Hydrogen Absorption-desorption Cycles Research Articles

Amorphous mixed transition metal oxides: A novel catalyst for boosting dehydrogenation of MgH2

Magnesium hydride (MgH2) has been recognized as a promising hydrogen storage material. However, the sluggish hydrogen desorption kinetics is one of the main factors hindering its practical applications. To enhance the dehydrogenation kinetics of MgH2, an amorphous mixed TiO2-ZrO2-V2O5 catalyst is synthesized in this work. After adding the as-synthesized catalyst into MgH2 by ball milling, the dehydrogenation activation energy can be decreased to 65.7 kJ mol−1. Meanwhile, the catalyzed MgH2 shows excellent cycling stability after fifty hydrogen absorption-desorption cycles. The significant improvement of hydrogen desorption kinetics is attributed to the synergistic effect of abundant oxygen vacancies and in situ formed multivalent species in the catalyst. This highlights the importance of designing and synthesizing efficient catalysts for dehydrogenation of MgH2.

Structure and bonding in TiNiSi type LaMgSnH intermetallic hydride

The work was aimed on reaching a better understanding of the effect of magnesium as a component of the hydride-forming LaMgSn intermetallic compound crystallising with the orthorhombic TiNiSi type of structure on the hydrogenation behaviours, crystal structure and bonding interactions with hydrogen. The LaMgSn structure is significantly expanded as compared to the earlier studied isotypic LaNiSn H storage material (volume expansion of 23%), as a result of a substitution of the smaller Ni atoms by much larger Mg atoms. This significantly affects the chemistry of the interaction of the intermetallic compound with hydrogen because a transition metal, Ni, in replaced by an active hydride-forming metal, Mg. The work involved computational studies of the electronic structure of the intermetallic compound and its hydride, and experimental studies of the hydrogenation behaviour and thermal stability of the formed hydride LaMgSnH, its structural characterisation by SR XRD and neutron powder diffraction, and Mössbauer spectroscopic studies of the stannide and its hydride. These studies showed that in the system LaMgSn-H2 a monohydride LaMgSnH is a thermodynamically favourable hydride composition. PDOS levels show that hydrogen and all constituting elemental metals, La, Mg and Sn, have peaks of electron density in the range between − 6 and − 4 eV indicating their hybridisation. The results show the hybridization of H atoms not only with bonded La and Mg atoms forming H-filled tetrahedra La3Mg, but also with Sn despite its atoms do not have bonding interactions with H. This explains the high stability of the metal substructure which does not disproportionate into the binary hydrides of La and Mg even when heated to 200 °C @ 20 bar H2, but instead forms an insertion type hydride. Formation of the monohydride LaMgSnH (Sp.gr. Pnma; a=8.1628(4); b= 4.5555(3); c= 9.2391(5) Å; V= 343.56(5) Å3) causes a small (1.26%) expansion of the unit cell volume compared to LaMgSn, and mainly proceeds along the [100] direction. Hydrogen absorption-desorption cycle results in a reversible formation of the initial compound LaMgSn, with the peak of hydrogen release occurring in vacuum at 355 °C, which is intermediate between the temperatures for the vacuum decomposition of the dihydrides MgH2 and LaH2. From the combined refinements of the Synchrotron (SR) XRD and Neutron Powder Diffraction (NPD) data, deuterium atoms completely and in an ordered way fill a half of the available La3Mg interstitial sites with metal-H/D distances of Mg-D= 2.026 Å; La-D= 2.381 and 2.502 Å. The occupied La3Mg sites are smaller in size than the vacant Mg3La tetrahedra. Sn and D exhibit a nonbonding interaction with the closest Sn-D separation of 3.033 Å. 119Sn Mössbauer spectra of LaMgSn and LaMgSnH show isomer shifts of 1.98(2) and 1.99(1) mm/s which are typical for the chemically similar stannides.

