Study on low-vanadium Ti–Zr–Mn–Cr–V based alloys for high-density hydrogen storage

To reduce the cost and modulate hydrogen storage performances of Ti-based Laves phase alloys for the application of inputting 3.2 MPa feed hydrogen and outputting 8 MPa hydrogen with water bath, three series of less-vanadium Ti–Zr–Mn–Cr–V based alloys were prepared by induction levitation melting, and their microstructure and hydrogen storage properties were systematically investigated. All alloys consist of a single C14-type Laves phase with well-distributed elements. With vanadium decreasing in Ti_0.95Zr_0.05Mn_0.9+xCr_0.9+xV_0.2-2x (x = 0–0.02) and Ti_0.93Zr_0.07Mn_1.1+yCr_0.7+zV_0.2-y-z (y = 0, 0.05, z = 0–0.05) stoichiometric alloys, the hydrogen equilibrium pressure increases and hydrogenation kinetics is slightly deteriorated. After introducing Ti hyper-stoichiometry, Ti_0.93+wZr_0.07Mn_1.15Cr_0.7V_0.15 (w = 0–0.04) alloys show decreased hydrogen equilibrium pressure, high hydrogen capacity and enhanced kinetics. Among alloys mentioned, Ti_0.95Zr_0.07Mn_1.15Cr_0.7V_0.15 has optimum performances including useable capacity of 1.07 wt% at working conditions, together with satisfactory cycling durability. This study guides for compositional design of high-density hydrogen storage multi-component alloys.     

Optimizing Ti–Zr–Cr–Mn–Ni–V alloys for hybrid hydrogen storage tank of fuel cell bicycle

AB₂-type Ti-based alloys with Laves phase have advantages over other kinds of hydrogen storage intermetallics in terms of hydrogen sorption kinetics, capacity, and reversibility. In this work, Ti–Zr–Cr-based alloys with progressive Mn, Ni, and V substitutions are developed for reversible hydrogen storage under ambient conditions (1–40 atm, 273–333 K). The optimized alloy (Ti_0.8Zr_0.2)_1.1Mn_1.2Cr_0.55Ni_0.2V_0.05 delivers a hydrogen storage capacity of 1.82 wt%, the hydrogenation pressure of 10.88 atm, and hydrogen dissociation pressure of 4.31 atm at 298 K. In addition, fast hydrogen sorption kinetics and low hydriding-dehydriding plateau slope render this alloy suitable for use in hybrid hydrogen tank of fuel cell bicycles.     

Notable hydrogen storage in Ti–Zr–V–Cr–Ni high entropy alloy

In the present investigation, we discussed the synthesis, structural and hydrogen storage behavior of high-entropy Ti–Zr–V–Cr–Ni equiatomic intermetallic alloy. This alloy was synthesized by arc melting in an argon atmosphere where base pressure was in the order of 10^?5 atm before purging with argon gas. The X-ray diffraction study revealed that the alloy is C14 type hexagonal Laves phase. The pressure composition isotherms (PCI) of this alloy were investigated with pressure ranges at 0–40 atmosphere. The total hydrogen storage capacities were found to be 1.52 wt%. The reversible hydrogen storage capacity was quite stable and only slight decreases in the storage capacity was observed after 10 cycles during hydrogen soaking. The demonstrations of hydrogen storage capacity of the Ti–Zr–V–Cr–Ni equiatomic alloy were thus established, indicating the future potential of developing this class of high entropy intermetallic based materials for hydrogen storage.     

