Advanced interpretation of hydrogen absorption process in LaMgNi3.6M0.4 (M = Ni,Mn, Al,Co, Cu) alloys using statistical physics treatment

To obtain good economic and environmental benefits, LaMgNi_3.6M_0.4 (M = Al, Mn, Ni, Co, Cu) alloys are investigated for the hydrogen storage. The absorption data of hydrogen in the tested alloys are measured experimentally at 373 K. The hydrogen absorption isotherms are analyzed using three models derived from statistical physics formalism. The adequate model permits to discover significant details about the absorption phenomenon via determining the density of the interstitial sites (D_m), the number of hydrogen atoms per site (n) and the energetic parameter ΔE. The results indicate that multi-atomic (n > 1) and multi-linking (n < 1) phenomena are feasible for hydrogen absorption in LaMgNi_3.6M_0.4 (M = Al, Mn, Ni, Cu, Co) metals. The effects of the substitutions of Ni with Mn, Co, Cu and Al on the hydrogen absorption capacity are investigated. The interaction hydrogen/metal is analyzed by the calculation of the absorption energies. The chemical interaction is the responsible for the hydrogen absorption phenomenon. The contribution of this work is to provide advanced investigations of the hydrogen absorption mechanism in LaMgNi_3.6M_0.4 (M = Al, Mn, Ni, Co, Cu) metals, which are promising alloys for the hydrogen storage.     

Improved hydrogen storage properties of Ti2CrV alloy by Mo substitutional doping

Controllable hydrogen release is of great importance to the practical application of hydrogen storage materials. Ti₂CrV alloy possesses the maximum hydrogen absorption capacity in the Ti–Cr–V series alloys, however, can hardly meet the reversible storage capacity of practical applications due to its stable dihydride. Here we report an advancement in hydrogen storage property of the Ti₂CrV alloy by Mo partial substitution for Ti. Although the hydrogen absorption kinetics slightly decreased with the increase of Mo content, the Mo substitution alloy achieves an effective hydrogen capacity of 2.23 wt% cutting-off at 0.1 MPa, much higher than Ti₂CrV alloy (0.8 wt%). It is ascribed that Mo partial substitution for Ti significantly decreased the dihydride stability as well as the enthalpy change value. The cyclic property of Ti₂CrV alloy drastically decreased, while Mo substitution alloy with smaller FWHM value can maintain 90% storage capacity after 20 cycles. Because lattice strain and distortion of the Ti₂CrV alloy were decreased by Mo doping.     

Influence of the synthesis route on hydrogen sorption properties of La2MgNi7Co2 alloy

Solid-gas and electrochemical hydrogenation properties of La₂MgNi₇Co₂ alloy are presented. Hydrogen concentration of 1.90 wt% at hydrogen pressure of 10 bar has been reached. The influence of the fabrication technology of La₂MgNi₇Co₂ alloy on electrochemical performance of the hydride electrode were studied and discussed. To evaluate electrochemical characteristics of La₂MgNi₇Co₂ electrodes including discharge capacity, self-discharge and kinetic parameters the galvanostatic charge/discharge technique was used. The studied samples were a multiphase. The presence of Mg-enriched phases (La₂MgO_x, (La, Mg)Ni₃ and LaMgNi₄) raises hydrogen capacity and makes an electrode less susceptible for the self-discharge effect. On the other hand Mg-presence in MH electrodes lowers the hydrogen desorption rate. It was found that, the dominant abundance of the LaNi₅ phase in the tested materials has a positive effect on the kinetic parameters of the hydride electrode.     

Hybrid nickel-metal hydride/hydrogen battery

High capacity, high efficiency and resource-rich energy storage systems are required to store large scale excess electrical energy from renewable energy. We proposed “Hybrid Nickel-Metal Hydride/Hydrogen (Ni-MH/H₂) Battery” using high capacity AB₅-type hydrogen storage alloy and high-pressure H₂ gas as negative electrode active materials. It was experimentally confirmed that hydrogen gas can be utilized as an active material of negative electrode by the presence of the AB₅-type hydrogen storage alloy. The experimental average cell voltage suggested that H₂ gas passed through the alloy in the form of atoms. The calculated gravimetric energy density of this hybrid battery increased up to 1.5 times of the conventional Ni-MH battery with low content of rare-earth element which is 32 wt% of the Ni-MH battery.     

