贮氢合金La-Mg-Ni系的贮氢性能

借助X-ray及吸氢性能测试装置研究了AB3型La-Mg-Ni系贮氢合金的结构和贮氢性能,测试了不同温度下合金的PCT曲线.结果表明,La-Mg-Ni系贮氢合金可获得(La,Mg)Ni3相组织;加Co,改善了合金的特性,并使平台压力降低.     

(LaCa3)0.5-xMg1+4xNi9(x=0,0.02,0.04,0.06,0.08,0.1)合金微观结构及储氢性能研究

AB₃型La-Mg-Ni系列储氢合金由于储氢容量优异、放电容量高、活化快等优势受到储能领域的关注.采用真空感应熔炼法制备了(LaCa₃)_0.5-xMg_1+4xNi₉(x=0,0.02,0.04,0.06,0.08,0.1)合金,表征合金的微观结构并测试储氢合金性能差异,研究合金A侧元素比例对合金性能影响的内在机理.合金活化性能受Mg元素取代量的影响明显,活化吸放氢速率随着Mg质量分数的增加先增加后减小.随着Mg替代量的增加,合金的最大吸放氢容量分别由1.866%和1.311%提高到1.972%和1.732%,吸放氢焓变绝对值分别由15.71 kJ/mol和17.88 kJ/mol降低到8.88 kJ/mol和9.28 kJ/mol,其热稳定性降低,这对改善热力学性能有积极作用.     

La_(1.8)Ca_(0.2)Mg_(14)Ni_3合金在甲苯溶液中球磨改性后的储氢性能

采用在甲苯介质中球磨以改善La1.8Ca0.2Mg14Ni3的储氢性能。随着球磨时间的增加,合金的吸放氢性能得到显著地提高,在20 h达到最高。其在513 K,4.0 MPa氢压下初次活化时,吸氢质量分数达到了3.95%,在3次活化后,300 K时的吸氢质量分数达到3.85%,在613 K,一个大气压的放氢质量分数在900 s内达到了4.92%。通过XRD和SEM分析,球磨后合金颗粒粒径明显减小且有非晶化趋势。在球磨过程中形成了电子络合体(electrondonor-acceptor,EDA)体系。合金颗粒粒径、非晶化程度和EDA共同作用使球磨20 h的合金表现出最优异的吸放氢性能。     

Mg3La化合物储氢性能及Ni的加入对其性能的影响

用X-ray衍射方法(XRD)研究了Mg3La合金和Mg3LaNi0.1合金吸放氢前后的结构变化.Mg3La合金和Mg3LaNi0.1合金在吸/放氢过程中的压力-组成-等温曲线(PCI)和吸氢动力学曲线表明合金能在室温下吸氢,并且具有良好的吸氢动力学特性,能在4 min之内达到饱和吸氢量的90%;其最大吸氢量分别为质量分数2.89%和2.73%.Mg3La金和Mg3LaNi0.1合金的室温吸氢动力学曲线可用Avrami-Erofeev方程拟合,说明吸氢过程符合形核长大机制.同时也计算了Mg3La-H氢化反应的熵和焓.     

La(Ni,Sn)5+x (x=0～0.35)贮氢合金的晶体结构与电化学性能

系统研究了La(Ni,Sn)_5+x（x=0~0.35) 无Co贮氢合金的化学计量比对其晶体结构及电化学性能的影响.X射线衍射分析仪（XRD）分析表明，上述合金均为单相CaCu₅结构.但在过计量比(x>0)合金的结构中，有部分1a位置元素（La）的原子被沿c轴定向排列的Ni-Ni“哑铃”对所替代，且其替代La原子的分数随x的增大而增多，从而导致合金晶胞的c轴及c/a比值明显增大，晶胞体积有所减小，并显著降低了合金的吸氢体积膨胀率.电化学测试表明，增大x值可使合金的循环稳定性得到显著提高，但也使合金的最大放电容量和高倍率放电性能有所降低.研究发现，由于合金的化学计量比增大会使其结构中含有较多的Ni-Ni“哑铃”对，合金的抗吸氢粉化能力得到了明显的改善，从而使合金在充放电过程中的反应比表面积有所减小、腐蚀速率得到抑制、循环稳定性得到显著提高.但合金反应比表面积的减小也导致了电极反应的速率的减小，从而使其高倍率放电性能有所降低.     

