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Sodium-ion batteries (SIBs) have been rapidly developed as an effective replacement or supplement for lithium-ion batteries (LIBs) due to the high natural abundance and low cost of sodium resources.

The work studies influence of yttrium on the crystal structure, hydrogenation properties and electrochemical behaviors of the PuNi3-type La2−xYxMgNi9 (x = 0.25 – 1.00) intermetallic alloys used as anodes of the Ni–MH batteries.

Structural, hydrogen storage, and electrochemical properties of LaMgNi4 alloy were investigated in this study to determine whether it can be used as an active material of the negative electrode in nickel–metal hydride (Ni/MH) batteries. X-ray diffraction study showed that amorphization occurs at the first dehydrogenation cycle and was recovered crystallization after 873 K annealing. Maximum hydrogen storage capacity reached 1.4 wt% in the first hydrogenation under 373 K. The reannealed alloy showed improved reversible hydrogen storage capacity at ∼0.9 wt% due to more LaNi5 phase composition. Electrodes prepared from the investigated alloy showed maximum discharge capacities of ∼340 mAh/g at 10 mA/g. The LaMgNi4 alloy electrode exhibited satisfactory cycling stability remaining 47% of its initial capacity after 250 cycles. The negative cohesive energy indicated the exothermic process and stable compound structures of the LaMgNi4 alloy and its hydrides via Density functional theory calculations.

The present work is focused on the studies of the phase-structural transformations in the La3-xMgxNi9 (x ​= ​1.0, 1.1 and 1.2) alloys as active materials of negative electrodes in the Nickel-Metal Hydride (Ni/MH) batteries. The phase equilibria and phase-structural transformations in the alloys were probed by in situ neutron powder diffraction (NPD) at the temperatures ranging from 300 ​K to 1273 ​K using the measurements of the equilibrated alloys at 8 setpoint temperatures of 300, 973, 1073, 1123, 1173, 1223, 1248 and 1273 ​K. Prepared by induction melting initial alloys were found to be multi-phase structured, containing up to 6 individual intermetallic compounds with different stoichiometric compositions. With the increase of the temperature and holding time, various transformations took place in the studied alloys. These included the formations and transformations of super-stacking intermetallics with variable ratios (La ​+ ​Mg)/Ni, 1:3, 2:7 and 5:19. With increasing temperatures, several systematic changes took place. (a) Abundances of (La,Mg)2Ni4 AB2 and (La,Mg)Ni3 AB3 type intermetallics gradually decreased before they melted/decomposed above 1073 ​K; (b) The (La,Mg)2Ni7 A2B7 type intermetallics began to decrease in abundances above 1123 ​K; (c) The transformation in the (La,Mg)5Ni19 intermetallics from 3R to 2H proceeded above 1223 ​K. The increase of Mg content had no obvious influence on (La,Mg)2Ni4 and (La,Mg)2Ni7 phases, and corresponding reactions R1 and R3 took place at the same temperatures as in the La–Ni system. However, with increasing Mg content the melting point of (La,Mg)5Ni19 phase increased while the melting point of the (La,Mg)Ni3 phase it decreased, leading to the variation of the reaction temperatures of the corresponding processes. The present study will assist in optimizing phase-structural composition of the alloys in the La–Mg–Ni system which contain Mg-modified layered structures by tailoring the high temperature annealing conditions.

Ni/ZnO nano-sponges have been successfully synthesized through optimized annealing of Ni/Zn-based organic framework (Ni/Zn-MOF). The annealed MOF provides the stable carbon structure with 3D interconnection and prevents structural collapse during the charging and discharging process. The annealing causes the incorporation of intrinsic Ni3+ in the surface of NiO nanoparticles, providing more reaction active sites. The oxygen vacancies in ZnO and heterostructure interfaces between NiO and ZnO promote the charge transformation. Based on the aforementioned advantages, the Ni/ZnO nanocomposites exhibit excellent electrocatalytic performances for supercapacitors. The specific capacitance can reach to 807 F·g−1 at 1 A·g−1 in the studied electrodes. After 5,000 cycles at 10 A·g−1, the cyclic stability remains excellent at 86% of the initial capacitance. Moreover, the as-prepared asymmetric supercapacitor exhibits a high energy density of 30.6 W·h·kg−1 at power density of 398 W·kg−1. This study is expected to provide new insights into exploring the potential mechanism of catalyst action.

Aqueous electrolytes are safe, economic, and environmentally friendly. However, they have a narrow potential window. On the other hand, organic electrolytes exhibit good thermodynamic stability but are inflammable and moisture sensitive. In this study, we prepared water–PEG–lipid ternary electrolytes (TEs). To combine the advantages of water, polyethylene glycol (PEG) and propylene carbonate (PC). The nonflammable mixed electrolytes exhibited a wide potential window of about 2.8 V due to the beneficial effects of PEG and PC. Using these TEs, a lithium manganate–active carbon ion capacitor could be operated at 2.4 V with an energy density of 32 Wh/kg, based on the total active electrode material (current density of 3.3 mA/cm2). This value was significantly higher than that achieved using an aqueous electrolyte, thereby rationalizing the higher energy density.