Effect of element substitution and surface treatment on low temperature properties of AB3.42-type La–Y–Ni based hydrogen storage alloy

The low-temperature performance (LTP) of AB_3.42-type La–Y–Ni hydrogen storage alloy was studied by methods of element substitution and surface treatment. The effect of Mn-additive on LTP of La_1·3Ce_0·5Y_4·2Ni_19.5-xMn_xAl (x = 0, 0.2, 0.5) was systematically investigated. Electrochemical studies showed that Mn-additive deteriorated the LTP of the alloy by reducing platform pressure, deteriorating kinetic performance and forming more oxides on the alloy surface. RE-substitution and hot alkali-ultrasonic treatment of La_1.3RE_0.5Y_4·2Ni_19·5Al (RE = Ce, Sm, Nd) alloys were applied to further optimize the LTP. The maximum discharge capacity and capacity retention at the 100th cycle of La_1·3Ce_0·5Y_4·2Ni_19·5Al alloy were 252.1 mA h/g and 87.1% at 243 K, respectively. Furthermore, the LTP of RE-substitution alloys at 243 K was conspicuously improved by surface treatment, which were raised from 214.7 mA h/g to 301.1 mA h/g by Sm-substitute, from 220.9 mA h/g to 303.9 mA h/g by Nd-substitute and from 252.1 mA h/g to 254.8 mA h/g by Ce-substitute.     

The effect of hydrogen on the electronic,mechanical and phonon properties of LaMgNi4 and its hydrides for hydrogen storage applications

Density functional theory calculations are used herein to explore the effect of hydrogen on the electronic, mechanical and phonon properties of LaMgNi₄ and its hydrides. The polycrystalline elastic moduli, Poisson's ratios and Debye temperatures are calculated based on the single-crystal elastic constants and Voigt-Reuss-Hill approximations. It is also found that all these materials are metallic behavior, ductile and anisotropic in nature. The mechanical anisotropy is discussed via several anisotropy indices and three-dimensional (3D) surface constructions. The effect of high temperature on the free energy, entropy, and heat capacity are also studied by using the quasi-harmonic Debye model. LaMgNi₄ and its hydrides are found to be energetically, mechanically and dynamically stable. Also, they are thermodynamically stable and the order of phase stability is LaMgNi₄H₇ > LaMgNi₄H₄ > LaMgNi₄H > LaMgNi₄. In addition, the highest gravimetric hydrogen storage capacity is found to be 1.74 wt% for LaMgNi4H₇.     

Structure and hydrogen storage properties of La1-xPrxMgNi3.6Co0.4 (x = 0–0.4) alloys prepared by melt spinning

Melt spinning technology was applied to prepared La_1-xPr_xMgNi_3.6Co_0.4 (x = 0–0.4) alloys, and phase composition, micro-structure, morphology and hydrogen storage properties were systematically investigated. The results show that the alloys contain two phases, LaMgNi₄ and LaNi₅ which have been detected by XRD and SEM. The grain of the alloys is refined by increasing Pr content and the phase abundance changed obviously. The hydrogen absorption capacity (wt%) of the alloys is 1.663, 1.659, 1.60, 1.593 and 1.566, corresponding the Pr substation of x from 0 to 0.4. The hydrogenation cycle stability indicates that the hydrogen capacity declined severely with the hydrogenation cycles. It is attributed to the hydrogen-induced amorphization which is confirmed by the XRD results after hydrogenation cycles. In order to recover the hydrogen storage capacity after cycles, the annealing treatment at 673 K for 3 h was carried out. And the XRD and HRTEM results show that the amorphization structure after hydrogen absorption/desorption cycles is re-crystallized by annealing treatment.     

