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Magnesium hydride solids doped with transition metals have received attention recently as prospective hydrogen storage materials for a green energy source and a hydrogen economy. In this study, MgTiHn (n = 1–20) clusters were investigated for the first time by employing the B3PW91 hybrid density functional theory computational chemistry technique with all electron basis sets to determine precise cluster structures and the maximum hydrogen capacity for this model system. We find that hydrogen atoms bind to the metal cluster core until a MgTiH14 saturation limit is reached, with hydrogen dissociation from this system occurring for MgTiH15 and larger cluster sizes. This MgTiH14 cluster contains a large 16.4% hydrogen by mass. This saturation size limit and hydrogen mass percent is larger than the analogous MgScHn system previously reported. The clusters relative stabilities and electronic properties are discussed along with a possible novel hydrogen dissociation pathway. MgTiH10 and MgTiH13 clusters are predicted to be especially stable species in this size range. [ABSTRACT FROM AUTHOR]

Hydrogen is a major nonmetallic impurity in the coolant of sodium-cooled fast reactors (SFRs) during normal operation. A higher hydrogen concentration than the gas–liquid equilibrium has been transiently detected in the gas space of actual SFR plants. The presence of several sodium compounds can increase hydrogen generation; however, a thorough understanding of the thermal behavior of candidate reactions is lacking. Herein, thermal analysis reveals the hydrogen release behavior of sodium hydride. Mass spectrometry indicates hydrogen generation with decreasing sample mass, indicating thermal decomposition. Detailed kinetic analysis based on master plot methods indicates that the hydrogen release reaction occurred through a mechanism involving random nucleation and growth of nuclei. Furthermore, the reaction rate was newly formulated based on a kinetic model function representing the above mechanism and the Arrhenius-type reaction rate constant comprising an activation energy of 119.0 ± 0.8 kJ mol−1 and a frequency factor of 1.8 × 107 s−1. These findings will enable the numerical simulation of the hydrogen release behavior in SFRs. [Display omitted] • Thermal analysis revealed the thermal behavior of sodium hydride as a hydrogen release source in sodium-cooled fast reactors. • Detailed kinetic analysis based on master plots showed the reaction rate and mechanism of the thermal decomposition. • A new formula was created for the reaction rate using an Arrhenius-type reaction rate constant and a kinetic model function. • Comparison of theoretical and experimental master plots confirmed a nucleation–growth-type reaction mechanism. [ABSTRACT FROM AUTHOR]

Complex hydrides, such as sodium borohydride (NaBH4), are attractive materials for hydrogen storage because of their high hydrogen capacity. However, practical application of these materials is limited because of their unfavorable hydrogen thermodynamics and poor kinetics. Herein, it is demonstrated that the inclusion of BF4− in NaBH4 results in remarkable Na+ conductivity of 1.5 × 10−3 S cm−1, which is 10 000 times higher compared to pure NaBH4 (7.0 × 10−8 S cm−1) at 115 °C. The ionic conductivity is also comparable to values reported for some of the best borohydride‐based conductors reported to date. More remarkably, this improvement of ionic conductivity is found to be correlated to lower hydrogen release temperatures for BF4−‐modified NaBH4 releasing hydrogen at a temperature of 200 °C instead of 510 °C in the case of pristine NaBH4. Nudged elastic band calculations based on density functional theory reveal that partial substitution of the [BH4]− groups in NaBH4 by BF4− may lead to the formation of distortions within the NaBH4 crystal lattice with favorable channels for Na+ mobility enabling the release of hydrogen at low temperatures. [ABSTRACT FROM AUTHOR]

The potential for decorating single Li, Na, or K atoms onto BeS monolayers and their subsequent hydrogen storage performance were investigated using first-principle density functional theory (DFT) calculations. The single-atom Li, Na, or K exhibited strong adhesion to the BeS monolayer, with binding energies of −2.662 eV, −1.982 eV, or −1.669 eV, respectively. Each Li or Na atom on BeS demonstrated the ability to capture four H 2 molecules, while a single K atom could bind only three H 2 molecules. Notably, Li exhibited stronger binding with stored H 2 compared to Na or K. Moreover, by increasing the number of Li atoms on each side of the BeS monolayer to nine, the storage of H 2 molecules was improved to a total of 54, concomitant with an advantageous average adsorption energy of −0.236 eV. This enhancement resulted in a significant increase in the hydrogen storage capacity to 6.514 wt%. Molecular dynamics simulations indicated a desorption temperature of approximately 450 K, with the 18 Li atoms remaining strongly bonded to the BeS due to their high diffusion energy of 0.578 eV. Thus, the Li-decorated BeS monolayer emerges as a promising substrate for achieving exceptional and reversible hydrogen storage performance. • Alkali-metal atom (Li, Na, or K) could be well dispersed on the BeS monolayer. • Li atom shows a stronger adsorption strength to H 2 molecules than Na or K. • 18 Li atoms on BeS can capture 54H 2 with an ideal E adsav of −0.236 eV. • Li atoms remain dispersed on BeS even at desorption temperature of the 54H 2. • Li-decorated BeS demonstrates a high hydrogen storage capacity of 6.514 wt%. [ABSTRACT FROM AUTHOR]

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The objective was to evaluate the impact of repeated exposure to hyperbaric hydrogen (90 MPa; 30 °C) and pressure release on the microstructure and mechanical behavior of PA11. Samples were analyzed after 1, 2, 5 and 10 cycles, by SAXS, WAXS, DMA, DSC, and a series of mechanical tests with variable triaxiality ratio. The most visible change in the residual state after desorption was a stiffening of the amorphous phase. It mainly originated from the first cycle, especially the first pressurization. The crystalline phase was slightly affected and no evidence of nano-voiding was brought in the residual state up to 10 cycles. Similar analyses were conducted during the first cycle's desorption transient. They showed a reversible plasticizing effect and a trend of nano-voiding vanishing after desorption but might promote damage upon further triaxial loading.

Complex hydrides, such as sodium borohydride (NaBH4), are attractive materials for hydrogen storage because of their high hydrogen capacity. However, practical application of these materials is limited because of their unfavorable hydrogen thermodynamics and poor kinetics. Herein, it is demonstrated that the inclusion of BF4− in NaBH4 results in remarkable Na+ conductivity of 1.5 × 10−3 S cm−1, which is 10 000 times higher compared to pure NaBH4 (7.0 × 10−8 S cm−1) at 115 °C. The ionic conductivity is also comparable to values reported for some of the best borohydride‐based conductors reported to date. More remarkably, this improvement of ionic conductivity is found to be correlated to lower hydrogen release temperatures for BF4−‐modified NaBH4 releasing hydrogen at a temperature of 200 °C instead of 510 °C in the case of pristine NaBH4. Nudged elastic band calculations based on density functional theory reveal that partial substitution of the [BH4]− groups in NaBH4 by BF4− may lead to the formation of distortions within the NaBH4 crystal lattice with favorable channels for Na+ mobility enabling the release of hydrogen at low temperatures.