Artículo escrito por un elevado número de autores, solo se referencian el que aparece en primer lugar, el nombre del grupo de colaboración, si le hubiere, y los autores pertenecientes a la UAM, Hydrides based on magnesium and intermetallic compounds provide a viable solution to the challenge of energy storage from renewable sources, thanks to their ability to absorb and desorb hydrogen in a reversible way with a proper tuning of pressure and temperature conditions. Therefore, they are expected to play an important role in the clean energy transition and in the deployment of hydrogen as an efficient energy vector. This review, by experts of Task 40 'Energy Storage and Conversion based on Hydrogen' of the Hydrogen Technology Collaboration Programme of the International Energy Agency, reports on the latest activities of the working group 'Magnesium- and Intermetallic alloys-based Hydrides for Energy Storage'. The following topics are covered by the review: multiscale modelling of hydrides and hydrogen sorption mechanisms; synthesis and processing techniques; catalysts for hydrogen sorption in Mg; Mg-based nanostructures and new compounds; hydrides based on intermetallic TiFe alloys, high entropy alloys, Laves phases, and Pd-containing alloys. Finally, an outlook is presented on current worldwide investments and future research directions for hydrogen-based energy storage

Hydrous electrolytes with high electrochemical potentials were obtained by hydrating water molecules into solutes to form high Li:water molar ratio electrolytes (HMRE). Solid polyethylene glycol (PEG) were employed to enhance the molar ratio of Li+ to water in the electrolytes while reducing the consumption of Li-salt. The obtained mole ratio of Li+ to water molecules in the hydrous electrolytes was greater than 1:1; however, the mass fraction of Li-salt was reduced to 61% (approximately 5.5 mol/kg, based on water and PEG). Compared with that of water-in-salt electrolytes, the mass fraction of Li-salt could be remarkably reduced by adding solid PEG. The electrochemical stability of the electrolytes improved considerably because of the strong hydration of Li+ by the water molecules. A beneficial passivation effect, arising from the decomposition of the electrolyte, at a wide potential window was observed.

Defects have always been considered as one of the important factors to reduce the laser damage thresholds of potassium dihydrogen phosphate (KH2PO4, KDP). However, crystal defects often do not exist singly but combine with each other to form clusters. In this study, hybrid density functional theory was used to investigate how the cluster defects affect the damage threshold of KDP crystals. The concentration of oxygen vacancy defects has little effect on the electronic structure, only influencing the torsion of the surrounding bond. Moreover, the cluster defects comprising FeP2− + VO2+ could cause a slight local variation of the lattice for KDP crystals. The defect state induced by FeP2− defect could introduce three defect states at 0.5, 1.2 and 4.0 eV, respectively. It could also introduce absorption peaks at around 200 nm in the yz plane. When the FeP2− + VO2+ cluster defect forms, the defect state shifts to CBM at about 1.0 eV as a whole due to electron depletion and accumulation for the H atom and its attached O atom. It could have an influence on electronic and optical properties by strengthening the charge transfer along the direction of x in the crystals. The calculation results could provide a good suggestion to improve the quality of the crystals by decreasing the concentration of the cluster defects in KDP crystal.

A C15 AB2 Laves-type Ti0.15Zr0.85La0.03Ni1.2Mn0.7V0.12Fe0.12 alloy was prepared by arc melting and annealing. Phase-structural composition, microstructure, hydrogen absorption-desorption properties, thermodynamic and electrochemical performances were characterized by X-ray diffraction, scanning electron microscopy, hydrogen absorption-desorption measurements and electrochemical characterization and were related to the use of the alloys as metal hydride battery anodes. The alloy contains a C15 FCC intermetallic compound as the main phase and a LaNi secondary phase as the minor constituent (∼1 wt%). During the electrochemical tests, the anode electrodes quickly, after just a few activation cycles, reached a maximum discharge capacity. This was related to the catalytic effect of the La-rich secondary phase which acted as a catalyst of hydrogen absorption-desorption. Annealing resulted in increase of the maximum discharge capacity from 345 mAh/g for the as cast alloy to 370 mAh/g. Furthermore, the annealed alloy showed a better high rate dischargeability and a higher cyclic stability. After 100 cycles with 100% DOD at discharge current density of 1C, the discharge capacity of the annealed alloy was very high, at a level of 90% of the initial capacity. The rates of hydrogen diffusion have been characterized by Potentiostatic Intermittent Titration Technique and Electrochemical Impedance Spectroscopy. With increasing an extent of transformation into the hydride, the H diffusion rate in the bulk of the alloy particles decreased. The maximum value of DH measured by PITT for the annealed alloy was observed for the nearly fully discharged electrode, (SOC 2%).

