An investigation on hydrogen storage kinetics of nanocrystalline and amorphous Mg2Ni1−xCox (x = 0-0.4) alloy prepared by melt spinning

In order to improve the hydrogen storage kinetics of the Mg₂Ni-type alloys, Ni in the alloy was partially substituted by element Co, and melt-spinning technology was used for the preparation of the Mg₂Ni_1−xCo_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The structures of the as-cast and spun alloys are characterized by XRD, SEM and TEM. The hydrogen absorption and desorption kinetics of the alloys were measured by an automatically controlled Sieverts apparatus. The electrochemical hydrogen storage kinetics of the as-spun alloys is tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys are calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves are plotted by an electrochemical workstation. The results show that the substitution of Co for Ni notably enhances the glass forming ability of the Mg₂Ni-type alloy. Furthermore, the substitution of Co for Ni, instead of changing major phase Mg₂Ni, leads to forming secondary phases MgCo₂ and Mg. Both the melt spinning treatment and Co substitution significantly improve the hydrogen absorption and desorption kinetics. The high rate discharge ability, the hydrogen diffusion coefficient and the limiting current density of the alloys significantly increase with raising both the spinning rate and the amount of Co substitution.     

Hydrogen storage characteristics of nanocrystalline and amorphous Mg2Ni-type alloys prepared by melt spinning

In order to improve the hydrogen storage characteristics of the Mg₂Ni-type alloys, Ni in the alloy is partially substituted by element Mn, and melt-spinning technology is used for the preparation of the Mg₂Ni_1−xMn_x (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys. The microstructures of the as-cast and spun alloys are characterized by XRD, SEM and HRTEM. The hydrogen absorption and desorption kinetics of the alloys are measured by an automatically controlled Sieverts apparatus. The electrochemical performances are tested by an automatic galvanostatic system. The results show that the as-spun Mn-free alloy holds typical nanocrystalline structure, whereas the as-spun alloys containing Mn displays a nanocrystalline and amorphous structure. The hydrogen absorption and desorption capacities and kinetics of the alloys increase with rising spinning rate. Additionally, melt spinning markedly improves the electrochemical hydrogen storage capacity and cycle stability of the alloys containing Mn. With an increase in the spinning rate from 0 (As-casts is defined as spinning rate of 0 m/s) to 30 m/s, the discharge capacity of the (x = 0.3) alloy mounts up from 92.3 to 211.1 mAh/g, and its capacity retaining rate at 20th charging and discharging cycle grows from 36.21% to 76.02%.     

Structural and electrochemical hydrogen storage properties of Mg2Ni-based alloys

Four different methods, i.e. hydriding combustion synthesis + mechanical milling (HCS + MM), induction melting (followed by hydriding) + mechanical milling (IM(Hyd) + MM), combustion synthesis + mechanical milling (CS + MM) and induction melting + mechanical milling (IM + MM), were used to prepare Mg₂Ni-based hydrogen storage alloys used as the negative electrode material in a nickel-metal hydride (Ni/MH) battery. The structural and electrochemical hydrogen storage properties of the Mg₂Ni-based alloys have been investigated systematically. The XRD results indicate that the as-milled products show nanocrystalline or amorphous-like structures. Electrochemical measurements show that the as-milled hydrides exhibit higher discharge capacity and better electrochemical kinetic property than the as-milled alloys. Among the four different methods, the HCS + MM product possesses the highest discharge capacity (578 mAh g⁻¹), the best high rate dischargeability (HRD) and the highest exchange current density (58.8 mA g⁻¹). It is suggested that the novel method of HCS + MM is promising to prepare Mg-based hydrogen storage electrode alloy with high discharge capacity and activity.     