Hydrogen diffusivity can play a crucial role in hydrogen-assisted degradation of steels. Herein, we investigate the hydrogen diffusion behavior in two X65 pipeline steels using desorption and permeation techniques. Gas charged samples were used for desorption experiments, while permeation tests were conducted using electrochemical charging. The Vintage steel, having a banded ferrite-pearlite microstructure, exhibits a significant influence of strong traps. A modified solution of Fick's 2nd law is proposed to account for the strong traps. At room temperature, the effective diffusivity in the Modern steel, which has homogenous ferrite-bainite microstructure, has a scatter factor of three, whereas for the Vintage steel, the factor is 17. The difference is explained by considering a concentration-dependent effective diffusivity and a tortuous diffusion path. Comparable values of the highest measured effective diffusivity at room temperature were obtained for the Modern and Vintage steels: 2.70 × 10−6 and 3.34 × 10−6 cm2/s, respectively. • Effect of microstructure, technique, and charging condition on measured diffusivity evaluated. • A modified solution to Fick's 2nd law was proposed to account for strong traps. • Significance of method used to determine effective diffusivity varied with steel. • Multiple major trap sites are present in the banded ferrite-pearlite microstructure. • Pearlite bands with low diffusivity can cause a tortuous diffusion path. [ABSTRACT FROM AUTHOR]

Metal hydride storage system (MHSS) has been widely used mostly because of its large storage capacity and high degree of safety. The improvement of the heat transfer performance is one of possible techniques to enhance the overall MHSS performance. The well arrangement of the heat exchanger structure from a semi-cylindrical coil heat exchanger with central return tube (SCHE-CR) significantly reduces the hydrogen absorption duration. However, the modelling of the thermal behaviour for the SCHE-CR during desorption process is missing in the literature. Therefore, this study aims to develop a model for both hydrogen absorption and desorption processes and analyse the thermal performance during the cycle. Phase change material (PCM) is incorporated with the heat exchanger for further improvement of the MHSS performance. The storage is designed under three different PCM configurations, including PCM jacket, pool bed, and capsule. The numerical results report that the duration of the absorption-desorption cycle is reduced by over 50% when using SCHE-CR instead of a helical coil. The PCM configurations, especially the PCM capsule, increase the MHSS performance, especially during the absorption. The duration of one cycle is decreased by at least 39% when combining the SCHE-CR with PCM. The HTF temperature significantly affects the MHSS performance, especially during the desorption. Reduction in HTF temperature reduces the absorption duration by at least 15%, while increasing the HTF temperature reduces the desorption duration by at least 25%. The new MHSS configuration would be beneficial to enhance the heat exchange during the absorption-desorption cycle of industrial MHSS applications. • A novel method for faster hydrogen storage. • 31% reduction of duration for one complete cycle. • PCM capsule improved hydrogen charging and discharging time. • 39% reduction of complete cycle, using capsule PCM. • Significant reduction of hydrogen desorption, under fluid temperature. [ABSTRACT FROM AUTHOR]

Magnesium hydride is one of the most promising solid-state hydrogen storage materials for on-board application. Hydrogen desorption from MgH2 is accompanied by the formation of the Mg/MgH2 interfaces, which may play a key role in the further dehydrogenation process. In this work, first-principles calculations have been used to understand the dehydrogenation properties of the Mg(0001)/MgH2(110) interface. It is found that the Mg(0001)/MgH2(110) interface can weaken the Mg-H bond. The removal energies for hydrogen atoms in the interface zone are significantly lower compared to those of bulk MgH2. In terms of H mobility, hydrogen diffusion within the interface as well as into the Mg matrix is considered. The calculated energy barriers reveal that the migration of hydrogen atoms in the interface zone is easier than that in the bulk MgH2. Based on the hydrogen removal energies and diffusion barriers, we conclude that the formation of the Mg(0001)/MgH2(110) interface facilitates the dehydrogenation process of magnesium hydride. [ABSTRACT FROM AUTHOR]

Hydrogen sorption characteristics of 5 kg-LaNi 5 reactor featuring conical fins and heat transfer tubes is experimentally studied at various water flow rates (V s :2.5, 5, 7 LPM), inlet temperatures (T s :30, 25, 20 °C), hydrogen pressures (P s :10, 15, 20, 25 bar). Higher V s , P s , and lower T s yield faster absorption through higher driving force (∝ln (P s / P eq), P eq : equilibrium pressure). Ninety percent absorption takes ∼12.3 and ∼13.7 min at V s :7 and 2.5 LPM (P s :15 bar, T s :30 °C). Faster atmospheric desorption needs higher T s and/or V s offering higher driving force (∝ (1-(1/ P eq)). 90% desorption takes ∼20.1 and ∼21.8 min for initial bed temperatures of 60 and 30 °C, (V s :5 LPM, T s :60 °C). Absorption of this 'Single Reactor' and five/ten (25/50 kg) such reactors in series and parallel are studied numerically. Series configuration stores five/ten-times hydrogen than 'Single Reactor' within the same duration by doubling/tripling V s (same P s , T s). Parallel configuration requires proportional water supply. H 2 storage reactor with internal 12 conical fins+4 tubes is experimentally studied. Absorption by 5 kg LaNi 5 under various operating parameters are compared. Atmospheric Desorption for different initial bed temperatures are observed. 5/10 reactors in series requires 2/3 times water flow rate to match performance. Parallel requires proportional water flow rate but facilitates uniform absorption. [ABSTRACT FROM AUTHOR]

The characteristics of fine-grained graphite, which will be used as the material for plasma-contacting elements of the T-15MD tokamak, are studied in this work. The density and porosity, thermal diffusivity and thermal conductivity, sizes of the crystalline grains and the amount of impurities in graphite are measured. The measurement results are compared with the corresponding characteristics of MPG-6, MPG-7, and MPG-8 graphite samples. The nature of the retention of hydrogen isotopes and methane in graphite and the conditions of desorption are determined depending on the temperature of preliminary annealing, its duration, and the exposure time of annealed samples in atmospheric gas under normal conditions. The effect of irradiation with deuterium ions of various energies on the regularities of hydrogen trapping and desorption is also considered. In all cases, attention is paid to the effect of experimental conditions on the retention and desorption of hydrogen, which remained in graphite from the time of its production and was trapped during exposure to air. Based on the obtained data and taking into account the expected conditions in the chamber of the T-15MD tokamak, the optimal conditions for annealing of graphite supplied from the manufacturer are identified, and the temperatures of the tokamak elements in contact with the plasma, which contribute to the removal of hydrogen from the graphite lining, are determined. [ABSTRACT FROM AUTHOR]

