Effects of La substitution on microstructure and hydrogen storage properties of Ti−Fe−Mn-based alloy prepared through melt spinning

The as-spun Ti_(1−x)La_(x)Fe_(0.8)Mn_(0.2)(x=0,0.01,0.03,0.06,0.09,molar fraction)alloys were prepared by melt spinning.The effects of La substitution for Ti on the microstructure,hydrogen storage kinetics and thermodynamics of TiFe-type Ti−Fe−Mn-based alloy were investigated.The as-spun alloys hold the TiFe single phase,which transforms to TiFeH_(0.06),TiFeH,and TiFeH_(2) hydrides after hydrogenation.La substitution promotes the formation of micro-defects(such as dislocations and grain boundaries)in the alloys,thus facilitating hydrogen diffusion.In addition,the hydrogen storage kinetics properties are improved after introducing La element.With the rise of La content,the hydrogen storage capacity decreases firstly and then increases,but the absolute value of hydriding enthalpy change(|ΔH|)increases firstly and then reduces.When x=0.01,the maximum value of|ΔH|is obtained to be(25.23±0.50)kJ/mol for hydriding,and the alloy has the maximum hydrogen absorption capacity of(1.80±0.04)wt.%under the conditions of 323 K and 3 MPa.

Microstructure, hydrogen storage thermodynamics and kinetics of La_5Mg_(95-x)Ni_x(x=5, 10, 15) alloys

The microstructure, hydrogen storage thermodynamics and kinetics of La5Mg95-xNix (x=5, 10, 15) ternary alloys with different Ni contents were investigated. The evolutions of the microstructure and phase of experimental alloys were characterized by X-ray diffractometry and scanning electron microscopy. The hydrogen storage kinetics and thermodynamics, and P-C-I curves were tested using a Sievert apparatus. It is found that increasing Ni content remarkably improves hydrogen storage kinetics but reduces the hydrogen storage capacity of alloys. The highest hydrogen absorption/desorption rate is observed in the La5Mg80Ni15 alloy, with the lowest hydrogen desorption activation value being 57.7 kJ/mol. By means of P-C-I curves and the van’t Hoff equation, it is determined that the thermodynamic performance of the alloy is initially improved and then degraded with increasing Ni content. The La5Mg85Ni10 alloy has the best thermodynamics properties with a hydrogenation enthalpy of -72.1 kJ/mol and hydrogenation entropy of -123.2 J/(mol·K).

Hydrogen storage performances of as-milled REMg_(11)Ni(RE=Y, Sm) alloys catalyzed by MoS_2

To compare the hydrogen storage performances of as-milled REMg11Ni-5MoS2(mass fraction)(RE=Y,Sm)alloys,which were catalyzed by MoS2,the corresponding alloys were prepared.The hydrogen storage performaces of these alloys were measured by various methods,such as XRD,TEM,automatic Sievert apparatus,TG and DSC.The results reveal that both of the as-milled alloys exhibit a nanocrystalline and amorphous structure.The RE=Y alloy shows a larger hydrogen absorption capacity,faster hydriding rate,lower initial hydrogen desorption temperature,superior hydrogen desorption property,and lower hydrogen desorption activation energy,which is thought to be the reason of its better hydrogen storage kinetics,as compared with RE=Sm alloy.

Electrochemical hydrogen storage behaviors of as-cast and spun RE-Mg-Ni-Co-Al-based AB2-type alloys applied to Ni-MH battery

Preparation of La-Mg-Ni-Co-Al-based AB2-type alloys La0.8-xCe0.2YxMgNi3.4Co0.4Al0.1(x=0,0.05,0.10,0.15,0.20)was performed using melt spinning technology.The influences of spun rate and Y content on structures and electrochemical hydrogen storage characteristics were studied.The base phase LaMgNi4 and the lesser phase LaNis were detected by X-ray diffraction(XRD)and scanning electron microscope(SEM).The variations of spinning rate and Y content cause an obvious change in phase content,but without altering phase composition,namely,with spinning rate and Y content growing,LaMgNi4 phase content augments while LaNi5 content declines.Furthermore,melt spinning and the replacing La by Y refine the grains dramatically.The electrochemical tests show a favorable activation capability of the two kinds of alloys,and the maximum discharge capacities are achieved during the first cycle.Discharge capacity firstly increases and subsequently decreases with spinning rate rising,while cycle stability is ameliorated and discharge capacity decreases with Y addition increasing.It is found that the amelioration of cycle stability is due to the enhancement of anti-pulverization,anti-corrosion and antioxidation abilities by both replacement of La with Y and melt spinning.Moreover,with the increase of Y addition and/or spinning rate,the electrochemical kinetics that contain charge transfer rate,limiting current density(IL),hydrogen diffusion coefficient(D)and the high rate discharge ability(HRD)firstly augment and then reduce.

