynamic properties, large volume change during hydrogen sorption cycles have greatly hindered the practical applications. Here in this review, our recent achievements of a new research direction on Mg-based metastable nano alloys with a Body-Centered Cubic (BCC) lattice structure are summarized. Different with other metals/alloys/complex hydrides etc. which involve significant lattice structure and volume change from hydrogen introduction and release, one unique nature of this kind of metastable nano alloys is that the lattice structure does not change obviously with hydrogen absorption and desorption, which brings interesting phenomenon in microstructure properties and hydrogen storage performances (outstanding kinetics at low temperature and super high hydrogen capacity potential). The synthesis results, morphology and microstructure characterization, formation evolution mechanisms, hydrogen storage performances and geometrical effect of these metastable nano alloys are discussed. The nanostructure, fresh surface from ball milling process and fast hydrogen diffusion rate in BCC lattice structure, as well as the unique nature of maintaining original BCC metal lattice during hydrogenation result in outstanding hydrogen storage performances for Mg-based metastable nano alloys. This work may open a new sight to develop new generation hydrogen storage materials. Highlights • Our achievements on Mg-based metastable nano alloys with BCC lattice are summarized. • Uniquely, BCC metal lattice in these alloys does not change obviously with hydrogen. • This metastable feature brings interesting microstructures and hydrogen storage performance. • Mechanisms of formation, and special hydrogen storage performance are discussed. [ABSTRACT FROM AUTHOR]

Abstract In this research, we proposed a highly sensitive hydrogen sensor based on a new suspended structure of cross-stacked multiwall carbon nanotube (MWCNT) sheet. MWCNT sheet is a kind of CNT film which has a super-high CNT alignment and can be easily prepared by drawing from the spinnable CNT array in large scales. By stacking the sheets onto an electrode with a 1 × 1 cm hole in mutually perpendicular directions, sensors with suspended cross-stacked structure were realized. Afterwards, a two-side Pd functionalization was introduced. The effects of suspended structure, cross-stacked structure and two-side Pd functionalization were investigated respectively. It was observed that the sample with 2 + 1 layers of cross-stacked MWCNT sheet and two-side 3 nm Pd deposition showed the best gas sensing performance with a relative resistance change of 35.30% at 4% H 2. This result indicates that the proposed sensor is one of the best among all reported MWCNT based hydrogen sensors. The method demonstrated in this research gives a potential solution for the mass production of CNT-based sensors with high sensitivity and reliability. Highlights • Highly sensitive hydrogen sensor was realized based on novel structured MWCNT sheets. • High response (35.30%@4%H 2) at room temperature and high reliability realized. • Suspended structure enlarged the surface area of MWCNT sheets for H 2 adsorption. • Cross-stacked structure improved the porosity of MWCNT sheets. • Two-side Pd functionalization realized high sensitivity. [ABSTRACT FROM AUTHOR]

Abstract Using neutron reflectometry, we investigated the deuterium desorption of Pd-covered Ti films that have been deuterated at 1 bar deuterium at room temperature and then exposed to air. The deuterium content was monitored continuously for the first two days. Thereafter, measurements were conducted periodically, spanning a period of up to 2 years. The films were in the thickness range of 10–300 nm and the desorption behaviour showed a strong dependence on the film thickness. The smaller the Ti film thickness the faster the Ti films desorbed the stored deuterium. Graphical abstract Image 1 Highlights • Deuterium desorption in thin Pd-covered Ti films was monitored over 2 years • The thinner the Ti films, the faster they desorb the deuterium • After 2 years a 10 nm thick Ti film desorbed 80% of its originally stored deuterium • After 4 days the deuterium concentration follows an exponential decay [ABSTRACT FROM AUTHOR]

Abstract A number of peculiarities in sorption behavior of metal hydride beds depending on the reactor geometry have been discovered. Comparison of PCT absorption and desorption isotherms was conducted for the same 500 g sample of La 0·9 Ce 0·1 Ni 5 -alloy and two different geometries: horizontal half-cylinder and vertical annular. This approach gives the way to directly investigate the influence of the bed geometry on the hydrogen sorption properties excluding the effect of other factors. The influence of the internal stresses in the fine dispersed beds of intermetallic compounds on their sorption properties is discussed in the present study. The occurrence of internal stresses in the vertical annular metal hydride bed results in the decrease of the hydrogen equilibrium pressure, increase of the enthalpy and entropy of hydrogen absorption and decrease of pressure hysteresis due to significantly stronger decrease of absorption pressure compared to desorption. The analysis of SEM images of the sample taken from the bottom of the working autoclave showed the presence of a macro particle which avoided the dispersion due to the agglomerated particles around. Highlights • Bed geometry influence hydrogen sorption properties of LaNi 5 based metal hydride. • Internal stresses in metal hydride bed decrease hydrogen equilibrium pressure. • Internal stresses in metal hydride bed influence hydrogen uptake. • Fast agglomeration formation prevents some of the particles to disperse at activation. [ABSTRACT FROM AUTHOR]

Abstract Density functional calculations are used to investigate hydrogen (H) behaviors in vanadium carbide (VC). Molecular H 2 dissociation, atomic H diffusion and penetration are analyzed using the transition state theory. H 2 prefers to be close to the surface as physical adsorption, providing an environment conducive for further dissociation, and dissociates into atomic H adsorbed at the top C atom sites with co-adsorption state. The dissociation rate on the surface is mainly limited by the temperature-controlled activation energy barrier. The adsorptivity of atomic H by the surface tends to decrease as increasing of H coverage. For atomic H penetration through the surface, a significantly endothermic energy barrier and the low diffusion prefactor suggest that the main resistant effect of H permeation takes place at the surface. Energetic, vibrational, electronic consequences, and quantum effects on the H behaviors are discussed thoroughly. Our theoretical investigation indicates VC is a promising hydrogen permeation barrier. Highlights • The H adsorption, dissociation and diffusion on (001) surface and bulk VC are studied by DFT method. • Energetic, vibrational, electronic consequences, and quantum effects on H behaviors in VC are discussed. • The main resistant effect of H permeation through VC takes place at (001) surface. • Theoretical investigation indicates VC is a promising hydrogen permeation barrier. [ABSTRACT FROM AUTHOR]