Hydrogen embrittlement is a serious phenomenon resulting in severe ductility deterioration of engineering materials due to the presence of hydrogen atoms. The low concentration of dissolved oxygen in deep-sea provide the condition for hydrogen production. Herein, the hydrogen permeation behavior in X70 pipeline steel in acid/alkaline environment under different hydrostatic pressure were investigated via electrochemical hydrogen permeation parameters. The results revealed the different trends of i∞ with increasing hydrostatic pressure. The phenomenon was described from the perspectives of hydrogen generation, absorption/desorption and permeation process by potentiodynamic polarization, linear sweep voltammetry (LSV) and EIS tests. The experimental permeation data were fitted with surface effect model and leads to the conclusion that the hydrostatic pressure greatly enhanced the adsorption rate and restricts the desorption rate of absorbed hydrogen atoms on the metal surface, thereby the process of atomic hydrogen compounding into hydrogen molecules is inhibited, leading to an increase in sub-surface hydrogen concentration (C0).

Thermal desorption behaviours of erbium trihydride (ErH 3) powders were studied using simultaneous thermogravimetry and thermal desorption spectroscopy (TG-TDS) method. The crystal structures and chemical compositions of the samples were investigated by X-ray diffraction analysis (XRD) and X-ray photoelectron spectroscopy (XPS), respectively. Two-peak structures were observed in the hydrogen desorption spectra and the corresponding activation energies were determined to be 160.7 and 212.3 kJ/mol, respectively. The phase transformation sequences during thermal desorption process were established by combining the changing trends in the temperature/hydrogen content with the Er–H phase diagram. It was established that the low-temperature and high-temperature peaks were related to the β + γ → β and α + β → α phase transformation steps, respectively. The origins of the observed TDS peaks and shoulders were attributed to the equilibrium hydrogen pressures of the phase regions that the decomposition reaction passed through. • Phase transformation sequence of ErH 2.7 decomposition was β + γ.→ β → α + β → α. • Oxygen concentration increased after thermal decomposition due to the oxidation of Er. • Hydrogen atoms in the tetrahedral sites of β phase were more stable than these of octahedral. • Equilibrium H 2 pressures were related to peaks of thermal desorption spectra. [ABSTRACT FROM AUTHOR]

The effects of vacancies on Mg 2 NiH 4 hydrogen desorption and capture are investigated by first principles calculations and the crystal structure, enthalpy and electronic structure are discussed in this work. The introduction of vacancies reduces the thermodynamic stability, and the dehydrogenation enthalpies of Mg 2 NiH 4 -V m (m = Mg1, Mg2, Mg3 and Ni) are lower than that of Mg 2 NiH 4. The dangling bonds are generated in Mg 2 NiH 4 –V Mg2 and Mg 2 NiH 4 –V Mg3 , corresponding to smaller changes of crystal structures and lower stabilities. The trapping of H atoms in Mg 2 NiH 4 -V m (m = Mg1, Mg2 and Mg3) can proceed spontaneously. The captured hydrogen atom H33 and the nearby N i H 4 4 − group forms a Ni–5H group in Mg 2 NiH 4 -V m (m = Mg1, Mg2 and Mg3). The weak hybridization of H33 with Ni d orbital and the generation of free electrons are responsible for the much higher formation enthalpy of Mg 16 Ni 8 H 33 –V Mg1 than Mg 16 Ni 8 H 33 –V Mg2 and Mg 16 Ni 8 H 33 –V Mg3. The strong hybridization between the H33 atom and the free H3 atom in Mg 16 Ni 8 H 33 –V Ni indicates that the addition of H33 leads to the transition of the electrons, and this process cannot take place spontaneously. This work confirms the positive effects of vacancies on Mg 2 NiH 4 and provides a new research perspective to control the hydrogen storage capacities of Mg-based alloys. • The effects of vacancies on Mg 2 NiH 4 hydrogen desorption and capture were investigated by first principles calculations. • The introduction of vacancies reduced the thermodynamic stability and the desorption enthalpy of the hydride Mg 2 NiH 4. • The trapping of H atoms in Mg 2 NiH 4 -V m (m = Mg1, Mg2 and Mg3) can proceed spontaneously. [ABSTRACT FROM AUTHOR]

The kinetics of hydrogen gas release from hafnium hydride are investigated by combining experiments and density functional theory. The material is a candidate neutron shield for compact nuclear reactors, where hydrogen release will lead to a degradation in moderating function. Experimentally, we have studied the decomposition of epsilon phase (HfH 2-x) powders from 25 to 1000 °C using thermogravimetry and X-ray diffraction. Isochronal heating reveals 3 characteristic desorption peaks corresponding to the release of hydrogen from each phase (ε-HfH 2-x , δ-HfH 1.6-x and α-Hf), at ∼ 350, 415, and 700 °C. This is well supported by the modelling output from density functional theory. A Kissinger analysis allowed for activation energies for desorption to be calculated (∼150 kJ/mol, 170 kJ/mol and 90 kJ/mol respectively). The peak shape and desorption rate data suggests that a second order diffusion limited reaction controls the ε→ε+δ desorption, a first order interface limited reaction controls ε+δ→δ, and a surface limited zeroth order reaction limits the desorption of the δ+α phases. The analysis suggests that, at least for δ→α regime, engineering solutions for improved thermal stability should focus on reductions in surface reactivity. [ABSTRACT FROM AUTHOR]

The objective was to evaluate the impact of repeated exposure to hyperbaric hydrogen (90 MPa; 30 °C) and pressure release on the microstructure and mechanical behavior of PA11. Samples were analyzed after 1, 2, 5 and 10 cycles, by SAXS, WAXS, DMA, DSC, and a series of mechanical tests with variable triaxiality ratio. The most visible change in the residual state after desorption was a stiffening of the amorphous phase. It mainly originated from the first cycle, especially the first pressurization. The crystalline phase was slightly affected and no evidence of nano-voiding was brought in the residual state up to 10 cycles. Similar analyses were conducted during the first cycle's desorption transient. They showed a reversible plasticizing effect and a trend of nano-voiding vanishing after desorption but might promote damage upon further triaxial loading. [Display omitted] • Up to ten hydrogen pressure cycles (90 MPa; 30 °C) were applied to PA11. • Plasticizing and slight nano-voiding were observed during the first decompression. • After desorption, the amorphous phase was stiffer than that in the unexposed material. • No significant residual damage was detected at the nano- and micro-scales. • No cumulation was observed between the first and the tenth cycles. [ABSTRACT FROM AUTHOR]

