200 NL H2 hydrogen storage tank using MgH2–TiH2–C nanocomposite as H storage material

MgH₂-based hydrogen storage materials are promising candidates for solid-state hydrogen storage allowing efficient thermal management in energy systems integrating metal hydride hydrogen store with a solid oxide fuel cell (SOFC) providing dissipated heat at temperatures between 400 and 600 °C. Recently, we have shown that graphite-modified composite of TiH₂ and MgH₂ prepared by high-energy reactive ball milling in hydrogen (HRBM), demonstrates a high reversible gravimetric H storage capacity exceeding 5 wt % H, fast hydrogenation/dehydrogenation kinetics and excellent cycle stability. In present study, 0.9 MgH₂ + 0.1 TiH₂ +5 wt %C nanocomposite with a maximum hydrogen storage capacity of 6.3 wt% H was prepared by HRBM preceded by a short homogenizing pre-milling in inert gas. 300 g of the composite was loaded into a storage tank accommodating an air-heated stainless steel metal hydride (MH) container equipped with transversal internal (copper) and external (aluminium) fins. Tests of the tank were carried out in a temperature range from 150 °C (H₂ absorption) to 370 °C (H₂ desorption) and showed its ability to deliver up to 185 NL H₂ corresponding to a reversible H storage capacity of the MH material of appr. 5 wt% H. No significant deterioration of the reversible H storage capacity was observed during 20 heating/cooling H₂ discharge/charge cycles. It was found that H₂ desorption performance can be tailored by selecting appropriate thermal management conditions and an optimal operational regime has been proposed.     

Effect of carbon addition on hydrogen storage behaviors of Li–Mg–B–H system

Various carbon additives were mechanically milled with LiBH₄/MgH₂ composite and their hydrogen storage behaviors were investigated. It was found that most of the carbon additives exhibited prominent effect on the host material. Among the various carbon additives, purified single-walled carbon nanotubes (SWNTs) exhibited the most prominent effect on the kinetic improvement and cyclic stability of Li–Mg–B–H system. Results show that LiBH₄/MgH₂ composite milled with 10 wt.% purified SWNTs additive can release nearly 10 wt.% hydrogen within 20 min at 450 °C, which is about two times faster than that of the neat LiBH₄/MgH₂ sample. On the basis of hydrogen storage behavior and structure/phase investigations, the possible mechanism involved in the property improvement upon carbon additives was discussed.     

Development of Ca–Mg–H2–ZrCl4 composite for hydrogen storage applications

Both CaH₂ and MgH₂ are good candidate for the development of hydrogen storage materials because of their high hydrogen storage capacity. However, both the hydrides are quite stable thermodynamically and required high temperature for hydrogen sorption process. The MgH₂–CaH₂ composite could show the favourable hydrogen sorption reaction because of Ca–Mg intermetallic formation. The idea motivated to perform the experiments starting with these metal hydrides. It has been found that the hydrogen sorption reaction kinetics improved substantially. The dihydrogen product has shown a few intermetallic of magnesium and calcium. The hydrogen sorption temperature and pressure of the alloy was remarkably improved by the doping with ZrCl₄ as a catalyst. The activation energy and the thermodynamic parameters of un-catalyzed and catalyzed alloy were studied. Present studied indicated that the CaH₂–MgH₂–ZrCl₄ could be a potential candidate for the mobile hydrogen storage system.     

Electrochemical performance studies on cobalt and nickel electroplated La–Mg–Ni-based hydrogen storage alloys

A novel electroplating treatment was applied onto La–Mg–Ni-based La_0.88Mg_0.12Ni_2.95Mn_0.10Co_0.55Al_0.10 alloy powders. The effect of cobalt or nickel metallic coating on morphological and electrochemical properties was studied. FESEM results showed that a dense layer of spherical cobalt particles with uniform radius and an undulate layer of lamellar nickel formed on the surface of the Co- and Ni-coated alloys, respectively. These coatings enhanced the conductivity and the catalytic activity, besides acting as a protective layer, thereby improving the electrochemical properties. The maximum discharge capacity increased from original 316 mAh/g to 335 mAh/g on Co-coated alloys and 336 mAh/g on Ni-coated ones, the cycling stability was enhanced and the self-discharge was suppressed. The high rate dischargeability (HRD) was ameliorated remarkably, and the HRD value at 1500 mA/g rose by 10% and 17%, for cobalt- and nickel-coated alloy electrodes respectively, which is believed to be ascribed to the improved kinetics from the metallic coatings on the surface.     