Electrochemical hydrogen storage performance of Mg–Ti–Zr–Ni alloys

Mg_1.5Ti_0.5−xZr_xNi (x = 0, 0.1, 0.2, 0.3, 0.4), Mg_1.5Ti_0.3Zr_0.1Pd_0.1Ni and Mg_1.5Ti_0.3Zr_0.1Co_0.1Ni alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that all the replacement elements (Ti, Zr, Pd and Co) perfectly dissolved in the amorphous phase and Zr facilitated the amorphization of the alloys. When the Zr/Ti ratio was kept at 1/4 (Mg_1.5Ti_0.4Zr_0.1Ni alloy), the initial discharge capacity of the alloy increased slightly at all the ball milling durations. The further increase in the Zr/Ti ratio resulted in reduction in the initial discharge capacity of the alloys. The presence of Zr in the Ti-including Mg-based alloys improved the cyclic stability of the alloys. This action of Zr was attributed to the less stable and more porous characteristics of the barrier hydroxide layer in the presence of Zr due to the selective dissolution of the disseminated Zr-oxides throughout the hydroxide layer on the alloy surface. Unlike Co, the addition of Pd into the Mg–Ti–Zr–Ni type alloy improved the alloy performance significantly. The positive contribution of Pd was assumed to arise from the facilitated hydrogen diffusion on the electrode surface in the presence of Pd. As the Zr/Ti atomic ratio increased, the charge transfer resistance of the alloy decreased at all the depths of discharges. Co and Pd were observed to increase the charge transfer resistance of the Mg–Ti–Zr–Ni alloys slightly.     

Remarkable hydrogen storage properties and mechanisms of the shell–core MgH2@carbon aerogel microspheres

Carbon aerogel (CA) microspheres with highly crumpled graphene–like sheets surface and network internal structure have been successfully prepared by an inverse emulsion polymerization routine, subsequently ball milled with Mg powder to fabricate Mg@CA. The Mg change into MgH₂ phases, decorating on the surface of the CA forming MgH₂@CA microspheres composite after the hydrogenation process at 400 °C. The MgH₂@CA microspheres composite displays MgH₂–CA shell–core structure and shows enhanced hydrogenation and dehydrogenation rates. It can quickly uptake 6.2 wt% H₂ within 5 min at 275 °C and release 4.9 wt% H₂ within 100 min at 350 °C, and the apparent activation energy for the dehydrogenation is decreased to 114.8 kJ mol^?1. The enhanced sorption kinetics of the composite is attributed to the effects of the in situ formed MgH₂ NPs during the hydrogenation process and the presence of CA. The nanosized MgH₂ could reduce the hydrogen diffusion distance, and the CA provides the sites for nucleation and prevents the grains from agglomerating. This novel method of in situ producing MgH₂ NPs on zero–dimensional architecture can offer a new horizon for obtaining high performance materials in the hydrogen energy storage field.     

Study of the performance of Ti–Zr based hydrogen storage alloys

The P–C–I and charging–discharging properties of three Ti–Zr based alloys have been studied. Ni substitution for Mn and Cr in the alloy was found to increase the plateau pressure of the P–C–I curve. In addition, the partial substitution of Cr by V greatly improved the discharge capacity. However, the six-element alloy, Ti_0.5Zr_0.5V_0.2Mn_0.7Cr_0.5Ni_0.6, degraded rapidly in the gas–solid reaction. Hydrogen contents in the alloy under low pressure were increased during hydrogen absorption–desorption cycling. Annealing at 1050°C for 4 h before the P–C–I experiment helped in releasing the retained hydrogen under low pressure. Only a slightly flattened P–C–I slope was obtained for the annealed alloy. Microstructures of the as-cast and annealed alloys were examined and related to the above results. Alloy powder was poisoned after 2-month storage in air, which resulted in the deterioration of discharge capacity. Surface pretreatment on alloy powders by HCl–HF solution decreased the activation time of charge–discharge reaction.     

Influence of Cr on the hydrogen storage properties of Ti-rich Ti–V–Cr alloys

In the present work, we studied the effects of Cr on the crystal structures and hydrogen storage properties of ternary alloys, Ti_0.7V_0.3−xCr_x and Ti_0.8V_0.2−xCr_x. Metal–hydrogen interactions were characterised by Thermal Desorption Spectroscopy (TDS) and in situ Synchrotron X-ray diffraction (SR-XRD). All initial alloys crystallise with body-centred cubic (BCC) crystal structures formed as solid solutions of V and Cr in Ti. Upon hydrogenation, the dihydrides (Ti,V,Cr)H₂ with face-centred cubic (FCC) structures are formed. An increase in the Cr content leads to systematic changes in the structure and hydrogenation behaviours. The changes include (a) contraction of the unit cells for the initial alloys and for the corresponding dihydrides; (b) slower hydrogen absorption kinetics and an increase in the incubation period for hydrogenation; (c) a decrease in the thermal stability of the saturated hydrides; and (d) a reduction in the apparent activation energy of hydrogen desorption. In situ SR-XRD and TDS studies of the FCC Ti–V–Cr hydrides indicated that their decomposition consists of five individual desorption events.     

