FeCoNiCrMo high entropy alloy nanosheets catalyzed magnesium hydride for solid-state hydrogen storage

The catalytic effect of FeCoNiCrMo high entropy alloy nanosheets on the hydrogen storage performance of magnesium hydride(MgH_(2))was investigated for the first time in this paper.Experimental results demonstrated that 9wt%FeCoNiCrMo doped MgH_(2)started to dehydrogenate at 200℃and discharged up to 5.89wt%hydrogen within 60 min at 325℃.The fully dehydrogenated composite could absorb3.23wt%hydrogen in 50 min at a temperature as low as 100℃.The calculated de/hydrogenation activation energy values decreased by44.21%/55.22%compared with MgH_(2),respectively.Moreover,the composite’s hydrogen capacity dropped only 0.28wt%after 20 cycles,demonstrating remarkable cycling stability.The microstructure analysis verified that the five elements,Fe,Co,Ni,Cr,and Mo,remained stable in the form of high entropy alloy during the cycling process,and synergistically serving as a catalytic union to boost the de/hydrogenation reactions of MgH_(2).Besides,the FeCoNiCrMo nanosheets had close contact with MgH_(2),providing numerous non-homogeneous activation sites and diffusion channels for the rapid transfer of hydrogen,thus obtaining a superior catalytic effect.

Combined “Gateway” and “Spillover” effects originated from a CeNi_(5) alloy catalyst for hydrogen storage of MgH_(2)

Efficient catalysts enable MgH2 with superior hydrogen storage performance.Herein,we successfully synthesized a catalyst composed of Ce and Ni (i.e.CeNi_(5) alloy) with splendid catalytic action for boosting the hydrogen storage property of magnesium hydride (MgH_(2))The MgH2–5wt%CeNi_(5) composite’s initial hydrogen release temperature was reduced to 174℃ and approximately 6.4wt%H_(2) was released at 275℃ within 10 min.Besides,the dehydrogenation enthalpy of MgH_(2) was slightly decreased by adding CeNi_(5).For hydrogenation,the fully dehydrogenated sample absorbed 4.8wt%H_(2) at a low temperature of 175℃.The hydrogenation apparent activation energy was decreased from(73.60±1.79) to (46.12±7.33) kJ/mol.Microstructure analysis revealed that Mg_(2)Ni/Mg_(2)NiH_(4) and CeH_(2.73) were formed during the process of hydrogen absorption and desorption,exerted combined“Gateway”and“Spillover”effects to reduce the operating temperature and improve the hydrogen storage kinetics of MgH_(2).Our work provides an example of merging“Gateway”and“Spillover”effects in one catalyst and may shed light on designing novel highly-effective catalysts for MgH_(2) in near future.

Dispersion of niquel on the microstructure in magnesium based alloys for hydrogen storage

Mg–Xwt.%Ni(X=5 and 20)alloys have been prepared by mechanical alloying using milling times of 15 and 30 h in a planetary ball milling to know the effects of magnesium with the addition of Ni as catalyst,dispersion on the microstructure,area surface and the efficiency of hydrogen storage.SEM-EDS,XRD and ImageJ^(■)software have been used to characterize the microstructure and chemical composition of the alloys.Hydriding experiments were performed as batch-type tests at 200,250 and 300℃ under 2 MPa H2 pressure during 30 min.These experiments resulted in varying amounts of MgH2 in the hydrided powders depending on composition and hydriding conditions.The best results point to an optimum Ni dispersion,which in turn depends on Ni content and milling time.

Geometric Effects of La_(1+x)Mg_(2-x)Ni_9 (x=0.0~1.0) Ternary Alloys on Their Hydrogen Storage Capacities

Structural analysis was made using X-ray diffraction (XRD) Rietveld refinement on a series of La1+xMg2-xNi9 (x=0.0-1.0) ternary alloys. Results showed that each of La1+xMg2-xNi9 alloys was a PuNi3-type structure stacked by LaNi5 and (La, Mg) Ni2 blocks. Electrochemical tests revealed that discharge abilities of these La-Mg-Ni ternary alloys mainly depended on their atomic distances between (La, Mg) and Ni, which could be modified by varying the atomic ratios of La/Mg.

Effect of ball milling on hydrogen storage of Mg_3La alloy

Hydrogen storage and microstructure of ball milled Mg3La alloy were investigated by X-ray diffraction and pressure-composition-isotherm measurement. The ball milled Mg3La alloy could absorb hydrogen up to 4wt.% at 300 ℃ for the first time, along with a decomposing course. Following tests showed that the average reversible hydrogen storage capacity was 2.7wt.%. The enthalpy and entropy of dehydrogenation reaction of the decomposed ball milled Mg3La and hydrogen were calculated. XRD patterns indicated the existence of MgH2 and LaH3 in the decomposed hydride and the formation of Mg when hydrogen was desorbed. After the first hydrogenation, all the latter hydrogenation/dehydrogenation reactions could be taken place between Mg and MgH2. The ball milled Mg3La alloy exhibited better hydriding kinetics than that of the as-cast Mg3La alloy at room temperature. The kinetic curve could be well fitted by Avrami-Erofeev equation.

