Scale-up of milling in a 100 L device for processing of TiFeMn alloy for hydrogen storage applications: Procedure and characterization

In this work, the mechanical milling of a FeTiMn alloy for hydrogen storage purposes was performed in an industrial milling device. The TiFe hydride is interesting from the technological standpoint because of the abundance and the low cost of its constituent elements Ti and Fe, as well as its high volumetric hydrogen capacity. However, TiFe is difficult to activate, usually requiring a thermal treatment above 400 °C. A TiFeMn alloy milled for just 10 min in a 100 L industrial milling device showed excellent hydrogen storage properties without any thermal treatment. The as-milled TiFeMn alloy did not need any activation procedure and showed fast kinetic behavior and good cycling stability. Microstructural and morphological characterization of the as-received and as-milled TiFeMn alloys revealed that the material presents reduced particle and crystallite sizes, even after such short time of milling. The refined microstructure of the as-milled TiFeMn is deemed to account for the improved hydrogen absorption-desorption properties.     

Effect of milling duration on hydrogen storage thermodynamics and kinetics of Mg-based alloy

Mechanical milling is widely recognized as the best method to prepare nano-structured magnesium based hydrogen storage materials. The composites La₇Sm₃Mg₈₀Ni₁₀ + 5 wt% TiO₂ (named La₇Sm₃Mg₈₀Ni₁₀–5TiO₂) whose structures are nano-crystal and amorphous accompanied by great hydrogen absorption and desorption properties were fabricated by mechanical milling. The research focuses on the effect of milling duration on the thermodynamics and dynamics. The instruments of researching the gaseous hydrogen storing performances include Sievert apparatus, DSC and TGA. The calculation of dehydrogenation activation energy was realized by applying Arrhenius and Kissinger formulas. The calculation results show the specimen milled for 10 h exhibits the optimal activation performance and hydrogenation and dehydrogenation kinetics. Extending or shrinking the milling duration will lead to the degradation of hydrogen storage performances. The as-milled (10 h) alloy at the full activated state can absorb 4 wt% hydrogen in 87 s at 473 K and 3 MPa and release 3 wt% H₂ in 288 s at 573 K and 1 × 10⁻⁴ MPa. The changed milling durations have little impact on the thermodynamic properties of experimental samples and the enthalpy change (ΔH) of the alloy milled for 10 h is 74.23 kJ/mol. Moreover, it is found that the as-milled (10 h) alloy displays the minimum apparent activation energy of dehydrogenation (59.1 kJ/mol), suggesting the optimal hydrogen storing property of the as-milled (10 h) alloy.     

Characterization of microstructure and surface oxide of Ti1.2Fe hydrogen storage alloy

In this study, we investigated the microstructures, hydrogen absorption kinetics, and oxide layers of TiFe and Ti_1.2Fe hydrogen storage alloys. Whereas the TiFe alloy has a single phase, the Ti_1.2Fe alloy is composed of three phases: TiFe, Ti₂Fe, and Ti₄Fe. Under no thermal activation process, the TiFe alloy does not absorb hydrogen, though the Ti_1.2Fe alloy starts to absorb hydrogen after 4 min of incubation time. From the XPS results, it is revealed that the Ti concentration in the oxide layer on the Ti₄Fe phase is higher than that on the TiFe phase, indicating that the Ti concentration in the oxide layer would be important in improving hydrogen absorption kinetics. Based on these results, the hydrogen absorption kinetics could be improved by adjusting composition, enabling the formation of a Ti-rich oxide layer.     

Study on the gaseous and electrochemical hydrogen storage properties of as-milled CeMgNi-based alloys

