Comparison of hydrogen-storage properties of Mg-14Ni-3Fe2O3-3Ti and Mg-14Ni-2Fe2O3-2Ti-2Fe

Magnesium with oxides or transition elements prepared by mechanical grinding under H2 (reactive mechanical grinding) showed relatively high hydriding and dehydriding rates when the content of additives was about 20 wt%. Ni, Fe₂O₃, and Fe were chosen as the oxides or transition elements to be added. Ti was also selected since it was considered to increase the hydriding and dehydriding rates by forming Ti hydride. Samples Mg-14Ni-3Fe₂O₃-3Ti (Sample A) and Mg-14Ni-2Fe₂O₃-2Ti-2Fe (Sample B) were prepared by reactive mechanical grinding, and their hydrogen storage properties were compared. The activated Sample A had a little smaller hydriding rate than the activated Sample B, but a higher dehydriding rate than the activated Sample B. Sample A exhibits quite a larger dehydriding rate and quantity of hydrogen desorbed for 60 min than any other Mg-xNi-yFe₂O₃-zM (M=transition metals) samples. An addition of a relatively larger amount of Ti is considered to lead to quite a high hydriding rate and a high dehydriding rate of Sample A.     

Phase transformations and hydrogen-storage characteristics of Mg-transition metal-oxide alloys

Samples with the compositions of 76.5 wt%Mg-23.5 wt%Ni (Mg-Ni), 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe₂O₃ (Mg-Ni-Fe₂O₃) and 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe₂O₃ (spray conversion) (Mg-Ni-scFe₂O₃), 71.5 wt%Mg-23.5 wt%Ni-5 wt% Fe (Mg-Ni-Fe) and 80 wt%Mg-13.33 wt%Ni-6.67 wt%Fe (Mg-13Ni-7Fe) were prepared by reactive mechanical grinding. Mg-13Ni-7Fe has the highest hydriding and dehydriding rates. After hydriding-dehydriding cycling, all the samples contain the Mg₂Ni phase. The samples with Fe₂O₃ and Fe₂O₃(spray conversion) as starting materials contain the Mg(OH)₂ phase after hydriding-dehydriding cycling as well as after reactive mechanical grinding. Mg-Ni-Fe and Mg-13Ni-7Fe contain the MgH₂ phase after reactive mechanical grinding. Phases, space groups, cell parameters, contents and crystallite sizes were analyzed by Full Pattern Matching Refinement program, one of the Rietveld analysis programs, from the XRD powder patterns of Mg-Ni-scFe₂O₃ after reactive mechanical grinding and after hydriding-dehydriding cycling. The MgH₂ phase formed in the Mg-Ni-Fe and Mg-13Ni-7Fe mixtures after reactive mechanical grinding is considered to help the pulverization of the materials during reactive mechanical grinding, leading to the high hydriding and dehydriding rates of these mixtures.     

Improvement of the hydrogen-storage kinetics of Mg by reactive mechanical grinding with 10 wt.% Fe2O3 and 5 wt.% Ni

The addition of Fe₂O₃ to Mg is believed to be able to increase the hydriding rate of Mg, and the addition of Ni is thought to be able to increase the hydriding and dehydriding rates of Mg. A sample Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) was prepared by mechanical grinding under H₂ (reactive mechanical grinding). The as-milled sample absorbed 4.61 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min. Its activation was accomplished after two hydriding-dehydriding cycles. The activated sample absorbed 4.59 wt.% of hydrogen at 593 K under 12 bar H₂ for 60 min, and desorbed 3.83 wt.% hydrogen at 593 K under 1.0 bar H₂ for 60 min. The activated Mg-(10wt.%Fe₂O₃, 5 wt.%Ni) had a slightly higher hydriding rate at the beginning of the hydriding reaction but a much higher dehydriding rate compared with the activated Mg-10 wt.%Fe₂O₃. prepared via spray conversion. After hydriding-dehydriding cycling, Fe₂O₃ was reduced, Mg₂Ni was formed by the reaction of Mg with Ni, and a small fraction of Mg was oxidized.     