Abstract In this work, we present the hydrogen adsorption capacity of Sc doped small boron clusters (B n Sc 2 , n = 3–10) using density functional theory. Almost no structural change was observed in the host clusters after hydrogen adsorption. Stabilities of the studied clusters were confirmed by various reactivity parameters such as hardness (η), electrophilicity (ω), and electronegativity (χ). The average adsorption energies was found in the range of 0.08–0.19 eV/H 2 inferring physisorption process, and the fact is also supported by the average distance from Sc to H 2 molecules which was in the range of 2.13 Å-2.60 Å. All the clusters were found to have gravimetric density satisfying the target set by the U.S. Department of Energy (US-DOE) (5.5 wt% by 2020). From Bader's topological analysis, it was confirmed that the nature of interaction was likely to be somewhat closed shell type. ADMP molecular dynamics simulations study was performed at different temperatures to understand the adsorption and dissociation of H 2 from the complexes. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Highlights • H 2 adsorption energies are very similar on different facets and K preadsorbed on hcp Co. • H atom adsorption was site and facet dependent on hcp Co. • H 2 dissociation energy barriers were negligible (0–0.07 eV) on clean hcp Co. • K has a slight inhibiting effect on the H atom adsorption and H 2 dissociation. • Different K species (K and KOH) exhibit similar effect on H 2 dissociation on hcp Co. Abstract Trace amounts of potassium (K) have a significant influence on the activity and selectivity of cobalt-based catalysts in Fischer–Tropsch synthesis (FTS), in which hydrogen adsorption and dissociation is one of the initial and most important steps. In this work, hydrogen adsorption and dissociation behavior on typical facets ((0001), (10–11), (10–12), (10–15) and (11–20)) of hcp Co with and without adsorbed K were systematically studied. H 2 molecular adsorption results showed that H 2 mainly adsorbed in the perpendicular mode and close to the state of free H 2. Different facets and pre-adsorbed K did not show obvious effects on the H 2 adsorption energy. Atomic hydrogen adsorption was site and facet dependent, but the maximum hydrogen adsorption energy on the different facets of hcp Co were similar (-2.64 to -2.67 eV) with the exception on the (11–20) facet where the adsorption energy was significantly lower (-2.44 eV). K had a slight destabilizing effect on the H atom adsorption on the former Co surfaces due to a very weak repulsive interaction between K and H atoms. The initial H 2 dissociation had negligible energy barriers (0–0.07 eV) on the clean surface of hcp Co, suggesting the direct dissociative adsorption of H 2. The energy barriers for H 2 dissociation are mainly caused by the approach of molecular H 2 towards the Co surface and the rotation of the H 2 molecule from the perpendicular mode to the parallel mode. The H 2 dissociation energy barriers increase by 0.02–0.17 eV after the pre-adsorption of K, indicating a slight inhibition of H 2 dissociation by K. However, the energy barriers for H 2 dissociation in the presence of K were also small (0.05–0.21 eV). This indicates that H 2 dissociates readily at typical Co-based FTS reaction temperatures (210–240 °C), both in the absence and presence of K. Different K species (K and KOH) exhibit similar effects on H 2 dissociation on hcp Co. The B 5 sites on the stepped facets, the preferred sites for K adsorption are not the most favorable site for H 2 dissociation, and K slightly hinders H 2 dissociation at the B 5 site of hcp Co. Graphical abstract Image, graphical abstract [ABSTRACT FROM AUTHOR]

Abstract We have systematically studied the hydrogen adsorption mechanism, hydrogen dissociation, and diffusion on the high-index experimentally-found Mg(10 1 ¯ 3) surface and made comparisons with the low-index Mg(0001) surface, using density-functional theory calculations. Various possible H adsorption sites and structures on the high-index Mg(10 1 ¯ 3) are considered with H coverage up to eight monolayers. Specifically, the hydrogen adsorption sequence is found to be A 1 -fcc, A 2 -fcc, A 1 -tetra Ⅱ, A 2 -tetra Ⅱ, A 3 -fcc, B 1 -hcp, B 2 -hcp and B 1 -octa. The H Mg H trilayer with Mg1.60+ and H0.80− is found to be very stable during initial H uptake, while the H electron gain of 0.8 e (i.e., H0.80−) is shown to be a reliable indicator of H-adsorbed Mg(10 1 ¯ 3) stability. Interestingly, on the one hand, H 2 dissociation is the role step during H uptake on Mg(10 1 ¯ 3) with an H 2 dissociation energy barrier of 0.87 eV, which is consistent with the value on the low-index Mg(0001) from previous first principle calculations. On the other hand, the H diffusion barriers along the closed-packed planes are lower than those perpendicular to the planes, verifying that more feasible diffusion paths are available on the high-index Mg(10 1 ¯ 3). These theoretical findings rationalize the previous joint experimental finding that the high-index Mg(10 1 ¯ 3) dramatically decreases H sorption temperatures, and provide an H adsorption mechanism on high-index Mg surface very different from that on low-index Mg(0001), thus improving the foundation of Mg-based hydrogen storage material designs. Graphical abstract Image 1 Highlights • High-index Mg surface facilitates H sorption and diffusion. • H adsorption on high-index surface has unique sequence and higher stability. • Mg high-index surface is a very promising hydrogen storage candidate. [ABSTRACT FROM AUTHOR]

Abstract In this work, the effect of the deposition parameters of a magnetron sputtered Ti adhesive intermediate layer on the morphology and hydrogen absorption properties of thin Pd films of about 100 nm was investigated. The insertion of an adhesive layer between a Pd film and a rigid substrate usually suppresses or reduces hydrogen absorption. In this study, it is shown that by tuning the surface topography of the intermediate layer the morphology, crystallographic texture and hydrogen absorption properties of the Pd film can be controlled. The surface topography of the Ti layer was characterized using atomic force microscopy. The surface topography strongly depends on the Ti deposition conditions and can vary from widely spread large islands to densely packed small-grained islands depending on thickness (between 1 and 6 nm) and sputter pressure (0.4 and 3 Pa). TEM and XRD analysis led to the conclusion that rough Ti intermediate layers result in Pd films with an open columnar structure with small voids, and a weak and broad (111) texture. Smooth Ti intermediate layers promote the formation of Pd films with a dense columnar structure with fewer voids, and a strong and sharp (111) texture. Changes in the Pd adatom surface diffusion and shadowing effects are the main cause of the observed differences. Pd films with an open columnar morphology and weaker texture show better hydrogen absorption properties with respect to absorption capacity and kinetics of the films with dense columnar morphology. By tuning the surface topography of the Ti adhesive layer, Pd films with controlled morphology and texture can be prepared such that no delamination from the substrate occurs without compromising on absorption properties. Highlights • Engineering the surface topography of the Ti adhesive layer to control of the overlying Pd film. • Pd film with open columnar structure allows faster hydrogen absorption in comparison to the compact morphology. • The kinetics of hydrogen absorption studied using the rate equation for solid-gas reactions. • Fast absorption kinetics and mechanical stability attained for the tuned Pd films on Ti adhesive intermediate layer. [ABSTRACT FROM AUTHOR]