Remarkable decrease in dehydrogenation temperature of Li–B–N–H hydrogen storage system with CoO additive

Cobalt monoxide (CoO) was introduced into the Li–B–N–H system as a catalyst precursor, and the hydrogen desorption behavior of the LiBH₄–2LiNH₂–xCoO (x = 0–0.20) composites was investigated. It was observed that the majority of hydrogen desorption from the CoO-added sample occurred simultaneously with the melting of α-Li₄BN₃H₁₀. Moreover, the 0.05CoO-added sample exhibited optimized dehydrogenation properties, desorbing 9.9 wt% hydrogen completely with an onset temperature of 100 °C and exhibiting a decrease of more than 120 °C in the onset dehydrogenation temperature with respect to that of the additive-free sample. The activation energy of hydrogen desorption for the 0.05CoO-added sample was reduced by 30%. XAFS measurements showed that the CoO additive was first reduced chemically to metallic Co during the initial stage of thermal dehydrogenation, and the newly produced metallic Co acted as the catalytic active species in favor of the creation of B–N bonding. More importantly, approximately 1.1 wt% of hydrogen could be recharged into the fully dehydrogenated 0.05CoO-added sample at 350 °C and a hydrogen pressure of 110 atm, which represents much better performance than that exhibited by the pristine sample.     

Experimental analysis of hydrogen storage performance of a LaNi5–H2 reactor with phase change materials

Energy storage, especially thermal energy storage, has an important place in terms of efficient use of energy. Systems in which phase change materials (PCMs) are used are among the thermal energy storage (TES) options, thanks to their advantages such as energy storage at almost constant temperature. The use of PCM as a TES material in the metal hydride (MH) reactor is an influential method to store the heat released by the exothermic reaction occurring in the hydrogen charging process and to recover this heat with the endothermic reaction occurring in the hydrogen discharge process. In the present study, hydrogen charge and discharge processes in a LaNi₅–H₂ reactor were experimentally investigated and compared with and without PCM. Therefore, a hybrid system was designed by integrating PCM around the cylindrical MH reactor filled with LaNi₅ alloy. The hydration process was carried out at both constant pressure and variable pressure. The temperature changes on the reactor surface and inside the PCM were measured over time. In experiments to determine the change in the amount of hydrogen stored in MH reactors over time, it was determined that the hydrogen storage pressure and reactor design significantly affect the hydrogen charge-discharge rate. Considering the use of MH reactors in transportation vehicles such as automobiles and submarines, designing a hybrid MH-PCM storage system is promising for the development of hydrogen storage technologies and transportation technologies.     

Structural characterization and hydrogen storage properties of MgH2–Mg2CoH5 nanocomposites

Mixtures of XMg–Co containing different amounts of Mg (X = 2, 3 and 7) were reactive milled under hydrogen atmosphere. 2Mg–Co only formed the Mg₂CoH₅ complex hydride, while the mixtures 3Mg–Co and 7Mg–Co formed different contents of Mg₂CoH₅ and MgH₂. Their structural features and hydrogen storage properties were analyzed by different techniques. In-situ synchrotron X-ray diffraction, combined with thermal analysis techniques, (differential scanning calorimetry, thermal gravimetric analysis and quadrupole mass spectrometer) was carried out to observe the behavior of the MgH₂–Mg₂CoH₅ mixtures during the first H-desorption. It was found that the presence of the Mg₂CoH₅ complex hydride has a beneficial effect on the first H-desorption of the MgH₂. Additionally, after first desorption, conventional hydrogenation under high pressure and high temperature of 3Mg–Co and 7Mg–Co samples led to the formation of the Mg₆Co₂H₁₁ complex hydride. The presence of Mg₆Co₂H₁₁ considerably impaired the desorption properties of the nanocomposites.     