Hydrogen storage properties of La1-xPrxMgNi3.6Co0.4（x=0-0.4） alloys with annealing treatment

The as-cast RE-Mg-Ni-b ased AB2-type La1-xPrxMgNi3.6Co0.4(x=0-0.4)alloys were prepared by vacuum induction melting followed by annealing treatment.The phase composition and structure were characterized by X-ray diffraction(XRD)and scanning electron microscope(SEM).The results show that LaMgNi4 and LaNi5 coexist in as-cast alloys,but only LaMgNi4 is detected in the annealed alloys.The morphology of annealed alloys is more homogeneous than that of as-cast alloys.The gaseous hydrogen storage and electrochemical properties were investigated by pressure-composition isotherm(P-C-T)and electrochemical measurements.The P-C-T curves of annealed alloys show flatter and wider pressure plateaus corresponding to absorption/desorption pressure plateaus of LaMgNi4 hydride.But the maximum hydrogen storage content of annealed alloys is lower than that of as-cast alloys.In consideration of the electrochemical properties,the annealed La0.8Pr0.2MgNi3.6Co0.4alloy exhibits a maximum discharge capacity of354.2 mAh·g-1.

A Comparison Study of Hydrogen Storage Thermodynamics and Kinetics of YMg11Ni Alloy Prepared by Melt Spinning and Ball Milling

Melt spinning （MS） and ball milling （BM） were employed to fabricate YMg11Ni alloy, and their structures and hydrogen storage performances were examined. The results reveal that the as-spun and as-milled alloys both exhibit the nanocrystalline and amorphous structure. The as-milled alloy shows a larger hydrogen absorption capacity as compared with the as-spun alloy. More than that, the as-milled alloy exhibits lower onset hydrogen desorption temperature than the as-spun one, which are 549.8 and 560.9 K, respectively. Additionally, the as-milled alloy shows a superior hydrogen desorption property to the as-spun one. On the basis of the time needed by desorbing hydrogen of 3 wt% H2, for the as- milled alloy, it needs 1106, 456, 343, and 180 s corresponding to hydrogen desorption temperatures of 593, 613, 633, and 653 K. However, for the as-spun alloy, the time needed is greater than 2928, 842, 356, and 197 s corresponding to the same temperatures. Hydrogen desorption activation energies of as-milled and as-spun alloys are 98.01 and 105.49 kJ/mol, respectively, which is responsible for that the as-milled alloy possesses a much faster dehydriding rate. By means of the measurement of pressure-composition-temperature （P-C-T） curves, the dehydrogenation enthalpy change of the alloys prepared by MS （△Hoe（MS）） and BM （△Hdc（BM）） is 81.84 and 79.46 kJ/mol, respectively, viz. △Hde（MS） 〉 △Hoc（BM）.

Research progress of TiFe-based hydrogen storage alloys

After being activated,TiFe alloys are widely concerned for their high hydrogen storage density due to their large reversible absorption and desorption capacity of hydrogen at room temperature,low price,abundant resources,moderate hydride decomposition pressure,and good hydrogen absorption and desorption kinetic performance.Meanwhile,TiFe alloys can be used as anode materials for secondary batteries,catalysts for hydrogenation,and storage media for thermal,solar,and wind energy,which has wide industrial application prospects.However,TiFe alloys have disadvantages such as difficult activation,easy toxicity,and large hysteresis.This review introduces the current research status and performance characteristics of TiFe-based hydrogen storage alloys,the phase structure,hydride phase structure,kinetic and thermodynamic models of TiFe alloys,as well as the application prospects of TiFe-based hydrogen storage alloys in practical production and the ways to improve their hydrogen storage performance,and presents the views on the future research priorities and development directions of TiFe-based hydrogen storage alloys.