Nanoscale microstructures and hydrogenation properties of an as-cast vanadium-based medium-entropy alloy

Vanadium-based hydrogen storage alloys have been widely investigated; however, alloys in the cast state are typically coarse-grained. In this study, an as-cast V₄₅Fe₁₅Ti₂₀Cr₂₀ medium-entropy alloy was prepared by arc melting, and microstructural analysis revealed that the alloy was composed of nanocrystals. The initial pretreatment temperature of the alloy was approximately 100 K lower than that of the as-cast coarse-grained alloy. At room temperature, the time required for the alloy to reach 90% saturation was only 140 s, indicating excellent hydrogen absorption kinetics. The alloy is fully activated after two hydrogen absorption/desorption cycles. The phase transformation of the alloy in the early hydrogenation stage was investigated using X-ray diffraction, and the results showed that the BCC phase was completely transformed into the BCT phase when hydrogen uptake was performed for 6 s. Furthermore, the apparent activation energy of dehydrogenation in the present alloy calculated using the Kissinger method was 69.8 ± 0.8 kJ/mol. The pressure-composition-isotherms tests showed that the hydrogen absorption capacity of the alloy at 295 K was 2.12 wt%. The hydrogenation/dehydrogenation enthalpy change of the alloy was calculated by the Van't Hoff equation, which was 30.90 ± 1.47 and 33.95 ± 0.41 kJ/mol, respectively. The present work demonstrates that nanostructured vanadium-based hydrogen storage alloys can be fabricated using traditional casting techniques. Our study also enriches the understanding of the microstructures of medium-entropy alloys, which may provide positive guidance for the design of novel vanadium-based hydrogen storage alloys.     

Effects of annealing temperature on the structure and properties of the LaY2Ni10Mn0.5 hydrogen storage alloy

The effects of annealing at 1123, 1148, 1173 and 1198 K for 16 h on the structure and properties of the LaY₂Ni₁₀Mn_0.5 hydrogen storage alloy as the active material of the negative electrode in nickel–metal hydride (Ni–MH) batteries were systematically investigated by X-ray diffraction (XRD), scanning electron microscopy linked with an energy dispersive X-ray spectrometer (SEM–EDS), pressure-composition isotherms (PCI) and electrochemical measurements. The quenched and annealed LaY₂Ni₁₀Mn_0.5 alloys primarily consist of Ce₂Ni₇- (2H) and Gd₂Co₇-type (3R) phases. The homogeneity of the composition and plateau characteristics of the annealed alloys are significantly improved, and the lattice strain is effectively reduced. The alloys annealed at 1148 K and 1173 K have distinctly greater hydrogen storage amounts, 1.49 wt% (corresponding to 399 mAh g^?1 in equivalent electrochemical units) and 1.48 wt%, respectively, than the quenched alloy (1.25 wt%, corresponding to 335 mAh g^?1 in equivalent electrochemical units). The alloys annealed at 1148 K and 1173 K have relatively good activation capabilities. The annealing treatment slightly decreases the discharge potentials of the alloy electrodes but markedly increases their discharge capacity. The maximum discharge capacities of the annealed alloy electrodes (372–391 mAh g^?1) are greater than the extreme capacity of the LaNi₅-type alloy (370 mAh g^?1). The cycling stability of the annealed alloy electrodes was improved.     

