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Realizing rapid and stable hydrogen sorption at low temperature is critical for magnesium-based hydrogen storage materials. Herein, liquid channels are built in magnesium hydride by introducing lithium borohydride ion conductors as an efficient route for improving its hydrogen sorption. For instance, the 5 wt% LiBH4-doped MgH2 can release about 7.1 wt.% H2 within 40 min at 300 °C but pure MgH2 only desorbs less than 0.7 wt.% H2, and more importantly it delivers faster desorption kinetics with more than 10 times enhancement to pure MgH2. The hydrogen absorption capacity of LiBH4-doped MgH2 can still be well kept at approximately 7.2 wt.% without obvious capacity degradation even after six absorption and desorption cycles. This approach is not only through building ion transfer channels as a hydrogen carrier for kinetic enhancement but also by inhibiting the agglomeration of MgH2 particles to obtain stable cyclic performance, which brings further insights to promoting the hydrogen ab-/desorption of other metal hydrides. [ABSTRACT FROM AUTHOR]

In order to satisfy the demand for the cyclic stability of commercial Ni-MH anodes, a PuNi3-type La0.6Gd0.2Mg0.2Ni2.6Co0.3Al0.1 alloy with excellent overall electrochemical properties was prepared by annealing the as-cast alloy sample at different temperatures for a week. The alloy had the highest PuNi3-type content of 86.9 wt% (1073 K), which offered a capacity retention of 69.6% after 100 cycles. However, 23.7 wt% PuNi3 type phase of the alloy constantly converted into the Ce2Ni7 type phase within a temperature increase of 50 °C, which improved the capacity retention by 12.1% under the same discharge capacity. We found that the addition of Gd did not change the stacked [LaMgNi4]/[LaNi5] superlattice and it maintained the structural stability of the crystal as well as its anti-corrosion, which is also a key factor to improve cyclic stability. These findings imply that alloys with both PuNi3-type and Ce2Ni7-type multiphase structures can be considered as a new choice for hydrogen storage. [ABSTRACT FROM AUTHOR]

The development of safe, efficient, and economic hydrogen storage technologies is key for implementation of a hydrogen-based energy economy. In the search for high-hydrogen content materials, attention in the past decade has shifted to amides and borohydrides, two representative solid-state chemical sorption materials with high hydrogen capacities that had not been previously explored for hydrogen storage. A large number of new amide and borohydride systems have recently been developed that expand the material scope for hydrogen storage. This article reviews the current progress in amides and borohydrides with emphases on material design and kinetic improvement. [ABSTRACT FROM AUTHOR]

High-pressure torsion (HPT) is widely used not only as a severe plastic deformation (SPD) method to produce ultrafine-grained metals but also as a mechanical alloying technique to synthesize different alloys. In recent years, there have been several attempts to synthesize functional high-entropy alloys using the HPT method. In this paper, the application of HPT to synthesize high-entropy materials including metallic alloys, hydrides, oxides and oxynitrides for enhanced mechanical and hydrogen storage properties, photocatalytic hydrogen production and high light absorbance is reviewed. [ABSTRACT FROM AUTHOR]

As the world evolves, so does the energy demand. The storage of hydrogen using metal hydrides shows great promise due to the ability to store and deliver energy on demand while achieving higher volumetric density and safer storage conditions compared with traditional storage options such as compressed gas or liquid hydrogen. Research is typically performed on lab-sized samples and tanks and shows great potential for large scale applications. However, the effects of scale-up on the metal hydride's performance are relatively less investigated. Studies performed so far on both materials, and hydride-based storage tanks show that the scale-up can significantly impact the system's capacity, kinetics, and sorption properties. The findings presented in this review suggest areas of further investigation in order to implement metal hydrides in real scale applications. [ABSTRACT FROM AUTHOR]

Storage of renewable energy remains a key obstacle for the implementation of a carbon free energy system. There is an urgent need to develop a variety of energy storage systems with varying performance, covering both long-term/large-scale and high gravimetric and volumetric densities for stationary and mobile applications. Novel materials with extraordinary properties have the potential to form the basis for technological paradigm shifts. Here, we present metal hydrides as a diverse class of materials with fascinating structures, compositions and properties. These materials can potentially form the basis for novel energy storage technologies as batteries and for hydrogen storage. [ABSTRACT FROM AUTHOR]