Influence of melt spinning and annealing treatment on structures and hydrogen storage thermodynamic properties of La0.8Pr0.2MgNi3.6Co0.4 alloy

La0.8Pr0.2MgNi3.6Co0.4 alloys were prepared by induction melting,annealing and melt spinning techniques.The influences of annealing treatment and melt spinning on phase structure and hydrogen storage properties were systematically investigated.The results of X-ray diffraction determine that the as-cast and as-spun La0.8Pr0.2MgNi3.6Co0.4 alloys consist of LaMgNi4 and LaNi5 phases,while only LaMgNi4 phase is present in the as-annealed alloy.The scanning electron microscope images illustrate that the grain of the alloy is significantly refined by melt spin ning tech no logy.The gaseous hydrogen storage kinetic and thermodynamic properties were measured by using a Sievert's apparatus at different temperatures.The maximum hydrogen storage capacity of the as-cast,as?spun and as-annealed La0.8Pr0.2MgNi3.6Co0.4 alloy is 1.699,1.637 and 1.535 wt.% at 373 K and 3 MPa,respectively.The annealed alloy has flatter and wider pressure plateaus compared with the as-cast and as-spun alloys,which correspond to the hydrogen absorption and desorption process of LaMgNi4 and corresponding hydride.Furthermore,the enthalpy and entropy changes of LaMgNi4 during hydrogenation at different temperatures were calculated using Van't Hoff methods.

Structure and electrochemical properties of LaMgNi4-xCox(x=0-0.8)hydrogen storage electrode alloys

LaMgNi（4-x）Cox（x = 0-0.8） electrode alloys used for MH/Ni batteries were prepared by induction melting. The structures and electrochemical hydrogen storage properties of the alloys were investigated in detail.X-ray diffraction（XRD） and scanning electron microscopy（SEM） analysis show that LaMgNi4 phase and LaNi5 phase are obtained. The lattice parameters of the two phases increase first and then decrease with Co content increasing.The electrochemical properties of the alloy electrodes were measured by means of simulated battery tests. Results show that the addition of Co does not change the discharge voltage plateau of the alloy electrodes. However, the maximum discharge capacity increases from 319.9 mAh·g^-1（x = 0）to 347.5 mAh·g^-1（x = 0.4） and then decreases to331.7 mAh·g^-1（x = 0.8）. The effects of Co content on electrochemical kinetics of the alloy electrodes were also performed. The high rate dischargeability（HRD） first increases and then decreases with Co content increasing and reaches the maximum value（95.0 %） when x = 0.4. Test results of the electrochemical impedance spectra（EIS）,potentiodynamic polarization curves and constant potential step measurements of the alloy electrodes all demonstrate that when Co content is 0.4 at%, the alloy exhibits the best comprehensive electrochemical properties.

Properties of Mechanically Milled Nanocrystalline and Amorphous Mg–Y–Ni Electrode Alloys for Ni–MH Batteries

Nanocrystalline and amorphous Mg2Ni-type Mg20-xYxNi10（x = 0,1,2,3 and 4） electrode alloys were fabricated using mechanical milling.The effects of the Y content and milling time on the microstructures and electrochemical performances of the alloys were investigated in detail.X-ray diffraction and transmission electron microscopy analyses revealed that the substitution of Y for Mg yields an obvious change in the phase composition and micro morphology of the alloys.When the Y content x ≤ 1,the substitution of Y for Mg does not change the major phase Mg2 Ni,but with a further increase in the Y content,the major phase of the alloys transforms into the YMg Ni4 YMg3 phase.A nanocrystalline and amorphous structure can be obtained by mechanical milling,and the amorphisation degree of the alloy visibly increases with increased milling time.Electrochemical measurements indicate that the discharge capacity of the alloys first increases and then decreases with increasing Y content and milling time.The substitution of Y for Mg dramatically ameliorates the cycle stability of the as-milled alloys,and the mechanical milling more or less impairs the cycle stability of the alloys.Furthermore,the high rate discharge ability,electrochemical impedance spectrum,Tafel polarisation curves and potential step measurements indicate that the electrochemical kinetic properties of the as-milled alloys first increase and then decrease with increasing Y content and milling time.