Investigation of hydrogen isotope effect on storage properties of Zr–Co–Ni alloys

The deuterium desorption pressure-composition isotherms (PCIs) of ZrCo_1−xNi_x-D₂ (x = 0, 0.1, 0.2 and 0.3) systems were generated in this study in the temperature range of 524–603 K using Sievert's type volumetric apparatus. Thermodynamic parameters like enthalpy and entropy change for deuterium desorption reactions involved in the ZrCo_1−xNi_x-D₂ systems were derived using the equilibrium pressure data of PCIs. In order to interpret the hydrogen isotope effect on the storage behaviour of ZrCo_1−xNi_x alloys, the results obtained in the present study were compared with the earlier reported data on the ZrCo_1−xNi_x-H₂ (x = 0, 0.1, 0.2 and 0.3) systems. This comparison revealed that these alloys show normal hydrogen isotope effect where the equilibrium pressure of D₂ is higher than that of H₂ at all experimental temperatures. Based on these observation, it is expected that at the ITER SDS operating conditions the equilibrium pressure of tritium, deuterium and hydrogen will follow the order: p(T₂) > p(D₂) > p(H₂) for these alloys.     

Development of hydrogen absorption–desorption experimental test bench for hydrogen storage material

A volumetric experimental set-up used for measuring hydrogen absorption–desorption characteristics of hydrogen storage material will be presented. Although the experimental set-up is mainly employed to do hydrogen absorption–desorption cycling (including pressure cycling and thermal cycling) measurement automatically, it also can incidentally provide general measurements such as pressure-composition-temperature (P–C–T) curves and kinetics measurements in manual way in the ranges of 0.004–12 MPa and 213–773 K. The experimental set-up can be used to investigate the influence of hydrogen absorption–desorption cycles to hydrogen storage properties of material. The leakage rate of the whole experimental set-up was evaluated systemically. The usability and reliability of the experimental set-up were checked with LaNi₅ and Pd/K (kieselguhr).     

Fast hydriding Mg–Zr–Mn–Ni alloy compositions for high capacity hydrogen storage application

Hydrogen is one of the best alternative to petroleum as an energy carrier. However, the development of a Hydrogen-based economy requires commercialization of safe and cost-effective Hydrogen storage system. In this paper, alloys belonging to Mg–Zr–Mn–Ni alloy system are synthesized using high energy ball milling method. The particle size evolution, chemical analysis and nano-scaled structures were characterized by using SEM, EDXS and XRD techniques, respectively. The optimized - highest hydrogen storing - alloy has particle size of about 8.36 ± 1.17 μm with crystallite size 16.99 ± 5.48 nm. Hydrogen absorption-desorption measurement is carried out on the principle of pressure reduction method. The alloy coded with MZ1 shows uptake of greater than 7 mass % H₂ at a charging temperature of 200 °C, indicating high gravimetric hydrogen storage capacity at relatively lower hydriding temperature. The optimized Mg–Zr–Mn–Ni alloy also shows considerably enhanced hydriding – dehydriding kinetics, compare to pure Mg.     