For gaining further insight into the involvement of the gaseous and electrochemical hydrogen storage properties of CeMg₁₂-type alloys, partial substitution and ball milling were both used to synthesize the nanocrystalline and amorphous CeMg₁₁Ni + x wt.% Ni (x = 100, 200) samples. This research aims at elucidating the functional roles of Ni content and milling time on samples' structure and hydrogen storage performance. X-Ray diffraction and high-resolution transmission electron microscope were used to reveal the micro constructions of alloys. To determine the gaseous hydrogen storage property, Sievert's apparatus and a thermal gravity analysis bonded with a H₂ probe were adopted. The dehydrogenation activation energy was computed in the Kissinger method. The electrochemical performances of the as-milled samples were measured through a constant current system. Further researches showed that the electrochemical performance of as-milled samples had been dramatically improved by increasing Ni content. With milling duration lengthens, the gaseous hydrogen absorption capacity, gaseous hydriding rate and high rate discharge capability of samples reached the maximal values, but electrochemical discharge capacity and gaseous dehydriding rate always increased. The dehydrogenation activation energy decrease resulted by improving Ni percent and milling duration was deemed as the cause of the excellent gaseous kinetics of samples.     

Investigations on gaseous hydrogen storage performances and reactivation ability of as-cast TiFe1-xNix (x=0, 0.1, 0.2 and 0.4) alloys

In this paper, Fe is partly substituted by Ni for improving the hydrogen storage properties of the TiFe alloy, such as the activation performance, hydrogen storage capacity, reactivation ability, optimum temperature range, thermodynamics and kinetics. The as-cast TiFe alloy contains the majority phase of TiFe and the minority phases of Ti₂Fe and TiFe₂. Increasing Ni content causes the majority phase of TiFe to increase firstly and then decrease again. The activation temperature reduces from 573 K for the TiFe alloy to 523 and 443 K for the TiFe_0·8Ni_0.2 and TiFe_0·6Ni_0.4 alloys respectively. Substituting Fe with Ni partly can lower the platform pressure for the P-C-T curves and increase the dehydrogenation enthalpy (ΔH_des). The TiFe_0·8Ni_0.2 alloy possesses the highest hydrogenation capacity. Adding Ni also is beneficial to expand the optimum temperature range, corresponding to the hydrogenation capacity higher than 0.800 wt%, which is 313–383, 313–503 and 313–573 K for the TiFe_1-xNi_x (x = 0.1, 0.2 and 0.4) alloys, respectively. All the alloys can be activated again at 573 K after being exposed to air for 5 min.     

Hydrogen storage property of as-milled La7RE3Mg80Ni10 (RE = Sm,Ce) alloys

Element replacement and mechanical milling are considered as the most effective ways to improve Mg-based alloys in their hydrogen storage performance. The as-milled La₇RE₃Mg₈₀Ni₁₀ (RE = Sm, Ce) alloys were prepared in this experiment by introducing both element replacement (replacing La by Ce or Sm partially) and mechanical milling technologies. The influence made by different replacing elements on the structure and hydrogen storage property of La₇RE₃Mg₈₀Ni₁₀ (RE = Sm, Ce) alloys was investigated in detail. X-ray diffraction, transmission electron microscope, automatic Sievert apparatus, thermogravimetry and differential scanning calorimetry were used to investigate the experimental alloys. The experiment reveals that a nanocrystalline and amorphous structure appears after mechanical milling. Moreover, comparing with the RE = Sm alloy, the RE = Ce alloy has a superior hydrogen desorption property, including larger hydrogen absorption capacity, faster hydriding/dehydriding rate, lower onset hydrogen desorption temperature, and lower dehydrogenation activation energy.     

Effect of oxygen addition on phase composition and activation properties of TiFe alloy

TiFe is one of the most promising hydrogen storage materials owing to its high volumetric hydrogen capacity, moderate operating temperature, and low cost. Oxygen is an inevitable impurity that affects the hydrogen storage properties of TiFe alloys. In this paper, the effect of oxygen addition on the phase composition and hydrogen storage properties of TiFe alloys is systematically investigated. We found that a high oxygen addition improves the initial hydrogen sorption of TiFe. The TiFe-O_3.78 alloy achieves full activation after two ab/desorption cycles at room temperature. The high oxygen content facilitates the formation of Ti₄Fe₂O oxide in TiFe alloy, leading to improved activation kinetics. Moreover, due to the oxygen addition, the amount of TiFe primary phase reduces, and the corresponding hydrogen capacity degrades. Increasing oxygen content also leads to a slight increase in the hydrogenation equilibrium pressure, but almost no impact on the thermodynamics of TiFe alloy.     