Crystal structure and hydrogen storage properties of a novel equiatomic TiZrNbCrFe high-entropy alloy (HEA) were studied. The selected alloy, which had a A 3 B 2 -type configuration (A: elements forming hydride, B: elements with low chemical affinity with hydrogen) was designed to produce a hydride with a hydrogen-to-metal atomic ratio (H/M) higher than those for the AB 2 - and AB-type alloys. The phase stability of alloy was investigated through thermodynamic calculations by the CALPHAD method. The alloy after arc melting showed the dominant presence of a solid solution C14 Laves phase (98.4%) with a minor proportion of a disordered BCC phase (1.6%). Hydrogen storage properties investigated at different temperatures revealed that the alloy was able to reversibly absorb and fully desorb 1.9 wt% of hydrogen at 473 K. During the hydrogenation, the initial C14 and BCC crystal structures were fully converted into the C14 and FCC hydrides, respectively. The H/M value was 1.32 which is higher than the value of 1 reported for the AB 2 - and AB-type HEAs. The present results show that good hydrogen storage capacity and reversibility at moderate temperatures can be attained in HEAs with new configurations such as A 3 B 2 /A 3 B 2 H 7. [Display omitted] • Novel TiZrNbCrFe a A 3 B 2 -type alloy was designed for hydrogen storage. • TiZrNbCrFe alloy showed a dominant presence of C14 Laves and minor BCC phases. • TiZrNbCrFe alloy reversibly absorb and fully desorb 1.9 wt% (H/M = 1.32) of hydrogen at 473 K. • After hydrogenation, the C14 and BCC phases were fully converted into the C14 and FCC hydrides. [ABSTRACT FROM AUTHOR]

Despite potential of hydride-forming alloys for hydrogen storage, there have been few alloys which can reversibly store hydrogen without heating or activation treatment. In this study, a high-entropy alloy is designed for room temperature hydrogen storage based on three criteria: total valence electron concentration (VEC) of 6.4, single-phase thermodynamic stability (examined by CALPHAD calculations) and AB 2 H 3 hydride formation (A: hydride-forming elements, B: elements without affinity to hydrogen, H: hydrogen). The designated alloy, TiZrCrMnFeNi containing 95 wt% C14 Laves phase, absorbs and desorbs 1.7 wt% of hydrogen (hydrogen-to-metal ratio: 1) at room temperature with a fast kinetics and without activation treatment. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Structural observations were carried out on particles obtained after hydrogenation cycling of the Ti 25 V 50 Cr 25 and Ti 10 V 75 Cr 15 alloys processed by surface or bulk severe plastic deformation using the surface mechanical attrition treatment (SMAT) and high-pressure torsion (HPT) techniques, respectively. The produced particles differ in morphologies and fracture mode due to the differences in hydrogen diffusion paths. The fracture mode for the SMAT-processed samples with the gradient microstructure was mainly intragranular, whereas it was intergranular for the nanograined HPT processed samples. Hydrogen diffusion, which initiated at the grain boundaries on the surface, created Ti-rich and V-lean areas. The powders contained mainly β-VH monohydride and partly γ-VH 2 dihydride, and an orientation relationship of (100) β //(110) γ and [001] β //[001] γ with an angular deviation of ∼2.5° was observed between the two phases using the electron backscattered diffraction (EBSD) analysis. • Bulk (HPT) and surface (SMAT) deformations were applied to Ti–V–Cr alloys. • Hydrogen pulverization of SMATed samples led to finer particles than HPT ones. • Due to the nanostructure, hydrogen diffuses at grain boundaries in HPTed samples. • Comparatively, the diffusion of hydrogen is mainly intragranular in SMATed samples. • Hydrides formation leads to Ti-rich and V-lean zones. [ABSTRACT FROM AUTHOR]

Safe and high-density storage of hydrogen is a key issue for development of hydrogen as a clean energy carrier. Hydride-forming materials are potential candidates for safe and high-density storage of hydrogen and among them; Mg-based alloys are the most investigated ones due to their high gravimetric capacity. The key issue for practical application of Mg-based alloys is that they do not desorb hydrogen without heating due to the strong hydrogen binding energy. In this study, we employed first-principles calculations to design a Mg-based alloy with a low hydrogen binding energy and room temperature hydrogen storage properties. The designated material, highly-homogenous Mg 4 NiPd with a BCC-based CsCl-type structure, was successfully synthesized by severe plastic deformation via the high-pressure torsion (HPT) method. The alloy exhibited reversible hydrogenation and dehydrogenation at room temperature with high phase stability. This discovery introduces a rational approach to design and synthesize new alloys for hydrogen storage using the concept of binding energy engineering. [ABSTRACT FROM AUTHOR]