Thermodynamic and kinetic isotope effects on hydrogen absorption by Pd–Al2O3 pellets

Palladium has been widely served as the separation material in the hydrogen isotope separation process on account of its unique hydrogenation characteristics. To reduce Pd pulverization effect and improve the gas flow rate, Pd–Al2O3 (Pd deposited on Al2O3) is commonly used as the separation material. It is crucial to grasp the hydrogen absorption and desorption thermodynamics and kinetic isotope effect of Pd–Al2O3 material, which favours raising the separation efficiency. In this work, the effect of PdO existing in the fresh Pd–Al2O3 on the thermodynamic character of Pd–Al2O3–H(D) system and the porous substrate effect on the hydrogen absorption kinetics of Pd–Al2O3 were investigated. It shows that PdO could totally reduce to Pd after primary hydrogen adsorption-desorption, leading to decreased hydrogen absorption capacity. However, it has no effect on the enthalpy and entropy values of Pd–Al2O3–H (D) system. The kinetic analysis of hydrogen adsorption of Pd–Al2O3 shows that the hydrogen absorption of Pd–Al2O3 could be fitted by Mample model, a special case of the JMAK model, and the interface-controlled model can be deduced. The porous substrate influences the rate of hydrogen adsorption of Pd–Al2O3. The SEM and XRD results show that after 60 hydrogen absorption-desorption cycles, the surface of Pd–Al2O3 pellet has a slight change with a pulverization rate of 3.3 wt%, although the high-strength alumina support can withstand the stress caused by Pd expansion during hydrogen absorption.

Application of nitrogen-doped graphene-supported titanium monoxide as a highly active catalytic precursor to improve the hydrogen storage properties of MgH2

MgH2 has broad prospects in energy storage applications; however, its poor thermodynamic properties and slow hydrogen absorption and desorption rates are unsuitable for commercial needs. In the present work, TiO@N-C (denoted as TTONC), a highly active catalytic precursor, was employed to improve the hydrogen storage properties of MgH2. The TTONC-catalyzed MgH2 could uptake hydrogen at room temperature, and the onset dehydrogenation temperature of TTONC-catalyzed MgH2 was 94 °C lower than that of pristine MgH2 (∼300 °C). Dehydrogenated TTONC-catalyzed MgH2 had a capacity retention rate of 95.2% after 50 hydrogen absorption-desorption cycles. The dehydrogenation and hydrogenation apparent activation energies of MgH2-TTONC were 90.5 kJ.mol−1 and 52.7 kJ.mol−1, respectively. The catalytic mechanism analysis revealed that the in situ formed Ti generated TiH2 in the hydrogenation process, and Ti/TiH2 acted as a hydrogen pump to diffuse hydrogen atoms in the hydrogen absorption/desorption process. The formation of stable CN layers with carbon structural defects on the surface of MgH2 inhibited the fragmentation and agglomeration of MgH2 particles, and they served as nucleation sites to enhance hydrogen diffusion. Hence, the dehydrogenation/hydrogenation properties and cyclic stability of MgH2 were greatly enhanced by the addition of TTONC.

Research on the Creep and Fatigue Evaluation Method of the Double-Layered Annulus Metal Hydride Bed Combined with Numerical Modeling and ASME Code

Applied to a hydrogen absorption-desorption cycle, the hydrogen storage bed will experience higher exchange temperatures and variety of mechanical load. Due to the complex structure of the double-layered annulus metal hydride bed and the importance of thermal stress on the failure of a metal hydride bed, the numerical modeling of its hot spot stress was carefully carried out. Moreover, in this paper, an analysis method considering the limit failure mode condition is proposed to deal with the stress analysis in the process of hydrogen absorption and desorption. According to the proposed analysis method, the maximum stress of thermal-structural coupling in the process of hydrogen absorption occurs at about 1/3 along the diameter direction and at the geometric mutation of the connection between the cooling pipe and the main body of the hydrogen storage bed in the process of hydrogen desorption. Apart from that, the hydrogen storage bed is also subjected to thermal-mechanical fatigue by the iterative process of absorption and desorption, and its operating temperature range is in the thermal creep temperature region. Based on the distribution of the stress and temperature, evaluation hot sites were selected and the ASME-NB and ASME-NH codes were used to evaluate fatigue and fatigue creep, respectively. The evaluation showed that the fatigue damage generated during its service life is small, while the creep damage is relatively large and the total damage generated during the service life of the hydrogen storage bed is within the safe range. Aiming at the structure and complex process of a double-layer hydrogen storage bed, creep and fatigue evaluation methods are proposed, various failure modes of hydrogen storage bed are highlighted, and the relationship between process parameters and life is established.