LaNi3.8Co1.1Mn0.1/TiMn1.5贮氢合金的结构和性能

为了探索一种新的掺杂方式对AB5型贮氢合金贮氢性能的影响,采用熔炼掺杂方法制备La-Ni3.8Co1.1Mn0.1/TiMn1.5(TiMn1.5质量分数为4%、8%)贮氢合金,利用PCTPro-2000气体吸附测量仪研究了合金的气态储氢性能。XRD和SEM分析显示,熔炼掺杂后合金主相为LaNi5相,出现少量(NiCo)3Ti相。P-C-T测试结果表明,(NiCo)3Ti相的出现对合金气态贮氢性能有较大影响,熔炼掺杂后合金吸放氢平台压和滞后效应降低,贮氢容量减少。掺杂TiMn1.5使得合金的氢化物的生成焓由原始合金的-27.35kJ/mol降至-29.14kJ/mol(掺杂质量分数8%的TiMn1.5),较高温度有利于合金中氢的释放,同时掺杂形成的(NiCo)3Ti相改善了合金吸/放氢动力学性能。     

可用于PEMFC燃料电池的钒基固体贮氢材料

介绍了V-Ti-Cr-Fe系列贮氢合金,该系列合金常温无需活化即可快速吸氢,放氢平台压可调,其1 atm以上的可逆吸放氢量超过质量分数2.0%,吸放氢循环500次的容量衰减小于30%.此外,由于利用了廉价的FeV80中间合金,解决了钒基贮氢合金价格昂贵的问题,是目前少有的综合性能优良的贮氢合金,可用于PEMFC燃料电池的高纯氢燃料的贮存载体.     

Cr替代量对TiFe合金活化性能与储氢性能的影响

TiFe基储氢合金因其储氢性能良好,原材料价格低廉而广受人们的关注,但活化困难这个问题阻碍了其在工业领域方面的应用.为了研究Cr替代量对于TiFe合金活化过程的影响,使用真空高频电磁感应熔炼炉制备了Ti_1.08Y_0.02Fe_0.8Mn_0.2-xCr_x(x=0,0.02,0.04)合金,测试合金的储氢性能并表征其微观结构.X射线衍射与透射电子显微镜的分析结果表明,试验后的合金中出现的新吸氢相CrH₂可以在试验条件下分解,增加了试验合金的可逆吸氢量.同时,Cr替代Mn显著缩短了合金的活化时间,降低了平台压.且随着Cr替代量的增加,合金的吸氢速率也随之增加.     

La0.67Mg0.33Ni2.5Cu0.5贮氢合金磁热处理工艺的正交设计

利用L9（34）正交表安排实验,考察磁热处理的温度、时间及磁感应强度对La0.67Mg0.33N i2.5Cu0.5合金的吸放氢反应热力学和动力学的影响,结合极差分析和方差分析研究了各因素对考核指标的显著性影响,并得到合金磁热处理的优化工艺：热处理温度850℃,处理时间1 h和磁感应强度4 T.在此条件下处理后的合金,吸放氢的质量分数分别为1.33%和1.14%,焓变为-59.69 kJ/mol,吸热峰顶所对应的温度为86.3℃,吸放氢特征时间（tξ=0.875）分别为11.2和108.7 s.结果表明,该合金与其它工艺下的样品相比,吸氢量最大,放氢后物相结构最稳定,吸热峰顶所对应的温度最低,吸放氢速度最快.     