Ammonium dihydrogen phosphate (NH4H2PO4, ADP) is an excellent nonlinear optical crystal and has had wide application. It was the same type of potassium dihydrogen phosphate (KH2PO4, KDP) with a similar crystal structure. The difference in structure and properties of ADP crystal in the presence of defects, especially cluster defects, was one of the important issues of concern in the research. In this work, first-principles calculation, coupled with HSE06 functional and the van der Waals-Wannier function method, was applied to investigate the structural stability and electronic properties induced by oxygen vacancy cluster defects and FeP2-+VO2+ cluster defects. And some spectra experiments, such as Raman spectroscopy, the Fourier transform infrared spectroscopy and the ultraviolet absorption spectroscopy, were also applied to investigate the detailed influence for ADP crystal doped with different Fe3+ concentration, which was grown with the “point-seed” rapid growth method. Combined with the theoretical results and the spectra tests, it confirmed that the structural changes in ADP crystal caused by oxygen vacancy cluster defect and FeP2-+VO2+ cluster defect were smaller than that in KDP crystal, mainly due to the restriction of hydrogen bonds and NH4+ group. With the increase of defect concentration, the microstructure stress could also damage the crystal structure due to the microscopic stress induced by Fe3+. The defect states moved towards right from 1.1 eV to 6.6 eV with the concentration of oxygen vacancy increasing. Similarly, the defect state composed of Fe 3d and O 2p states induced by FeP2- defect also moved to the conduction band minimum. The absorption peaks around 220-350 nm induced by FeP2- defect and FeP2-+VO2+ cluster defect were along the xy plane. It provided a good suggestion based on the calculation that it was very important to minimize defects or control cluster defect concentration during crystal growth.

This study aims to guide the future design of metal-organic frameworks (MOFs) for hydrogen storage. At 77 K, azulenedicarboxylate (ADC)-substituted MOF-5 increases the hydrogen adsorption rate and hydrogen uptake capacity when the pressure exceeds 12 bar. At 297 K, ADC substitution significantly increases hydrogen adsorption when the pressure exceeds 5 bar. The grand-canonical Monte Carlo (GCMC) detailed analyses indicate that with increased pressure, hydrogen molecules in MOFs tend to be located at the corner region, organic linkers, and the center of cores. Meanwhile, high pressure adsorption shows that the large space due to ADC substitution leads to reduced steric effect around metal sites. Analysis of density of states illustrates that the introduced organic linkers may contribute sufficient electrons and enhance electron flow. These electrons can induce an electric field-effect, which increases the polarisation of hydrogen atoms and molecules surrounding linkers. Amongst the studied MOFs, substitution with Ni exerts no obvious effect on hydrogen storage.

We reveal the interaction of H with He in pure W and W-Ta alloy based on first-principles calculations. We show a strong attraction between H and He in both systems that drives H segregation towards He. The substitutional He and tetrahedral interstitial H defects in W-Ta alloy are more energetically favorable than pure W due to the decreased electronic density of the replaced Ta atom. Moreover, 1 He-Vac complex in both systems can trap as many as 12 H atoms. Based on the calculated formation energy of Hn-He-Vac complexes, the H3-He-Vac has the lowest formation energy in both systems. We believe that such understanding is generally applicable for H bubble formation in metals and metal alloys.

The rod-shaped CeO2@C architectures have been synthesized by novel and facile methods initially from metal–organic frameworks (MOFs). The MOF-derived material showed a pseudocapacitance of 1102 F g−1 at 2 A g−1 and 418 F g−1 at a high current density of 20 A g−1 and had excellent cyclic stability of about 2.3% decrease after 5000 cycles. Results revealed that favorable effects of dispersed partially graphitic carbon in the CeO2@C composite could improve electronic conductivity, which made this product be an alternative high-performance electrode for supercapacitors.

The structural composition and electrochemical capacity of four AB2 Laves-type intermetallic alloys with various Ti/Zr ratios (TixZr1−xLa0.03Ni1.2Mn0.7V0.12Fe0.12, x = 0.12, 0.15, 0.18, and 0.22) were investigated in this study. The alloys were characterized by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. These data revealed the coexistence of the main phase of the C15-type FCC Laves-type AB2 compounds with a secondary La–Ni intermetallic that was present in minor amounts. Increasing the Ti substitution for Zr caused the gradual shrinkage of the unit cells of the C15 phase. The neutron powder diffraction studies demonstrated that in the trihydride (Ti, Zr, V)(Ni, Mn, Fe, V)2D3.2, D atoms filled A2B2 tetrahedra, whereas V atoms occupied not only conventional 16d sites but also partially replaced Zr/Ti at 8a sites. All studied alloys showed similar activation behaviors, wherein four cycles were required to realize the highest electrochemical capacity of the anodes. The Ti12/Zr88 alloy demonstrated excellent full discharge capacity that reached 466 mAh/g. The Ti22/Zr78 alloy electrode exhibited good cycling stability (retention rate of ~71%) after 500 cycles and a superior high-rate discharge capability (retention rate of ~71%) at a discharge current density of 400 mA/g. The cycling of the Ti22/Zr78 alloy electrode was studied by electrochemical impedance spectroscopy (EIS) to understand the reasons for the deterioration of cycling capacity, which was related with the pulverization of the alloys and increase in irreversible capacity.