Structural features of 18R-type long-period stacking ordered phase in Mg85Zn6Y9 alloy and the Ni doping effect on its hydrogen storage properties

Magnesium-based alloys with 18R-type long-period stacking ordered (LPSO) structures have attracted wide attention for structural and functional applications. To understand hydrogen storage properties of 18R phase, the Mg85Zn6Y9 alloy with 94 wt.% of 18R-type LPSO phase is prepared in this work. The 18R phase has a layered structure where Y-Zn-Mg and Mg layers alternately stack along the c-axis. In the Y-Zn-Mg layers, Y, Zn and partial Mg sites are co-occupied by Y and Mg, Zn and Mg, and Mg and Zn/Y atoms, respectively. Thus the 18R phase is easily decomposed into α-MgH2, γ-MgH2, YH2, YH3, C14-type Laves phase MgZn2 and minor CsCl-type Y(Mg,Zn) during ball milling under hydrogen atmosphere. After further hydrogen absorption-desorption cycling, Y(Mg,Zn) disappears gradually and C14 phase transforms into C15-type Laves phase. By contrast, the Mg85Zn6Y9 alloy has better hydrogen storage kinetics and cycle durability than pure Mg because of the catalytic effect of YH2/YH3 on hydrogen absorption-desorption and inhibition role of Laves phase in Mg crystallite growth. Moreover, the introduction of Ni into Mg85Zn6Y9 sample leads to a further decrease in activation energy of hydrogen desorption from 106.39 to 96.78 kJ mol−1 due to the formation of Mg2Ni. This work not only provides new insights into structural features and hydrogen storage characteristics of 18R phase but offers an effective method for improving hydrogen storage properties.

Roles of in situ-formed NbN and Nb2O5 from N-doped Nb2C MXene in regulating the re/hydrogenation and cycling performance of magnesium hydride

The industrial use of magnesium hydride (MgH2) as a potential solid hydrogen storage material is limited because of its poor thermodynamic properties. In the present work, nitrogen-doped niobium carbide-supported niobium pentoxide (N-Nb2O5@Nb2C) was prepared using Nb2AlC and NH3·H2O as precursors and then employed to enhance the hydrogen storage properties of MgH2. It was found that in situ-formed NbN and Nb2O5 in N-Nb2O5@Nb2C-doped MgH2 could destabilize MgH2, improving the hydrogen storage properties of MgH2 at low temperatures. The N-Nb2O5@Nb2C-doped MgH2 composite started to release hydrogen at 178 °C and could uptake 5.0 wt% of hydrogen within 1.95 min at 90 °C and within 5 h at 30 °C. The capacity retention ratio of N-Nb2O5@Nb2C-doped MgH2 was 98.6%, which was much higher than that of additive-free MgH2 (73.5%) after 100 hydrogen absorption–desorption cycles. The mechanism analysis revealed that the presence of NbN and Nb2O5 could restrain the grain size of MgH2, provide more active sites and hydrogen diffusion paths, weaken the interaction between Mg and H, and elongate the length of Mg-H bond; thus, the cyclic stability and reversible hydrogen storage performance of MgH2 were significantly improved.

Hydrogen absorption-desorption cycle decay mechanism of palladium nanoparticle decorated nitrogen doped graphene

As a hydrogen storage material, palladium nanoparticle decorated nitrogen doped graphene (Pd/N-rGO) has drawn much attention owing to its high absorption capacity at moderate conditions. However, its hydrogen absorption-desorption cycle performance, which is essential for their practical application, has been rarely studied. In this paper, a simple and convenient high temperature thermal reduction method was used to synthesize nitrogen-doped graphene decorated with Pd nanoparticles (Pd/N-rGO). Taken it as a representative, the hydrogen absorption-desorption cycle performance of Pd/N-rGO was investigated. The results showed that after three cycles the hydrogen storage capacity dropped from 2.9 ​wt% to 0.8 ​wt% at 25 ​°C and 4 ​MPa pressure. It was found that the palladium nanoparticles shed from Pd/N-RGO sheet after cycle performance test, and then agglomerated. These phenomena will weaken the hydrogen spillover effect, leading to the decrease of hydrogen storage capacity. Meanwhile, decreased defects reduce the hydrogen absorption sites, which will thus deteriorate the hydrogen storage capacity.