Hydrogen storage properties of a Ni,Fe and Ti-added Mg-based alloy

Mg-5wt%Ni-2.5wt%Fe-2.5wt%Ti (referred to as Mg-5Ni-2.5Fe-2.5Ti) hydrogen storage material was prepared by reactive mechanical grinding, after which the hydrogen absorption and desorption kinetics were investigated using a Sievert-type volumetric apparatus. A nanocrystalline Mg-5Ni-2.5Fe-2.5Ti sample was prepared by reactive mechanical grinding and hydriding-dehydriding cycling. Analysis by the Williamson-Hall method from an XRD pattern of this sample after 10 hydriding-dehydriding cycles showed that the crystallite size of Mg was 37.0 nm and that its strain was 0.0407%. The activation of Mg-5Ni-2.5Fe-2.5Ti was completed after three hydriding-dehydriding cycles. The prepared Mg-5Ni-2.5Fe-2.5Ti sample had an effective hydrogen-storage capacity near 5 wt% H. The activated Mg-5Ni-2.5Fe-2.5Ti sample absorbed 4.37 and 4.90 wt% H for 5 and 60 min, respectively, at 593K under 12 bar H₂, and desorbed 1.69, 3.81, and 4.85 wt% H for 5, 10 and 60 min, respectively, at 593K under 1.0 bar H₂.     

Hydriding/dehydriding properties of Mg-Ni-based ternary alloys synthesized by mechanical grinding

The Mg-Ni-based ternary alloys Mg2-xTixNi(x=0, 0.2, 0.4) and Mg2Ni1-xZrx(x=0, 0.2, 0.4) were successfully synthesized by mechanical grinding. The phases in the alloys and the hydriding/dehydriding properties of the alloys were investigated. Mg2Ni and Mg are the main hydrogen absorption phases in the alloys by XRD analysis. Hydriding kinetics curves of the alloys indicate that the hydrogen absorption rate increases after partial substitution of Ti for Mg and Zr for Ni. According to the measurement of pressure-concentration-isotherms and Van't Hoff equation, the relationship between ln p(H2) and 1 000/T was established. It is found that while increasing the content of correspondingly substituted elements at the same temperature, the equilibrium pressure of dehydriding increases, the enthalpy change and the stability of the alloy hydride decrease.     

磁场辅助烧结法制备La0.67Mg0.33Ni3储氢合金

采用磁场辅助烧结合成法（MASS）制备了化学计量比为La0.67Mg0.33Ni3的储氢合金,通过X射线衍射（XRD）、等温定容法（PCT）和差示扫描量热法（DSC）分析了合金的相结构和吸放氢性能。XRD结果显示：合金主相为PuNi3型结构的(La, Mg)Ni3,氢化后分解为以La2Ni7、MgNi2和LaNi3结构为主的复相产物,合金因吸氢发生晶格膨胀。PCT测试表明：1 T磁场下合成的合金在室温下具有最小的滞后系数（0.480）、最大的放氢量1.307（质量分数,%）,综合性能最优。该合金放氢DSC曲线上有2个交叠的吸热峰,分别对应于(La, Mg)Ni3和LaNi5氢化后的放氢过程。     

Influence of Ti, Mn, Fe, and Ni addition upon thermal stability and decomposition temperature of the MgH2 phase of alloys synthesized by reactive mechanical alloying

Influence of addition of some transition metals (TMs), mainly Ti, Mn, Fe and Ni, to magnesium upon thermal stability of the hydride phase MgH₂ synthesized due to reactive mechanical alloying (RMA) in hydrogen atmosphere at pressure 1.2 MPa was studied employing the thermodesorption spectroscopy (TDS) method. The TDS spectra registered differ from each other by their shapes and fine-structure peculiarities. This fact allows to conclude about a different influence of the TMs under consideration upon the feature of hydrogen distribution on location sites in the hydride phase and, consequently, upon its decomposition temperature. We have made an attempt to elucidate the origin of the mentioned influence of the TMs upon the effects derived. A correlation between the degree of dispersion of TM alloying the MgH₂ hydride and its decomposition temperature was observed. It has been established that, addition of 10 wt% Ti reveals the maximum influence on decreasing decomposition temperature of the hydride phase. The X-ray photoelectron O 1s core-level spectrum of the specimen contained the addition of 10 wt% Ti shows decreasing a quantity of oxygen-contained structures, catalyst poisons, adsorbed on its surface.     