Controllable nitrogen-doped carbon layers coated on NiCoO2 (NiCoO2@N-C) as anode materials are successfully synthesised by facile hydrothermal method and post-annealing treatment. Benefiting from the synergistic merits of carbon and nitrogen, the as-synthesised NiCoO2@N-C delivered an excellent capacitance of 1000 F g−1 at 1 A g−1 and a high specific capacitance of 491 F g−1 at 50 A g−1. After 5000 cycles at 10 A g−1, the cyclic stability remains 91% of the initial capacitance. Moreover, the assembled asymmetric supercapacitor exhibits a high energy density of 45.9 Wh kg−1 at a power density of 375 W kg−1. The NiCoO2@N-C hybrid nanostructure was investigated by using X-ray powder diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Brunauer–Emmett–Teller (BET) techniques. In situ X-ray absorption near edge structure (XANES) spectroscopy was used to track the changes of NiCoO2@N-C electrode under electrochemical working conditions and confirmed that Ni had more significant electrochemical activity than Co. These findings provide new insights into the role of heteroatom doping for high-performance supercapacitors in future applications.

Density functional theory calculations have been performed to study the stability and the interactions of/between small helium clusters at the W(001) surface. Among the studied He clusters, all the He atoms prefer to stay under the second atomic layer from the surface, instead of surface and subsurface. Trapping of multiple He in tungsten surface can induce formation of a new vacancy at nearby lattice site, and the Hen-V (n = 2 and 3) complexes are formed concurrently. The electronic densities of states (DOS) and charge-density distribution are presented for di-helium and tri-helium clusters. Calculated He formation energies and He-vacancy binding energies improve understanding of He trapping behavior and diffusion mechanisms in tungsten surface.

Hierarchically porous activated carbon (PAC) and Ni@C composite materials have been synthesized initially from MOF-5 and bimetallic Ni(II)-doped MOF-5s with the effective incorporation of Ni2+ ions into the frameworks. The products (PAC-1, Ni@C-1 and Ni@C-2) derived from MOFs contained rich micro/mesoporous structure and high specific surface areas (SSA): 2247, 919, and 484 m2 g−1, respectively. Interestingly, LiBH4 doped with Ni@C-1 showed the lowest onset temperature around 180 °C and fastest dehydrogenation kinetics. Results reveal that favorable synergistic effects of nanoconfinement and catalysis in Ni@C materials may improve hydrogen desorption kinetics, which demonstrates a promising strategy for the hydrogen-storage application of LiBH4.

We investigated the properties of He defects, the migration of a single He atom and the formation of He clusters in W–Ta (atomic ratio 1:1) alloy via first-principles density functional theory calculations. Results showed that He most preferred to occupy the substitutional site first and then the tetrahedral and octahedral interstitial sites. The formation energies of interstitial He in W–Ta alloy are between in bulk W and Ta. While the formation energies of substitutional He in W–Ta alloy were higher than those in bulk W and Ta. Structural relaxation and energy calculations revealed that the formation energies of He clusters linearly increased with cluster size. The binding energies of even-numbered He clusters were lower than those of their neighbouring odd-numbered He clusters. The migration calculation showed that the energy of SubTa was lower, and it had stronger attraction to He atom. Density of state and electronic structure were analysed to reveal the underlying mechanisms governing cluster formation. Results demonstrated that the hybridizations of p-projected DOS of He and its neighbouring metal atoms were responsible for the site-preference order of He in DOS. Moreover, the differences in charge density between He and W(Ta) were negative under all conditions, suggesting the repulsive interaction of He and W(Ta) in W–Ta alloy. This study provides a good reference for evaluating the influence of He on the performance of W–Ta alloy for plasma-facing materials.

The present work is focused on the studies of structure, hydrogen storage and electrochemical properties of the La3-xMgxNi9 (x = 1.0, 1.1 and 1.2) alloys as active materials of negative electrodes in the Nickel-Metal Hydride (Ni/MH) batteries. A change of Mg content affects properties of the studied alloys such as the phase homogeneity, hydrogen storage and electrochemical capacities, cycle stability, and high-rate discharge performance. X-ray diffraction study shows that Mg substitution for La and annealing of the La3-xMgxNi9 alloys promotes the formation of more homogeneous materials, with a predominant formation of the target AB3 PuNi3 structure type intermetallics. The electrodes prepared from the annealed alloys show the maximum discharge capacities of ∼400 mAh g−1 at discharge current density of ∼60 mA/g. The high rate discharge-abilities (HRD) at the discharge current density of 350 mA g−1 keep high values of the remaining reversible discharge capacities, ∼86, 85 and 80%, for the La2MgNi9, La1·9Mg1·1Ni9 and La1·8Mg1·2Ni9 alloy electrodes, respectively. After 200 cycles with 100% depth of discharge (DOD), the La1·9Mg1·1Ni9 alloy electrode exhibits a very good cycling stability with its discharge capacity remaining at a level of ∼64% of its initial capacity.