Stress reduction in a hydride container by the addition of a glidant agent

Hydrogen absorbing materials, such as metal hydrides, present a possible solution for hydrogen storage. During the absorption process these materials swell, which can put the mechanical integrity of its container at risk. One possibility is to increase the flowability of the absorbing material, usually a fine cohesive powder, so that it can rearrange within its container during the swelling stage. In this work, we study if this rearrangement could be improved by the addition of Aerosil, a type of colloidal silica widely used as glidant agent. The walls of a stainless steel reactor are instrumented with strain gauges to measure the accumulation of stresses due to hydrogen absorption-desorption cycles. We explore the container filled with pure LaNi5 absorbing material previously activated, so as with different Aerosil-added proportions. Results show that Aerosil allows avoiding stress build-up, for all glidant concentrations used in present study.

Synergistic catalytic effects of ZIF-67 and transition metals (Ni, Cu, Pd, and Nb) on hydrogen storage properties of magnesium

MgTM/ZIF-67 nanocomposites were prepared by the deposition-reduction method using ZIF-67, MgCl2, and TMClx (TM = Ni, Cu, Pd, Nb) as raw materials. The dehydrogenation activation energies of MgTM/ZIF-67 (TM = Ni, Cu, Pd, Nb) nanocomposites were calculated to be 115.4 kJ mol−1 H2, 115.7 kJ mol−1 H2, 113.6 kJ mol−1 H2, and 75.8 kJ mol−1 H2, respectively; hence, the MgNb/ZIF-67 nanocomposite manifested the best comprehensive hydrogen storage performance. The hydrogen storage capacity of the MgNb/ZIF-67 nanocomposite was hardly attenuated after the 100th hydrogen absorption-desorption cycle. The dehydrogenated enthalpies of MgH2 and CoMg2H5 in MgNb/ZIF-67 hydride were calculated to be 72.4 kJ mol−1 H2 and 81.0 kJ mol−1 H2, respectively, which were lower than those of additive-free MgH2 and Mg/ZIF-67. The improved hydrogen storage properties of MgNb/ZIF-67 can be ascribed to the CoMg2–Mg(Nb) core-shell structure and the catalytic effects of NbH and niobium oxide nanocrystals.

Growth kinetics of MgH2 nanocrystallites prepared by ball milling

MgH2 is one of promising hydrogen storage materials due to its high hydrogen capacity of 7.6 wt%. However, MgH2 nanocrystallites easily grow up during hydrogen absorption―desorption cycling, leading to deterioration of hydrogen storage properties. To clarify the growth kinetics of MgH2 crystallites, the growth characteristics of MgH2 nanocrystallites are investigated in this work. The growth exponents of MgH2 nanocrystallites in pure MgH2 and MgH2―10 wt% Pr3Al11 samples are evaluated to be n = 5 and n = 6, respectively. Meanwhile, their activation energies for crystallite growth are also determined to be 109.2 and 144.2 kJ/mol, respectively. The increase of growth exponent and rise of activation energy for crystallite growth in MgH2―10 wt% Pr3Al11 composite are ascribed to the presence of nano-sized Pr3Al11 phase.

Compositional dependence of hydrogenation performance of Ti-Zr-Hf-Mo-Nb high-entropy alloys for hydrogen/tritium storage

A series of Ti-Zr-Hf-Mo-Nb high-entropy alloys with different Mo concentrations were developed as candidate materials for hydrogen/tritium storage in solid phase. The crystal structures and hydrogenation properties of the Ti-Zr-Hf-Mo-Nb alloys were investigated by X-ray diffraction and differential scanning calorimetry techniques. All the alloys have a body-centred cubic single phase structure. The results demonstrate that the cell volume of the Ti-Zr-Hf-Mo-Nb hydride decreases with increasing Mo concentration, which reduces their thermal stability. The theoretical calculation proposes that the lower binding energy of the Ti-Zr-Hf-Mo-Nb hydride decreases the thermal stability of Ti-Zr-Hf-Mo-Nb alloys with higher Mo content. The great hydrogenation performance for all the Ti-Zr-Hf-Mo-Nb alloys is owing to their reversible single-phase transformation during the hydrogen absorption-desorption cycle, which would be beneficial to improving the hydrogen recycling rate and preventing the disproportionation. The compositional dependence of the hydrogenation performance of the Ti-Zr-Hf-Mo-Nb alloys was established and will be useful in designing novel hydrogen/tritium storage materials to satisfy the requirements of different application fields in hydrogen, solar thermal and nuclear energy.