Influences on the H<Subscript>2</Subscript>-sorption properties of Mg of Co (with various sizes) and CoO addition by reactive grinding and their thermodynamic stabilities

We attempted to improve the H₂-sorption properties of Mg by mechanical grinding under H₂ (reactive grinding) with Co (with various particle sizes) and with CoO. The thermodynamic stabilities of the added Co and CoO were also investigated. CoO addition has the best influence and addition of smaller particles of Co (0.5–1.5 μm) has a better effect than the addition of larger particles of Co on the H₂-sorption properties of Mg. The activated Mg+10 wt.% CoO sample has about 5.54 wt% hydrogen-storage capacity at 598 K and the highest hydriding rate, showing an H_a value of 2.39 wt.% after 60 min at 598 K, 11.2 bar H₂. The order of the hydriding rates after activation is the same as that of the specific surface areas of the samples. The reactive grinding of Mg with Co or CoO and hydriding-dehydriding cycling increase the H₂-sorption rates by facilitating nucleation of magnesium hydride or α solid solution of Mg and H (by creating defects on the surface of the Mg particles and by the additive), and by making cracks on the surface of Mg particles and reducing the particle size of Mg, thus shortening the diffusion distances of hydrogen atoms. The cobalt oxide is stable even after 14 hydriding cycles at 598 K under 11.2 bar H₂. Discharge capacities are measured for the sampple Mg+10 wt.%CoO and Mg+10wt.%Co (0.5−1.5 μm) with good hydrogen-storage properties.     

Hydrogenation reaction of Mg-Based alloys fabricated by rapid solidification

Mg-23.5wt%Ni-xwt%Cu (x=2.5, 5 and 7.5) alloys for hydrogen storage were prepared by melt spinning and crystallization heat treatment. The alloys were ground by a planetary ball mill for 2 h in order to obtain a fine powder. The Mg-23.5Ni-5Cu alloy had crystalline Mg and Mg₂Ni phases. Mg-23.5Ni-5Cu had an effective hydrogen capacity of near 5 wt%. The activated Mg-23.5Ni-5Cu alloy absorbed 4.50 and 4.84 wt%H at 573K under 12 bar H₂ for 10 and 60 min, respectively, and desorbed 3. 21 and 4.81 wt%H at 573K under 1.0 bar H₂ for 10 and 30 min, respectively. The activated Mg-23.5Ni-5Cu alloy showed a quite high hydriding rate like Mg-10Fe₂O₃, and higher dehydriding rates than the activated Mg-xFe₂O_3?yNi. This likely resulted because the melting before melt spinning process has led to the homogeneous distribution of Ni and Cu in the melted Mg, and the Mg-23.5Ni-5Cu alloy has a larger amount of the Mg₂Ni phase than the Mg-xFe₂O_3?yNi alloy.     

Electrochemical hydriding performance of Mg–TM–Mm (TM=transition metals,Mm=mischmetal) alloys for hydrogen storage

Eighteen as-cast binary Mg–Ni, Mg–Mm and ternary Mg–Ni–Mm and Mg–Ni–TM (TM=transition metals (Cu, Zn, Mn and Co); Mm = mischmetal containing Ce, La, Nd and Pr) alloys were hydrided by an electrochemical process to determine the alloys with the most potential for electrochemical hydrogen storage. The alloys were hydrided in a 6 mol/L KOH solution at 80 °C for 480 min and at 100 A/m². To assess the electrochemical hydriding performance of alloys, maximum hydrogen concentrations, hydrogen penetration depths and total mass of absorbed hydrogen in the alloys were measured by glow discharge spectrometry. In addition, the structures and phase compositions of the alloys both before and after hydriding were studied by optical and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. It was determined that the highest total amount of hydrogen was absorbed by the Mg–25Ni–12Mm and Mg–26Ni (mass fraction, %) alloys. The maximum hydrogen concentrations in the Mg–25Ni–12Mm and Mg–26Ni alloys were 1.0% and 1.6%, respectively. The main hydriding product was the binary MgH₂ hydride, and the ternary Mg₂NiH₄ hydride was also detected in the Mg–25Ni–12Mm alloy. The electrochemical hydriding parameters achieved are discussed in relation to the structures of alloys, alloying elements and hydriding mechanisms.     