Synthesis and hydrogen storage characteristics of Mg–B–H compounds by a gas–solid reaction

Magnesium borohydride [Mg(BH₄)₂] is an attractive complex hydride for hydrogen storage. In this study, attempts to synthesize Mg(BH₄)₂ were carried out by a solid–gas reaction through MgH₂ and B₂H₆ in the absence of a liquid medium. The source of B₂H₆ was obtained by heating a mixture of NaBH₄ and ZnCl₂. The profile of pressure versus temperature indicated that the absorption kinetics of B₂H₆ by MgH₂ were slow. Structural analysis confirmed the formation of Mg–B–H compounds. The reaction products presented two-step hydrogen release during heating. A small amount of hydrogen could be released from the as-synthesized Mg–B–H compounds at a low temperature of 215 °C. The slow reaction kinetics were significantly affected by the surface conditions of the MgH₂ powders.     

Investigation on hydrogen storage properties of as-cast,extruded and swaged Mg–Y–Zn alloys

In this work, three different states of Mg-9.1Y-1.8Zn alloys including as-cast, extruded and swaged were prepared by semi-continuous casting, extrusion and swaging processes, respectively. Their compositions, microstructures and hydrogen storage properties were investigated. The results show that Mg-9.1Y-1.8Zn alloys in three different states are all composed of Mg and long-period stacking ordered (LPSO) phases. The LPSO phases occurs to break and decompose after hydrogenation and in-situ forms the YH_{χ(χ = 2,3)} nano-hydrides. The nano-hydrides can be used as in-situ catalysts to improve the hydrogen storage properties of alloys. Meanwhile, many nanocrystalline grains appear in the core of alloy after swaging, and the average grain size ranges from 80 to 200 nm. The presence of nanocrystals may increase the specific surface area of alloy, facilitating the diffusion and absorption of hydrogen. Comparatively, the swaged alloy exhibits the largest hydrogen storage capacity and excellent hydrogen sorption kinetics relative to other states of alloys.     

Effects of graphite addition and air exposure on ball-milled Mg–Al alloys for hydrogen storage

Magnesium hydride (MgH₂) is a promising candidate as a hydrogen storage material. However, its hydrogenation kinetics and thermodynamic stability still have room for improvement. Alloying Mg with Al has been shown to reduce the heat of hydrogenation and improve air resistance, whereas graphite helps accelerating hydrogenation kinetics in pure Mg. In this study, the effects of simultaneous Al alloying and graphite addition on the kinetics and air-exposure resistance were investigated on the Mg₆₀Al₄₀ system. The alloys were pulverized through high-energy ball milling (hereinafter HEBM). We tested different conditions of milling energy, added graphite contents, and air exposure times. Structural characterization was conducted via X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM). H₂ absorption and desorption properties were obtained through volumetry in a Sieverts-type apparatus and Differential Scanning Calorimetry (DSC). The desorption activation energies were calculated using DSC curves through Kissinger analysis. Mg₆₀Al₄₀ with 10 wt% graphite addition showed fast activation kinetics, even after 2 years of air exposure. Graphite addition provided a catalytic effect on ball-milled Mg–Al alloys by improving both absorption and desorption kinetics and lowering the activation energy for desorption from 189 kJ/mol to 134 kJ/mol. The fast kinetics, reduced heat of reaction, and improved air resistance of these materials make them interesting candidates for potential application in hydride-based hydrogen storage tanks.     

Effect of Sm on the cyclic stability of La–Y–Ni-based alloys and their comparison with RE–Mg–Ni-based hydrogen storage alloy