Hydrogen storage behaviour of Cr- and Mn-doped Mg2Ni alloys fabricated via high-energy ball milling

This paper describes the efficient preparation of an Mg₂Ni alloy for hydrogen storage via high-energy ball milling mechanical alloying for 2 h. The degree of alloy amorphisation increases with increasing ball-milling time. Ball milling for 4 h affords partially amorphous alloys exhibiting the best hydrogen storage performance. Partial substitution of Ni with Cr and Mn improves the hydrogen absorption/desorption thermodynamics, kinetics and cycling performance of the alloy. Specifically, partial Mn substitution improves the cycling performance and reduces the activation energy of the hydrogen desorption reaction, effectively improving the hydrogen desorption kinetic performance. Mg₂Ni_0.8Mn_0.2 shows the best cycling and hydrogen absorption/desorption kinetic performances. Partial Cr substitution reduces the entropy and enthalpy changes of the hydrogen absorption/desorption reaction and effectively reduces the temperature of the initial hydrogen absorption/desorption reaction. In particular, Mg₂Ni_0.9Cr_0.1 shows the best thermodynamic performance.     

Effects of Zr doping on activation capability and hydrogen storage performances of TiFe-based alloy

Activation difficulty is the key problem limiting the application of TiFe-based hydrogen storage alloys. The addition of transition group elements helps to improve the activation properties of TiFe-based hydrogen storage alloy. In our previous work, the Ti_1.08Y_0.02Fe_0.8Mn_0.2 alloy exhibits extremely high hydrogen storage capacity (1.84 wt%) at room temperature with excellent kinetic properties, but it still needs an incubation period of about 1500s. In this study, the composition of Ti_1.08Y_0.02Fe_0.8Mn_0.2Zr_x (x = 0, 0.02, 0.04, 0.06, 0.08) alloys was prepared by electromagnetic induction melting. The quantitative analysis of elements by energy dispersive spectrometer shows that in the second phase region containing Zr, the content of Ti element is significantly higher than that of Fe. Meanwhile, the first-principle calculation on Zr-doped TiFe system indicates that Zr is more attractive to substitute Ti than Fe. Therefore, the doping of Zr partially replaces the Ti. The solubility of Zr in TiFe is limited, when x ≤ 0.04, the alloy consists of pure TiFe phase. When x > 0.4, the excess Zr forms precipitates, which reduces the reversible hydrogen absorption and desorption capacity of the TiFe alloy. The addition of Zr significantly shortens the activation time and reduces the plateau pressure of TiFe alloys. The Ti_1.08Y_0.02Fe_0.8Mn_0.2Zr_0.04 alloy can be directly activated without the incubation period and its absolute values of enthalpy change (ΔH) and entropy change (ΔS) are minima (ΔH for 23.2 kJ/mol and ΔS for 83.1 J/mol/K).     

Hydrogen storage properties of TiFe-based ternary mechanical alloys with cobalt and niobium. A thermochemical approach

Ternary alloys of general composition (TiFe)_100-xM_x (M = Co, Nb) have been synthesized from pure metals through high-energy ball milling. The maximum concentration of alloying components allowing formation of single phase TiFe-type compounds has been defined as 2 at.%. The hydrogenation behavior of the mechanical alloys in comparison with the arc-melted ones of the same composition has been studied by a combination of volumetric and calorimetric techniques. Influence of the alloy composition and the synthesis mode on the crystal structure of TiFe and its hydrides has been evaluated. It has been shown that the thermochemical method based on calorimetric titration provides more accurate information about phase transformations in the nanocrystalline metal hydride systems. The obtained results show that the third components slightly affect the hydrogen storage performance of non-equilibrium mechanical alloys in contrast with alloys produced by conventional melting.     