Electrochemical hydriding and thermal dehydriding properties of nanostructured hydrogen storage MgNi26 alloy

The MgNi26 alloy was prepared by three different methods of gravity casting (GC), mechanical alloying (MA) and rapid solidification (RS). All samples were electrochemically hydrided in a 6 mol/L KOH solution at 80 °C for 240 min. The structures and phase compositions of the alloys were studied using optical microscopy and scanning electron microscopy, energy dispersive spectrometry and X-ray diffraction. A temperature-programmed desorption technique was used to measure the absorbed hydrogen and study the dehydriding process. The content of hydrogen absorbed by the MgNi26-MA (approximately 1.3%, mass fraction) was 30 times higher than that of the MgNi26-GC. The MgNi26-RS sample absorbed only 0.1% of hydrogen. The lowest temperature for hydrogen evolution was exhibited by the MgNi26-MA. Compared with pure commercial MgH2, the decomposition temperature was reduced by more than 200 °C. The favourable phase and structural composition of the MgNi26-MA sample were the reasons for the best hydriding and dehydriding properties.

Hydrogen sorption properties of Mg-20wt.%Fe_(23)Y_(8) composite prepared by reactive mechanical alloying

Mg-20wt.%Fe_(23)Y_(8) composite was successfully prepared by reactive mechanical alloying(RMA).X-ray diffraction(XRD)measurement shows that the main phases of composite are MgH_(2) and Mg2FeH6.The composite exhibits excellent hydrogen abs/desorption properties and can absorb 4.36wt.%and 5.72wt.%hydrogen at 473 and 573 K in 10 min under 3.0 MPa hydrogen pressure,respectively.The composite can desorb 5.27wt.%hydrogen at 573 K in 30 min under 0.02 MPa hydrogen pressure.Compared with the pure MgH_(2),the hydrogen desorption temperature of Mg-20wt.%Fe_(23)Y_(8) composite is decreased about 40℃.It is supposed that both the catalyst effect of Fe-Y distributed in Mg substrate and the crystal defects play the main role in improving hydrogen sorption properties of Mg-20wt.%Fe_(23)Y_(8) composite.

Optimizing FeCoNiCrTi high-entropy alloy with hydrogen pumping effect to boost de/hydrogenation performance of magnesium hydride

The exploration of efficient,long-lived and cost-effective transition metal catalysts is highly desirable for the practical hydrogen storage of magnesium hydride(MgH_(2)) in sustainable energy devices.Herein,FeCoNiCrTi high-entropy alloy(HEA) nanosheets were prepared via a facile wet chemical ball milling strategy and they were introduced into MgH_(2) to boost the hydrogen storage performance.The refined HEA exhibited superior catalytic activity on MgH_(2).In contrast to additive-free MgH_(2),the initial desorption temperature of the constructed MgH_(2)-HEA composite was reduced from 330.0 to 198.5℃ and a remarkable 51% reduction in the dehydrogenation activation energy was achieved.Besides,the MgH_(2)-HEA composite only required one-twentieth time of that consumed by pure MgH_(2) to absorb 5.0 wt% of H_(2) at 225℃.The synergy between the "hydrogen pumping" effect of Mg_2Ni/Mg_2NiH_4 and Mg_2Co/Mg_2CoH_5 couples,as well as the good dispersion of Fe,Cr and Ti on the surface of MgH_(2) contributed to the enhanced de/hydrogenation performance of the MgH_(2)-HEA composites.This study furnishes important steering for the design and fabrication of multiple transition metal catalysts and may push the commercial application of magnesium-based hydrides one step forward.

Impact of severe plastic deformation on kinetics and thermodynamics of hydrogen storage in magnesium and its alloys

Magnesium and its alloys are the most investigated materials for solid-state hydrogen storage in the form of metal hydrides,but there are still unresolved problems with the kinetics and thermodynamics of hydrogenation and dehydrogenation of this group of materials.Severe plastic deformation(SPD)methods,such as equal-channel angular pressing(ECAP),high-pressure torsion(HPT),intensive rolling,and fast forging,have been widely used to enhance the activation,air resistance,and hydrogenation/dehydrogenation kinetics of Mg-based hydrogen storage materials by introducing ultrafine/nanoscale grains and crystal lattice defects.These severely deformed materials,particularly in the presence of alloying additives or second-phase nanoparticles,can show not only fast hydrogen absorption/desorption kinetics but also good cycling stability.It was shown that some materials that are apparently inert to hydrogen can absorb hydrogen after SPD processing.Moreover,the SPD methods were effectively used for hydrogen binding-energy engineering and synthesizing new magnesium alloys with low thermodynamic stability for reversible low/room-temperature hydrogen storage,such as nanoglasses,high-entropy alloys,and metastable phases including the high-pressureγ-MgH2 polymorph.This work reviews recent advances in the development of Mg-based hydrogen storage materials by SPD processing and discusses their potential in future applications.