Phase structure and hydrogen storage properties of LaMg_（3.70）Ni_（1.18） alloy

The phase structure and hydrogen storage properties of LaMg_3.70Ni_1.18 alloy were investigated. The LaMg_3.70Ni_1.18 alloy consists of main LaMg₂Ni phase, minor La₂Mg₁₇ and LaMg₃ phases. The alloy can be activated in the first hydriding/dehydriding process, and initial LaMg₂Ni, La₂Mg₁₇, and LaMg₃ phases transfer to LaH_2.34, Mg, and Mg₂Ni phases after activation. The reversible hydrogen storage capacity of the LaMg_3.70Ni_1.18 alloy is 2.47 wt.% at 558 K, which is higher than that of the LaMg₂Ni alloy. The pressure-composition-temperature (PCT) curves display two hydriding plateaus, corresponding to the formation of MgH₂ and Mg₂NiH₄. However, only one dehydriding plateau is observed, owing to the synergetic effect of hydrogen desorption between MgH₂ and Mg₂NiH₄. The uptake time for hydrogen content to reach 99% of saturated state is less than 250 s, and 90% hydrogen can be released in 1200 s in the experimental conditions, showing fast kinetics in hydriding and dehydriding. The activation energies of the LaMg_3.70Ni_1.18 alloy are −51.5 ± 1.1 kJ/mol and −57.0 ± 0.6 kJ/mol for hydriding and dehydriding, respectively. The hydriding/dehydriding kinetics of the LaMg_3.70Ni_1.18 alloy is better than that of the Mg₂Ni alloy, owing to the lower activation energy values.     

Catalytic effect of Ni nanoparticles on the desorption kinetics of MgH2 nanoparticles

Mg and Ni nanoparticles were prepared by hydrogen plasma-metal reaction (HPMR). MgH₂ nanoparticles were obtained by hydriding the Mg nanoparticles. Hydrogen storage kinetics of the MgH₂ nanoparticles doped with different amount of Ni nanoparticles was investigated by differential scanning calorimetry (DSC) and hydrogen desorption rate measurements. The obtained samples show superior hydrogen storage kinetics. 6.1 wt% hydrogen is desorbed in 10 min at 523 K under an initial pressure of 0.01 bar of H₂ when the proportion of Ni nanoparticles is 10 wt%. The desorption rate increases when enhancing the amount of catalyst. However, the activation energy of desorption does not decrease any more when the amount of Ni exceeds a value. The enhanced desorption kinetics are mainly attributed to the accelerated combination process of hydrogen atoms by the Ni nanoparticles on the surface of MgH₂.     

多壁碳纳米管载镍对镁基合金储氢性能影响

采用化学法制备多壁碳纳米管载镍催化剂(Ni/MWNTs),并将其加入到镁粉中,结合氢化燃烧合成(HydridingCombustionSynthesis,HCS)和机械球磨(MechanicalMilling,MM),即HCS+MM复合技术制备Mg85-Nix/MWNTs15-x(x代表质量百分数,x=3,6,9,12)合金。通过X射线衍射仪、透射电子显微镜、扫描电镜以及气体反应控制器研究了材料的晶体结构、微观形貌和吸放氢性能。结果表明:Mg85-Ni9/MWNTs6合金具有最佳综合吸放氢性能,其在373K,吸氢量达到5.68%(质量分数,下同),且在100s内就基本达到饱和吸氢量;在523K,1800s内的放氢量达到4.31%。Ni/MWNTs催化剂的添加,不但起到催化的作用,而且MWNTs具有优异的纳米限制作用,使得催化剂的粒径限制在纳米级,有利于限制产物中Mg2NiH4颗粒的长大。另外Ni与MWNTs存在协同催化作用,当它们达到一定比例时,对合金的吸放氢促进作用达到最优化,明显改善了合金的吸放氢性能。     