Microstructure and hydrogen storage properties of non-stoichiometric Zr–Ti–V Laves phase alloys

The non-stoichiometric C15 Laves phase alloys namely Zr_0.9Ti_0.1V_x (x = 1.7, 1.8, 1.9, 2.1, 2.2, 2.3) are designed and expected to investigate the role of defect and microstructure on hydrogenation kinetics of AB₂ type Zr-based alloys. The alloys are prepared by non-consumable arc melting in argon atmosphere and annealed at 1273 K for 168 h to ensure the homogeneity. The microstructure and phase constitute of these alloys are examined by SEM, TEM and XRD. The results indicate the homogenizing can reduce the minor phases α-Zr and abundant V solid solution originating from the non-equilibrium solidification of as-cast alloys. Twin defects with {111}<011 > orientation relationship are observed, and the role of defects on hydrogenation kinetics is discussed. Hydrogen absorption PCT characteristics and hydrogenation kinetics of Zr_0.9Ti_0.1V_x at 673–823 K are investigated by the pressure reduction method using a Sievert apparatus. The results show the hypo-stoichiometric alloys preserve faster hydrogenation kinetics than the hyper-stoichiometric ones due to the decrease of dendritic V. The excess content of Zr₃V₃O phase decreases the hydrogenation kinetics and the stability of hydrides. In addition, the different rate controlled mechanisms during hydrogen absorption are analyzed. The effects of non-stoichiometry on the crystal structure and hydrogen storage properties of Zr_0.9Ti_0.1V_x Laves alloys are discussed.     

Fabrication of ball-milled MgO–Mg(OH)2-hydromagnesite composites and evaluation as an air-stable hydrogen storage material

A phase stability map of metallic magnesium powder, exposed to environmental conditions for 12 months (Mg-12M) and subjected to different high-energy ball-milling speeds and milling times, was constructed. Mg-12M−160 [½MgO-⅓Mg(OH)₂-⅙hydromagnesite] and Mg-12M−640 [¼MgO-⅝Mg(OH)₂-⅛hydromagnesite] composites were obtained changing the milling conditions. The correlation among the accumulated energy (ΔE_accum), the impact energy (ΔE_hit), and the phase stability under different high-energy ball-milling conditions were generated. The Mg-12M−160 composite had a hydrogen storage capacity of 0.63 wt% at −196 °C and 8.3 bar, although further hydrogen adsorption at higher pressures is expected. Structural defects play a significant role in the adsorption capacity. A representation of the possible absorption mechanism is proposed.     

Construction of core−shell MOF@hydroxide hybrids with strong hetero-interface interaction for photocatalytic hydrogen evolution

Metal?organic framework (MOF)-based photocatalysts enabling the separation of photogenerated electron?holes pairs for efficient photocatalytic hydrogen production have been the focus of considerable attention lately as a solution to reduce energy related problems. In this study, the Ni²⁺ etching of a typical Ti-based MOF(NH₂-MIL-125) to synthesize a defective NH₂-MIL-125@Ni (OH)₂ photocatalyst is reported. Ni²⁺ was selected to hydrolyze and etch the NH₂-MIL-125 to obtain defective NH₂-MIL-125@Ni (OH)₂ was a strong hetero-interface interaction heterojunction, while maintaining the NH₂-MIL-125 structure. The construction of defects increased the number of active sites, and the Ni (OH)₂ cocatalyst further enhanced the photogenerated electron-holes separation efficiency. Under visible light for a duration of 4 h, H₂ production reached a rate of 502.32 μmol g^?1.     

Enhanced hydrogen storage properties of Ti–Cr–Nb alloys by melt-spin and Mo-doping

Ti–Cr–Nb hydrogen storage alloys with a body centered cubic (BCC) structure have been successfully prepared by melt-spin and Mo-doping. The crystalline structure, solidification microstructural evolution, and hydrogen storage properties of the corresponding alloys were characterized in details. The results showed that the hydrogen storage capacity of Ti–Cr–Nb ingot alloys increased from 2.2 wt% up to around 3.5 wt% under the treatment of melt-spin and Mo-doping. It is ascribed that the single BCC phase of Ti–Cr–Nb alloys was stabilized after melt-spin and Mo-doping, which has a higher theoretical hydrogen storage site than the Laves phase. Furthermore, the melt-spin alloy after Mo doping can further effectively increase the de-/absorption plateau pressure. The hydrogen desorption enthalpy change ΔH of the melt-spin alloy decreased from 48.94 kJ/mol to 43.93 kJ/mol after Mo-doping. The short terms cycling test also manifests that Mo-doping was effective in improving the cycle durability of the Ti–Cr–Nb alloys. And the BCC phase of the Ti–Cr–Nb alloys could form body centered tetragonal (BCT) or face center cubic (FCC) hydride phase after hydrogen absorption and transform to the original BCC phase after desorption process. This study might provide reference for developing reversible metal hydrides with favorable cost and acceptable hydrogen storage characteristics.     