Structure and hydrogen storage properties of three Ti 31 V 26 Nb 26 Zr 12 M 5 multicomponent alloys with M = Fe, Co and Ni are investigated. The alloys synthesized by arc melting are characterized via X-Ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The as-cast ingots present multi-phase dendritic structures composed mainly of BCC phases and small amounts of C14 Laves phases. Upon hydrogenation, each alloy absorbs around 1.9 H/M (number of hydrogen atoms per metal atoms) at room temperature. XRD of fully hydrogenated samples shows the formation of multi-phase structures composed of FCC and C14 hydrides. Thermo Desorption Spectroscopy (TDS) shows that the hydrogenated alloys present multi-step desorption processes with wide temperature ranges and low onset temperatures. XRD of partially hydrogenated samples indicate the presence of intermediate BCC hydrides. XRD of desorbed samples suggest reversible reactions of absorption/desorption: BCC + C14 alloy ↔ intermediate BCC hydride + C14 hydride ↔ FCC + C14 hydrides. • Ti 31 V 26 Nb 26 Zr 12 M 5 (M = Fe, Co, or Ni) multicomponent alloys were synthesized. • The alloys presented multi-phase structures composed of BCC and Laves C14 phases. • Fully hydrogenated samples formed multi-phase structures (FCC + C14 hydrides). • Partially hydrogenated samples showed the formation of intermediate BCC hydrides. • Desorbed samples suggest reversible multi-step processes of absorption/desorption. [ABSTRACT FROM AUTHOR]

Sustainable development of hydrogen energy is a prime concern to address the rising energy demand and the global energy problem since the hydrogen economy is reliable for clean and carbon-free energy carriers. Despite well-established commercial sector technologies, boil-off losses, explosive nature, and leakage risk still exist with compressed and liquefied storage. One of the significant remedies, solid-state hydrogen storage, improves bulk density and gravimetric capacity and addresses safety concerns. The rising popularity of light and heavy fuel cell vehicles is projected to promote the advancement of onboard solid-state hydrogen technology. The present review focuses on the importance of existing porous materials, polymers, metal, and complex metal hydrides for solid-state hydrogen storage and the dominance of Si nanostructures (SiNSs). The fabrication techniques of porous silicon, porous silicon nanowires, and Si quantum dots are accentuated. The review provides insights into the hydrogen-assisted properties, regularities, the importance of hydrogen energy on automobiles for alleviating climate change phenomena, and the application of SiNSs for hydrogen storage with other transition and alkali earth materials to overcome the issues. It highlights the importance of catalysts in resolving the existing reversibility and desorption issues associated with hydrogen energy storage. Different popular desorption techniques considering the pore dimensions are discussed. The evaluation may enable energy providers and Si-based fuel cells to be better customized, promoting the development of the hydrogen energy economy. • Solid-state H 2 storage overcomes the low energy storage density and safety issues. • High surface area of Silicon nanostructures facilitates atomic hydrogen storage. • Doping and alloying are possible techniques to enhance H 2 affinity at adsorbents. • Synergetic effect of PS and carbon nanostructures enhances storage capacity. • Water-based desorption is efficient, cost-effective, and low energy consumer. [ABSTRACT FROM AUTHOR]

To investigate the influence of thermal effects on the hydrogen desorption performance of the metal hydride hydrogen storage system, a two-dimensional numerical model was established based on a small metal hydride hydrogen storage tank, and its accuracy was verified by the temperature variations in the reaction zone of the hydrogen storage tank during hydrogen desorption. In addition, the influence of the heat transfer medium on the heat and mass transfer performance of the hydrogen desorption reaction was analyzed. An external heat transfer bath was added to simulate the thermal effect of the model during the hydrogen desorption reaction. The temperature and type of heat transfer medium in the heat transfer bath were modified, and the temperature and reaction fraction variations in each zone of the hydrogen storage model were analyzed. The results showed that under heat transfer water flow, the reaction rate in the center region of the hydrogen storage tank was gradually lower than that in the wall region. The higher the temperature of water flow, the shorter the total time required for the hydrogen desorption reaction and the shortening amplitude is reduced. The variations in the temperature and hydrogen storage capacity during hydrogen desorption were similar, with water and oil as the heat transfer medium, under the same flow rate and heat transfer temperature, however, the heat transfer time and hydrogen desorption time of water were about 10% and 5% shorter than that of oil, respectively. When the air was used as the heat transfer medium, the heat transfer rate of the air convection in the channel was lower than the heat transfer rate of the tank wall, reducing the temperature difference between the air and alloy on both sides of the wall, decreasing heat transfer efficiency, and significantly prolonging the time required for hydrogen desorption. [ABSTRACT FROM AUTHOR]

Hydrogen remains an attractive energy carrier because it is abundant, environmentally friendly and has the highest gravimetric energy density of any known substance. Despite this high gravimetric energy density, hydrogen suffers from a low volumetric energy density as a room-temperature gas. To maximize volumetric energy density, storing hydrogen as a magnesium hydride is an efficient and economically viable route, owing to the low weight and high earth abundance of magnesium. A long-lasting obstacle for using magnesium is the high temperature required to release hydrogen once absorbed by magnesium. Although nanoscale magnesium is known to have a favorable effect on the hydrogen desorption temperature, it is not sufficient. In this work, hydrogen absorption and release was investigated by measuring optical changes, which correspond to certain hydrogen concentrations in magnesium nanoparticles. Remarkably, hydrogen desorption from the magnesium nanoparticle assembled thin films at room temperature could be achieved by illumination. This photo-stimulated hydrogen desorption introduces an effective and simple method to enable reversible hydrogen storage in magnesium. The sensitivity of the optical method here used is demonstrated by the fact that even hydrogen absorption from ambient air at 1 ppm has been measured. This work demonstrates that hydrogen can be efficiently stored and released from magnesium nanoparticles using only photons. • Formation of small magnesium nanoparticles with gas aggregation nanoparticle source. • Hydrogenation of magnesium nanoparticles and visualisation of the process. • Photo-stimulated hydrogen desorption. • Hydrogen detection from ambient. [ABSTRACT FROM AUTHOR]