The LaY₂Ni_9.7Mn_0.5Al_0.3 and LaSm_0.3Y_1.7Ni_9.7Mn_0.5Al_0.3 alloys have been synthesized to investigate the effect of Sm partial substitution for Y on the cyclic stability of A₂B₇-type La–Y–Ni-based alloys. Their cyclic properties were also compared with the A₂B₇-type (RE_0.85Mg_0.15)₂(NiAl)₇ (RE = Rare Earth) alloys. The gas-solid and electrochemical cycle lives were tested. The structural stability, pulverization, and oxidation/corrosion performances were studied by X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical methods. The partial substitution of Sm for Y improves anti-corrosion and anti-pulverization performances, thereby increasing the cycle life of A₂B₇-type La–Y–Ni-based hydrogen storage alloys. The A₂B₇-type RE–Y–Ni-based alloys exhibit better crystal structure stability, but the gas-solid and electrochemical cyclic stability is worse than A₂B₇-type (RE_0.85Mg_0.15)₂(NiAl)₇ alloys due to easier pulverization of particles and the oxidation of Y elements.     

First-principles calculations on superconductivity and H-diffusion kinetics in Mg–B–H phases under pressures

Focusing towards ternary metal hydrides has recently been regarded as a new avenue for research in pressure-dependent high-temperature superconductors, thanks highly to a fairly large number of permutations of alloying metals, even metalloids, with hydrogen. Herein, new phases of Mg ? B ? H ternary hydrides are predicted from the first-principles evolutionary techniques, as a result of which the corresponding phonon and electronic calculations for the three candidate phases are performed successively to confirm their dynamic stability and the possibility to become conductors. The metallic MgBH₉ undergoes a superconducting phase with a maximum T_c of 64 K at 110 GPa, with its spectral function predominantly active around optical modes. The significant increase in cumulative electron-phonon coupling constant is associated with a relatively low cutoff frequency according to the bandwidth function. As for the non-metallic candidate, hydrogen-vacancy diffusion kinetics of the MgB₂H₈ phase are determined by means of total energy calculations. Stable pathways at varying pressure are reported, suggesting that elevated pressure lowers the activation energy which is presumably due to an optimal level of average nearest H ? H(B) inter-fragment distances.     

High glass forming ability correlated with microstructure and hydrogen storage properties of a Mg–Cu–Ag–Y glass

Thermal characterization of an as-cast Mg₅₄Cu₂₈Ag₇Y₁₁ bulk metallic glass revealed that this alloy exhibits excellent glass forming ability. High-resolution X-ray diffraction study and transmission electron microscopy show that heating and isothermal annealing treatment results in the nucleation of nanocrystals of several phases. The average size of these nanocrystals (∼15–20 nm) only slightly varies with prolonged annealing, only their volume fraction increases. High-pressure calorimetry experiments indicate that the as-cast fully amorphous alloy exhibits the largest enthalpy of hydrogen desorption, compared to partially and fully crystallized states. Since the fully crystallized alloy does not desorb hydrogen, it is assumed that hydrogen storage capacity correlates only with the crystalline volume fraction of the partially crystallized Mg₅₄Cu₂₈Ag₇Y₁₁ BMG and additional parameters (crystalline phase selection, crystallite size, average matrix concentration) do not play a significant role.     

Characterization and first principle study of ball milled Ti–Ni with Mg doping as hydrogen storage alloy

Microstructures, electrochemical properties of Ti–Ni and ternary Ti–Ni–Mg alloy were studied after they had been submitted to high-energy ball milling. Influence of milling time and Mg addition on the microstructures of the mechanically milled Ti–Ni alloys was investigated by XRD, SEM. Cycling performances of the electrodes prepared by the milled powders were measured under galvanostatic conditions. It is found that the binary Ti–Ni alloy undergoes a refinement, dynamical recrystallization and amorphization process. With doping of Mg to the starting Ti–Ni powders, an FCC Ti–Mg structure was detected along with the main TiNi BCC phase. First principle calculation was applied to compare the thermodynamic stabilities of several binary alloys involving Ti, Ni and Mg. It was decided that the final product of milling Mg doped Ti–Ni contains an FCC structured TiMg₃ phase, which damages electrochemical performance in general as a result of coating effect on the TiNi phase.     

