镁基储氢合金氢化物Mg2NiH4的制备及性能研究

以不经压制的Mg、Ni混合粉末为原料,利用氢化燃烧合成法在合成温度850 K和1.8 MPa初始合成氢压下制备了镁基储氢合金氢化物Mg2NiH4,并利用XRD及PCT仪分析了其物相组成和储氢性能.研究表明,产物由单一物相Mg2NiH4组成,无未反应的Ni和不完全氢化的Mg2NiH0.3;相对于传统熔炼法制备的Mg2Ni,氢化燃烧合成产物具有更高的氢化活性,在没有任何活化处理的前提下,第一次吸氢就能以很快的速度达到饱和吸氢量,同时在任何吸氢温度下均具有较好的吸氢动力学性能,且随温度的降低,最大吸氢量降低幅度较小,平台压和吸放氢温度的关系为:lgP(0.1 MPa)=-3 187.6/ T 6.362 4(吸氢),lgP(0.1 MPa)=-3 468.4/T 6.694 3(放氢).     

La1.5Mg0.5Ni7-xCox(x=0～1.8)贮氢合金结构和电化学性能研究

La1.5Mg0.5Ni7-xCox(x=0～1.8)贮氢合金电极由高频感应熔炼加热处理制备得到.合金结构分析表明,合金主相为Ce2Ni7型结构,Mg原子分布在Ce2Ni7型单胞结构的Laves相单元中,而Co原子则分布在CaCu5单元中.随着合金中Co含量的增多,点阵参数和单胞体积呈增大趋势,氢化物变的更加稳定.合金的吸放氢平台在298K条件下介于1.01×103～1.01×104Pa之间,吸放氢滞后效应较小.合金电极的电化学分析表明合金具有390mAh/g以上的放电容量和良好的活化特性,Co元素不利于合金电极循环稳定性的改善,氢在合金中的扩散是电极反应的控制步骤.La1.5Mg0.5Ni7.0合金电极表现出较好的综合电化学性能.     

机械球磨制备La2Mg17/Ni复合材料的微观结构及气态吸放氢性能

为提高La2Mg17贮氢合金的吸放氢性能,以机械球磨La2Mg17+Ni+NbF5在氩气为保护气氛围下制备复合材料。采用XRD分析了球磨后复合材料的微观结构,用SEM观察了其形貌。通过自动控制的Sieverts设备测试了材料的吸放氢动力学性能。研究表明混合球磨后复合材料的吸放氢性能有了显著的提高,进一步说明Ni粉、NbF5促使了材料纳米晶/非晶结构的形成,而该结构的形成是材料吸放氢性能提高的主要原因。     

Mg2Ni纳米材料的电化学性能初步研究

时机械合金化制备的Mg2Ni纳米材料进行了循环伏安测试,获得了样品随扫描速度和温度变化的循环伏安曲线.测试结果表明:氧化峰的电位随扫描速度的加快有所正移;机械合金化制备的样品在室温下的吸氢性能显著增强,吸放氢速度随温度的升高而加快.X射线小角散射结果表明高能球磨制备的Mg2Ni粉末具有1～5nm以及5～10nm范围内的粒度分布,较小的粒度使得吸/放氢反应的活性位置增多和放氢的扩散路径降低,这可能是机械合金化制备的Mg2Ni纳米材料贮氢性能显著提高的原因.     

Mg2Ni纳米材料的电化学性能初步研究

对机械合金化制备的Mg2Ni纳米材料进行了循环伏安测试，获得了样品随扫描速度和温度变化的循环伏安曲线。测试结果表明：氧化峰的电位随扫描速度的加快有所正移；机械合金化制备的样品在室温下的吸氢性能显著增强，吸放氢速度随温度的升高而加快。X射线小角散射结果表明高能球磨制备的Mg2Ni粉末具有1-5nm以及5-10nm范围内的粒度分布，较小的粒度使得吸／放氢反应的活性位置增多和放氢的扩散路径降低，这可能是机械合金化制备的Mg2Ni纳米材料贮氢性能显著提高的原因。     

纳米晶复合物Mg—Ni—V2O5催氢性能研究

研究了纳米晶复合物Mg-Ni-V2O5的吸放氢性能及其在放氢过程中的温度变化规律。该复合物是在氢气作为保护气的条件下，用机械合金化方法从镁粉，镍粉和五氧化二钒直接通过球磨制备而成的，试样在球磨过程中能发生吸氢反应（MAR），经过较长时间球磨之后，试样基本能完全吸氢，该试样具有很好的充放氢性能，放氢温度也有所降低，例如该复合在200℃可以在60s内充氢达6．2％（质量分数）以上，在300℃，0.1MPa下，可以在700s内使放氢量达到6．0％（质量分数）以上。     

氢化燃烧合成Mg-Mg2Ni储氢合金组成和性能研究

利用氢化燃烧合成法制备了镁基储氢合金Mg-Mg2Ni,分析了镁镍配比和镁粉粒径对HCS产物组成和储氢性能的影响.研究结果表明,HCS产物主要由Mg2Ni及Mg的氢化物MgH2、Mg2NiH4和Mg2NiH0.3组成,没有Ni相的存在,当Mg:Ni＞2:1时,较粗镁粉原料的使用对燃烧合成产物Mg2Ni的氢化活性影响不大,但会降低反应剩余Mg的氢化活性.随原料中镁镍配比的增加,HCS产物中MgH2的相对含量逐渐增加,HCS产物的氢化动力学性能逐渐降低,吸氢量却先增加后降低,Mg:Ni=7.85:1时具有最大的吸氢量4.87wt.%,同时由较细镁粉得到的HCS产物的氢化速率和吸氢量大于较粗镁粉,但两者之间的差别会随镁镍配比的降低而减小.     