Physisorption is the general dominating adsorption mode on pure carbonaceous materials. In this study, we examined if chemisorbed hydrogen can be accomplished without incorporating metals on carbon surfaces. We constructed two 100-atom amorphous carbon (a-C) models with different microenvironments (42 % 2-fold, 52 % 3-fold, and 6 % 4-fold coordinated carbon atoms and 18 % 2-fold and 82 % 3-fold, respectively) using ab initio molecular dynamics (AIMD) simulations to mimic activated carbon samples in reality. The structural, energetic, electronic structure and kinetic properties of hydrogen adsorption, migration, and desorption on the a-C surfaces were analyzed using density functional theory (DFT) and AIMD calculations, which showed that: (1) hydrogen molecules could spontaneously dissociate on the convex side of 2-fold coordinated carbon atoms. Physisorption of hydrogen molecules mainly took place on 3-fold coordinated carbon atoms. (2) Regarding the multiple hydrogen adsorption, the entire a-C model could uptake around 156 hydrogen atoms with the adsorption energy per hydrogen atom about −0.70 to −0.60 eV at high hydrogen pressure. In addition, we found that the average individual adsorption energy of a single hydrogen atom on different carbon atoms could be used as a quick prediction for the saturated hydrogen adsorption energy. (3) The migration barrier of a hydrogen atom between two adjacent carbon atoms was about 2 eV at both low and high hydrogen coverage, indicating that hydrogen mobility on this designed a-C model was low. The desorption of a hydrogen molecule can take place at 300 K using AIMD calculation, but not for atomic hydrogen desorption. In this work, we demonstrated that hydrogen chemisorption could take place on this designed a-C without the decoration of metal particles to enhance hydrogen adsorption amounts. The materials design to balance hydrogen chemisorption, migration, and desorption shall be considered in the future. [Display omitted] • Spontaneous H 2 splitting on amorphous carbon is shown by DFT calculations. • High hydrogen uptake is achieved on this designed amorphous carbon. • Low hydrogen mobility is predicted by DFT and AIMD calculations at 300 K. [ABSTRACT FROM AUTHOR]

There is an ongoing discussion in the literature if simulations of electrochemical reactions should be performed at constant electrode potential. In this context we examine the timescales at which electrochemical processes take place. We take molecular dynamics simulation of hydrogen desorption from graphene and gold as examples. Charge transfer processes are governed by the accompanying solvent reorganization, and their speed is determined by the solvent dynamics, whose timescale is of the order of picoseconds — the exact value depends on the details of the system. In contrast, double layer relaxation, which controls the electrode potential, requires times of the order of nanoseconds. We suggest that this difference is due to the fact, that solvent reorganization is a local phenomenon, while double layer relaxation involves the whole solvent between working and reference electrodes, which is of macroscopic dimensions. We conclude, that simulations of electrochemical reactions should not be performed at constant potential. In contrast, calculations for thermodynamic properties can be performed at constant potential or at constant charge, since the question of timescales does not arise in this case. • Molecular dynamics simulations of proton desorption are presented to illustrate an electrochemical reaction. • The timescale of the reaction itself is governed by the solvent friction on the saddle point. • The reaction is followed by the relaxation of the double layer, which is much slower. • The external potentiostat starts to act long after the reaction is over. • The electrode potential is not constant on the timescale of DFT-based simulations. [Display omitted] [ABSTRACT FROM AUTHOR]

Differential scanning calorimetry coupled with simultaneous evolved gas analysis (DSC-EGA) on aged δ-Pu samples shows that most radiogenic helium remains trapped within the Pu matrix at temperatures very close to, or slightly above, the melting temperature. Our results indicate that helium release from 50-year-old δ-Pu occurs as a burst just below the melting temperature (>0.994 T m), with subsequent pressure oscillations as temperature increases. Subordinate quantities of H 2 were also released along with helium. The helium emission tails off and ceases above ∼720 – 750°C. In a δ-Pu alloy aged 6 years, the initial helium burst occurs slightly above melting (∼1.015 – 1.042 T m), with a discrete, larger helium spike occurring between 670 and 686°C. The proximity of helium release to the liquidus transition presented challenges in the deconvolution of overlapping process enthalpies, the liquidus endotherm, and the exotherm resulting from bubble collapse, annealing and gas expulsion. Helium's strong affinity for vacancy binding in a 2He-vac configuration is predicted by Density Functional Theory (DFT) modeling. The measured stored energy associated with the He release events in a 50-year-old δ alloy is on the order of ∼10–11 J/g, which is significantly higher than stored energies measured in the sub-solidus regimes (∼2 J/g) that are related to the solid-state annealing of processing- and radiation-induced defects. This implies that aged δ Pu alloys have a remarkable resilience to accommodate the lattice strain produced by the internal pressure of the helium bubbles and provides further insight into the thermodynamic behavior of aged δ Pu. [Display omitted] • DSC-EGA analyses of aged δ-Pu samples document the emanation of a He + H 2 gas burst, while the metal is in the ε-phase. • During the 1st melt, an exothermic energy spike occurs immediately after the onset of normal endothermic melting. • Energy release during 1st melt is ∼10 J/g, corresponding to annealing of gas-filled voids formed due to self-irradiation. • Helium's affinity for vacancy binding, illustrated using DFT modeling, accounts for its abundance in the gas burst. • Aged δ−Pu alloys can accommodate lattice strain produced by gigapascal-scale internal pressures of He bubbles. [ABSTRACT FROM AUTHOR]

Using metal hydride for hydrogen storage in stationary applications and for transportation is a promising technology due to its advantages of large hydrogen storage capacity, low pressure and low energy consumption. Combining the metal hydride reactor with PCM is expected to recover the heat generated during the hydrogen absorption and use it for hydrogen desorption, thus improving the energy efficiency of the system. This paper proposes a metal hydride reactor integrated with honeycomb fins and PCM to enhance heat transfer. Based on simulations, the results show that the achieved hydrogen storage capacity is 1.326 wt%, the gravimetric and volumetric storage densities are 0.411% and 14.76 kg of H 2 per m3, respectively, and the mean saturated rates are 1.222 × 10−3 g s−1 and 0.773 × 10−3 g s−1 for absorption and desorption processes. Compared with the reactor without fins, the mass and volume of the reactor using honeycomb fins are increased, resulting in a decrease in gravimetric and volumetric storage density, but a increase in reaction rate during hydrogen absorption and desorption processes. Based on this structure, we also propose a honeycomb fin reactor filled with sandwich PCM to further accelerate the heat transfer in the reaction process. Compare to the reactor with PCM only filled on the periphery of the honeycomb fins, the hydrogen absorption and desorption times are shortened by about 86.4% and 81.1%, respectively. In addition, different reactor structures are compared using multiple KPIs to provide relevant suggestions for the reactor optimization. The obtained research results can provide a reference for effective thermal management methods in MH storage systems. • A metal hydride reactor integrated with honeycomb fins and PCM was proposed. • The comparison of reactor without fins and the effects of fin size were studied. • The placement of PCM and MH was optimized. • Multiple KPIs were used to evaluate the hydrogen absorption and desorption processes. • The optimized reactor performed better than other forms of reactors. [ABSTRACT FROM AUTHOR]