Kinetics in Mg-based hydrogen storage materials:Enhancement and mechanism

Mg-based materials have been intensively studied for hydrogen storage applications due to their high energy density up to 2600 Wh/kg or 3700 Wh/L.However,the Mg-based materials with poor kinetics and the necessity for a high temperature to achieve 0.1 MPa hydrogen equilibrium pressure limit the applications in the onboard storage in Fuel cell vehicles(FCVs).Over the past decades,many methods have been applied to improve the hydriding/dehydriding(H/D)kinetics of Mg/MgH 2 by forming amorphous or nanosized particles,adding catalysts and employing external energy field,etc.However,which method is more effective and the intrinsic mechanism they work are widely differing versions.The hydrogenation and dehydrogenation behaviors of Mg-based alloys analyzing by kinetic models is an efficient way to reveal the H/D kinetic mechanism.However,some recently proposed models with physical meaning and simple analysis method are not known intimately by researchers.Therefore,this review focuses on the enhancement method of kinetics in Mg-based hydrogen storage materials and introduces the new kinetic models.

Preparation and hydrogen sorption properties of Mg-Cu-Y-H systems

Mg-xwt.%CuY(x=15,20,25)composites were successfully prepared by reactive mechanical alloying(RMA).X-ray diffraction(XRD)measurement shows that main phases of the as milled composites are MgH_(2) and Mg_(2)Cu,and they converted into Mg and MgCu_(2) after dehydrogenation,respectively.Pressure-Composition-Isotherm(PCI)test shows that the composites exhibit double pressure plateau at each isothermal desorption process.The hydrogen absorption and desorption kinetics of the composites become worse with increasing x content,indicating that Mg-Cu phase has a negative effect on the hydrogen sorption properties of the composites.It is supposed that the good hydrogen sorption properties of the composites attribute to the catalyst effect of yttrium hydride distributed in Mg substrate and the particles size reduction and crystal defects formed by RMA.

Enhancing hydrogen storage properties of MgH_(2) using FeCoNiCrMn high entropy alloy catalysts

Herein,we report the successful preparation of the FeCoNiCrMn high entropy alloy(HEA)loaded MgH_(2) and HEA’s effect on the hydrogen storage properties of Mg/MgH_(2).The HEA shows high catalytic activity toward hydrogen dissociation and recombination reaction,and successfully suppressed activation energy of dehydrogenation reaction from 151.9 to 90.2 kJ mol-1.Moreover,part of Co and Ni can react with Mg,and produce Mg_(2) Co/Mg_(2) CoH 5 and Mg_(2) Ni/Mg_(2) NiH_(4) during the hydrogen storage processes,further en-hancing dehydrogenation reaction through the“hydrogen pumping”mechanism.Asa result,the MgH_(2)-5 wt%HEA composite can release 5.6 wt%of H_(2) at 280℃ within 10 min,and absorb 5.5 wt%H_(2) within 0.5 min at 150℃.The loaded HEA shows robustness against particle aggregation,leading to stable re-versible hydrogen storage processes at least 50 times.These findings show the synergistic effects of HEA on Mg-based hydrogen storage materials,providing an additional degree of freedom for catalyst design.

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 Mg_(85)Zn_(6)Y_(9)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 intoα-MgH_(2),γ-MgH_(2),YH_(2),YH_(3),C14-type Laves phase MgZn_(2)and minor CsCl-type Y(Mg,Zn)during ball milling under hydrogen atmosphere.Af-ter further hydrogen absorption-desorption cycling,Y(Mg,Zn)disappears gradually and C14 phase trans-forms into C15-type Laves phase.By contrast,the Mg_(85)Zn_(6)Y_(9)alloy has better hydrogen storage kinetics and cycle durability than pure Mg because of the catalytic effect of YH_(2)/YH_(3)on hydrogen absorption-desorption and inhibition role of Laves phase in Mg crystallite growth.Moreover,the introduction of Ni into Mg_(85)Zn_(6)Y_(9)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 Mg_(2)Ni.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.