Abstract High Entropy Alloys (HEA), where five or more elements are mixed together in near equiatomic ratios offer promising properties as hydrogen storage materials due to their ability to crystallize in simple cubic structures in the presence of large lattice strain originating from the different sizes of the atoms. In this work, the hydrogen absorption and desorption as well as the cycling properties of the TiZrNbHfTa HEA have been studied by in situ Synchrotron X-Ray diffraction, Pressure-Composition-Isotherm, Thermal Desorption Spectroscopy and Differential Scanning Calorimetry. The alloy crystallizes in a cubic bcc phase and undergoes a two-stage hydrogen absorption reaction to a fcc dihydride phase with an intermediate tetragonal monohydride, very similar to the V-H system. The hydrogen absorption/desorption in TiZrNbHfTa is completely reversible and the activation energy of desorption could be calculated. Furthermore, we have observed an interesting macrostructure following parallel planes after the formation of the dihydride phase, which is retained after desorption. Graphical abstract Image 1 Highlights • Hydrogen absorption/desorption properties of the bcc TiZrNbHfTa high entropy alloy are reported. • TiZrNbHfTa absorbs hydrogen forming a fcc dihydride with an intermediate tetragonal monohydride. • The hydrogen absorption/desorption is completely reversible. • An interesting macrostructure following parallel planes is observed for the dihydride phase. [ABSTRACT FROM AUTHOR]

Abstract LaNi 5 -type alloys are commercial materials for the negative electrode in Ni-MH rechargeable batteries. Partial substitution of La by mischmetal (Mm) and of Ni by elements like Co, Al, and Mn significantly improve the cycle stability and high-rate discharge capacity of the electrodes. The partial substitution of Ni by Cu was studied previously for several selected ternary alloys with a special focus on crystal structure change upon substitution and gas phase hydrogen absorption. We present in this paper the results of the study of the electrochemical activation, discharge kinetics, equilibrium charge/discharge, and cycle life of electrodes made from four different LaNi 5-x Cu x (x = 0.1, 0.5, 0.9, 1) alloys in order to provide full insights into utilization of these alloys. Highlights • Increasing substitution of Ni by Cu atoms leads to an increase of the unit cell volume. • The rate of activation improves with increased Cu content in the alloys. • The discharge kinetics improves with increased Cu content in the alloys. [ABSTRACT FROM AUTHOR]

Highlights • N doped carbon-wrapped Mo x C heterophase sheets are synthesized via in situ carbonation. • N-Mo x C@C HSs effectively combine the respective advantages of both γ-MoC and β-Mo 2 C. • Heterostructures possess a synergistically-enhanced activity on the interface and surface of γ-MoC/β-Mo 2 C. • N-Mo x C@C HSs exhibit excellent activity and stability in acid media. Abstract Advancement of non-precious-metal catalysts for hydrogen evolution reactions (HER) with both prominent activity and excellent stability has been becoming an ongoing challenge in the following decades. Herein, N-doped carbon-wrapped molybdenum carbide heterophase (γ-MoC and β-Mo 2 C) sheets (N-Mo x C@C HSs) were prepared by a facile chemical vapor reduction (CVR) procedure and following calcination at desired temperatures. The best HER electrocatalytic activity of N-Mo x C@C HSs was detailedly examined in 0.5 M H 2 SO 4 , which exhibited a small overpotential of 172 mV (10 mA cm−2) with a Tafel slope of only 60 mV dec−1 and durability. The improved HER activities and catalytic stability were due to heterocrystal Mo x C, nitrogen doping, and carbon coating. Particularly, this study effectively combined the respective advantages of both γ-MoC and β-Mo 2 C via the interface effect and matched polarity of hydrogen adsorption. [ABSTRACT FROM AUTHOR]

Abstract The catalytic effect of nickel is addressed to decorate the multi-walled carbon nanotubes for the purpose of hydrogen storage. The hydrogen sorption/desorption are investigated using the volumetric technique. Nickel nanoparticles are distributed on the surface of nanotubes using the laser ablation/chemical reduction treatments. The hydrogen uptake is elevated at higher nickel population up to a certain value and then experiences a significant drop for larger nickel content. The laser treatment is accompanied by the induced pores around nanotubes. This gives rise to the creation of the larger pores at higher laser doses leading to decrease the hydrogen trapping. Despite the pore size distribution strongly alters during both synthesis methods, however the abundance of small pore size in laser treatments is relatively higher than the that of the other technique. In comparison, the laser ablation demonstrates a relatively smaller desorption temperature against chemical one, mainly owing to the formation of larger pore size/volume. Generally, the hydrogen trapping efficiently takes place in the laser treated samples against chemical reduction method. The highest value of hydrogen storage ∼1% (0.6% weight) is corresponding to 12.3% (13% weight) of nickel loading via the laser ablation (chemical reduction). Highlights • Ni NPs are dispersed on the surface of CNTs using the PLA/CR treatments. • The hydrogen uptake is elevated at higher Ni population up to a certain value. • Highest value of hydrogen storage ∼1% wt is corresponding to 12.3% wt of Ni by PLA. • Highest value of hydrogen storage ∼0.6% wt is corresponding to 13% wt of Ni via CR. [ABSTRACT FROM AUTHOR]

Abstract We present a simple method of variable temperature process that can potentially enhance the hydrogen storage properties of a large variety of solid state materials. In this approach, hydrogen gas is first introduced at about room temperature, which is followed by a gradual increase to a preset maximum temperature value, T max. Using this approach, we investigated hydrogen absorption properties of vertically aligned arrays of magnesium nanotrees and nanoblades fabricated by glancing angle deposition (GLAD) technique, and conventional Mg thin film. Weight percentage (wt%) storage values were measured by quartz crystal microbalance (QCM). After exposing Mg samples to H 2 at 30 bar and 30 °C, dynamic absorption measurements were conducted as the temperature was increased from 30 °C to maximum values of T max = 100, 200, and 300 °C all within 150 min. QCM measurements revealed that variable temperature method results in significant improvements in hydrogen storage values over the ones obtained by conventional constant temperature process. At a low effective temperature T eff = 165 °C (T max = 300 °C), we achieved storage values of 6.19, 4.76, and 2.79 wt% for Mg nanotrees, nanoblades, and thin film, respectively. Graphical abstract Image 1 Highlights • A new variable temperature process was developed to enhance hydrogen storage. • Mg nanoblades and nanotrees were fabricated by glancing angle deposition (GLAD). • Hydrogen absorption and desorption properties were investigated using QCM. • Hydrogen storage rates were enhanced when variable temperature process was used. [ABSTRACT FROM AUTHOR]