Development and Application of Hydrogen Storage

Hydrogen,as a secure,clean,efficient,and available energy source,will be successfully applied to reduce and eliminate greenhouse gas emissions.Hydrogen storage technology,which is one of the key challenges in developing hydrogen economy,will be solved through the unremitting efforts of scientists.The progress on hydrogen storage technology research and recent developments in hydrogen storage materials is reported.Commonly used storage methods,such as high-pressure gas or liquid,cannot satisfy future storage requirement.Hence,relatively advanced storage methods,such as the use of metal-organic framework hydrides and carbon materials,are being developed as promising alternatives.Combining chemical and physical hydrogen storage in certain materials has potential advantages among all storage methods.Intensive research has been conducted on metal hydrides to improve their electrochemical and gaseous hydrogen storage properties,including their hydrogen storage capacity,kinetics,cycle stability,pressure,and thermal response,which are dependent on the composition and structural feature of alloys.Efforts have been exerted on a group of magnesium-based hydrides,as promising candidates for competitive hydrogen storage,to decrease their desorption temperature and enhance their kinetics and cycle life.Further research is necessary to achieve the goal of practical application by adding an appropriate catalyst and through rapid quenching or ball milling.Improving the kinetics and cycle life of complex hydrides is also an important aspect for potential applications of hydrogen energy.

Hydrogen Storage Thermodynamics and Dynamics of Nd–Mg–NiBased Nd Mg_(12^-)Type Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous Nd Mg_（12^-）type Nd Mg_（11）Ni＋ x wt% Ni（x=100, 200） hydrogen storage alloys were synthesized by mechanical milling. The effects of Ni content and milling time on hydrogen storage thermodynamics and dynamics of the alloys were systematically investigated. The gaseous hydrogen absorption and desorption properties were investigated by Sieverts apparatus and differential scanning calorimeter connected with a H_2 detector. Results show that increasing Ni content significantly improves hydrogen absorption and desorption kinetics of the alloys. Furthermore,varying milling time has an obvious effect on the hydrogen storage properties of the alloys. Hydrogen absorption saturation ratio（R^a_（10）; a ratio of the hydrogen absorption capacity in 10 min to the saturated hydrogen absorption capacity） of the alloys obtains the maximum value with varying milling time. Hydrogen desorption ratio（R^d_（20）, a ratio of the hydrogen desorption capacity in 20 min to the saturated hydrogen absorption capacity） of the alloys always increases with extending milling time. The improved hydrogen desorption kinetics of the alloys are considered to be ascribed to the decreased hydrogen desorption activation energy caused by increasing Ni content and milling time.

Hydrogen Storage Performances of Nanocrystalline and Amorphous NdMg11Ni+x wt% Ni （x=100, 200） Alloys Synthesized by Mechanical Milling

Nanocrystalline and amorphous NdMg12-type NdMg11Ni+x wt%Ni(x=100,200)alloys were successfully prepared through ball milling(BM).The microstructures and electrochemical properties were systematically studied to get a more comprehensive understanding of the sample alloys.The maximum discharging capacity could be obtained at only two cycles,indicating that as-milled alloys have superior activation capability.The more the Ni content,the better the electrochemical properties of the as-milled samples.To be specific,the discharge capacities of x=100 and x=200(BM 20 h)samples are 128.2 and 1030.6 mAh/g at 60 mAh/g current density,respectively,revealing that enhancement of Ni content could significantly improve the discharging capacities of the samples.Additionally,milling duration obviously influences the electrochemical properties of the samples.The discharging capacity always rises with milling duration prolonging for the x=100 sample,but that of the(x=200)sample shows a trend of first augment and then decrease.The cycling stability of the(x=100)alloy clearly decreases with extending milling duration,whereas that of the(x=200)alloy first declines and then augments under the same conditions.In addition,the high rate discharge(HRD)abilities of the sample display the maximal values as milling duration changes.The HRD(HRD=C300/C60×100%)values of the as-milled alloys(x=100,200)are 80.24%and 85.17%,respectively.