This work was focused on studies of temperature-induced phase-structural transformations in the as-cast La 2 MgNi 9 metal hydride battery electrode alloy. The interactions in the alloy were studied by in situ neutron powder diffraction at temperatures ranging from 300 K to 1273 K. Initial alloy is multi-phase structured, containing six different intermetallics with five stoichiometric compositions. These include the targeted rhombohedral La 2 MgNi 9 as the main phase constituent, together with three electrochemically active intermetallics, La 3 MgNi 14 (3R), La 4 MgNi 19 (2H) and La 4 MgNi 19 (3R). Furthermore, the alloy contained two “ballast” intermetallics, LaNi 5 and LaMgNi 4 . Various transformations take place on heating, leading to the significant changes in the contents of the constituent intermetallics, first of all to the disappearance of LaNi 5 and LaMgNi 4 . Thermal volume expansions of the studied intermetallics were well fitted by the linear dependences and resulted in similar values of 4.3–5.5 vol.% at 1223 K as compared to 300 K.

This work was aimed at in situ studies of the phase-structural transformations in an Mg- and Nd-modified LaNi 3 intermetallic having a bulk composition La 1.5 Nd 0.5 MgNi 9 , as related to its performance as battery anode material in the Ni-Metal Hydride batteries. The interactions in the La 1.5 Nd 0.5 MgNi 9 system were studied by in situ neutron diffraction in a temperature range 300–1248 K. Two alternative processes of preparation of the alloy were studied: (a) Synthesis from a mixture of the powders La 0.75 Nd 0.25 Ni 5 + La 0.75 Nd 0.25 MgNi 4 ; and (b) annealing of the alloy prepared by induction melting. Various transformations take place in the samples on heating, leading to the formation of four new phases, all with the stacking structures of the intermetallic alloys having three variable ratios (RE + Mg)/Ni, 1:3, 2:7 and 5:19. Further to (La 0.75 Nd 0.25 ) 2 MgNi 9 with a rhombohedral PuNi 3 type, there were formed (La 0.75 Nd 0.25 ) 3 MgNi 14 with a rhombohedral Gd 2 Co 7 structure and two polymorphic modifications of (La 0.75 Nd 0.25 ) 4 MgNi 19 compound, a high temperature hexagonal Pr 5 Co 19 type and a low temperature rhombohedral Ce 5 Co 19 type. In every case the unit cell parameters showed shrinking as compared to the La-based analogues. Nd substitution for La in La 2 MgNi 9 promotes the formation of a more homogeneous alloy, with a predominant formation of the target AB 3 intermetallic. Properly homogenized La 1.5 Nd 0.5 MgNi 9 alloy shows a more flat and longer plateau, both in the course of hydrogen absorption–desorption and under electrochemical charge–discharge. An apparent hydrogen diffusion coefficient in alloy bulk appears to be higher as compared to Nd-free alloy, contributing to a better reversibility under a high-rate operation at high discharge current densities, while maintaining a good cycle stability.

Present paper investigates Ti0.25Zr0.75Ni1.35-xMn0.65Vx (x = 0, 0.05, 0.1, and 0.15) alloys as anode active materials of metal hydride batteries. The AB2 Laves-type alloys are prepared using arc melting and annealing. The as-cast alloys contain the major C15 and/or C14 intermetallic compounds together with the Ti–Ni and Zr–Ni secondary phases. The annealing promotes the homogeneity of the alloys and dismisses the non-Laves phases. As the V contents increase, the C15-type Laves phase transforms to the C14 structure. In addition, the unit cells of the Laves phase increase as the V contents in the alloys increase. All the studied alloy electrodes reach their maximum discharge capacities during the first 10 activation cycles. After charge/discharge 100 cycles at 300 mAg−1, the discharge capacity retentions of all the studied alloy electrodes keep more than 75%. Annealing treatment and V substitution increase the full discharge capacity from ~230 mAg−1 for N1 alloy to ~430 mAhg−1 for A4 alloy. The synthetic effects between V substitution and annealing are studied on improving the phase structure and the electrochemical properties of AB2-type Laves phase alloys.

This work focused on the structural and electrochemical properties of AB2-type Zr/Ti-based metal hydride anode alloys. The as-cast and annealed Ti0·24Zr0·76Ni1·1Mn0·7V0.2 alloys were characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical characterization (EC). X-ray diffraction (XRD) results indicated the presence of homogenous C14 Laves phase in the annealed alloy, and the major C15 and C14 phases coexisted with the TiNi and Zr9Ni11 secondary phases in the as-cast alloy. SEM images showed the phase compositions in these alloys and confirmed the significant decrease in the secondary phases of the annealed alloy. During EC, the as-cast alloy showed better activation performance than the annealed alloy. This result was related to the catalytic effect of the Ti-/Zr-related secondary phases during electrochemical reactions. Annealing increased the maximum discharge capacity from ∼350 mAh/g for the as-cast alloy to ∼400 mAh/g for the annealed alloy during activation. The annealed alloy also showed considerable cycling stability and a slightly high discharge rate. We developed a C14-Laves phase metal hydride alloy showing a discharge capacity ∼400 mAh/g at a 100 mA/g rate (C/4) suitable for electric vehicle (EV) application.