Abstract Samples with compositions of 95 wt% Mg + 5 wt% CMC (Carboxymethylcellulose, Sodium Salt) (named Mg-5CMC) and 90 wt% Mg + 10 wt% CMC (named Mg-10CMC) were prepared through milling in a hydrogen atmosphere (transformation-involving milling). After activation, Mg-5CMC had a larger amount of hydrogen absorbed in 60 min, U (60 min), than Mg-10CMC and milled Mg at 593 K. At the cycle number (CN) of four, Mg-5CMC had a very high beginning hydrogen uptake rate (1.45 wt% H/min) and a very large effective hydrogen-storage capacity of about 7.4 wt%. Mg-5CMC released 4.76 wt% H in 60 min at 648 K in hydrogen of 1.0 bar. It is believed that CMC melted during milling, and that since CMC has high viscosity, sliding between Mg particles and hardened steel balls was prevented, leading to effective milling (generation of defects and cracks and reduction of particle size). As far as we know, this study is the first in which a polymer CMC was added to Mg to improve the hydrogen uptake and release properties of Mg. Graphical abstract Image 1 Highlights • Preparation of a polymer Carboxymethylcellulose (CMC)-added Mg alloy by milling in hydrogen. • Hydrogen-storage capacity of about 7.4 wt% by activated Mg-5CMC at 593 K in hydrogen of 12 bar. • A very high initial hydrogen uptake rate of 1.45 wt% H/min at 593 K in 12 bar hydrogen after activation. • Addition of CMC is more effective than additions of halogen compounds, oxides, or metals. • First study where CMC is added by milling in hydrogen to improve hydrogen-storage properties of Mg. [ABSTRACT FROM AUTHOR]

The paper presents Monte Carlo simulation of the hydrogen absorption in palladium and palladium-silver alloy of the composition PdxAg1-x (x = 0.7-0.9) at 293-373 K temperature and 0.1 MPa pressure. Hydrogen atoms in palladium lattice locate mostly in octahedral holes in a face-centered cubic unit cell. In palladiumsilver alloy with the increased Ag content, the absorption energy distribution of hydrogen becomes wider. The interatomic Ag-H distance is shorter than Pd-H distance that means that when contacting with Ag atoms, H atoms occupy less stable tetrahedral holes. When the amount of silver in the alloy grows up to 30 аt.% H atoms are more likely to locate in tetrahedral vacancies resulting in the stability decrease of the system with hydrogen dissolved in the bulk of the material. [ABSTRACT FROM AUTHOR]

I report detections of four new H  i  21-cm absorbers associated with sources at intermediate redshifts, 0.7 < |$z$| < 1.0. The sources are part of a sample of 11 radio-loud galaxies, all at 0.7 < |$z$| < 1.0, that were searched for associated H  i  21-cm absorption using uGMRT. Previously, just four such absorbers were known in the literature at these redshifts; the current observations have increased the total to eight. The results indicate that the detection fraction at intermediate redshifts could be as high as that at lower redshifts, |${\approx } 30{{\ \rm per\ cent}}$|⁠, on contrary to a much lower detection fraction observed in samples at |$z$| > 1. Three detections show strong blueshifted features, indicating cold gas outflows. These three sources also tentatively show excess [O  ii ] line luminosity compared to a bulk of the remaining sample, possibly suggesting that the hosts of these active galactic nuclei harbour different environments, either due to interaction with the radio jets or due to excess star formation in the host galaxy. Further, a cold H  i mass outflow rate of ≈78 M⊙ yr−1, assuming |$\rm {\mathit{ T}_{s} = 1000}$|  K, is estimated for the detection towards SDSS J014652.79−015721.2, at |$z$| = 0.959 04, which is the highest till date in comparison to similar estimates available in the literature. [ABSTRACT FROM AUTHOR]

The present research was aimed at determining the effects of the oxide layers on hydrogen absorption, microstructure and mechanical properties of the Zircaloy-2 and Zr 702 alloys. The oxidation was made at 350 °C, 700 °C and 900 °C for 10 to 30 min in laboratory air, followed by hydrogen cathodic charging for 72 h and annealing at 400 °C for 4 h. The slow strain rate tests were carried out on oxidized, charged and annealed specimens. The oxidation resulted in thick and cracked, more for Zr 702 alloy, layer. After oxidation at 350 °C, the appearance of hydrides in Zircaloy-2 and absence of hydrides in Zr 702 alloy were observed. After oxidation at high temperatures no current flow was noticed at applied voltage up to 5 V, and no hydrogen or hydrogen cracks. The observed effects were attributed to the phase structure of investigated alloys at low hydrogen content. [ABSTRACT FROM AUTHOR]

Abstract Magnesium surface dope with vanadium has been considered as one of the best material for the hydrogen storage application. Optimization of vanadium concentration doping is important to retain the hydrogen storage capacity above 6 wt %. Vanadocene, bis(η5-cyclopentadienyl) vanadium, with the formula V(C 5 H 5) 2 , commonly abbreviated as Cp 2 V is considered as the best precursor for the vanadium to dope the optimized concentration of vanadium over the Mg surface. The vanadium doping over the magnesium has been studied by X-ray photoelectron spectroscopy (XPS) in details. The vanadium doped Mg has been found to be hydrogenated even at 0 °C under nominal hydrogen pressure (above plateau pressure). Besides, the dehydrogenation temperature was also found to be below 200 °C which is remarkable less as compared to pure magnesium, and comparable to the best catalysts for Mg-MgH 2 system reported till date. Graphical abstract Image 1 Highlights • Doping of V over Mg is possible by bis(cyclopentadienyl)vanadium II. • The hydrogen sorption kinetics improves. • The apparent activation energy decreases. • The thermodynamics of sorption reaction has not changed. [ABSTRACT FROM AUTHOR]

Abstract The hydrogen adsorption capacity of dual-Ti-doped (7, 7) single-walled carbon nanotube (Ti-SWCNTs) has been studied by the first principles calculations. Ti atoms show different characters at different locations due to local doping environment and patterns. The dual-Ti-doped SWCNTs can stably adsorb up to six H 2 molecules through Kubas interaction at the Ti 2 active center. The intrinsic curvature and the different doping pattern of Ti-SWCNTs induce charge discrepancy between these two Ti atoms, and result in different hydrogen adsorption capacity. Particularly, eight H 2 molecules can be adsorbed on both sides of the dual-Ti decorated SWCNT with ideal adsorption energy of 0.198 eV/H 2 , and the physisorption H 2 on the inside Ti atom has desirable adsorption energy of 0.107 eV/H 2 , ideal for efficient reversible storage of hydrogen. The synergistic effect of Ti atoms with different doping patterns enhances the hydrogen adsorption capacity 4.5H 2 s/Ti of the Ti-doped SWCNT (VIII), and this awaits experimental trial. Graphical abstract Image 1 Highlights • H 2 adsorption capacity of typical dual-Ti-doped SWCNTs was studied using DFT methods. • Ti-SWCNTs have ideal adsorption energy for efficient reversible H 2 storage. • Synergistic effect of different doping Ti atoms makes the H 2 adsorption to 4.5H 2 s/Ti. • Ti atom with different doping pattern has different H 2 adsorption capacity. • Ti 2 insertion makes Ti-SWCNT adsorbing eight H 2 s from the tube's inside and outside. [ABSTRACT FROM AUTHOR]