High-performance La–Mg–Ni-based alloys prepared with low cost raw materials

La–Mg–Ni-based hydrogen storage alloys showed good application prospects owing to their high hydrogen storage capacity. However, the poor cycling stability was a key problem. In order to improve the cycling stability, low cost YFe_0.85 master alloy was used as raw material to prepare La–Mg–Ni-based La_0.8-xY_xMg_0.2Ni_3-0.85xFe_0.85x (x = 0.50, 0.55, 0.60) hydrogen storage alloys by powder sintering method. The alloys were mainly composed of PuNi₃ phase and MgCu₄Sn phase. With the increase of Y and Fe, the cell parameters of PuNi₃ phase decreased. Lower mismatch coefficient promoted the cycling stability. As the case of x = 0.60, the capacity retention rate rose up to 95.45%. Aside from the cycling stability, appropriate substitution content contributed to higher capacity and satisfactory kinetics. As the case of x = 0.55, the hydrogen storage capacity reached 1.529 wt%, and hydriding time for the x = 0.60 alloy shrank to 76.7% of that for alloys without Y and Fe at 303 K.     

Effect of V content on hydrogen storage properties and cyclic durability of V–Ti–Cr–Fe alloys

Vanadium-based body-centered-cubic (BCC) alloys are ideal hydrogen storage media because of their high reversible hydrogen capacities at moderate conditions. However, the rapid capacity decay in hydrogen ab-/desorption cycles prevents their practical application. In this work, V-based BCC alloys with three different V contents (V₂₀Ti₃₈Cr_41.4Fe_0.6, V₄₀Ti_28.5Cr_30.1Fe_1.4, V₆₀Ti₁₉Cr₁₉Fe₂, named as V20, V40, V60) were prepared by arc melting, and their microstructures and hydrogen ab-/desorption properties were investigated systematically. XRD results show that there is a number of C15-Laves phase presence in V20, which does not appear in V40 and V60. Meanwhile, the lattice constant of the BCC phase clearly decreases as the V content rises. These differences result in a hydrogen storage capacity of only 1.82 wt% for V20 alloy, but 2.13 wt% for V40 and 2.14 wt% for V60, and an increment in hydrogen ab-/desorption plateau pressure. The V40 and V60 alloys are chosen in de-/hydrogenation cycle test owing to higher effective storage capacities, and the results show that the V60 alloy has better cycle durability. According to the microstructural analysis of the two alloys during the cycles, the micro-strain accumulates, the cell volume expands, the particles pulverizes and the defects increase during the cycles, which eventually lead to the attenuation of the hydrogen storage capacity. The increment of the V content obviously improves the elastic properties of the alloy, which further diminishes the micro-strain accumulation, cell volume expansion, particle pulverization and defect increase, eventually resulting in a higher capacity retention and better cyclic durability.     

Microstructure and hydrogen storage properties of (Ti0.32Cr0.43V0.25) + x wt% La (x = 0–10) alloys

The composite alloy of Ti_0.32Cr_0.43V_0.25 with x wt% La (where x = 0–10) was prepared by arc melting technique. The effect on hydrogen storage capacity, flatness of the plateau pressure, and residual hydrogen was investigated in La added Ti_0.32Cr_0.43V_0.25. Crystalline phase and microstructure of the prepared composite alloy were investigated and characterized by XRD, SEM and TEM. The crystal structure was refinement using Rietveld analysis. The effective hydrogen storage capacity of the composite alloy was found comparable to the parent alloy, when 5 wt% La was added. The effective hydrogen capacity (∼2.31 wt%) was close to that of the parent alloy (2.35 wt%) and the plateau slope was significantly improved from 30.5 of the parent alloy to 14.6. Appropriate mechanisms associated with the improved flatness by the La addition has been discussed in terms of the refined crystalline structure. Using TG/DTA method we have shown the differences in the interaction of residual hydrogen with the BCC phase of both parent alloy and 5 wt % La mixed alloy.     