Effects of Ni Content and Ball Milling Time on the Hydrogen Storage Thermodynamics and Kinetics Performances of La–Mg–Ni Ternary Alloys

The eifects of Ni content and ball milling time on the hydrogen storage thermodynamics and kinetics performances of asmilled La5Mg95-xNix(x=5,10,15)ternary alloys have been investigated.The evolution of microstructure and phase of experimental alloys in the absorption/desorption process has been characterized by XRD,SEM and HRTEM.The hydrogen storage kinetics and thermodynamics performances and PCI curves have been tested using the Sievert apparatus.It is found that the rising of Ni content remarkably improves the hydrogen storage kinetic performance,but reduces hydrogen storage capacity.And with the increase in milling time,hydrogen desorption activation(Ea)value decreases firstly and then increases;the minimum value is 47.6 kJ/mol,and the corresponding milling time is 10 h for La5Mg85Ni10 alloy.As for the thermodynamics properties,the hydrogenation enthalpy(△H)and hydrogenation entropy(△S)both decrease firstly and then increase with the rising of Ni content and milling time.The composite La5Mg85Ni10 alloy milled for 10 h exhibits the best thermodynamics and kinetics performances,the lowest Ea of 47.6 kJ/mol,absorption of 5.4 wt.%within 5 min and desorption of 5.2 wt.%within 3 min at 360℃and the lowest△H and△S of 72.1 kJ/mol and 123.2 J/mol/K.

Microstructure and hydrogen storage properties of Mg-based Mg85Zn5Ni10 alloy powders

Mg85Zn5Ni10 ternary alloy was synthesized through vacuum induction melting for the first time.Phase compositions and microstructures of Mg85Zn5Ni10 alloy powders were analyzed by X-ray diffraction (XRD)and scanning electron micro- scopy (SEM).By utilizing a Sieverts apparatus,the hydrogenation and dehydrogenation properties of Mg85Zn5Ni10 powders were measured systematically.XRD and SEM results indicated that the Mg85Zn5Ni10 alloy powders contained the major phase Mg,the eutectic Mg-Mg2Ni and Mg-MgZn2 mixtures.The possible reaction pathway can be inferred as follows:Mg +Mg2Ni +MgZn2 +H2←→MgH2+Mg2NiH4 +MgZn2,indicating that MgZn2 did not react with H2. After activation,the Mg85Zn5Ni10 alloy powders could absorb 5.4 wt.% hydrogen reversibly and held an excellent hydrogenation kinetics at a relatively low temperature.At 360 ℃,the alloy powders desorbed 5.351 wt.% hydrogen in 264 s.However,it only had fast dehydrogenation kinetics above 300 ℃.The existence of MgZn2 contributed to improving the kinetic properties.During the hydriding and dehydriding,the formed cracks and defects promoted the kinetics and thermodynamic properties.The activation energy for dehydrogenation was 75.514 kJ/mol.The enthalpy change values of hydrogenation and dehydrogenation were calculated to be -73.064 kJ/mol and 76.674 kJ/mol,respectively,indicating that melting with Ni and Zn could improve the thermodynamic property of Mg slightly.

Improved hydrogen storage performance of as-milled Sm-Mg-Ni alloy by adding CeO2

To investigate the influence of adding CeO2 on the hydrogen storage characteristics of Sm-Mg-Ni-based SmMg11Ni-type alloy,mechanical milling was utilized to synthesize SrnMg11Ni and SmMg11Ni +5 wt.%CeO2 (named SmMg11Ni- 5CeO2)alloys.The microstructure of as-castand as-milled samples was measured via X-ray diffractometer and transmission electron microscope.Sieverts device was utilized to measure the isothermal hydriding and dehydriding kinetics. The non-isothermal dehydrogenation performance was explored by thermogravimetry and differential scanning calorimetry.The hydrogen desorption activation energy of the compound metal hydride can be computed by both Arrhenius and Kissinger methods.The related data show that adding CeO2 can engender a very slight influence on the hydrogen storage thermodynamics,but it can result in an obvious reduction in hydrogen absorption and desorption capacities.Furthermore,the hydrogen desorption performance of experimental alloys is conspicuously ameliorated by the addition of CeO2,viz.lowering the initial hydrogen desorption temperature and enhancing hydrogen desorption rate.The hydrogen desorpfion activation energies with and without CeO2 addition are 84.28 and 100.31 kJ/mol,respectively,with an obvious decrease of 16.03 kJ/mol.This is thought to be responsible for the ameliorated hydrogen desorption kinetics by adding CeO2.