Abstract H 2 dissociation barriers on Ag (111), Ag monolayer on WC (0001) (Ag ML /WC), Ag monolayer doped by Pt atom on WC (0001) (Ag ML Pt-d/WC) surface are decreasing from 1.07 to 0.03 eV. The ab initio atomistic thermodynamic data shows that at typical planar SOFC operating temperatures of 923–1073 K, under 100000-ppm pH 2 S/pH 2 , Ag ML Pt-d/WC can be sulfur free clean surface. Therefore, compared with traditional Nickel/Yttria-stabilized zirconia (Ni/YSZ) Solid Oxide Fuel Cells (SOFCs) anode, Ag ML Pt-d/WC shows high activity towards H 2 dissociation and high tolerance of sulfur poisoning. Graphical abstract Ag ML Pt-d/WC shows high activity towards H 2 dissociation and high tolerance of sulfur poisoning. Image 1 Highlights • A strategy to design an ideal sulfur tolerant anode material is proposed. • H 2 dissociation and sulfur adsorption on fours surfaces are presented. • Ag ML Pt-d/WC shows high activity towards H 2 dissociation. • Ag ML Pt-d/WC shows high tolerance towards sulfur poisoning. [ABSTRACT FROM AUTHOR]

Abstract Using Aspen Plus simulations, exergy analyses of hydrogen-rich syngas production via biomass staged-gasification are carried out for three configurations, namely, staged-gasification with pyrolysis gas combustion and char gasification (C-1), staged-gasification with pyrolysis gas reforming and char gasification (C-2), and staged-gasification with pyrolysis gas reforming and char combustion (C-3). The results show that, for the gasification and reforming processes, the exergy loss of pyrolysis gas with tar reforming is less than that of char gasification. As for the system, it is conducive to generating hydrogen by making full use of the hydrogen element (H) in biomass instead of the H in water. The benefits of C-1 are that it removes tar and produces higher yield and concentration of hydrogen. However, C-2 is capable of obtaining higher exergy efficiency and lower exergy loss per mole of H 2 production. C-3 theoretically has greater process performances, but it has disadvantages in tar conversion in practical applications. The appropriate gasification temperature (T G) are in the range of 700–750 °C and the appropriate mass ratio of steam to biomass (S/B) are in the range of 0.6–0.8 for C-1 and C-3; the corresponding parameters for C-2 are in the ranges of 650–700 °C and 0.7–0.8, respectively. Highlights • Biomass staged-gasification processes for H 2 -rich syngas are proposed and simulated. • Thermodynamic performances of three systems are optimized by exergy analyses. • Exergy losses of pyrolysis gas reforming are less than that of char gasification. • Producing hydrogen by making full use of H element in biomass has higher efficiency. [ABSTRACT FROM AUTHOR]

Abstract The structures and hydrogen adsorption properties of {Cr 3 F(H 2 O) 2 O[(O 2 C)-C 6 H 4 -(CO 2)] 3 ・nH 2 O(n∼25)} (MIL-101) and its Pd composites have been investigated by X-ray diffraction (XRD) analysis, transmission electron microscope (TEM), X-ray photoelectron spectroscopy (XPS), and specific surface area tests (BET). The as-prepared Pd/MIL-101 composites were microporous and maintained three-dimensional topology of MIL-101 before and after Pd loading that existed in the skeleton. A carbon bridge was formed between Pd metal and MIL-101 to improve the hydrogen storage. The loaded Pd reduced the hydrogen absorption enthalpy of MIL-101, and thus improved the storage of hydrogen compared with MIL-101. The diffusion coefficient reached 7.233 × 10−9 in the Pd/MIL-101 nanocomposites. Highlights • The Pd/MIL-101 composite adsorbents were prepared. • The load of Pd reduced the enthalpy of hydride generation. • The load of Pd increased the diffusion coefficient and improved the hydrogen storage performance. [ABSTRACT FROM AUTHOR]

Highlights • DFT calculations show the stability of Ti and Rh dimers on N-doped graphene. • Ti interacts stronger with N-doped graphene than Rh. • Physical and Kubas molecular states and dissociated states were detected. • Metal d orbital hybridization with N 2p z and N lone pair electrons in sp2 orbital is observed. • Spontaneously dissociation of H 2 on supported Ti and Rh dimers were found. Abstract A theoretical study using density functional theory was employed to analyze the hydrogen adsorption on Rh 2 and Ti 2 dimers decorating pyridine and pyrrolic-like nitrogen doped graphene. First, an analysis of geometry, stability, projected density of states, overlap population and charge distribution was performed to understand the interaction between Rh and Ti metal adatoms and dimers with pyridinic and pyrrolic graphene. Charge transfer occurs from metal to substrate in all cases. An investigation of H 2 adsorption on Rh and Ti metals dimers on pyridinic and pyrrolic N-doped graphene was also performed. Molecular adsorption states were observed for Ti on pyridinic graphene and for Rh on both substrates. H 2 dissociative adsorption occurs on both metal supported dimers. H 2 s states hybridize with the Rh and Ti d band, forming localized and dispersed states in concordance with the mechanisms observed for H 2 adsorption. The activation energies were calculated obtaining values smaller than 0.59 eV, indicating that the dissociation of H 2 can occur spontaneously at room temperature. HSE06 hybrid functional was used to test the accuracy of PBE-D2 functional in the activation energy calculation. Adsorption in the molecular states occurs with no barriers. [ABSTRACT FROM AUTHOR]