First-principles calculations were carried out to clarify the effect of Ti and Nb dopants on the structure, energetics, and electronic properties of NaAlH 4 in bulk and surface. Our calculations revealed that Ti preferred to substitute for the AlH site of AlH 4 unit, whereas Nb preferred to substitute for the Al atom in bulk. Structural analysis showed that the structure of Nb-doped NaAlH 4 bulk was looser than Ti-doped NaAlH 4 bulk. The analysis of density of states illustrated that Ti interacted with Al atoms in covalent bonds, whereas Nb interacted with Al atoms mainly in weak ionic bonds in Ti- and Nb-doped NaAlH 4 bulk. Thus, the diffusion of hydrogen atoms and AlH x units was more favorable in Nb-doped bulk than in Ti-doped bulk. The location of Nb atom in the NaAlH 4 (001) surface was investigated, and an active NbAl 2 H 10 –Al 2 H 6 complex was observed. The results of hydrogen removal energies of the complex indicated that the removal of H atoms, especially the H atoms in the Al 2 H 6 unit, was much simpler than in pure NaAlH 4 .

The synergistic effect of Li–Ti and K–Ti dopants on the energy, structure and electronic properties of NaAlH4 has been investigated using density functional theory and ab initio molecular dynamics. Pair distribution functional analyses show that the substitution of NaAlH4 by Li2Ti and K2Ti favor not only the release of H2 but also the reductions in the barrier energies of (AlH4)− units. Density of states analyses suggest that the weakening of Al–H bonds in Li2Ti- and K2Ti-doped NaAlH4 is attributed to the formation of Ti–Al and Ti–H phases. Bader atomic charges analyses imply that the strong interaction of Li–Al prevent the further formation of Ti–Al clusters. The results of H removal energies analyses reveal that both Li2Ti and K2Ti are favorable catalysts for NaAlH4. Thus, that a Li2Ti dopant, with lighter weight than K2Ti, can be applied as a favorable catalyst for NaAlH4 has been given for the first time.

The dehydrogenation kinetics of LiBH 4 incorporated within various carbon nanotubes has been studied. It is demonstrated that the desorption kinetics of LiBH 4 could be greatly promoted using a simple melt infiltration method and LiBH 4 confined in modified multi-walled carbon nanotubes (MWCNTs) shows the best desorption kinetics. The structural properties of carbon nanotubes and confined samples are demonstrated by means of transmission electron microscopy, powder X-ray diffraction and Raman spectroscopy. The crystal structure of MWCNTs and single-walled carbon nanotubes (SWCNTs) are almost unchanged after ball milling. But high energy ball milling leads to a decrease in the average nanotube length and introduces a great amount of local disorder and structural defects in the CNTs, which may provide a considerable kinetic improvement.

Structural, electronic and energetics properties of Nb-doped LiBH 4 (010) surface have been studied based on the first-principles density functional theory calculations. Three kinds of local structures are found during the dehydrogenation reaction of LiBH 4 , the most two favorable hydrogen desorption pathways are found to lead to NbH 2 -BH 2 -(BH 4 ) 3 complex when the Nb occupies the top site of single B atom and lead to NbH 2 -(BH 3 ) 2 complex when the Nb occupies the bridge site of two adjacent B atoms. The formation of NbH 2 and BH 2 units in the NbH 2 -BH 2 -(BH 4 ) 3 complex as well as the catalytic effect of Nb on the structures of surrounding (BH 4 ) − units due to the orbital overlaps between Nb and inner B-H bonds in the complex. For the NbH 2 -(BH 3 ) 2 complex, NbH 2 and NbB 2 phases may be formed in sequence accompanied by the dehydrogenation reaction. The results are in good agreement with the report of Wang, KK et al. experimentally. The calculated average hydrogen desorption energies of Nb-doped LiBH 4 (010) surface are smaller than the pure LiBH 4 (010) surface about 1.7 eV and 1.5 eV, respectively. These properties reveal that the import of Nb has great effect on reducing the bond strength of B-H.

This paper describes the hydrogen storage properties of Mg 2 Ni 0.9 Cr 0.1 alloy and aims to elucidate the effect of doping Cr on the hydrogen sorption/desorption kinetics upon cycling. Mg 2 Ni 0.9 Cr 0.1 alloy shows stable absorption capacity, and its absorption/desorption rates further improve after cycling. The calculated activation energy for dehydrogenation was 53 kJ/mol at the 3rd cycle, and decreased to 36 kJ/mol at the 20th cycle. XRD combined with SEM exhibits that Cr dopant substitutes for Mg or Ni after ball milling and the lattice structure remains stable over 20 cycles. EXAFS was used to investigate the local coordination of Ni and Cr atoms in the ball-milled and cycled samples. For the ball-milled sample, the strong Cr–Ni bonds weaken the Cr–Mg bonds, thereby destabilizing all Cr-doped phases. After 20 cycles, the stable Ni 1 –Mg 1 bonds may be dominant and control the structural stability of Mg 2 Ni phases.

In this study, Mg1.9NiTi0.1 alloy was synthesized by mechanical alloying and its cyclic hydrogen storage behaviors were investigated. It was found that titanium substituting magnesium in Mg1.9NiTi0.1 alloy notably improves the absorption/desorption kinetics. Upon cycling, the kinetic rates of absorption/desorption further increase, whereas the hydrogen storage capacity decreases. To identify the micro-structural evolution of Mg1.9NiTi0.1 alloy during cycling, we used X-ray diffraction, scanning electron microscope, and extended X-ray absorption fine structure. After ball milling, the decrease of Mg–Ni atomic interaction lowers the stability of Ti-doped phases and has positive effect on the absorption/desorption behaviors. After 20 cycles, the decrease in the cycling capacity may be attributed to the increasing MgNi2 content. Further studies revealed that some amounts of Mg2Ni transform into MgNi2, which result in great decrease in effective hydrogen storage capacity.