Mg_(50)Ni_(50-x)Ti_x合金的吸放氢性能

研究了Mg50 Ni50 -xTix 合金的非晶形成能力与非晶合金电极的吸放氢性能。结果表明 :在Mg50 Ni50 -xTix合金中 ,当Ti替代Ni元素的量低于 1 5% (摩尔分数 )时 ,机械合金化能够得到几乎单一的非晶态合金 ;用Ti替代Ni形成的三元非晶合金能降低镁镍合金的平衡氢压 ;少量的Ti替代能改善合金的电化学吸放氢容量 ,使合金电极的吸放氢循环稳定性得到提高。这被认为是在三元合金中钛元素减缓了合金中镁元素的氧化腐蚀进程所致。     

Improvement in hydrogen sorption properties of Mg by reactive mechanical grinding with Cr2O3, Al2O3 and CeO2

We tried to improve the hydrogen sorption properties of Mg by mechanical grinding under H₂ (reactive mechanical grinding) with oxides Cr₂O₃, Al₂O₃ and CeO₂. The hydriding rates of Mg are reportedly controlled by the diffusion of hydrogen through a growing Mg hydride layer. The added oxides can help pulverization of Mg during mechanical grinding. A part of Mg is transformed into MgH₂ during reactive mechanical grinding. The Mg+10wt.%Cr₂O₃ powder has the largest transformed fraction 0.215, followed in order by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. The Mg+10wt.%Cr₂O₃ powder has the largest hydriding rates at the first and fifth hydriding cycle, followed in order by Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. Mg+10wt.%Cr₂O₃ absorbs 5.87wt.% H at 573 K, 11 bar H₂ during 60 min at the first cycle. The Mg+10wt.%Cr₂O₃ powder has the largest dehydriding rates at the first and fifth dehydriding cycle, followed by Mg+10wt.%CeO₂ and Mg+10wt.%Al₂O₃. It desorbs 4.44 wt.% H at 573 K, 0.5 bar H₂ during 60 min at the first cycle. All the samples absorb and desorb less hydrogen at the fifth cycle than at the first cycle. It is considered that this results from the agglomeration of the particles during hydriding–dehydriding cycling. The average particle sizes of the as-milled and cycled powders increase in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of hydrogen absorbed or desorbed for 1 h for the first and fifth cycles decrease in the order of Mg+10wt.%Cr₂O₃, Mg+10wt.%Al₂O₃ and Mg+10wt.%CeO₂. The quantities of absorbed or desorbed hydrogen increase as the average particle sizes decrease. As the particle size decreases, the diffusion distance shortens. This leads to the larger hydriding and dehydriding rates. The Cr₂O₃ in the Mg+10wt.%Cr₂O₃ powder is reduced after hydriding–dehydriding cycling. The much larger chemical affinity of Mg than Cr for oxygen leads to a reduction of Cr₂O₃ after cycling.     

元素取代和磁热处理对La0.67Mg0.33Ni3-xMx(M=Co,Cu)(x=0,0.5)合金贮氢性能的影响

研究了Co和Cu取代Ni以及磁热处理对La0.67Mg0.33Ni3-xMx(M=Co,Cu)(x=0,0.5)合金吸放氢反应热力学和动力学性能的影响。结果表明,Ni被Co和Cu元素部分替代后,合金的吸放氢量增大,放氢温度降低,吸放氢特征时间(tc)减小,吸放氢过程中的扩散活化能降低。磁热处理明显地提高了3种铸态合金的吸氢量,增大了吸放氢平台宽度,改善了合金的吸放氢动力学性能,其中磁热处理对La0.67Mg0.33Ni2.5Co0.5合金改性效果最好,吸放氢量分别为1.40%和1.32%(质量分数,下同),放氢峰所对应的温度为77.8℃,吸放氢特征时间"tc"为91.4和379.3s,吸放氢扩散活化能分别为16.3和23.3kJ/mol。     

HCS+MM法制备镁基复合储氢材料结构及储氢性能

采用氢化燃烧合成法制备Mg95Ni5-x%TiFe0.8Mn0.2Zr0.05(x=0, 10, 20, 30)(质量分数)复合物,然后将氢化燃烧合成产物进行机械球磨得到镁基复合储氢材料。采用XRD、SEM、EDS及PCT研究材料的相结构、表面形貌、颗粒化学成分以及吸放氢性能。研究表明,添加30% TiFe0.8Mn0.2Zr0.05合金形成的复合物具有最佳的综合吸放氢性能：在373 K,50 s内基本达到饱和吸氢量4.11% (质量分数);在493和523 K,1800 s内放氢量分别为1.91%和4.3%;其起始放氢温度为420 K,与Mg95Ni5相比降低了20 K,吸放氢性能的改善与复合物的组织结构密切相关。此外,TiFe0.8Mn0.2Zr0.05的加入改善了复合物的放氢动力学性能     