Effect of Fe substitution on first hydrogenation kinetics of TiFe-based hydrogen storage alloys after air exposure

This study investigated how Fe substitution with Ni, Co, Cu, Mn, and Cr affected the first hydrogenation behavior of air-exposed TiFe-based hydrogen storage alloys. The alloy ingots were crushed into powders and exposed to air for 1 h to analyze the first hydrogenation kinetics. Although Fe was substituted with up to 30% of Ni, Co, and Cu, the alloys had a single TiFe phase. In addition, the TiFe_0·7Ni_0·2Co_0.1 and TiFe_0·7Co_0·2Ni_0.1 alloys also had a single TiFe phase in spite of the simultaneous substitution. The composition of the oxide layer changed by the addition of Ni, Co, and Cu, but the alloys did not absorb hydrogen. In the TiFe_0·8Mn_0.2 and TiFe_0·8Cr_0.2 alloys, a dual-phase microstructure consisting of TiFe and Mn/Cr-rich C14 Laves phase was formed, with a larger amount in TiFe_0·8Cr_0.2. Both samples absorbed hydrogen after air exposure without any thermal activation process. Comparing the first hydrogenation kinetics, TiFe_0·8Cr_0.2 had a shorter incubation time and faster hydrogen absorption rate than TiFe_0·8Mn_0.2.     

Gas hydrogen absorption and electrochemical properties of Mg24Ni10Cu2 alloys improved by Y substitution,ball milling and Ni addition

Mg₂₄Ni₁₀Cu₂ and Mg₂₂Y₂Ni₁₀Cu₂ alloys were prepared via vacuum induction melting, and the nanocrystalline/amorphous Mg₂₄Ni₁₀Cu₂ and Mg₂₄Ni₁₀Cu₂ + 100 wt% Ni alloys were synthesized through ball milling method. Microstructure and hydrogen storage properties of the alloys were investigated and compared as well. The results suggest that adding Ni in the milling process significantly promotes formation of amorphous and nanocrystalline structure. For these four alloys, the as-milled Mg₂₄Ni₁₀Cu₂ with 100 wt% Ni shows the best hydrogen storage performances that 2.03 wt% hydrogen content can be absorbed just in 1 min, and the electrochemical capacity reaches to 899.2 mAh/g. Furthermore, ball milling with Ni promotes the charge transfer reaction and hydrogen diffusion ability which is advantageous to the high rate discharge ability.     

Effect of Sm content on activation capability and hydrogen storage performances of TiFe alloy

Element substitution is an efficient method to enhance the activation property of TiFe alloys. In this paper, Zr, Mn and Ni were utilized to replace Fe in the alloy partially, and different content rare earth Sm substitute Ti in the alloy. The alloys with nominal compositions of Ti_1.1-xFe_0.6Ni_0.1Zr_0.1Mn_0.2Sm_x (x = 0–0.08) were made through vacuum induction melting. The microstructure, composition and hydrogen storage property of alloys were measured in detail by X-ray diffraction, scanning electron microscope, high-resolution transmission electron microscopy and automatically Sievert apparatus. The results reveal that the as-cast alloys contain TiFe as major phase and Ti₂Fe as secondary phase. Sm addition refines the grain of alloys obviously. All alloys have good activation properties and can be completely activated without any heat treatment. The activation performance can be further improved by partially replacing Ti with Sm, and the incubation period of activation can be shortened greatly.     

Improved hydrogen storage kinetics of nanocrystalline and amorphous Pr-Mg-Ni-based PrMg12-type alloys synthesized by mechanical milling

In this paper, the nanocrystalline and amorphous PrMg₁₁Ni + x wt.% Ni (x = 100, 200) alloys were synthesized by mechanical milling. The gaseous and electrochemical hydrogen storage performances were studied in detail. The results reveal that increasing Ni content facilitates the glass forming of the alloys, and it significantly improves the gaseous and electrochemical hydrogen storage kinetics performance. Furthermore, milling time varying significantly affects the hydrogen storage properties of the alloys. The hydrogen capacity of the alloys first increases and then decreases with milling time prolonged. The hydriding rate and high-rate discharge ability (HRD) of the as-milled alloys have maximum values with milling time varying. But dehydriding rate always increases with milling time prolonged. The improved gaseous hydrogen storage kinetics of alloys are convinced to be ascribed to a reduction in hydrogen desorption activation energy caused by increasing Ni content and prolonging milling time.     