Co替代Ni改善纳米晶和非晶Mg2Ni型合金的贮氢动力学

为了改善Mg2Ni型合金的贮氢动力学性能,用Co部分替代合金中的Ni,用快淬技术制备了Mg2Ni1？xCox（x=0,0.1,0.2,0.3,0.4）贮氢合金。用XRD、HRTEM表征了快淬态合金的微观结构,用自动控制的Sieverts设备测试了合金的吸放氢动力学性能,用程控电池测试仪测定了合金薄带的电化学贮氢动力学。结果表明：Co替代Ni提高了Mg2Ni型合金的非晶形成能力,合金的非晶化程度随着Co含量的增加而增加。此外,Co替代Ni显著地改善了合金的贮氢动力学,当Co含量从0增加到0.4时,快淬态（15m/s）合金在5min内的吸氢饱和率从81.2%增加到84.9%,20min的放氢率从17.60%增加到64.79%,氢扩散系数从1.07×10-11cm2/s增加到2.79×10？11cm2/s,极限电流密度从46.7mA/g增加到191.7mA/g。     

Influence of rapid quenching on hydrogen storage characteristics of nanocrystalline Mg2Ni-type alloys

Nanocrystalline Mg2Ni-type alloys with nominal compositions of Mg20Ni10–xCux(x=0,1,2,3,4,mass fraction,%) were synthesized by rapid quenching technique.The microstructures of the as-cast and quenched alloys were characterized by XRD,SEM and HRTEM.The electrochemical hydrogen storage performances were tested by an automatic galvanostatic system.The hydriding and dehydriding kinetics of the alloys were measured using an automatically controlled Sieverts apparatus.The results show that all the as-quenched alloys hold the typical nanocrystalline structure and the rapid quenching does not change the major phase Mg2Ni.The rapid quenching significantly improves the electrochemical hydrogen storage capacity of the alloys,whereas it slightly impairs the cycling stability of the alloys.Additionally,the hydrogen absorption and desorption capacities of the alloys significantly increase with rising quenching rate.     

Improvement of the electrochemical hydrogen storage performance of Mg2Ni by the partial replacements of Mg by Al, Ti and Zr

Mg₂Ni, Mg_1.5Al_0.5Ni, Mg_1.5Zr_0.5Ni, Mg_1.5Ti_0.5Ni, Mg_1.5Zr_0.25Al_0.25Ni, Mg_1.5Zr_0.25Ti_0.25Ni and Mg_1.5Ti_0.25Al_0.25Ni alloys were synthesized by mechanical alloying and their electrochemical hydrogen storage characteristics were investigated. X-ray diffraction studies showed that while Al was retarding, Zr and Ti were facilitating the amorphization of Mg₂Ni phase. The initial discharge capacities of Mg_1.5Ti_0.5Ni, Mg_1.5Zr_0.5Ni and Mg_1.5Al_0.5Ni alloys were 414, 322 and 166 mA h g⁻¹, respectively. Although Mg_1.5Al_0.5Ni alloy had very low initial discharge capacity, the capacity retaining rate of this alloy was much better than those of Ti- and Zr-including alloys. The potentiodyanamic polarization experiments in 6 M KOH solution presented that Mg was passive and Ni was immune in the charge/discharge potential range (−1.0 V_Hg/HgO and −0.5 V_Hg/HgO). At the same conditions Ti and Zr had moderate, and Al had extremely higher dissolution rates. The analysis by the electrochemical impedance spectroscopy revealed that the increase in the charge transfer resistance of Mg_1.5Al_0.5Ni alloy was relatively low with the increase in depth of discharge. This observation was attributed to the formation of the porous unstable Mg(OH)₂ layer due to the high rate dissolution of the disseminated Al₂O₃ and thus the exposition of the underlying electro-catalytically active Ni sites. The charge transfer resistance of Mg_1.5Ti_0.5Ni alloy increased sharply with the increase in depth of discharge possibly due to the stabilizing effect of Ti-oxide on Mg(OH)₂. The presence of Ti-oxide, however, was predicted to make Mg(OH)₂ barrier layer more penetrable by hydrogen atoms, since the increased stability of the surface layer the cyclic stability of Mg_1.5Ti_0.5Ni alloy was relatively satisfactory.     