The enhanced hydrogen storage performance of (Mg–B–N–H)-doped Mg(NH2)–2LiH system

Doping Mg(NH₂)₂–2LiH by Mg₂(BH₄)₂(NH₂)₂ compound exhibits enhanced hydrogen de/re-hydrogenation performance. The peak width in temperature-programmed desorption (TPD) profile for the Mg(NH₂)₂–2LiH–0.1Mg₂(BH₄)₂(NH₂)₂ was remarkably shrunk by 60 °C from that of pristine Mg(NH₂)₂–2LiH, and the peak temperature was lowered by 12 °C from the latter. Its isothermal dehydrogenation rate was greatly improved by five times from the latter at 200 °C. XRD, FTIR and NMR analyses revealed that a series of reactions occurred in the dehydrogenation of the composite. The prior interaction between LiH and Mg–B–N–H yielded intermediate LiBH₄, which subsequently reacted with Mg(NH₂)₂ and LiH in molar ratio of 1:6:9 to form Li₂Mg₂(NH)₃ and Li₄BN₃H₁₀ phases. The observed 6Mg(NH₂)₂–9LiH–LiBH₄ combination dominated the hydrogen release and soak in the composite system, and enhanced the kinetics of the system.     

Experimental investigation on sorption performance of new high–efficiency,inexpensive H2 getters in high–vacuum,variable density–multilayer insulated hydrogen storage equipment

Hydrogen (H₂) is released by the manufactured materials, which results in the deterioration of the insulation performance of liquid hydrogen (LH₂) storage tanks. The getter is found in the vacuum annular space of equipment and helps maintain the high vacuum of LH₂ tanks. Palladium oxide (PdO), an effective H₂ getter, is expensive, resource–constrained and unsuitable for the LH₂ equipment. Therefore, suitable and inexpensive alternatives were examined using LH₂ storage tanks, to maintain the insulation property of the high–vacuum variable–density multilayer insulation (VDMLI) equipment better. Eight types of H₂ getters were designed using in the LH₂ tanks, and classified into three categories, namely, chemical, physical and physico–chemical getters (PCNHG). The sorption performance of new H₂ getters was compared with that of PdO. PdO could be replaced by in the 7:1, 5:1 and 4:1 ratio by PCNHG1, PCNHG2 and CNHG in the LH₂ tanks, respectively. The results demonstrated that the sorption capacity of PCNHG1 and PCNHG2 were 1.70 and 2.14 times that of the same type of getters in the market (16.35% and 20.62% higher than that of PdO, respectively). Their average H₂ sorption efficiency was 1.17 times and 1.05 times of that of PdO, respectively. The minimum thermal conductivity exhibited by CNHG was only 6.34% of that of PdO, and the sorption capacity of CNHG was 1.82 and 1.44 times that of PCNHG1 and PCNHG2, respectively. However, the sorption capacities of PCNHG1, PCNHG2 and CNHG were belows that of PdO. These results help facilitate reduction in the expense of H₂ getters and provide an important reference to enhance the sorption performance of getters.     

Formation and hydrogen storage behavior of nanostructured Mg2FeH6 in a compressed 2MgH2–Fe composite

The present study focuses on enhancing the yield of Mg₂FeH₆ and its hydrogen storage performances through a novel high-pressure compression approach. For which, MgH₂ and Fe powders are first mechanically milled in a molar ratio of 2:1 and subsequently compressed to a cylindrical pellet. Due to the compression, the yield of Mg₂FeH₆ in the compressed 2MgH₂–Fe pellet (90%) has been increased by 24% as compared to the reference ball-milled powder (66%). The thermodynamic destabilization of Mg₂FeH₆ in the pelletized sample is observed through measuring the pressure-composition isotherms, resulting in the reduced ab/desorption enthalpy for the pellet sample (−68.34 and 75.61 kJ/mol H₂, respectively). The hydrogen uptake and release kinetics of Mg₂FeH₆ is remarkably fast, and it can store/release about 5 wt% H in less than 2.5 min at 400 °C. The faster hydrogen ab/desorption kinetics corresponds to the lower activation energies (36 and 95 kJ/mol H₂, respectively). The excellent yield of Mg₂FeH₆ and its improved hydrogen storage properties for the compressed pellet are primarily attributed to the microstructural modifications upon high-pressure compression, and also the obtained results for Mg₂FeH₆ ternary hydride are linked to the literature data based on theoretical calculations.