Hydrogen trapping behavior and diffusion induced by the microstructure of shielded metal and flux-cored arc weldments (SMAW and FCAW) were characterized using a combination of high-resolution microstructural characterization methods, hydrogen trap site studies, and a modeling technique. H trapping by HAGBs that was found by TDS was confirmed by NanoSIMS with a cryogenic stage. Cellular automaton modeling results showed that in grain sizes smaller than a critical grain size, the hydrogen diffusion coefficient decreases with decreasing grain size, indicating that H trapping dominates short-circuit diffusion mechanism along high-angle grain boundaries (HAGBs). These results firstly show that smaller grain size and high HAGB density in the FCAW specimen results in a lower H diffusion coefficient and higher density of relatively strong HAGB traps, and a lower total desorbed hydrogen content in the FCAW specimen. Also, it was suggested that the fraction of acicular ferrite grains can define the HAGB content in the alloy, and can be a determinant factor in the behavior of weldments in H-containing media. [Display omitted] • High density of high-angle grain boundaries (HAGB) in flux-cored arc weld (FCAW). • The model shows low H diffusion coefficient for low grain size (GS) of the welds. • Higher H trapping by strong HAGB and lower H diffusion coefficient in FCAW specimen. • H trapping by HAGBs confirmed by nano secondary ion mass spectroscopy. • H trapping dominates short-circuit diffusion mechanism along HAGBs in small GSs. [ABSTRACT FROM AUTHOR]

To investigate the influence of thermal effects on the hydrogen desorption performance of the metal hydride hydrogen storage system, a two-dimensional numerical model was established based on a small metal hydride hydrogen storage tank, and its accuracy was verified by the temperature variations in the reaction zone of the hydrogen storage tank during hydrogen desorption. In addition, the influence of the heat transfer medium on the heat and mass transfer performance of the hydrogen desorption reaction was analyzed. An external heat transfer bath was added to simulate the thermal effect of the model during the hydrogen desorption reaction. The temperature and type of heat transfer medium in the heat transfer bath were modified, and the temperature and reaction fraction variations in each zone of the hydrogen storage model were analyzed. The results showed that under heat transfer water flow, the reaction rate in the center region of the hydrogen storage tank was gradually lower than that in the wall region. The higher the temperature of water flow, the shorter the total time required for the hydrogen desorption reaction and the shortening amplitude is reduced. The variations in the temperature and hydrogen storage capacity during hydrogen desorption were similar, with water and oil as the heat transfer medium, under the same flow rate and heat transfer temperature, however, the heat transfer time and hydrogen desorption time of water were about 10% and 5% shorter than that of oil, respectively. When the air was used as the heat transfer medium, the heat transfer rate of the air convection in the channel was lower than the heat transfer rate of the tank wall, reducing the temperature difference between the air and alloy on both sides of the wall, decreasing heat transfer efficiency, and significantly prolonging the time required for hydrogen desorption.

The hydrogen trap sites and corresponding hydrogen binding energies in an Al–Cu–Mg alloy with the different microstructures were investigated to unravel the environmental hydrogen embrittlement (HE) behavior of the alloy. The results showed that hydrogen can reside at interstitial lattices, dislocations, S′-phase, and vacancies. In the aged specimen with the highest hydrogen content, it was firstly reported that hydrogen resided at S′-phase particles with relatively high binding energy, which is a determinant factor on HE resistance of the alloy. In the cold-rolled specimen, high content of hydrogen trapped at dislocations with a reversible nature leads to intergranular hydrogen-assisted cracking. In the solution-treated specimen, hydrogen migration to the surface due to low trap density results in low hydrogen content and prevents the GBs from reaching critical hydrogen concentration. The obtained results clearly reveal that trap site density, and the nature of trap sites can determine environmental HE susceptibility of the alloy. • H trapping in the cold-rolled sample was dominated by weak traps, i.e. dislocations. • H trapping at dislocation led to H-assisted crack nucleation along grain boundaries. • T6 sample was highly resistant to H due to trapping at strong traps, i.e. S′-phase. • Trap density is effective in the retention and mobility of H in aluminum alloys. • It was firstly reported that S′-phase has critical role on H sensitivity of 2024. [ABSTRACT FROM AUTHOR]

Transition metal doped magnesium hydride solids are a leading candidate for hydrogen storage materials. In this investigation, MgScH n clusters (n = 1–20) are theoretically studied using density functional theory and Møller-Plesset perturbation theory. It is determined that hydrogen binds successively to the MgSc diatomic metal center up to MgScH 13 when the cluster becomes saturated at 15.9% hydrogen by mass. In contrast to earlier predictions, we shown that for MgScH 14 and larger clusters molecular hydrogen dissociates from the core cluster structure. A local minimum is observed on the potential energy surface for larger clusters where dissociated hydrogen interacts with a negatively charged hydride of the core cluster in a dipole-induced dipole intermolecular force, providing insight into the dissociation pathway in bulk magnesium hydride materials doped with transition metals. Analysis of the frontier orbitals and natural bonding analysis of these clusters support this logical dissociation pathway. • MgScH n clusters are studied with density functional theory and ab initio methods. • MgScH n structures are determined by unbiased global optimization procedures. • MgScH 13 (15.9% hydrogen by mass) is largest cluster without dissociated hydrogen. • Dissociating H 2 can have temporary dipole moments coordinating to anionic hydride. • Cluster HOMO primarily consists of a hydride s atomic orbital in Sc-Mg-H backbone. [ABSTRACT FROM AUTHOR]

Body-centered cubic (BCC) alloys are considered as promising materials for hydrogen storage with high theoretical storage capacity (H/M ratio of 2). Nonetheless, they often suffer from sluggish kinetics of hydrogen absorption and high hydrogen desorption temperature. Carbon materials are efficient hydrogenation catalysts, however, their influence on the hydrogen storage properties of BCC alloy has not been comprehensively studied. Therefore, in this paper, composites obtained by milling of carbon catalysts (carbon nanotubes, mesoporous carbon, carbon nanofibers, diamond powder, graphite, fullerene) and BCC alloy (Ti 1.5 V 0.5) were extensively studied in the non-hydrogenated and hydrogenated state. The structure and microstructure of the obtained materials were studied by scanning and transmission electron microscopes, X-ray diffraction (XRD), and Raman spectroscopy. XRD and Raman measurements showed that BCC alloy and carbon structures were in most cases intact after the composite synthesis. The hydrogenation/dehydrogenation studies showed that all of the used carbon catalysts significantly improve the hydrogenation kinetics, reduce the activation energy of the dehydrogenation process and decrease the dehydrogenation temperature (by nearly 100 K). The superior kinetic properties were measured for the composite with 5 wt % of fullerene that absorbs 3.3 wt % of hydrogen within 1 min at room temperature. [Display omitted] • Mechanical milling without milling balls prevents serious damage of carbon additives. • BCC alloy catalysed by fullerene absorbs 3.3 wt% of hydrogen within a minute. • The addition of carbon catalysts decreases the dehydrogenation temperature by 100 K. • The dehydrogenation process activation energy is twice reduced in studied composites. [ABSTRACT FROM AUTHOR]