Abstract Nowadays, catalytic doping has been regarded as one of the most promising and effective methods to improve the sluggish kinetics of magnesium hydride (MgH 2). Herein, we synthesized Ni/TiO 2 nanocomposite with the particle sizes about 20 nm by an extremely facile solvothermal method. Then, the Ni/TiO 2 nanocomposite was doped into MgH 2 to enhance its reversible hydrogen storage properties. A remarkably enhancement of de/rehydrogenation kinetics of MgH 2 can be achieved by doped with Ni/TiO 2 nanocomposite, compared to that solely doped with Ni or TiO 2 nanoparticles. The hydrogen desorption peak temperature of MgH 2 Ni/TiO 2 is 232 °C, which is 135.4 °C lower than that of ball-milled MgH 2 (367.4 °C). Moreover, the MgH 2 Ni/TiO 2 can desorb 6.5 wt% H 2 within 7 min at 265 °C and absorb ∼5 wt% H 2 within 10 min at 100 °C. In particular, the apparent activation energy of MgH 2 Ni/TiO 2 is obviously decreased from 160.5 kJ/mol (ball-milled MgH 2) to 43.7 ± 1.5 kJ/mol. Based on the analyses of microstructure evolution, it is proved that metallic Ni particles can react with Mg easily to form fine Mg 2 Ni particles after dehydrogenation, and the in-situ formed Mg 2 Ni will transform into Mg 2 NiH 4 in the subsequent rehydrogenation process. The significantly improved hydrogen absorption/desorption properties of MgH 2 Ni/TiO 2 can be ascribed to the synergistic catalytic effect of reversible transformation of Mg 2 Ni/Mg 2 NiH 4 which act as "hydrogen pump", and the multiple valence titanium compounds (Ti4+/3+/2+) which promote the electrons transfer of MgH 2 /Mg. Highlights • Ni/TiO 2 with particle sizes ∼20 nm was synthesized and doped into MgH 2. • MgH 2 Ni/TiO 2 starts to release hydrogen at 190 °C with ∼6.5 wt% H 2. • Enhanced hydrogen storage properties are due to synergistic catalytic mechanism. [ABSTRACT FROM AUTHOR]

Abstract Modification of compounds like LaNi 5 toward ternary compositions change alloy hydrogen storage properties and influence resistance to hydrogen contamination. Below thermodynamic properties of ternary alloys LaNi 4.75 M 0.25 are investigated with ab initio methods and synthesized in order to select the composition with hydrogen sorption properties not worse than LaNi 5. The specific volume change, surface segregation energy and change of the hydride formation enthalpy are calculated for 34 elements (M: Ag, Al, Au, B, Bi, Ca, Cd, Cu, Cr, Fe, Ga, Ge, In, Ir, K, Mg, Mn, Mo, Nb, Pb, Pd, Pt, Rh, Ru, Sb, Sn, Ti, V, W, Y, Zn, Zr) substituting Ni. Five ternary compounds are synthesized and analyzed with respect to crystal structure and hydrogen sorption properties. Compounds like LaNi 4.75 Ag 0.25. and LaNi 4.75 Pb 0.25 show favorable stability and H 2 sorption thermodynamics. The substituting elements segregating toward the surface are expected to be catalytically active for hydrogen contamination gasses. Graphical abstract Image 1 Highlights • Theoretical prediction of thermodynamic properties of 34 ternary LaNi 5-x M x alloys for hydrogen storage. • Pressure-concentration isotherms for new nominal LaNi 4.75 Ag 0.25 H x , LaNi 4.75 Pb 0.25 H x hydrides. • Surface segregation in ternary LaNi 5-x M x alloys. • Correlation of the volume expansion in ternary LaNi 5-x M x alloys with the atomic radii of Ni substituting elements. • The site preference for Ni substitution in LaNi 5. [ABSTRACT FROM AUTHOR]

Abstract Covalent organic frameworks (COFs), a class of carbon-based polymeric materials have the potential to be used as hydrogen adsorbent. Three dimensional (3D) COFs, due to their low density and high surface area, although have higher hydrogen adsorption, they have less stability than two dimensional (2D) COFs. Here we studied porphyrin group containing 2D COF, namely H 2 ,P-COF for hydrogen storage using density functional theory (DFT) and grand canonical Monte Carlo (GCMC) simulations and the results were compared with the most common 2D COFs, COF-1 and COF-5. Cylindrical shaped 2D COFs where isolated unit blocks are stacked in multiple layers due to van der Waals interactions between individual layers, increase the effective surface area for hydrogen storage. A further modification has been done by bridging the inter-layer gap by pyridine molecules. Insertion of pyridine increases the separation distance of layers of 2D COFs as well as the free volume. Feasibility of the structure formation and stability of all the structures were checked using DFT study. To ensure the structural stability of bridged COFs after hydrogen loading, alternating layers of COF were bridged. Single, bi, tri and tetra -pyridine molecules were chemically bonded with the existing carbon ring present in between two C 2 O 2 B rings to form pyridine bridged H 2 ,P-COFs. Our GCMC results show a significant increase in storage capacity which is mainly due to an increase in the free volume of the material. The highest capacity of ∼ 5.1 wt% and 20 g H 2 /L at 298 K and 100 bar, above the gravimetric DOE goal, has been found at room temperature for tetra-pyridine doped porphyrin COF structure. Highlights • Multiple layers of 2D COFs are stacked to form a tubular shaped COF. • The layers of porphyrin COFs are bridged by pyridine molecules. • Pyridine bridged porphyrin COFs are able to cross the gravimetric DOE target at room temperature. • The storage mainly increases due to the high free volume of the materials. • The modified structures do not hinder the structural stability and the heat of adsorption. [ABSTRACT FROM AUTHOR]

Abstract Hydrogen sorption and storage in a solid matrix can greatly improve its safety and efficiency when compared to the compressed gas or liquid hydrogen storage system, and kinetics mechanisms are of interest towards the development of such materials. In this study, the composites of Mg-Ni-Cu doped with singe-walled carbon nanotubes (Mg-Ni-Cu/CNTs) were synthetized. The activation performance, isothermal hydrogen sorption and desorption were systematically tested, and the experimental data were analyzed using the shrinking core model. The results show that three cycles of hydrogen sorption and desorption may be enough to fully activate Mg-Ni-Cu/CNTs and the stability can be kept for 150 cycles. A 10.1 wt% of Cu and 50.3 wt% of Ni in Mg-Ni-Cu/CNTs facilitates the hydrogen sorption and a reversible hydrogen capacity of ∼3.35 wt% can be achieved at 310 °C and 3.0 atm, and hydrogen capacity and kinetics shows significant decline during contact with 1.0 vol% CO impurity. Considering desorption at 600 °C, the kinetic profiles are about linear and desorption is completed within minutes. The gas-solid reaction processes for hydrogen sorption undergo three different rate-limiting stages, and hydrogen desorption can only be divided into two stages of surface chemical reaction and product layer diffusion. Highlights • MgNiCu/CNTs are active in H 2 sorption at 310 °C and 3.0H 2 pressure. • Cu, Ni and CNTs can facilitate H 2 sorption of Mg and increase stability. • H 2 sorption and kinetics are deteriorated during contact with CO impurity. • Kinetics mechanisms and rate-limiting steps were determined by SCM. [ABSTRACT FROM AUTHOR]