镁氢化和镁镍共晶反应对氢化燃烧合成产物储氢性能的影响

通过改变氢化燃烧合成Mg2Ni中镁氢化反应的保温时间,以及镁镍合成反应温度和合成保温时间,来研究镁氢化反应、镁镍燃烧合成反应对产物Mg2Ni储氢性能的影响。实验结果表明,镁氢化反应保温120min时,产物的首次吸氢动力学性能变差;合成温度的提高有利于吸氢量的提高（合成温度850K时,吸氢量最大可达3．36wt％）;保温时间的延长对于产物吸氢量的影响随合成温度的差异而表现不同。     

烧结温度对La0.67Mg0.33Ni3合金气态储放氢性能的影响

采用磁场辅助烧结法(MASS)制备La0.67Mg0.33Ni3合金,研究了烧结温度对合金相结构、微观形貌及吸放氢性能的影响。结果显示,973～1123K温度下烧结的合金主相均是PuNi3型结构的(La、Mg)Ni3。活化及动力学测试表明,1023K烧结的合金经过2个循环就能完全活化并在30s内达到最大容量的90%,最大吸氢量达到1.58%(质量分数);PCT结果显示,该合金滞后系数为0.519,吸氢量为1.525%(质量分数),放氢量为1.474%(质量分数),放氢率为0.967,各项性能均为最优。     

氢化燃烧合成Mg2NiH4及氢化物放氢温度的研究

报道了原料中不同镍含量对氢化燃烧合成Mg2NiH4的影响和生成物中各氢化物的放氢温度等相关研究.氢化燃烧合成的结果表明:当镍含量＜54.6%时,随着镍含量增加,氢化燃烧合成物中的Mg2NiH4增加,MgH2减少;DSC-TG曲线的结果表明,Mg2NiH4、Mg2NiH0.3和MgH2分别在650、683、719K附近产生放氢吸热和失重.     

镁的氢化反应对氢化燃烧合成储氢合金Mg2NiH4纯度的影响

本文主要通过改变在镁氢化反应温度的保温时间,研究不同合成压力、合成温度下,中间反应-镁的氢化反应对氢化燃烧合成Mg2NiH4的影响.初步探讨了镁的氢化反应与燃烧合成Mg2Ni反应及其氢化反应的内在联系.研究结果表明:镁的充分氢化在促进Mg-Ni燃烧合成反应的同时有效地提高了Mg2Ni的氢化活性,这一结果为工业化低压合成纯Mg2NiH4提供了可行途径,但在低温下仅延长镁的氢化时间,产物中少量的Ni很难消除.     

氢化燃烧合成镁基储氢合金的电化学性能的研究

研究了氢化燃烧合成Mg2NiH4产物的电化学性能，并探索了机械球磨处理对产物电化学性能的影响。电化学测试表明，HCS产物不经任何处理，最大放电容量仅为45.13mAh／g；产物球磨后最大放电容量和高倍率放电能力得到提高，如产物经球磨1h后，最大放电容量增至259．24mAh／g，产物添加3％（质量分数）的石墨球磨5h，最大放电容量增加了10倍以上，达到481．50mAh/g。     

Effect of surface oxidation on the hydriding and dehydriding of Mg<Subscript>2</Subscript>Ni alloy produced by hydriding combustion synthesis

Hydriding combustion synthesis (HCS) has been regarded as an innovative process for the preparation of high active magnesium-based hydrogen storage alloys. For the purpose of understanding the interrelation of the unique hydrogen storage properties and the surface characteristics of the HCS product, the samples of Mg₂Ni alloy/hydride with and without exposure to air were prepared from the HCS product of Mg₂NiH₄. The hydriding and dehydriding properties were compared and the surface compositions were analyzed by means of X-ray photoelectron spectroscopy (XPS) and auger electron spectroscopy (AES). It was shown that the air exposure considerably decreases the hydriding activity of Mg₂Ni. Absorbing of 3.0 wt.% of hydrogen under the conditions of 603 K and 3.0 MPa after the air exposure takes 1500 s, which is six times longer than for the unexposed alloy. The hydrogen desorption of the hydride are also impeded by the air-exposure, which results in the increase of dehydriding temperature from 450 K to 540 K. XPS and AES analyses indicated that Mg segregates and exists in the form of hydroxide on the surface of the air-exposed sample, which is responsible for the degradation of the hydriding and dehydriding properties. It was confirmed that the fresh surfaces generated during the dehydriding process of the as-synthesized hydride product contributes to the high activity of the HCS product in the first cycle of the hydriding determination.     