Hydrogen storage properties of V0.3Ti0.3Cr0.25Mn0.1Nb0.05 high entropy alloy

In this paper, we present the synthesis, first hydrogenation kinetics, thermodynamics and effect of cycling on the hydrogen storage properties of a V_0.3Ti_0.3Cr_0.25Mn_0.1Nb_0.05 high entropy alloy. It was found that the V_0.3Ti_0.3Cr_0.25Mn_0.1Nb_0.05 alloy crystallizes in body-centred cubic (BCC) phase with a small amount of secondary phase. The first hydrogenation is possible at room temperature without incubation time and reaches a maximum hydrogen storage capacity of 3.45 wt%. The pressure composition isotherm (P–C–I) at 298 K shows a reversible hydrogen desorption capacity of 1.78 wt% and a desorption plateau pressure of 80.2 kPa. The capacity loss is mainly due to the stable hydride with the desorption enthalpy of 31.1 kJ/mol and entropy of 101.8 J/K/mol. The hydrogen absorption capacity decreases with cycling due to incomplete desorption at room temperature. The hydrogen absorption kinetics increases with cycling and the rate-limiting step is diffusion-controlled for hydrogen absorption.     

Influence of Mn or Mn plus Fe on the hydrogen storage properties of the Ti-Cr-V alloy

To increase the hydrogen storage capacity and the plateau pressure of the Ti_0.32Cr_0.43V_0.25 alloy, a fraction of the Cr was replaced with Mn or a combination of Mn and Fe. When Mn was used alone, the effective hydrogen storage capacity increased to about 2.5 wt% though the plateau pressure showed no significant change. When Fe was added with Mn, however, both the effective hydrogen storage capacity and the plateau pressure increased. The BCC (body centered cubic) lattice parameter of the alloy decreased linearly with the Fe content, but it was not affected by Mn alone. The effective hydrogen storage capacity of the Ti_0.32Cr_0.32V_0.25Fe_0.03Mn_0.08 alloy was about 2.5 wt%, higher than 2.35 wt% in the original alloy. The estimated usable hydrogen stored in the Ti_0.32Cr_0.32V_0.25Fe_0.03Mn_0.08 alloy was 2.71 wt% in the temperature and pressure range of 293–353 K and 5–0.002 MPa, respectively.     

Effects of ball milling time on the microstructure and hydrogen storage performances of Ti21.7Y0.3Fe16Mn3Cr alloy

TiFe alloy can store hydrogen at room temperature and low hydrogen pressure, and its theoretical hydrogen storage capacity is up to 1.8 wt%. However, TiFe alloy needs to be activated at high pressure (5 MPa hydrogen) and high temperature (673–723 K), which limits the practical application of TiFe alloy. The as-cast Ti_21.7Y_0.3Fe₁₆Mn₃Cr alloy was milled for 0, 0.5, 0.75, 1, and 3 h to study the effects of ball milling on phase structures and hydrogen storage performances. Emphasis was focused on the activation process of as-milled alloys at different temperatures, including the activation process at 483, 443, and 403 K. The results show that the alloys were consisted of TiFe phase, and [Fe, Cr] solid solution. The nanocrystalline boundary produced by milling and the phase boundary provided by the second phase provide a large number of channels for hydrogen diffusion and promote the improvement of hydrogen storage performances. The time required for activation process of as-milled alloys was significantly reduced, and the activation time of as-milled (0.75 h) was only 4 min, and its enthalpy variation for hydrogen absorption and desorption was 22.943 and 26.215 kJ mol⁻¹ H₂, respectively.     

Heterofullerene C48B12-impregnated MOF-5 and IRMOF-10 for hydrogen storage: A combined DFT and GCMC simulations study