Abstract Transition-metal nanoparticles (NPs) can catalytically improve the hydrogen desorption/absorption kinetics of MgH 2 , yet this catalysis could be enhanced further by supporting NPs on carbon-based matrix materials. In this work, Co NPs with a uniform size of 10 nm loaded on carbon nanotubes (Co@CNTs) were synthesized in situ by carbonizing zeolitic imidazolate framework-67 (ZIF-67). The novel Co@CNTs nanocatalyst was subsequently doped into MgH 2 to remarkably improve its hydrogen storage properties. The MgH 2 -Co@CNTs starts to obviously release hydrogen at 267.8 °C, displaying complete release of hydrogen at the capacity of 6.89 wt% at 300 °C within 15 min. For absorption, the MgH 2 -Co@CNTs uptakes 6.15 wt% H 2 at 250 °C within 2 min. Moreover, both improved hydrogen capacity and enhanced reaction kinetics of MgH 2 -Co@CNTs can be well preserved during the 10 cycles, which confirms the excellent cycling hydrogen storage performances. Based on XRD, TEM and EDS results, the catalytic mechanism of MgH 2 -Co@CNTs can be ascribed to the synergetic effects of reversible phase transformation of Mg 2 Co to Mg 2 CoH 5 , and physical transformation of CNTs to carbon pieces. It is demonstrated that phase transformation of Mg 2 Co/Mg 2 CoH 5 can act as "hydrogen gateway" to catalytically accelerate the de/rehydrogenation kinetics of MgH 2. Meanwhile, the carbon pieces coated on the surfaces of MgH 2 particles not only offer diffusion channels for hydrogen atoms but also prevent aggregation of MgH 2 NPs, resulting in the fast reaction rate and excellent cycling hydrogen storage properties of MgH 2 -Co@CNTs system. Graphical abstract Image 1 Highlights • Co@CNTs nanoparticles were in situ synthesized by carbonizing ZIF-67. • MgH 2 Co@CNTs uptakes/releases 6.15 wt% H 2 at 250 °C (2 min)/280 °C (30 min). • Catalytic mechanism is ascribed to the synergetic effects of Mg 2 Co/Mg 2 CoH 5 transformation and carbon pieces. [ABSTRACT FROM AUTHOR]

Abstract An austenitic stainless steel (SUS316L) was prepared with and without addition of solute nitrogen. The effect of cold-working and nitrogen addition on hydrogen solubility and hydrogen diffusion were investigated. High-pressure hydrogen gas and thermal desorption techniques were used. Increasing dislocation densities were related to a higher hydrogen content and higher nitrogen content related to a lower hydrogen content. Both dislocations and nitrogen had a negligible effect on hydrogen diffusion. The different hydrogen contents in the dislocations and the metal lattice, as well as trapping and diffusion activation energies explained the lack of effect of dislocations on hydrogen solubility. Highlights • Nitrogen addition reduces the hydrogen solubility. • Increasing the dislocation density increases the hydrogen solubility. • Nitrogen addition hinders the increase of hydrogen solubility caused by increase in dislocation density. • Neither nitrogen addition nor increases in dislocation density affect the hydrogen diffusivity. [ABSTRACT FROM AUTHOR]

Abstract This paper presents a zero-dimensional (0D) model of hydride tank. The model aims to study the dynamic heat and mass transfers during desorption process in order to investigate the thermal-fluidic behaviors of this hydride tank. This proposed model has been validated experimentally thanks to a tailor-made developed test bench. This test bench allows the hydride characterization at tank scale and also the energetic characterization. The simulation results of the heat exchanges and mass transfer in and between the coupled reaction bed, show good agreement with the experimental ones. It is shown that the heat produced by a Proton Exchange Membrane Fuel Cell (PEMFC) (estimated starting from an electrical model) is enough to heat the metal alloy (FeTi) and therefore release the hydrogen with a sufficient mass flow rate to supply the PEMFC. Furthermore, the obtained results highlight the importance of the developed model for energy management of the coupling of fuel cell and hydride tank system. Highlights • A hydrogen storage. • Energetic modeling of the hydride tank. • Presentation of the two characterization process PCT and energetic during hydrogen desorption. • Experimental validation. [ABSTRACT FROM AUTHOR]

Abstract The effect of H 2 O pressure (P H2O) on CH 4 formation turnover rate (TOF CH4) was evaluated as a function of Rh cluster size. In-situ DRIFTS and kinetic measurements were used to study the CO hydrogenation at methanation conditions on two Rh/Al 2 O 3 catalysts with different cluster sizes (Rh-1nm and Rh-3nm). It was observed a significant effect of P H2O on TOF CH4 over Rh-1nm catalysts, while the rate on Rh-3nm resulted insensible to the H 2 O pressure. The mean Rh cluster sizes were estimated by H 2 chemisorption, TEM and XPS analyses. It is confirmed the structural sensitivity of the CO methanation reaction on supported Rh catalysts as the TOF CH4 resulted significantly higher in the larger clusters. Nonetheless, lower apparent activation energy was measured in smaller Rh clusters, which is successfully explained by the energies involved into the parameter of the proposed L-H kinetic model. CO adsorption isotherms were obtained from in-situ DRIFTS experiments at 280–340 °C. The enthalpy and entropy values for CO adsorption indicate that the CO binds more strongly on the low-coordinated surface of Rh atoms. In-situ DRIFTS results demonstrate that the CO coverage is unaffected by P H2 and P H2O , regardless of Rh dispersion, thus excluding H* and H 2 O* as most abundant surface intermediates of the Kinetics. The infrared and kinetic measurements on both catalysts are consistent with a mechanism of CO bond dissociation assisted by H*. Data are well represented by a single-site-L-H model that successfully captures the effect of P H2 , P CO and P H2O on TOF CH4. This model contains a parameter (k') that represents the ratio between the rates of C* removal by O* and H* at Rh surface and explains the stronger kinetic effect of P H2O on TOF CH4 observed over smaller Rh clusters. Graphical abstract Image 1 Highlights • TOF CH4 decreases with P H2O on Rh-1nm but it is insensible to P H2O on Rh-3nm. • CO coverage is unaffected by P H2 and P H2O , regardless of Rh dispersion. • A L-H model successfully captures the effect of P H2 , P CO and P H2O on TOF CH4. • Ratio between rates of C* removal by H* and O* is higher on smaller Rh clusters. [ABSTRACT FROM AUTHOR]