氢化燃烧合成Mg2NiH4产物高活性特征及分析

氢化燃烧合成法(HCS法)是镁基储氢合金制备的新方法,具有省能、省时、产物高活性等显著优点,近年来引起了国内外广泛关注.本文通过XRD、SEM和PCT等手段研究了氢化燃烧合成Mg2NiH4产物高活性的特征,并从物相组成、颗粒特性和氢化反应等方面揭示了HCS产物高活性的机理.结果表明,氢化燃烧合成Mg2NiH4产物在没有任何活化处理的前提下,第一次吸氢就能达到饱和吸氢量,且在不同温度下均具有比传统熔炼法产物Mg2Ni高的氢化活性;纯的物相组成、多孔的颗粒特性、大量微裂纹的存在和小的晶粒尺寸是其高活性的内在原因.本研究对控制HCS产物的微结构并进一步改善其储氢性能具有重要意义.     

Thermal desorption of hydrogen from Mg2Ni hydrogen storage materials

In order to investigate the influence of HCS on the hydrogen occupation site of Mg2Ni alloy, the thermal desorption technique has been applied to Mg2Ni hydride made by hydriding combustion synthesis (HCS). Mg2Ni was made under low temperature in a short time by the HCS compared to conventional melting process. At various initial hydride wt% from 0.91 to 3.52, the sample was heated to 623 K at a rate of 1.0 K/min. The starting temperature of the evolution of hydrogen goes higher as the initial hydride wt% increases. Only one peak is shown in the case of the small initial hydride wt%. But two peaks appeared with increasing initial hydride wt%. The activation energies obtained by the first and second peaks are 113.0 and 99.5 kJ/mol respectively. The two site occupation model by Darriet et al. was proved. The influence of HCS on the hydrogen occupation site of Mg2Ni alloy is nonexistent.     

Thermal Stability of Amorphous Hydride Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45)

The thermal stability of amorphous ternary hydrides Mg_(50)Ni_(50)H_(54) and Mg_(30)Ni_(70)H_(45) and their corre-sponding amorphous binary alloys Mg_(50)Ni_(50) and Mg_(30)Ni_(70) were studied with X-ray diffraction(XRD) and differential scanning calorimetry(DSC). Samples of the amorphous alloys were preparedby mechanical alloying and the amorphous hydrides were obtained by charging the alloys with gas-eous hydrogen at 3.0 MPa and 423 K. It was found that the amorphous hydrides released most oftheir hydrogen before the crystallization of the essentially hydrogen depleted amorphous alloy. Thecrystallization temperature of amorphous Mg_(50)Ni_(50)H_(54) elevated and that of amorphousMg_(30)Ni_(70)H_(45) did not change in relation to the original binary amorphous alloy. This is very excep-tional for amorphous hydrides. The reason for the effects of hydrogen absorption/desorption on thecrystallization of amorphous alloys was discussed.     

熔体快淬对纳米晶和非晶Mg20Ni10-xCox(x≈0～4)合金电化学贮氢性能的影响

为了改善Mg2Ni型合金的电化学贮氢性能,用Co部分替代合金中的Ni.用快淬工艺制备了纳米晶和非晶Mg20Ni10-xCox(x=0、1、2、3、4)贮氢合金,分析了铸态及快淬态合金的微观结构,测试了合金的电化学贮氢性能.研究了Co替代Ni及快淬工艺对合金电化学贮氢性能的影响.结果表明,Co替代Ni不改变合金的Mg2Ni主相,但形成了第二相MgCo2.在快淬(x=0)合金中没有发现非晶相,但快淬(x=4)合金显示了纳米晶、非晶结构,表明Co替代Ni提高了Mg2Ni型舍金的非晶形成能力.熔体快淬显著的改善了合金的电化学贮氢性能,合金放电容量和电化学循环稳定性均随淬速的增加而增加.     

Improvement in hydrogen storage characteristics of magnesium by mechanical alloying with nickel

The hydriding and dehydriding kinetics of Mg are reviewed. It is reported that the hydriding and dehydriding reactions of Mg are nucleation-controlled under certain conditions and progress by a mechanism of nucleation and growth, and that the hydriding rates of Mg are controlled by the diffusion of hydrogen through a growing Mg hydride layer.The hydriding and dehydriding kinetics of Mg can be improved in consequence by a treatment such as mechanical alloying, which can facilitate the nucleation by creating defects and shorten diffusion distances by reducing the effective particle size of Mg.The hydriding and dehydriding characteristics of mechanically-treated Mg and mechanically-alloyed mixtures with the compositions Mg-x wt Ni (x=5, 10,25 and 55) are studied.The Mg₂Ni phase develops in the mechanically-alloyed mixtures. The Mg-10wt% Ni and Mg-25 wt% Ni mixtures are activated easily, show much larger hydrogen storage capacities and much higher hydriding rates, and higher dehydriding rates, than other magnesium- based alloys or mixtures.