镁基固态储氢材料的研究进展

氢能有望成为脱碳时代的“理想燃料”。高性能储氢材料的发现、开发和改性是未来发展固态储氢和氢能源利用的关键。而氢化镁(MgH2)具有储氢能力强、自然储量丰富、环境友好等特点,在固态储氢材料领域备受关注。但是氢化镁较高的热力学稳定性、缓慢的动力学性能,以及循环过程中不可避免的团聚和粗化等问题在一定程度上限制了镁基固态储氢材料的大规模投产和实际应用。近年来,大量研究工作聚焦于镁基储氢材料的热/动力学改性,目前已经取得了大量的成果。本文通过回顾国内外相关文献,综述了改善镁基固态储氢材料储氢性能的最新研究进展,着重介绍了合金化、纳米化、引入催化剂等改性策略,阐述了不同策略具体的改性机理。最后对未来的发展方向进行了展望,旨在为高性能镁基储氢材料的研发提供借鉴与指导。

Hydrogen storage performance and phase transformations in as-cast and extruded Mg-Ni-Gd-Y-Zn-Cu alloys

Thermal-mechanical processing of magnesium-based materials is an effective method to tailor the hydrogen storage performance.In this study,Mg-Ni-Gd-Y-Zn-Cu alloys were prepared by Direct Chill(DC)casting,with and without extrusion process.The influences of microstructure evolution,introduced by DC casting and thermal-mechanical processing,on the hydrogen storage performance of Mg-Ni-Gd-Y-ZnCu alloys were comprehensively explored,using analytical electron microscopy and in-situ synchrotron powder X-ray diffraction.The result shows that the extruded alloy yields higher hydrogen absorption capacity and faster hydrogen ab/desorption kinetics.As subjected to extrusion processing,theα-Mg grains in the microstructure were significantly refined and a large number of 14H type long-period stacking ordered(LPSO)phases appeared on theα-Mg matrix.After activation,there were more nanosized Gd hydride/Mg2Ni intermetallics and finer chips.These modifications synergistically enhance the hydrogen storage properties.The findings have implications for the alloy design and manufacturing of magnesiumbased hydrogen storage materials with the advantages of rapid mass production and anti-oxidation.

氢化燃烧法合成镁基储氢合金进展

以Mg2 Ni为例系统综述了氢化燃烧法制备镁基储氢合金的进展 ,包括其工作原理 ,氢化燃烧法和其它制备镁基储氢合金方法的比较 ,影响氢化燃烧的因素以及材料的氢化特性。较为详细地介绍了国内外的研究状况并进行比较 ,通过比较Mg2 Ni、Mg2 FeH6 、Mg2 CoH5等储氢合金的吸氢性能 ,指出制备镁基储氢合金的理想发展方向应该是采用复合方法获得实用产品 ,即结合氢化燃烧 ,机械合金化 ,多元化 ,纳米化等方法 ,制备非晶态合金 ,以期达到低温下吸放氢量大于 5 %(质量分数 ) ,具有良好的动力学性能 ,使用寿命长 ,低价格的效果。

镁基储氢合金改性的研究进展

介绍了镁基合金的合成方法及主要的镁基合金的性能改善方法 。

镁基储氢合金制备新方法——氢化燃烧合成法

相对于高温熔炼法、置换扩散法、固相扩散法和机械合金化法而言,氢化燃烧合成法是制备镁基储氢合金的新方法,近年来受到了国内外的足够关注。本文简要介绍了氢化燃烧合成法的方法、机理以及研究进展。

镁铜合金储氢材料的制备及对高氯酸铵热分解过程的影响

采用置换-扩散法制备了镁铜合金储氢材料(Mg2Cu-H),并对其结构进行了表征.结果表明,Mg2Cu经过氢化得到的镁铜合金储氢材料不是单一晶相,而是MgCu2和MgH2的混合物.用热分析法(DSC)研究了镁铜合金储氢材料对固体火箭推进剂常用氧化剂——高氯酸铵(AP)热分解过程的影响.结果表明,镁铜合金储氢材料可以显著促进AP的热分解过程,加快热分解速率,降低高温热分解温度,使DSC表观分解热明显增大.Mg2Cu-H对AP热分解过程的促进作用明显强于Mg2Cu.随着加入量增加,镁铜合金储氢材料对AP热分解的催化促进作用增强.探讨了镁铜合金储氢材料促进AP热分解过程的作用机制.

贮氢合金进展

对贮氢合金的工作原理及应用 ,贮氢合金的基本类型及开发历史和发展趋势进行了综合评述。MmNi5系稀土合金和Laves相合金的开发应用已较为成熟 ,但其贮氢密度不高。高容量型的钒固溶体型合金和镁基合金是贮氢合金发展的新趋势。目前主要通过添加合金元素 ,开发制备工艺 ,改进微观相组织结构并兼以适当的表面处理 ,以提高钒固溶体型合金和镁基合金常温常压下的吸放氢特性及活化性能。