We investigate the structural, elastic and electronic properties of Li2B12H12 using the first-principles method. Our calculations show that the lowest energy structure of Li2B12H12 is monoclinic C2/m type. We take the monoclinic C2/m Li2B12H12 as a representative to carry out the corresponding theoretical studies. The independent elastic constants are successfully obtained from the strain energy–strain curve calculations. The Shear and Young‘s moduli, as well as Poisson‘s ratio for ideal polycrystalline Li2B12H12 are calculated. The shear anisotropic factors and elastic anisotropy of Li2B12H12 are analyzed. The Debye temperature and the average elastic wave velocity are derived from theoretical elastic constants. According to the obtained results, the monoclinic C2/m Li2B12H12 is found to be mechanically stable and brittle at zero temperature and zero pressure. Furthermore, the density of states and electron charge density distributions are studied. The insulator Li2B12H12 is a technologically interesting indirect hydrogen storage material for further studies.

The crystal structure and local atomic arrangements surrounding Ti atoms were determined for He-charged hexagonal close-packed (hcp) Ti films and measured at glancing angles by synchrotron radiation X-ray diffraction (XRD) and extended X-ray absorption fine structure (EXAFS) spectroscopy, respectively. The charged specimens were prepared by direct current magnetron sputtering with a He/Ar mixture. He atoms with a relatively medium concentration (He/Ti atomic ratio as high as 17 at.%) were incorporated evenly in the deposited films. XRD results showed the changes in the peak intensities in Ti films with different He contents. EXAFS Fourier Transform analysis indicated that the average Ti–Ti distance decreased significantly, and proved the existence of phase transition.

We have presented a study of the elastic properties of orthorhombic Pnma structural LiBH4 by first-principles calculations using a projected augmented plane-wave method. The single crystal elastic constants are successfully obtained from the stress–strain relationship calculations and the strain energy–strain curves calculations, respectively. The Shear and Young‘s moduli as well as Poisson‘s ratio for ideal polycrystalline LiBH4 are calculated. The bulk moduli are in good agreement with recent experimental and theoretical results. The linear compressibility and the directional dependent Young‘s modulus are also calculated. The shear anisotropic factors and the elastic anisotropy of Pnma LiBH4 are analyzed. The Debye temperature and the average elastic wave velocity are derived from theoretical elastic constants. According to the obtained results, the Pnma LiBH4 is found to be mechanically stable and ductile at zero temperature and zero pressure.

Compared with titanium oxide (TiO2) and zirconium chloride (ZrCl4), cerium oxide (CeO2) significantly affects the dehydrogenation properties of lithium alanate (LiAlH4). CeO2-doped LiAlH4 samples obtained in different decomposition states were characterized by in situ X-ray diffraction, synchrotron radiation powder X-ray diffraction (PXD) data, and X-ray absorption fine structure (XAFS). PXD and XAFS analyses reveal that CeO2 is present as a cubic CeO2−x phase and behaves as a true catalyst. Ce4+ reduction affects the ability of Li to donate its charge to AlH4, thereby weakening the Al–H bond and causing hydrogen to desorb at lower temperatures. Beyond 180 °C, approximately 50% of the O atoms of the CeO2 catalyst are removed, which results in the formation of long-range disorder rhombohedral Ce7O12 phase and an opposite effect on the dynamics.

Herein, we present a comparison of the electrochemical hydrogen-storage characteristics of two state-of-art Laves phase-based metal hydride alloys (Zr21.5Ti12.0V10.0Cr7.5Mn8.1Co8.0Ni32.2Sn0.3Al0.4 vs. Zr25.0Ti6.5V3.9Mn22.2Fe3.8Ni38.0La0.3) prepared by induction melting and hydrogen decrepitation. The relatively high contents of lighter transition metals (V and Cr) in the first composition results in an average electron density below the C14/C15 threshold (e/a~6.9) and produces a C14-predominated structure, while the average electron density of the second composition is above the C14/C15 threshold and results in a C15-predominated structure. From a combination of variations in composition, main phase structure, and degree of homogeneity, the C14-predominated alloy exhibits higher storage capacities (in both the gaseous phase and electrochemical environment), a slower activation, inferior high-rate discharge, and low-temperature performances, and a better cycle stability compared to the C15-predominated alloy. The superiority in high-rate dischargeability in the C15-predominated alloy is mainly due to its larger reactive surface area. Annealing of the C15-predominated alloy eliminates the ZrNi secondary phase completely and changes the composition of the La-containing secondary phase. While the former change sacrifices the synergetic effects, and degrades the hydrogen storage performance, the latter may contribute to the unchanged surface catalytic ability, even with a reduction in total volume of metallic nickel clusters embedded in the activated surface oxide layer. In general, the C14-predominated alloy is more suitable for high-capacity and long cycle life applications, and the C15-predominated alloy can be used in areas requiring easy activation, and better high-rate and low-temperature performances. © 2017 The Authors. This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