Hydrogen storage thermodynamic and dynamic properties of as-milled CeMgNi-based CeMg12-type alloys

Ni was chosen to partially substitute the Mg of alloys to investigate the effect on hydrogen storage dynamics of NdMg₁₂-type alloy. The amorphous and nanocrystalline alloys were synthesized by mechanical milling technology based on CeMg₁₁Ni + x wt% Ni (x = 100, 200) alloys. This paper systematically narrates and investigates the influences of Ni content and milling duration on hydrogen storage performance. Sievert apparatus and differential scanning calorimetry (DSC) were utilized for investigating the de-/hydriding performances of samples. Both Arrhenius and Kissinger methods were utilized in this paper for estimating the dehydrogenation activation energy of hydrides, and found that enhancing Ni content can decrease the thermodynamic parameters (ΔH and ΔS) of alloys slightly and improve the dehydriding dynamics significantly. Furthermore, the hydrogen storage property can be affected significantly by adjusting milling time. With varying milling time, the hydrogen storage capacities can reach the maximum values of 5.691 and 5.904 wt% for x = 100 and 200 alloys separately. The hydrogen absorption saturation ratio (R^a(10)) at 573 K and 3 MPa also obtains maximum values with the variation of milling time, namely 90.17% and 99.32% for x = 100 and 200 alloys separately. The hydrogen desorption ratio (R^d(20)) always increases with milling time increasing. To be specific, prolonging milling time from 5 to 60 h results in the increase of R^d(20) at 593 K from 37.55% to 47.21% for x = 100 alloy and 47.29%–61.70% for x = 200 alloy.     

Investigations on hydrogen storage performances and mechanisms of as-cast TiFe0.8-mNi0.2Com (m=0, 0.03, 0.05 and 0.1) alloys

In order to improve the hydrogen storage performances of TiFe-based alloys, a new type of TiFe_0.8-mNi_0.2Co_m (m = 0, 0.03, 0.05 and 0.1) alloys were prepared through vacuum medium-frequency induction melting. XPS results showed that the composition of surface oxide film contains TiO₂, FeO and NiO for the cobalt-free alloy, and it also includes CoO and Co₃O₄ besides the above oxides for the cobalt-containing alloys. The activation temperature is 523, 403, 383 and 373 K for the TiFe_0.8-mNi_0.2Co_m (m = 0, 0.03, 0.05 and 0.1) alloys, respectively. The changes of the composition and microstructure of the surface oxide film are the root causes of the reduction of the activation temperature. XRD and SEM analyses showed that all the alloys are composed of the majority phase of TiFe phase and non-hydrogenated phase of Ti₂Fe phase. Adding appropriate amount of cobalt is beneficial to inhibiting the generation of Ti₂Fe phase and increasing the cell volume of TiFe phase. The hydrogenation capacity is proportional to the content of TiFe phase, which is 1.11, 1.48, 1.54 and 1.29 wt% for the TiFe_0.8-mNi_0.2Co_m (m = 0, 0.03, 0.05 and 0.1) alloys at 313 K, respectively. The hydrogenation plateau performance also is improved correspondingly.     

Effect of cobalt on the microstructure and hydrogen sorption performances of TiFe0.8Mn0.2 alloy

The microstructures and the hydrogen sorption performances of TiFe_0.8Mn_0.2Co_x (x = 0, 0.05, 0.10, 0.15) and TiFe_0.8Mn_0.2-yCo_y (y = 0.05, 0.10) alloys have been investigated. For TiFe_0.8Mn_0.2Co_x alloys, the lattice parameters of TiFe phase decreased and the Laves phase contents increased with the addition of Co. With the increase of Co content in TiFe_0.8Mn_0.2Co_x alloys, the maximum hydrogen storage capacities of TiFe_0.8Mn_0.2Co_0.05 and TiFe_0.8Mn_0.2Co_0.10 alloys decreased, but the effective hydrogen capacities increased, which is ascribed to the improved flatness of the α-β desorption plateau. Substitution of Co for Mn in TiFe_0.8Mn_0.2-yCo_y alloys can effectively lead to single phase of TiFe alloys. Therefore, TiFe_0.8Mn_0.2-yCo_y alloy showed a deteriorated activation property, but its effective hydrogen capacity increased remarkably due to the obviously improved flatness of the α-β desorption plateau. The addition of Co might adjust the change of the octahedral intersitial environment caused by Mn doping in TiFe phase, which contributes to the improved flatness of the α-β desorption plateau and hence the increased effective hydrogen capacity.     