Despite high interest in compact and safe storage of hydrogen in the solid-state hydride form, the design of alloys that can reversibly and quickly store hydrogen at room temperature under pressures close to atmospheric pressure is a long-lasting challenge. In this study, first-principles calculations are combined with experiments to develop high-entropy alloys (HEAs) for room-temperature hydrogen storage. Ti x Zr 2-x CrMnFeNi (x = 0.4-1.6) alloys with the Laves phase structure and low hydrogen binding energies of -0.1 to -0.15 eV are designed and synthesized. The HEAs reversibly store hydrogen in the form of Laves phase hydrides at room temperature, while (de)hydrogenation pressure systematically reduces with increasing the zirconium fraction in good agreement with the binding energy calculations. The kinetics of hydrogenation are fast, the hydrogenation occurs without any activation or catalytic treatment, the hydrogen storage performance remains stable for at least 1000 cycles, and the storage capacity is higher than that for commercial LaNi 5. The current findings demonstrate that a combination of theoretical calculations and experiments is a promising pathway to design new high-entropy hydrides with high performance for hydrogen storage. [Display omitted] [ABSTRACT FROM AUTHOR]

[Display omitted] • Effect of air exposure on hydrogen storage behavior of Mg 2 NiH 4 − additive was studied. • Both hydrogen absorption and desorption kinetics were enhanced after air exposure. • Mg 2 NiH 4 –TiH 2 exhibited excellent air stability after air exposure for 30 days. • Air-exposed Mg 2 NiH 4 –TiH 2 showed the highest hydrogen storage capacity retention. • A ternary-synergistic effect was proposed for the Mg 2 NiH 4 –TiH 2 during air exposure. Air stability of magnesium-based hydrogen storage materials is one of the key challenges for its large-scale application, as the hydrides could be oxidized easily during air exposure. In this work, TiH 2 and graphite were added into magnesium nickel hydride (Mg 2 NiH 4) by short-time (0.5 h) mechanical milling to clarify the effect of air exposure on hydrogen storage behavior of the composites. Among the various Mg 2 NiH 4 –additive composites, the Mg 2 NiH 4 –TiH 2 composite showed the highest hydrogen desorption and absorption capacity retention of 76.9 % and 75.6 % after air exposure for 30 days, respectively. It is worth noting that both the hydrogen absorption and desorption kinetics of the composites were enhanced after air exposure, especially for the Mg 2 NiH 4 co-added with TiH 2 and graphite composite. The excellent air stability and enhanced hydrogen reaction kinetics of Mg 2 NiH 4 –TiH 2 composite should be attributed to the ternary-synergistic effect, including the protective effect of passivation layer, catalytic and sacrificial effect of TiH 2 , and catalysis of in-situ formed Ni-based products. They prevented further oxidation of the active matrix and provided more active sites for hydrogen absorption and desorption reactions. Our findings might guide the design and development of reversible metal hydrides with excellent reaction activity and air stability. [ABSTRACT FROM AUTHOR]

Complex hydride Mg(BH 4 )(NH 2 ), which consists of double anion BH 4 − and NH 2 − , was synthesized and the crystal structure was analyzed by synchrotron X-ray diffraction. The mixture sample of Mg(BH 4 ) 2 + Mg(NH 2 ) 2 prepared by ball milling was reacted and crystallized to Mg(BH 4 )(NH 2 ) by heating at about 453 K. This crystal phase transforms into amorphous phase above 473 K and subsequently the dehydrogenation begins. The crystal structure of Mg(BH 4 )(NH 2 ) was determined from measurement data at 453 K (chemical formula: Mg 0.94 (BH 4 ) 1 (NH 2 ) 0.88 , crystal system: tetragonal, space group: I4 1 (No.80), Z = 8, lattice constants: a = 5.814(1), c = 20.450(4) Å at 453 K). Mg(BH 4 )(NH 2 ) is ionic crystal which the cation (Mg 2+ ) and the anions (BH 4 − and NH 2 − ) are stacking alternately along the c -axis direction. Two BH 4 − and two NH 2 − tetrahedrally coordinate around Mg 2+ ion. [ABSTRACT FROM AUTHOR]