MgCo 2 and MgNiCo crystallize with hexagonal Laves type intermetallic structures of the C14 type and do not form hydrides at ambient hydrogen pressures. However, applying high hydrogen pressures in the GPa range forces the hydrogen absorption and leads to the formation of multi-phase compositions, which contain approximately 2.5 atoms H per formula unit of MgCo 2 or MgNiCo and remain thermally stable under normal conditions. The hydrogenation of MgCo 2 resulted in its decomposition to a ternary Mg 2 CoD 5 deuteride and metallic cobalt. Phase-structural transformations accompanying the vacuum desorption of deuterium in the temperature range of 27–500 °C were studied using in situ neutron powder diffraction. The investigation showed a complete recovery of the initial MgCo 2 intermetallic via a Hydrogenation-Disproportionation-Desorption-Recombination process. At 300 °C, the Mg 2 CoD 5 deuteride first decomposed to elementary Mg and hexagonal Co. At 400 °C, a MgCo phase was formed by interaction between Mg and Co. At the highest processing temperature of 500 °C, a solid-state interaction of MgCo and Co resulted in the recovery of the initial MgCo 2 . The interaction of MgNiCo with deuterium under the synthesis conditions of 2.8 GPa and 200 °C proceeded in a more complex way. A very stable ternary deuteride MgNi 2 D 3 was leached away while Co was separated in the form of Mg 2 CoD 5 and the remaining nickel formed a solid solution with Co with the approximate composition Ni 0.7 Co 0.3 . The thermal desorption of deuterium from MgCo 2 D 2.5 and from MgNiCoD 2.5 has been studied by Thermal Desorption Spectroscopy with deuterium released into a closed volume. The observed effects nicely correlate with changes in the phase structural composition of the hydrides formed. MgCo 2 is a new example of the hydrogen storage alloy, in which a successful HDDR processing results in the reversible formation of the initial intermetallic at much lower temperatures than in the equilibrium phase diagram of the Mg-Co system.

Multi-substituted LaNi 5 alloys prepared by annealing, activating, and cycling were investigated systematically using synchrotron radiation X-ray diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), and X-ray photoelectron spectroscopy to clarify the evolution of the structural properties of the alloys. XRD and Rietveld analysis results show that annealing and activation can cause changes in the isotropy of the lattice constants of the LaMn x Ni y phase. EXAFS data on the La-L3-edge show variations in atomic distances between La–Mn and La–Ni during annealing. Chemical shifts in the La 3 d and Ni 2 p core levels induced by activation can be determined with very high levels of accuracy using energy differences Δ E B (Ni 2 p 1/2 –La 2 d 5/2 ). The decrease in the cycling capacity may also be attributed to the oxidation of La and Ni in the alloys during cycling, which can resist the reaction of hydrogen absorption.

Extended X-ray absorption fine structure (EXAFS) measurements at room temperature at the Ti, V, and Cr K absorption edges were applied to a TiVCrMn alloy subjected to 300 cycles of hydrogen absorption-desorption. The model of the cubic symmetry and atom random distribution is used to fit the EXAFS spectra. The FEFF calculations show relatively good agreement using this model. The EXAFS analysis reveals the variation of local structure of the TiVCrMn alloy with cycling. Aside from the Ti–Cr and Cr–Cr distances, noticeable changes in the other bond lengths were observed during cycling, which can be due to the entrance of hydrogen and lattice contraction in the alloy cells.

The evolution of crystal structure and chemical state of Mg1.9Al0.1Ni alloy during hydrogen absorption–desorption cycling was examined by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). We research the hydrogen storage capacity of the Mg1.9Al0.1Ni by the H/D kinetic curves. The H/D kinetic curves indicate that the hydrogen storage capacity increased with the increased cycles and the samples were activated after 10 cycles have the maximum hydrogen storage capacity. The local structure of Ni atoms was studied by extended X-ray absorption fine structure (EXAFS). The EXAFS results indicate the Ni–Ni bonds distance has no obviously change with the cycles increasing, whereas the Ni–Mg bond lengths increase, and the Ni–Mg bond lengths are longer obviously than before 10 cycles whereas it has no obviously change after 10 cycles.

Properties of various defects of He and H atoms in W?Ta alloys are investigated based on density functional theory. The tetrahedral interstitial site is the most configured site for self-interstitial He and H in W and W?Ta alloys. Only a single He atom favors a substitutional site in the presence of a nearby vacancy. However, in the coexistence of He and H atoms in the presence of the vacancy, the single H atom favors the tetrahedral interstitial site (TIS) closest to the vacancy, and the He atom takes the vacancy center. The addition of Ta can reduce the formation energy of TIS He or H defects. The substituted Ta affects the charge density distribution in the vicinity of the He atom and decreases the valence electron density of the H atoms. A strong hybridization of the H s states and the nearest W d state s exists in W 53 He 1 H 1 structure. The sequence of the He p projected DOS at the Fermi energy level is in agreement with the order of the formation energy of the He?H pair in the systems.