Hydrogen storage property improvement of La–Y–Mg–Ni alloy by ball milling with TiF3

Ball milling the powders of Mg-based alloys with transition metal compounds is effective for improving their hydrogen storage performances. In this experiment, the alloys of La_1.7Y_0.3Mg₁₆Ni + x wt.% TiF₃ (x = 0–10) were prepared through mechanical milling technology. XRD, SEM, HRTEM and granulometry were used to measure the composition and microstructure of alloys. The isothermal hydrogen storage property was measured by a Sievert apparatus. The results reveal that the TiF₃ additive in ball-milled samples transforms into MgF₂ and TiH₂ after the first hydrogen absorption. Adding TiF₃ enhances the crystallinity and reduces the average particle and crystallite sizes of alloys, which is beneficial to accelerating hydriding and dehydriding kinetics. Adding 7 wt% TiF₃ into alloy decreases the dehydrogenation activation energy from 72.2 to 64.0 kJ/mol and improves the hydrogen absorption rate at low temperatures, absorbing 3.50 wt% H in 0.5 min at 323 K.     

Effect of ball milling time on microstructure and electrochemical properties of CeMg12+100%Ni hydrogen storage alloy

Abstract

In order to improve hydrogen storage performances of CeMg₁₂ type alloys, ball milling technology was used for preparing nanocrystalline/amorphous CeMg₁₂+100%Ni composite hydrogen storage alloys. The microstructures and morphologies of alloy samples were characterised by X-ray diffraction, scanning electron microscopy and high resolution transmission electron microscopy. The electrochemical hydrogen storage characteristics of as milled alloys were tested by an automatic galvanostatic system. The electrochemical impedance spectra were plotted by an electrochemical workstation (PARSTAT2273). The hydrogen diffusion coefficients D in the alloys were calculated by virtue of potential step method. The results show that the amount of nanocrystalline/amorphous Mg₂Ni phase and Ni phase within alloy samples increase with prolonging milling time. Prolonging of ball milled duration markedly improves the electrochemical discharge properties and cyclic stability of alloy samples. The amorphisation degree of the milling alloys increases with rising milling duration. Furthermore, the high rate dischargeability, electrochemical impedance spectra and potential step measurement all indicate that electrochemical kinetics of alloy electrodes first increases and then decreases with increasing ball milling.     

Effects of ultra-high pressure on phase compositions,phase configurations and hydrogen storage properties of LaMg4Ni alloys

The influences of ultrahigh pressure (UHP, under 5 GPa) on phase compositions, phase morphologies and hydrogen storage properties of LaMg₄Ni alloys were studied. The X-ray diffraction patterns show that the as-cast alloy consists of La₂Mg₁₇, LaMg₂Ni and Mg₂Ni phases, whereas a new LaMg₃ phase is observed in the UHP samples in addition to LaMg₂Ni and Mg₂Ni phases. The scanning electron microscopy graphs indicate that the phase distribution is more homogenous in the UHP alloys than in the as-cast one. Additionally, the microstructure of the UHP alloy heat-treated at 973 K is finer than that at 823 K. Both the reversible hydrogen storage capacity and the plateau of hydrogen pressure of the UHP alloys are close to those of the as-cast one. Of particular interest is that both UHP alloys exhibit better activation properties compared with the as-cast alloy. Moreover, the dehydriding onset temperature of the UHP alloys (5 GPa at 973 K) is about 490 K, which is obviously lower than that of the as-cast alloy. The amount of hydrogen desorption in the UHP alloy (5 GPa at 973 K) is 2.69 wt.% at 573 K, which corresponds to 89.6% of the saturated capacity. However, the corresponding values change to 1.75 wt.% and 58.3% in the as-cast alloy, respectively. It is confirmed the UHP treatment is one of effective approaches to tune the hydrogen storage performances of those rare earth–magnesium–nickel alloys.