Hydrogenated diamond-like carbon (DLC: H) films were successfully fabricated on the surface of 13Cr super martensitic stainless steel by high-pulsed power chemical vapour deposition. The mechanical and tribological properties of the films related to the substrate bias voltages were investigated. The results showed that the surface hardness and tribological properties of the substrate after DLC film deposition were improved. The DLC films became dense, the grain size and roughness reduced, and the deposition rates increased as the bias voltage increased. In addition, the dense DLC films directly led to high nanohardness and elastic modulus. The H content decreased with an increase in the bias voltage, which may be the primary reason for nanohardness and modulus enhancement. Due to the relatively high H/E* and H2/E*3 ratios of films corresponded to high elastic strain and plastic deformation resistances reduced the wear loss, and the localized graphitization on the surface provided solid lubrication. [ABSTRACT FROM AUTHOR]

[Display omitted] • Internal electric field of BaTiO 3 promote formic acid dehydrogenation on Pd/TBT(C)@SC. • Internal electric field strength is adjusted by heating at different temperatures. • Mesoporous carbon shell on BaTiO 3 shields particle size and electronic effects. • The internal electric field promotes the desorption of adsorbed H from Pd surface. • The apparent activation energy of FAD is significant reduced on Pd/TBT(C)@SC-800. Formic acid is a desirable liquid hydrogen storage compound for solving transport and storage problems of hydrogen for onboard fuel cells. Optimizing adsorption/desorption energy of intermediates can directly modulate the performance of Pd catalysts in formic acid dehydrogenation (FAD). Herein, we introduce internal electric field with controllable strength to regulate the adsorption/desorption of intermediates on Pd. Non-ferroelectric cubic-phase barium titanate (CBT) is heat-treated at high temperature to obtain ferroelectric tetragonal-phase barium titanate (TBT(C)), which exhibits internal electric field. The strength of the internal electric field is successfully adjusted by heat treatment at different temperatures. The size of Pd nanoparticles is restricted between 2.2 and 2.7 nm, and the electronic effect of Pd is effectively eliminated by coating TBT(C) with mesoporous carbon shell (TBT(C)@SC). Experimental results prove that the internal electric field promotes the desorption of hydrogen on Pd. Pd/TBT(C)@SC-800 obtained by heat treatment at 800 °C, with the optimal internal electric field strength, exhibits high activity and hydrogen selectivity for FAD. This work provides a new strategy for designing FAD catalysts. [ABSTRACT FROM AUTHOR]

In the research, we firstly reported the morphology and microstructure evolution of surface hydride in Zircaloy-4-500 ppmH during hydrogen desorption process. The morphological evolution of surface hydride in hydrogen desorption process was investigated with BSE-TOPO and AFM, revealing that the spot-like or string convex features along surface hydride were present at 573 K and disappeared at 1073 K. The microstructure observation with TEM (prepared with cryo-FIB) indicates that the surface region of convex feature actually consists of two layers of fine α-Zr grains, which were the hydrogen-depletion region created by hydrogen release. The formation mechanism of surface hydride convex was the diffusion of hydrogen from the internal to the surface, leading to the generation of multiple δ-hydrides in sub-surface. Therefore, the hydrogen desorption mechanism was also proposed. As the channeling of hydrogen release, surface hydride actually plays a crucial part in hydrogen desorption process. [Display omitted] • The formation of string convex feature along surface hydride was firstly reported. • The surface region of convex feature consists of two layers of fine α-Zr grains. • The diffusion of hydrogen leads to the phase transformation of α-Zr to δ-hydrides. • Surface hydrides act as the channeling of hydrogen release in desorption process. [ABSTRACT FROM AUTHOR]

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Intrinsic reaction coordinate (IRC) data regarding the interactions of water with a carbene-like active site located at the edge of a polyaromatic hydrocarbon [1–3] has been obtained using density functional theory (DFT) and the 6–31g(d) basis set as implemented in the Gaussian 16 software [4]. The data is presented as two videos (frontal and lateral mechanism views) combining four consecutive IRC calculations corresponding to the four different transition states presented on “https://doi.org/10.1016/j.carbon.2020.01.011” [3] (Figure 6, side approach). These videos provide powerful insights on two key aspects: a) the rotational process that occurs during water adsorption and b) the hydrogen gas desorption process during water gasification of carbons.

This study presents numerical modeling and simulations of thermal fluid flows in high-volumetric-density metal hydride beds during hydrogen (H 2) adsorption and desorption within the lattice Boltzmann method (LBM) framework. A novel LBM is developed for predicting the flow and conjugate heat transfer in a practical lab apparatus involving a combination of solid chamber, free expansion zone, and porous media metal hydride that have not been addressed to date. With a correction term in the collision operator and a new equilibrium distribution function, the present model has a consistent expression of the heat capacity ratio for different fluid regions and derives the correct form of macroscopic energy and generalized momentum equations (including Darcy, Brinkman, and Forchheimer terms). The model is then validated through comparisons of the simulated results with previous experimental data under different initial pressure and temperature conditions for LaNi 5 –H 2 storage systems as well Mg–H 2 reactors, achieving excellent agreement. In addition, accounting for conjugate heat transfer and other porous forces in the present LBM yields improved predictions over prior numerical approaches. • A novel LBM is presented for conjugate heat transfer during hydrogen storage. • Simulations of reactor with fluid, porous, and solid zones are firstly conducted. • The proposed model shows improved predictions up to 68% over prior approaches. • The LBM solver achieves 72% of ideal scalability on HPC clusters with 256 cores. [ABSTRACT FROM AUTHOR]

It is highly desirable to develop efficient and cost-effective composite catalysts to replace noble metal Pt for hydrogen evolution reaction (HER). For an excellent HER catalyst, both the adsorption and desorption of intermediate H atoms on it should be easy. However, except metal platinum, most individual species cannot satisfy this requirement. Fe-B is an active HER catalyst with strong ability to adsorb H atoms. In our previous work, we found that when Fe-B alloy was decorated with metal Fe particles (Fe-B@Fe), the resultant composite displayed a significant synergic effect for HER compared to single Fe-B and Fe. The role of the decorated Fe on Fe-B is to improve H 2 desorption. Because the desorption of H 2 molecule from Ni is easier than from Fe, we expect Fe-B@Ni to be a more efficient HER catalyst than Fe-B@Fe. Herein, we transform Fe-B@Fe into Fe-B@Ni by a facile displacement reaction. As a proof of concept, the as-prepared Fe-B@Ni catalyst exhibits much higher electrocatalytic and photocatalytic activity for hydrogen production than the pristine Fe-B@Fe. At the current density of −100 mA cm−2, the overpotential of Fe-B@Ni in 1.0 mol L−1 KOH is close to that of 20 wt% Pt/C. The highest apparent quantum yield (AQY) for dye-sensitized photocatalytic hydrogen evolution reaches 51% at 420 nm. The possible mechanisms have been proposed. These findings provide new insights for designing and fabricating new HER composite catalysts for electrocatalytic and photocatalytic hydrogen evolution. [ABSTRACT FROM AUTHOR]