快淬纳米晶/非晶Mg2Ni型合金的电化学贮氢性能（英文）

用快淬工艺制备纳米晶和非晶Mg2Ni型Mg2Ni1-xMnx(x=0,0.1,0.2,0.3,0.4)合金,获得长度连续、厚度约30μm,宽度约25mm的薄带。用XRD、HRTEM分析快淬合金薄带的微观结构,用程控电池测试仪测试合金薄带的电化学性能,用电化学工作站(PARSTAT2273)测试快淬薄带的交流阻抗谱(EIS),测试电位阶跃后的阳极电流—时间响应曲线,并计算氢在合金中的扩散系数(D)。结果表明,快淬(x=0)合金均具有典型的纳米晶结构,而快淬(x=0.4)合金显示纳米晶和非晶结构,这证实Mn替代Ni有利于Mg2Ni型合金形成非晶相。Mn替代Ni显著地改善了合金的电化学贮氢性能,包括放电容量和电化学循环稳定性。当Mn替代量从0增加到0.4时,20m/s快淬态合金的放电容量从96.5mA·h/g增加到265.3mA·h/g,20次充放循环后的容量保持率(S20)从31.3%增加到70.2%。此外,高倍率放电能力(HRD)、交流阻抗(EIS)以及电位阶跃测试结果都表明,随着Mn替代量的增加,合金电极的电化学动力学性能先增加而后降低。     

Investigation on Gaseous and Electrochemical Hydrogen Storage Kinetics of As-Quenched Nanocrystalline Mg2Ni-type Alloys

为了改善Mg2Ni型合金气态及电化学贮氢动力学性能,用Cu部分替代合金中的Ni,用快淬技术制备Mg2Ni1-xCux(x=0,0.1,0.2,0.3,0.4)合金,用XRD、SEM、HRTEM分析铸态及快淬态合金的微观结构;用自动控制的Sieverts设备测试合金的气态贮氢动力学性能,用程控电池测试仪测试合金的电化学贮氢动力学.结果表明,所有快淬态合金均具有纳米晶结构,无非晶相形成.Cu替代Ni不改变合金的主相Mg2Ni,但使合金的晶粒显著细化.快淬处理及Cu替代均显著地提高合金的气态及电化学贮氢动力学性能.当淬速从0m/s(铸态被定义为淬速0 m/s)增加到30 m/s时,Mg2Ni0.8Cu0.3合金在5 min内的吸氢饱和率从57.2％增加到92.87％,20 min的放氢率从21.6％增加到49.6％,高倍率放电能力(HRD)从40.6％增加到73.1％,氢扩散系数(D)从1.02×10-11 cm2/s增加到4.08×10 -11 cm2/s,极限电流密度(IL)从113.0 mA/g增加到715.3 mA/g.     

Effects of cyclic hydriding-dehydriding reactions of Mg2Ni alloy on the expansion deformation of a metal hydride storage vessel

A high-temperature reaction vessel system was set up to study the wall deformation during cyclic hydriding/dehydriding reactions of Mg₂Ni powders at 255 °C. Effects of packing fraction and initial particle size of Mg₂Ni powders were characterized. Results indicated that a strain accumulation was found on the wall surface with progressive cycles of hydriding/dehydriding reactions. The wall strain varied with position, as a lower position had a larger deformation. Such an accumulation and position-dependence of wall strain in the vertical hydride storage vessel could be attributed to a pulverization-densification mechanism. At a given vessel position, the hoop strain was increased with increasing packing fraction from 50 to 70 vol%. For a 50-vol% packing fraction, the wall deformation was enlarged when the initial powder size was increased from 200 mesh (74 μm) to 100 mesh (149 μm). After 50 cycles of hydriding/dehydriding reactions, the particle size was significantly reduced to about 1 μm.     

铸态及快淬态无钴AB5型贮氢合金的循环稳定性

对AB5型LaxMm1-x(NiMnSiAlFe)49(x=0,0.45,0.75,1.00,摩尔分数)贮氢合金进行了快淬处理,研究了La含量及快淬工艺对合金微观结构及电化学循环稳定性的影响.结果表明:La含量的增加对铸态合金的循环稳定性没有明显影响,但使快淬态合金的循环稳定性下降,且快淬处理能显著提高合金的循环稳定性.当La替代量从0增加到1.00时,经300次充放循环后,铸态合金的容量保持率(Rh)从59.2%增加到59.8%;16 m/s淬速快淬态合金的容量保持率从83.9%下降到65.0%.对于x=0.45的合金,当淬速从0(铸态被定义为淬速等于0)增加到28 m/s时,容量保持率从59.8%增加到75.8%.     