Ni/SiO2 core–shell catalysts for catalytic hydrogen production from waste plastics-derived syngas

Ni/SiO₂ core–shell catalysts were prepared by deposition–precipitation method and used to produce hydrogen from waste plastics-derived syngas. The SiO₂ core synthesized by the Stöber process was used as the support. This core was synthesized using various solvents, and the effect of these solvents on the morphologies and catalytic performance of the Ni/SiO₂ core–shell catalysts was investigated. The synthesis parameters of the Ni/SiO₂ catalysts were further investigated to enhance the metal–support interaction and dispersion of Ni on the SiO₂ support. The highest catalytic activity of 181 mmol/g-h was achieved when the Ni/SiO₂ core–shell catalyst was synthesized in methanol (Ni/SiO₂–M) and reacted at 800 °C at a water-addition rate of 0.75 g-H₂O/h. The Ni/SiO₂–M catalyst, which possessed strong metal–support interaction nickel phyllosilicates, high specific area, small particle size, and homogeneous metal dispersion, exhibited the best long-term stability.     

Fabrication of Mg–Ni–Sn alloys for fast hydrogen generation in seawater

Mg-2.7Ni-x wt.% Sn(x = 0–2) alloys were fabricated to promote hydrogen generation kinetics of Mg-2.7Ni alloy. The Sn in Mg-2.7Ni-Sn alloys exists as Mg₂Sn phase at the grain boundary and solid solution at the Mg matrix. The Mg₂Sn at the grain boundary acts as the initiation site for pitting corrosion and the dissolved Sn in the alloy causes pitting corrosion by locally breaking the surface oxide film in the Mg matrix in seawater. The Mg-2.7Ni-1Sn alloy showed an excellent hydrogen generation rate of 28.71 ml min^?1 g^?1, which is 1700 times faster than that of pure Mg due to the combined action of galvanic and intergranular corrosion as well as pitting corrosion in seawater. As the solution temperature was increased from 30 to 70 °C, the hydrogen generation rate from the hydrolysis of the Mg-2.7Ni-1Sn alloy was dramatically increased from 34 to 257.3 ml min^?1 g^?1. The activation energy for the hydrolysis of Mg was calculated to be 43.13 kJ mol^?1.     

Synthesis of Cu@FeCo core–shell nanoparticles for the catalytic hydrolysis of ammonia borane

Non-noble Cu@FeCo core–shell nanoparticles (NPs) containing Cu cores and FeCo shells have been successfully in situ synthesized via a facile chemical reduction method. The NPs exerted composition-dependent activities towards the catalytic hydrolysis of ammonia borane (NH₃BH₃, AB). Among them, the Cu_0.3@Fe_0.1Co_0.6 NPs showed the best catalytic activity, with which the max hydrogen generation rate of AB can reach to 6674.2 mL min⁻¹ g⁻¹ at 298 K. Kinetic studies demonstrated that the hydrolysis of AB catalysed by Cu_0.3@Fe_0.1Co_0.6 NPs was the first order with respect to the catalyst concentration. The activation energy (Ea) was calculated to be 38.75 kJ mol⁻¹. Furthermore, the TOF value (mol of H₂. (mol of catalyst. min)⁻¹) of Cu_0.3@Fe_0.1Co_0.6 NPs was 10.5, which was one of the best catalysts in the previous reports. The enhanced catalytic activity was largely attributed to the preferable synergistic effect of Cu, Fe and Co in the special core–shell structured NPs.     

Alanate–borohydride material systems for hydrogen storage applications

Alteration of the thermodynamic stability of selected borohydride/alanate systems, including the combination of LiBH₄ with NaAlH₄ and LiBH₄ with CaCl₂ and LiAlH₄, was investigated to determine the possibility of forming intermediate stability mixed AlH₄⁻–BH₄⁻ phase.