Characterization of a magnesium-based alloy after hydriding-dehydriding cycling (n=1–150)

The cycling performance of Mg-15 wt% Ni-5 wt% Fe₂O₃ alloy (named Mg-15Ni-5Fe₂O₃) was investigated by measuring the absorbed hydrogen quantity as a function of the number of cycles and by examining the variations in the phases and microstructures with cycling. The sample was hydriding-dehydriding cycled 150 times. The absorbed hydrogen quantity decreased as the number of cycles increased from the second to the 150th cycle. The H_a value varied almost linearly with the number of cycles. The maintainability of the absorbed hydrogen quantity was 73.8%, and the degradation rate was 0.007 wt%/cycle for the hydriding reaction time of 60 min. After the 9th hydriding-dehydriding cycle, Mg, Mg₂Ni, MgO, and Fe were observed. After 150 cycles, the quantity of the MgO increased. The phases were analyzed using MDI JADE 6.5, a software system designed for XRD powder pattern processing, from the XRD pattern of the Mg-15Ni-5Fe₂O₃ alloy after the 9th hydriding-dehydriding cycle. The crystallite size and strain of the Mg were then estimated using the Williamson-Hall technique.     

Development of hydrogen-storage alloys by mechanical alloying of Mg with Fe and Co

The hydriding and dehydriding kinetics of Mg are reviewed. In order to improve the reaction kinetics of Mg with hydrogen, mechanically-alloyed Mg-10 wt.%Fe and Mg-10 wt.%Co mixtures are prepared and their hydrogen-storage properties are investigated. The activation of Mg-10 wt.%Fe is easier than that of Mg-10 wt.%Co. However, The hydriding rates (at 569–589 K, 7–11 bar H₂) and dehydriding rates (at 589 K, 1.0 bar H₂) of the mechanically-alloyed Mg-10wt.%Co are higher than those of the mechanically-alloyed Mg-10 wt.%Fe after activation. The H_a value of Mg-10 wt.%Co after 60 min is 3.08 wt.% at 589 K under 11 bar H₂ and its H_d value after 60 min is 1.48 wt.% at 589 K under 1.0 bar H₂. Mg-10 wt.%Co has a smaller particle size than has Mg-10 wt.%Fe after hydriding and dehydriding cycling. The mechanical alloying of Mg with Fe and Co and the hydriding-dehydriding cycling increased the hydriding and dehydriding rates by facilitating nucleation (by creating defects on the surface of the Mg particle and by the additive) and by shortening the diffusion distances (by reducing the Mg particle sizes).     

Improving hydrogen storage performance of Li–Mg–N–H system by adding niobium hydride

Hydrogen storage properties of 2LiNH2 – MgH2 –xNbH(x = 0 and 0.05) composites and the catalysis of NbH on hydrogen sorption reaction of the Li–Mg– N–H system were investigated. Hydrogen sorption properties of 2LiNH2 –MgH2 system are effectively improved by adding NbH. Temperature programmed desorption results show the addition of NbH reduces the dehydriding onset temperature of 2LiNH2 –MgH2 system by 21 K. Approximate 3.62 wt% hydrogen in 2LiNH2 –MgH2 – 0.05NbH composite is released following a 500 min at 433 K, whereas the amount of hydrogen desorption is only *3.16 wt% for the pristine system under the same condition. The sample with NbH exhibits higher dehydriding rate compared with the pristine one. Moreover, hydrogen absorption rate increases by adding NbH into the 2LiNH2 – MgH2 system. Hydrogen absorption capacity of the samples with NbH is 3.23 wt% within 400 min, which is higher than that of pristine sample. Fine NbH particles homogeneously distribute in the 2LiNH2 –MgH2 –0.05NbH composite, and catalyze the hydrogen sorption reaction rather than reacts as a reactant into new compound.