The effect of chemical coating with Ni on the electrode properties of Mg2Ni alloy

Mg₂Ni alloy prepared by powder sintering was chemically coated with 10% nickel by weight. The effects of the nickel coating on the surface appearance, the structure of the alloy and the electrode characteristics were investigated. The discharge capacity and cycle life of the nickel-coated alloy electrode were greatly increased in comparison with values for the bare alloy because of the changed phase structure and surface properties.     

Electrochemical characteristics of Mg2−xZrxNi (x = 0–0.6) electrode alloys prepared by mechanical alloying

The electrode alloys Mg_2−xZr_xNi (x = 0, 0.15, 0.3, 0.45 and 0.6) were prepared by mechanical alloying (MA). Mg in the alloy was partially substituted with Zr in order to improve the electrochemical characteristics of the Mg₂Ni-type alloy. The microstructures and the electrochemical characteristics of the experimental alloys were measured systemically. The effects of substituting Mg with Zr and MA technique on the microstructures and electrochemical performances of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the substitution of Zr is favourable for the formation of an amorphous phase. For a fixed milling time, the amorphous phase in the alloy grows with increasing Zr content. The electrochemical measurement indicates that the substitution of Zr can dramatically enhance the discharge capacity with preferable cycle stability, and it markedly improves the discharge voltage characteristic of the alloys. For x ≤ 0.3, the discharge capacity of the alloys monotonically increases with milling time. But for x > 0.3, it has a maximum value with the change of milling time.     

Co替代Ni对快淬Mg2Ni型合金结构及电化学贮氢性能的影响

为了改善Mg2Ni型贮氢合金的电化学贮氢性能,以Co部分替代合金中的Ni,用快淬工艺制备Mg2Ni型Mg2Ni1-xCox(x=0,0.1,0.2,0.3,0.4)合金,获得长度连续、厚度约为30μm、宽度约为25 mm的快淬合金薄带。并用XRD、SEM、HRTEM分析快淬态合金薄带的微观结构;用DSC研究快淬薄带的热稳定性;用程控电池测试仪测定合金薄带的电化学贮氢性能;探索Co替代Ni对快淬Mg2Ni型合金结构及电化学贮氢性能的影响。结果表明:在快淬无Co合金中没有发现非晶相,但快淬含Co合金中存在明显的非晶结构,证明Co替代Ni提高了Mg2Ni型合金的非晶形成能力。Co替代Ni使快淬态合金的热稳定性略有提高,显著地改善了合金的电化学贮氢性能,包括放电容量、电化学循环稳定性以及高倍率放电性能,这主要归因于Co替代Ni导致结构的变化以及非晶形成能力的提高。     

DFT studies of hydrogen storage properties of Mg0.75Ti0.25

Absorption energies of hydrogen in Mg_0.75Ti_0.25 alloys as a function of the hydrogen concentration were calculated using Density Functional Theory. Four types of structures of alloys and their hydrides including TiAl₃, ZrAl₃, AuCu₃, and segregated types of structures were considered. The stability of the configurations, and the structural and electronic bonding properties were studied. The hydrogenation properties depend highly on the structure of the alloys. The ordered alloys have very similar properties to that of pure Mg. For segregated alloys, the hydrogenation properties can be divided to Ti-like, ordered alloy-like and Mg-like from low to high hydrogen concentration. The formation energies show that for the four structures, segregated Mg_0.75Ti_0.25 is favored for alloys, whereas TiAl₃ type of Mg_0.75Ti_0.25H₂ are favored for hydrides. Therefore hydrogen induced structural rearrangement of the intermetallic structures of the Mg_0.75Ti_0.25 might occur upon hydrogen cycling. For the non-homogenous Mg-Ti-H system, further phase segregation of Ti in Mg might occur. Partial dehydrogenation with some hydrogen remaining in the Ti-rich region may improve reversibility.     