Abstract In this work, the hydrogen sorption properties of AZ31 magnesium alloys with various additions of nickel (Ni) (i.e., Ni (X = 0, 2, 4) wt.%) were investigated. Cast ingots with different AZ31/Ni P compositions were fabricated using a gravitating mechanical stir casting (GMSC) method. Two different processes, namely, equal channel angular pressing (ECAP) and high energy ball milling (HEBM) were performed to improve its hydrogen storage properties. The particle size of the sample powders were measured by laser diffraction analysis. The microstructures, powder morphologies, and phase transformation were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and x-ray diffraction (XRD) analysis. The hydrogen sorption kinetics were measured by a Sievert's type apparatus. The results showing the impact of the ECAP and HEBM processes on the hydrogen storage properties were compared. The AZ31-4 Ni ECAP processed sample showed a maximum hydrogen storage capacity of 7.0 wt.% at 2322 s with complete desorption of all the hydrogen in less than 5 min at a temperature of 375 °C. On the other hand, the pure AZ31 alloy which was treated with the HEBM process showed the maximum hydrogen capacity of 6.5 wt.% at 2393 s with desorption of all the hydrogen within 6 min. In addition, the activation energy, as illustrated by the Kissinger plot, revealed that the activation energy of the ECAP processed AZ31-4 Ni was 104.73 (KJ/mol), obviously lower than the material processed by HEBM and pure MgH 2. Graphical abstract Image 1 Highlights • Alloy composition fabricated by GMSC method. • AZ31-4Ni-ECAP reaches the H 2 storing capacity of 7.0 wt.%. • AZ31-4Ni-ECAP alloy exhibits activation Energy of (104.73 kJ/mol). • ECAP shows better results than HEBM. [ABSTRACT FROM AUTHOR]

Abstract In this study, Mg+5at%V+5at%Ni alloys are prepared by wet mechanical alloying (MA) in an organic solvent under a purified argon atmosphere. The hydrogen absorption capacities of the samples are evaluated at 473 K at an initial hydrogen pressure of 0.2 MPa in a Sieverts apparatus. First, to obtain the ideal hydrogen absorption and desorption characteristics, organic solvents for milling are changed. Among the alloy samples milled with different organic solvents, the maximum hydrogen absorption capacity is obtained for the alloy prepared with benzene. After determining the organic solvent, the milling time was varied from 3 to 8 h. The maximum hydrogen absorption capacity of 5.15 mass% can be achieved in 7 h-milling. Furthermore, the apparent hydrogen diffusion coefficients are obtained by fitting the temporal change of the hydrogen absorption capacity with a theoretical curve. The theoretical curves are calculated, assuming that the particle shape is a sphere and the size of the sample is 40 μm. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Intensification of hydrogen adsorption capacity, stability, and production yield for Cu-BDC@rGO composite. • Fast and continuous synthesis of Cu-BDC@rGO composite materials by MW-assisted microfluidic heating for the first time. • Investigating the effect of Cu-BDC@GO shape (worm-like and sandwich-like) or synthesis root on hydrogen adsorption. • Reducing reaction time and reactor size upto few seconds and micrometers for synthesis of MOF-Carbon hybrid materials. • Using RSM experimental design to evaluate the effective parameters. Abstract In this study, pure Cu-BDC and composite Cu-BDC@rGO were produced by combining microwave irradiation and microfluidics (MW-assisted microfluidic) to intensify the hydrogen adsorption. To compare two heating methods, pure Cu-BDC was synthesized by both MW-assisted microfluidic and conventional heating methods. Results showed that the production yield and hydrogen adsorption capacity of Cu-BDC was 18% and 26% greater for MW-assisted microfluidic heating, respectively. In addition to the results, this method brings some advantageous such as lower reaction time, lower reactor size, more uniform crystal shape, and lower crystal size compared to conventional heating. So, the MW-assisted microfluidic method was selected for further investigations. Response surface method (RSM) applied to find the optimum synthesis condition of the material for hydrogen uptake. In this regard, GO content, metal/linker molar ratio, and microwave (MW) time selected as independent, and the hydrogen adsorption at 77 K and 40 bar selected as the dependent response. Also, experiments showed that the one pot synthesis of Cu-BDC@rGO (sandwich-like adsorbent) has the best hydrogen uptake compared to pure Cu-BDC (cubic adsorbent) and the other sample (worm-like adsorbent) which is confirmed the effect of modulating synthesis route. Finally, it must be said that the incorporation of GO and MW-assisted microfluidic heating improved the specific surface area, pore volume, throughput, and thermal stability of the adsorbent. [ABSTRACT FROM AUTHOR]

Abstract Adsorption of impurity atoms or molecules on the surface of photocatalysts may improve or worsen the photocatalytic activity due to chemical bond relaxations. Herein, we demonstrate the influence of molecular adsorbates such as H 2 , F 2 , Cl 2 , Br 2 , and I 2 on the electronic properties and photocatalytic activity of the nitrogenated holey graphene (C 2 N) using hybrid density functional calculations including van der Waals interaction. Hydrogen and halogen molecules prefer to physisorb on the holey site except F 2 which has substantial chemisorption. The halogens tend to draw electrons from C 2 N monolayer due to their high electronegativity and thereby introduce new band states which significantly alters the opto-electronic and photocatalytic properties. Although F 2 and Br 2 adsorbed C 2 N have favorable band edge positions, I 2 adsorbed C 2 N is more promising for hydrogen production because of its appropriate band edge positions relative to the water redox potentials. Optical absorption spectra reveals that all these systems are visible light active and therefore they could harvest more incoming light. We have demonstrated here for the first time that intermediate bandgap states can be introduced in C 2 N system by adsorbing halogen molecules and our theoretical findings suggest that I 2 adsorbed C 2 N monolayer is a promising candidate for photocatalytic water splitting. Graphical abstract Image 1 [ABSTRACT FROM AUTHOR]

Highlights • Hydrogen permeation in a PdAg alloy is traced in situ by UHV and ambient XPS. • Spectral variations of the surface Ag atom are observed at the adsorption process. • Pd atoms were found to be reactive sites during hydrogen absorption. • The Pd segregation likely promotes the hydrogen permeation. Abstract The hydrogen permeation process is crucial for hydrogen purification through a metal alloy. At the initial stage, it is connected with the dissociation and adsorption of hydrogen on the surface; subsequently, the process involves hydrogen absorption in the bulk. On the PdAg 23 alloy, we investigated the mechanisms of adsorption and absorption by in-situ ultrahigh vacuum and ambient pressure X-ray photoelectron spectroscopy (AP-XPS) measurements, respectively. During the adsorption under a H 2 pressure of 5 × 10−8 Torr at 300–620 K, the surface Ag atoms act as adsorption sites for the hydrogen atoms. The AP-XPS results show that hydrogen absorption is significantly enhanced above 473 K under H 2 exposure at 1.5 Torr, which is likely correlated to the α - β hydride phase transition occurring around 473 K. Hydrogen preferentially bonds with the Pd atoms rather than the Ag atoms in the case of hydrogen absorption into the PdAg 23 alloy. The atomic fractions of Pd on the surface were enhanced after hydrogen absorption, and hydrogen adsorption at a hydrogen pressure of 5 × 10−8 Torr at 620 K. This surface segregation of Pd atoms provides more reactive sites for hydrogen absorption, which may promote the hydrogen permeability of a PdAg 23 alloy. [ABSTRACT FROM AUTHOR]