A Novel TiZrHfMoNb High-Entropy Alloy for Solar Thermal Energy Storage.

An equiatomic TiZrHfMoNb high-entropy alloy (HEA) was developed as a solar thermal energy storage material due to its outstanding performance of hydrogen absorption. The TiZrHfMoNb alloy transforms from a body-centered cubic (BCC) structure to a face-centered cubic (FCC) structure during hydrogen absorption and can reversibly transform back to the BCC structure after hydrogen desorption. The theoretical calculations demonstrated that before hydrogenation, the BCC structure for the alloy has more stable energy than the FCC structure while the FCC structure is preferred after hydrogenation. The outstanding hydrogen absorption of the reversible single-phase transformation during the hydrogen absorption–desorption cycle improves the hydrogen recycling rate and the energy efficiency, which indicates that the TiZrHfMoNb alloy could be an excellent candidate for solar thermal energy storage.

Fundamental Material Properties of the 2LiBH4-MgH2 Reactive Hydride Composite for Hydrogen Storage: (II) Kinetic Properties

Reaction kinetic behaviour and cycling stability of the 2LiBH4–MgH2 reactive hydride composite (Li-RHC) are experimentally determined and analysed as a basis for the design and development of hydrogen storage tanks. In addition to the determination and discussion about the properties; different measurement methods are applied and compared. The activation energies for both hydrogenation and dehydrogenation are determined by the Kissinger method and via the fitting of solid-state reaction kinetic models to isothermal volumetric measurements. Furthermore, the hydrogen absorption–desorption cycling stability is assessed by titration measurements. Finally, the kinetic behaviour and the reversible hydrogen storage capacity of the Li-RHC are discussed.

Microstructures and hydrogen absorption–desorption behavior of an A2B7-based La-Mg-Ni alloy

The microstructural changes during hydrogen absorption–desorption cycles of an A2B7-based La-Mg-Ni alloy with a nominal composition of La1.5Mg0.5Ni7.0 were systematically investigated by powder X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM). The ternary La-Mg-Ni alloy was mostly composed of 2H-A2B7 phase with minor inclusions of 3R-A5B19, 2H-A5B19 and 3R-AB3 phases existing as parts of intergrowth structures with the major A2B7 phase. Most parts of the major 2H-A2B7 phase containing Mg exhibited an excellent crystal structure retention after the hydrogen absorption–desorption cycles at 80 °C. Two types of defected bands were found to develop after the first hydrogen absorption–desorption cycle. The first ones are amorphous bands developed inside the minor 3R-AB3 phase, while the second ones develop as heterogeneously strained regions inside the major 2H-A2B7 phase. Both the defected bands are considered to be responsible for the irreversible hydrogen capacity of the A2B7-based La1.5Mg0.5Ni7.0 alloy during the hydrogen absorption–desorption cycles at 80 °C.

Function of aluminum in crystal structure of rare earth–Mg–Ni hydrogen-absorbing alloy and deterioration mechanism of Nd0.9Mg0.1Ni3.5 and Nd0.9Mg0.1Ni3.3Al0.2 alloys

We investigated in detail the effect of incorporating Al in the crystal structure of rare earth–Mg–Ni hydrogen-absorbing alloys, which were developed as candidate materials for the metal hydride (MH) negative electrode in commercial Ni–MH batteries, using synchrotron powder X-ray diffraction. Partially substituting the Ni part with Al changes the lattice parameter of the major A2B7 phase, eliminating a mismatch between the AB2 units and the AB5 units. The change of the lattice parameter in the alloy leads to good hydrogen reversibility and good durability. Furthermore, we observed the alloy after 30 hydrogen absorption–desorption cycles using a scanning transmission electron microscope image. Consequently, we found that the surface layer of the Nd0.9Mg0.1Ni3.5 alloy had an amorphous state, while the surface layer of the Nd0.9Mg0.1Ni3.3Al0.2 alloy did not. We confirmed that the deterioration mechanism of the Nd0.9Mg0.1Ni3.3Al0.2 alloy was due to partial expansion of the AB2 unit along the c-axis; the local area of deterioration expanded during the cycling period.