Structure and electrochemical properties of hypo-stoichiometric hydrogen storage alloys prepared by twin-roller rapid quenching process

1 Introduction AB5-type rare-earth-based hydrogen storage al- loys have widely been used as negative electrode materials for nickel-metal hydride batteries due to their inherent advantages, especially high hydrogen storage capacity, easy activation and lo…     

Electrocatalytic activity and electrochemical hydrogen storage of Ni-La alloy prepared by electrodeposition from aqueous electrolyte

Ni-La alloy coating was prepared by electrodeposition. The effect of cathodic current density on the La content of the alloy coatings was discussed. It is found that the content of La in the alloy increases with increasing the cathodic current density. The microstructures and codeposition mechanism of Ni-La alloy coatings were investigated by means of X-ray diffraction (XRD) and cyclic voltammetry (CV). The results demonstrate that the Ni-La alloy is FCC and codeposited by the induced mechanism. The hydrogen evolution reaction (HER) on the electrodeposited Ni-La alloy electrodes in alkaline solution was evaluated by Tafel polarization curves. It is found that La-Ni alloy coating exhibites much higher exchange current density for HER than pure Ni electrode, and that the exchange current density increases with increasing the La content of alloys. The good electrocatalytic activity for HER of this Ni-La alloy is attributed to the synergism of the electronic structure of La and Ni. The electrodeposited La-Ni alloys have a certain dectrochemical hydrogen storage capacity of 34- 143 mAh/g, which increases with increasing the La content of alloys.     

Mg2Si热电材料与Cu/Ni复合电极的接头界面及性能

为保证热连接过程中热电材料与导流电极之间实现良好连接,同时形成有效的阻隔界面防止界面元素扩散致使材料性能下降,本研究以Cu片作电极,引入中间层Ni箔作扩散阻挡层,采用电场激活压力辅助烧结(FAPAS)法,在合成高纯硅化镁(Mg_2Si)热电材料的同时,同步制得Cu/Ni/Mg_2Si热电接头。利用SEM、EDS以及XRD对接头界面的微观相组成、元素扩散特征以及新相生长规律进行了探讨,并且采用热震试验和四探针法对接头分别进行了力学性能和电传输性能的测试。结果表明,合成的Mg_2Si纯度高,高温热膨胀性能稳定;Ni层能有效阻隔界面元素扩散,与Mg_2Si实现良好的冶金结合,连接界面新相层的生成次序依次为Mg_2Si Ni3和Mg2Ni。Cu/Ni/Mg_2Si具有较好的热膨胀匹配性能,连接界面在持续60次的热震循环后依然保持完整。随着时效时间延长,界面扩散层增厚,接触电阻有所增大,与t~(1/2)具有近线性关系,且700℃下未时效的接头获得最小接触电阻率112μ?·cm~2。     

Effects of rapid quenching on structure and cycle stability of La-Mg-Ni-Co type hydrogen storage alloy

In order to improve the cycle stability of La-Mg-Ni-Co type alloy electrode, rapid quenching technology was employed. The effects of rapid quenching on the microstructure and cycle stability of the alloy were investigated. The obtained results show that the La2Mg(Ni0.85Co0.15)9M0.1 (M=B, Cr) alloy electrodes are composed of (La, Mg)Ni3 phase, LaNi5 phase and a small amount of the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast MB alloy, and the Ni2B phase in the alloy nearly disappears after rapid quenching. Rapid quenching technology can slightly improve the cycling life of the alloy. When the quenching rate increases from 0 m·s -1 (As-cast is defined as quenching rate of 0 m·s-1 ) to 30 m·s -1 , the cycle lives of the MB, M Cr alloys enhance from 86 and 87 cycles to 106 and 119 cycles, respectively. On the other hand, the average capacity decay rates of the MB, M Cr alloys decrease from 1.7172 and 1.7178 mAh·g-1·cycle-1 to 1.5751 and 1.3060 mAh·g-1·cycle-1 after 86 charge-discharges cycling, respectively.     

Microstructure and hydrogen storage properties of Mg-Sn nanocomposite by mechanical milling

To improve the hydrogen storage properties, the composition and microstructure of Mg-Sn alloys were modified through fabricating Mg/Mg₂Sn nanocomposite by mechanical alloying. The microstructures were characterized by X-ray diffraction and scanning electron microscopy. It is found that Mg₂Sn instead of Mg(Sn) solid solution is preferably formed during milling process. Although Mg₂Sn is not a hydriding phase, the in situ formed nanosized Mg₂Sn facilitates hydrogen absorption/desorption of Mg by forming Mg/Mg₂Sn nanocomposite. The mechanically milled Mg-5 at.% Sn nanocomposite exhibits slightly elevated plateau pressure and destabilized thermodynamics due to the introduction of large amount of interface energy in Mg/Mg₂Sn nanocomposite.