Influence of annealing on microstructure and hydrogen storage properties of V48Fe12Ti15Cr25 alloy

V48Fe12Ti15Cr25 alloy was prepared using vacuum arc melting and was subsequently annealed for 10 h at 1273 K.The effects of annealing on the hydrogen storage properties and microstructure of the V48Fe12Ti15Cr25 alloys were investigated.The results indicated that the alloy consisted of main body-centered cubic,Ti-rich,and TiFe phases.After annealing,the kinetic properties of the alloy were improved but its hydrogen storage capacity was slightly reduced.The kinetic mechanisms of the hydrogen absorption and desorption of the alloys were studied.The dehydrogenation enthalpy of the alloy was decreased by 2.57 kJ/mol after annealing.Differential scanning calorimetry indicated that the hydride decomposition temperature of the annealed alloy was decreased.The hydrogen desorption activation energies of the as-cast and annealed alloys were calculated to be 79.41 and 71.25 kJ/mol,respectively.The results illustrated that annealing was a beneficial method of improving the kinetic and thermodynamic properties of the hydrogen absorption/desorption of the alloy.

Structure and electrochemical characteristics of Mg–Ti–Ni-based electrode alloys synthesized by mechanical milling

The vacuum induction melting was adopted to fabricating Mg_(50−x)Ti_(x)Ni_(45)Al_(3)Co_(2)(x=0,1,2,3,4 at.%)composites protected by the high-purity helium atmosphere.Subsequently,the surface modification treatment of the as-cast alloys was carried out by mechanically coating nickel.The amorphous and nanocrystalline Mg_(50−x)Ti_(x)Ni_(45)Al_(3)Co_(2)(x=0–4)+50 wt.%Ni hydrogen storing alloys as the negative materials in batteries were prepared through ball milling,and the influences of milling time and Ti dosage on the structure and electrochemical hydrogen storing behaviors of the corresponding samples were studied in detail.The electrochemical testing reveals that the as-milled alloys have excellent performances and can finish the electrochemical hydrogenation and dehydrogenation at indoor temperature.In the first cycle without activation,the ball milling alloy obtains the maximum value of discharge capacity.Discharge capacity and cyclic steadiness of the composites conspicuously grow as Ti content and milling duration increase.Concretely,the capacity retaining rate at 100th cycle and the discharge capacity of 30 h milling samples augment from 53%to 78%and from 435.2 to 567.2 mAh/g with changing Ti content from 0 to 4.The same performances of the alloy(x=4)are enhanced from 61%to 78%and from 379.9 to 567.2 mAh/g,respectively,with extending milling duration.Moreover,high rate discharge ability,potential-step measurements,potentiodynamic polarization curves and electrochemical impedance spectrum manifest that the electrochemical kinetics properties can achieve significant amelioration as Ti content varies and milling duration is extended.

Structure and electrochemical hydrogen storage characteristics of nanocrystalline and amorphous MgNi-type alloy synthesized by mechanical milling

Both element substitution and surface modification were utilized to enhance the electrochemical performances of Mg–Ni-based alloys. Nanocrystalline and amorphous -Mg1?xCexNi0.9Al0.1 (x?=?0–0.08)?+?50 wt.% Ni hydrogen storage alloys were synthesized through mechanical milling. The sample alloys show excellent activation property and have good electrochemi-cal hydrogenation and dehydrogenation property at normal temperature. The discharge capacity has a peak value with Ce content varying which is 461.6 mAh/g for 10-h milled alloy, while that of -Ce0.04 alloy augments from 352.6 to 536.9 mAh/g with milling time extending from 5 to 30 h. Cycle stability is conspicuously improved with Ce content and milling duration augment. To be specific, when cycle number is fixed at 100, the capacity retention rate augments from 41% to 72% after Ce dosage rising from 0 to 0.08 for the 10-h milled alloy and from 58% to 76% after milling duration extending from 5 to 30 h for -Ce0.06 alloy. Additionally, the electrochemical kinetics of the alloys own peak values with Ce proportion varying;however, they always rise with milling duration extending.