Structural change of NdNi3 during hydrogen absorption-desorption cycle

The structural change of NdNi3 during the hydrogen absorption-desorption cycle and the P–C isotherm have been investigated. The maximum hydrogen capacity achieved in the first absorption process is 1.05 H/M. After the first desorption, 0.75 H/M of hydrogen capacity remains in the alloy. The trigonal crystal structure of the original alloy (R-3m) transforms to monoclinic (C2/m) in the first absorption. The crystal structure of the hydride phase remains monoclinic during the first desorption. The metal sublattice expands anisotropically during phase transformation from the alloy to the monoclinic hydride (NdNi3H4.0); a, b, and c axes expand by 8%, 7%, and 44%, respectively. The volumes of the unit cell, and the Nd2Ni4 and NdNi5 cells expand by more than 60%. Phase transformation of NdNi3Hx is irreversible during the first absorption-desorption cycle.

Effect of elemental substitution on the structure and hydrogen storage properties of LaMgNi4 alloy

Intermetallic compounds with the nominal formula LaMgNi3.6M0.4 (M=Ni, Co, Mn, Cu, Al) were prepared through induction melting, and the structure and hydrogen storage properties of the resultant alloys were extensively investigated. Results showed that the alloys exhibit sizable hydrogen absorption capacity and that elemental substitution significantly influences their microstructure and hydrogen storage properties. The discharge capacities of the alloy electrodes decrease in the order Co>Ni>Al>Cu>Mn. Moreover, the electrochemical kinetics of the alloys depend on their microstructures and phase compositions. Smaller grain size is helpful to improve the electrochemical kinetics. The gaseous hydrogen absorption capacities of the alloys are approximately 1.7wt.% in the first hydrogenation process. Cracking caused by hydrogenation and dehydrogenation also significantly improves the hydrogen absorption kinetics of the alloy particles. The hydrogen storage capacities of the alloys rapidly decrease with increasing cycle number. This result is attributed to amorphisation of the LaMgNi4 phase during hydrogen absorption–desorption cycling (H2-induced amorphisation). Our findings provide new insights into the capacity degradation mechanism of La–Mg–Ni system hydrogen storage alloys that may improve their cycling stability.

Hydrogen storage and cyclic properties of (VFe)60(TiCrCo)40-xZrx (0 ≤ x ≤ 2) alloys

Hydrogen storage and cyclic properties of (VFe)60(TiCrCo)40-xZrx (0 ≤ x ≤ 2) alloys had been investigated systematically. The results showed that the alloys when x = 0 and 0.5 consist of BCC main phase, C14 Laves phase and CeO2 phase, while Zr-based FCC phase appears in the alloys when x = 1 and 2, and the contents of the Laves phase and the Zr-based FCC phase increase with the increment of Zr substitution for Ti. Zr substituted compositions were found to have better hydrogen absorption kinetics but the hydrogen storage capacities decrease as the substitution amounts increase. Owing to that Zr element can reduce the micro-strain accumulation in the crystal lattice during the hydrogen absorption-desorption cycles, the cyclic properties of the (VFe)60(TiCrCo)40-xZrx alloys are improved. As Zr content increases, the desorption capacity fading rate of (VFe)60(TiCrCo)40-xZrx decreases and the best cyclic property was obtained when x = 2 with only 4.5% capacity decay after 10 cycles in this work.

Decaying behaviors of V40(TiCr)51Fe8Mn hydrogen storage alloys with different particle sizes

The decaying behaviors of V40(TiCr)51Fe8Mn hydrogen storage alloys with different particle sizes from −60 to −500meshes were investigated systematically in this work. XRD results indicated that particle sizes of the alloys affect little on the phase transformation from Body-centered Cubic (BCC) to Body-centered Tetragonal (BCT) before and after hydrogenation and dehydrogenation, respectively. The hydrogen desorption capacities of the alloys decrease with increasing the number of hydrogen absorption–desorption cycles, but their decaying rates can be obviously restrained as starting particle sizes change from −60 down to −400meshes. Data fitting showed that the variation of the hydrogen desorption capacity has a similar exponential rule to cycle numbers as that of the micro-strain in the alloys. Possible reasons of the capacity decay are discussed. However, a superfine alloy with −500meshes showed much larger decaying rate, which was possibly attributed to the poisoning of foreign gases. Generally speaking, the smaller the particle size, the less the micro-strain in the lattice. Namely, the alloy powders with finer sizes have less micro-stress and correspondingly better cycling stability (within −400 meshes in this work).