We tackle the role of austenite in multiphase steels on hydrogen diffusion systematically for the first time, considering a range of factors such as morphology, interface kinetics and the additional effect of point traps using both experiments and modelling. This follows the findings from part I where we showed that austenite cannot be parametrised and modelled as point traps under the assumption of local equilibrium, unlike grain boundaries and dislocations. To solve this, we introduce a 2D hydrogen diffusion model accounting for the difference in diffusivities and solubilities between the phases. We first revisit the as-quenched martensite permeation results from part I and show that the extremely low H diffusivity there can be partly explained with the new description of austenite but is partly likely due to quench vacancies. We then also look at the H absorption and desorption rates in a duplex steel as a case study using a combination of simulations and experiments. The rates are shown to depend heavily on austenite morphology and the kinetics of H transition from ferrite to austenite and that an energy barrier is likely associated to this transition. We show that H diffusion through the ferrite matrix and austenite islands proceeds at similar rates and the assumption of negligible concentration gradients in ferrite occasionally applied in the literature is a poor approximation. This approach is also applicable to other austenite-containing steels as well as other multiphase alloys. [ABSTRACT FROM AUTHOR]

MgH 2 is one of promising hydrogen storage materials, but Mg crystallites grow up very fast during hydrogen desorption, leading to the degradation of hydrogen storage properties. Therefore the growth behavior and mechanism of Mg crystallites during hydrogen desorption of nanocrystalline MgH 2 were investigated in this work. It was found that the transformation from MgH 2 to Mg occurred by the surface-controlled 'nucleation and growth' mechanism. After the instantaneous nucleation of Mg at free surfaces of MgH 2 particles, Mg crystallites grew through three stages, namely one-dimensional, then two-dimensional and finally one-dimensional growths. In the second stage, Mg crystallites grew quickly as compared with other stages. After complete hydrogen desorption, the average Mg crystallite size in MgH 2 −10 wt% Pr 3 Al 11 sample was smaller than that in pure MgH 2 sample due to the presence of Pr 3 Al 11. • Transformation from MgH 2 to Mg occurs by nucleation and growth mechanism. • Mg crystallites grow through three stages during hydrogen desorption of MgH 2. • Mg crystallites grow quickly in the second growth stage. • Pr 3 Al 11 leads to the decrease of Mg crystallite size after hydrogen desorption. Image 1 [ABSTRACT FROM AUTHOR]

The aim of this work is to experimentally study, the behavior of a metal-hydrogen reactor (MHR) subjected to the action of an external magnetostatic field, during hydrogen absorption and desorption by the LaNi5 hydride. The reactor was surrounded by a copper coil crossed by a continuous current delivered by a DC generator. In this study, the mass of the absorbed and desorbed hydrogen was measured and plotted for different initial temperatures and pressures functions of the applied magnetostatic field. The ratio of the hydrogen mass absorbed or desorbed with and without supplying a magnetostatic field was estimated after which the change in the saturation magnetization per 1 mol of desorbed hydrogen atom (ΔM s), for the LaNi 5 compound; was determined. The results demonstrated that while the increase in temperature was not beneficial for the absorption reaction, it improved the desorption process. The increase in pressure leads to an increase in the absorbed hydrogen mass. The effect of the applied magnetostatic field was observed especially for the lowest temperatures in the case of the absorption reaction. In fact, we noticed a small increase in the absorbed mass, which decreased and disappeared in the highest temperatures. It was found that the magnetostatic field had no effect on the desorption reaction for the tested fields and temperatures. The low value of ΔM s confirmed the paramagnetic nature of the sample. • Improvement of the hydrogen mass absorbed when applying a magnetic field. • Estimation of the value of the ΔM s for the LaNi 5 hydride. • Estimation of hydrogen mass stored ratio with and without a magnetostatic field. [ABSTRACT FROM AUTHOR]

Magnesium hydride is considered to be one of the most promising hydrogen storage materials, although it nevertheless has some problems, such as the high value of the activation energy of hydrogen desorption. To solve this problem, some scientists have proposed adding nanocarbon materials, in particular carbon nanotubes, to magnesium hydride. Currently, a detailed understanding of the mechanisms of obtaining composites based on magnesium hydride and carbon nanotubes is lacking, as is our understanding of the effect of nanocarbon additives on the activation energy and temperature of hydrogen desorption depending on the parameters of the composite synthesis. In addition, the data obtained at various values of milling parameters are very different, and in some works the effect of carbon nanomaterials on the hydrogen properties of magnesium hydride was not confirmed at all. Thus, it is important to determine the effect of nanocarbon additives on the properties of hydrogen storage of magnesium hydride under various milling parameters. This work is devoted to the study of the effect of nanocarbon additives on magnesium hydride and the determination of the dependences of the hydrogen desorption temperature and activation energy on the synthesis parameters. Composite powders containing MgH2 with 5 wt.% single-walled carbon nanotubes (SWCNT) were prepared using a planetary ball mill. The milling was carried out at various milling speeds, namely 300, 660, and 900 rpm. Results suggested that the structure of the nanotubes is preserved with prolonged grinding of magnesium hydride and SWCNT in a ball mill for 180 min at a relatively low grinding speed of 300 rpm. The composite obtained with these parameters has the lowest temperature of hydrogen desorption and an activation energy of H2 desorption of 162 ± 1 kJ/mol H2, which is 15% lower than that of the magnesium hydride MgH2 (189 ± 1 kJ/mol H2).

Aluminum hydride is particularly attractive as a hydrogen storage material due to its high hydrogen volumetric capacity and relatively low hydrogen desorption temperature. However, the properties of nanoscale α‑AlH3 particles are not studied completely due to the difficulties in their synthesis. In this work, we report the synthesis of nanoscale α-AlH3 based on a modified method, together with its activation energy measurements and hydrogen release kinetics. We have discovered that the dehydrogenation activation energy (93.23 kJ/mol) of nanoscale α-AlH3 is remarkably lower than that of micrometer-sized α-AlH3, which further expand practical application of AlH3. Moreover, we demonstrate that the decomposition kinetics of nanoscale α-AlH3 is controlled by nucleation and growth of the aluminum phase in three dimensions. This work first time provides systematic investigation of thermodynamic properties of nano-scale AlH3, which paves the way for its practical applications. [ABSTRACT FROM AUTHOR]