The H₂ storage properties of isoreticular metal-organic framework materials (IRMOFs), MOF-5 and IRMOF-10, impregnated with different numbers and types of heterogeneous C₄₈B₁₂ molecules were investigated using density functional theory and grand canonical Monte Carlo (GCMC) calculations. The excess hydrogen adsorption isotherms of IRMOFs at 77 K within 20 bar indicate that suitable number and type of C₄₈B₁₂ molecules play a crucial role in improving the H₂ storage properties of IRMOFs. Among the studied pure and nC₄₈B₁₂ (n = 1, 2, 4, 8) in Ci symmetry impregnating into MOF-5, at 77 K under 6 bar, MOF-5-4C₄₈B₁₂ with a 3.5 wt% and 29.9 g/L hydrogen storage density, and at 77 K under 12 bar, the pure MOF-5 with a 4.9 wt% and 31.0 g/L hydrogen storage density has the best hydrogen storage properties. Whereas, among the studied pure and nC₄₈B₁₂ (n = 1, 2, 4, 8) in S6 symmetry impregnating into IRMOF-10, IRMOF-10-8C₄₈B₁₂ always shows the best hydrogen storage properties among the pure and C₄₈B₁₂-impregnated IRMOF-10 at 77 K within 20 bar. IRMOF-10-8C₄₈B₁₂ has a 6.0 wt% and 34.6 g/L hydrogen storage density at 77 K under 6 bar, and has a 7.1 wt% and 41.4 g/L hydrogen storage density at 77 K under 12 bar. The confinement effect of IRMOFs on C₄₈B₁₂ molecules, and steric hindrance effect of C₄₈B₁₂ molecules on IRMOFs mainly affects the H₂ uptake capacity by comparing the absolute H₂ molecules in individual IRMOFs units, C₄₈B₁₂ molecules, and IRMOFs-nC₄₈B₁₂ compounds. The absolute hydrogen adsorption profiles show that eight C₄₈B₁₂ molecules impregnating into MOF-5 can exert obvious steric effects for H₂ adsorption. The saturated gravimetric and volumetric H₂ densities of IRMOF-10-8C₄₈B₁₂ higher than those of MOF-5-8C₄₈B₁₂ due to with larger free volume.     

Excellent catalytic effect of LaNi5 on hydrogen storage properties for aluminium hydride at mild temperature

The catalytic effect of rare-earth hydrogen storage alloy is investigated for dehydrogenation of alane, which shows a significantly reduced onset dehydrogenation temperature (86 °C) with a high-purity hydrogen storage capacity of 8.6 wt% and an improved dehydrogenation kinetics property (6.3 wt% of dehydrogenation at 100 °C within 60 min). The related mechanism is that the catalytic sites on the surface of the hydrogen storage alloy and the hydrogen storage sites of the entire bulk phase of the hydrogen storage reduce the dehydrogenation temperature of AlH₃ and improve the dehydrogenation kinetic performance of AlH₃. This facile and effective method significantly improves the dehydrogenation of AlH₃ and provides a promising strategy for metal hydride modification.     

Hydrogen storage in TiZrNbFeNi high entropy alloys,designed by thermodynamic calculations

The hydrogen storage properties of the novel equiatomic TiZrNbFeNi and non-equiatomic Ti₂₀Zr₂₀Nb₅Fe₄₀Ni₁₅ high entropy alloys (HEAs) were studied. These alloys were designed with the aid of thermodynamic calculations using the CALPHAD method due to their tendency to form single C14 Laves phase, a phase desirable for room-temperature hydrogen storage. The alloys, which were synthesized by arc melting, showed a dominant presence of C14 Laves phases with the (Zr, Ti)₁(Fe, Ni, Nb, Ti)₂ constitution and small amounts of cubic phases (<1.4 wt%), in good agreement with the thermodynamic predictions. Hydrogen storage properties, examined at room temperature without any activation procedure, revealed that a maximum hydrogen storage capacity was reached for the equiatomic alloy in comparison to the non-equiatomic alloy (1.64 wt% vs 1.38 wt%) in the first cycle; however, the non-equiatomic alloy presented superior reversibility of 1.14 wt% of hydrogen. Such differences on reversibility and capacity among the two alloys were discussed based on the chemical fluctuations of hydride-forming and non-hydride-forming elements, the volume per unit cell of the C14 Laves phases and the distribution of valence electrons.     

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.     

Hydrogen storage properties of new A3B2-type TiZrNbCrFe high-entropy alloy

Crystal structure and hydrogen storage properties of a novel equiatomic TiZrNbCrFe high-entropy alloy (HEA) were studied. The selected alloy, which had a A₃B₂-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 AB₂- 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 AB₂- 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 A₃B₂/A₃B₂H₇.