LaNi_（3.8）Co_（1.1）Mn_（0.1）/TiMn_（1.5）贮氢合金的结构和性能

为了探索一种新的掺杂方式对AB5型贮氢合金贮氢性能的影响,采用熔炼掺杂方法制备La-Ni3.8Co1.1Mn0.1/TiMn1.5（TiMn1.5质量分数为4%、8%）贮氢合金,利用PCTPro-2000气体吸附测量仪研究了合金的气态储氢性能。XRD和SEM分析显示,熔炼掺杂后合金主相为LaNi5相,出现少量（NiCo）3Ti相。P-C-T测试结果表明,（NiCo）3Ti相的出现对合金气态贮氢性能有较大影响,熔炼掺杂后合金吸放氢平台压和滞后效应降低,贮氢容量减少。掺杂TiMn1.5使得合金的氢化物的生成焓由原始合金的-27.35kJ/mol降至-29.14kJ/mol（掺杂质量分数8%的TiMn1.5）,较高温度有利于合金中氢的释放,同时掺杂形成的（NiCo）3Ti相改善了合金吸/放氢动力学性能。     

Structures and Electrochemical Performances of As-spun RE-Mg-Ni-Mn-based Alloys Applied to Ni-MH Battery

The La-Mg-Ni-Mn-based AB₂-type La_1-xCe_xMgNi_3.5Mn_0.5 (x = 0, 0.1, 0.2, 0.3, and 0.4) alloys were fabricated by melt spinning technology. The effects of Ce content on the structures and electrochemical hydrogen storage performances of the alloys were studied systematically. The XRD and SEM analyses proved that the experimental alloys consist of a major phase LaMgNi₄ and a secondary phase LaNi₅. The variation of Ce content causes an obvious change in the phase abundance of the alloys without changing the phase composition. Namely, with the increase of Ce content, the LaMgNi₄ phase augments and the LaNi₅ phase declines. The lattice constants and cell volumes of the alloys clearly shrink with increasing Ce content. Moreover, the Ce substitution for La results in the grains of the alloys clearly refined. The electrochemical tests showed that the substitution of Ce for La obviously improves the cycle stability of the as-spun alloys. The analyses on the capacity degradation mechanism demonstrate that the improvement can be attributed to the ameliorated anti-corrosion and anti-oxidation ability originating from substituting partial La with Ce. The as-spun alloys exhibit excellent activation capability, reaching the maximum discharge capacities just at the first cycling without any activation treatment. The substitution of Ce for La evidently improves the discharge potential characteristics of the as-spun alloys. The discharge capacity of the alloys first increases and then decreases with growing Ce content. Furthermore, a similar trend also exists in the electrochemical kinetics of the alloys, including the high rate discharge ability (HRD), hydrogen diffusion coefficient (D), limiting current density (I_L) and charge transfer rate.     

Electrochemical properties and structure of MlNi_(5-x)Sn_x system

The electrochemical properties and structure of M1Ni5-xSnx(x=0-0.5) hydrogen storage alloys were investigated by pressure-composition isotherms, electrochemical measurements, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and atomic parameters. With a small amount of tin substitution, the cycle life increases by 52% (0.5C) and 42% (1.0C), but maximum discharge capacity decreases only by 3.0% and 3.5%, respectively. The cycle life is obviously improved by the low volume expansion and the formed SnO2 surface layers upon electrochemical cycling. The substitution of Ni by Sn leads to an increase of the unit cell volume and charge-discharge cycle life and decrease of the plateau pressure, hysteresis and the hydrogen storage capacity. The standard enthalpy of hydride formation decreases with increasing tin substitution. The main factor that influences the standard enthalpy of the hydriding reaction is the number of the outer orbit electrons and not the atomic size factor.     

Effect of melt spinning on gaseous hydrogen storage characteristics of nanocrystalline and amorphous Nd-added Mg_2Ni-type alloys

Nanocrystalline and amorphous Mg-Nd-Ni-Cu quaternary alloys with a composition of(Mg_(24)Ni_(10)Cu_2)_(100-x)Nd_x(x=0, 5, 10, 15, 20) were prepared by melt spinning technology and their structures as well as gaseous hydrogen storage characteristics were investigated. The XRD, TEM and SEM linked with EDS detections reveal that the as-spun Nd-free alloy holds an entire nanocrystalline structure but a nanocrystalline and amorphous structure for the as-spun Nd-added alloy, implying that the addition of Nd facilitates the glass forming in the Mg_2Ni-type alloy. Furthermore, the degree of amorphization of the as-spun Nd-added alloy and thermal stability of the amorphous structure clearly increase with the spinning rate rising. The melt spinning ameliorates the hydriding and dehydriding kinetics of the alloys dramatically. Specially, the rising of the spinning rate from 0(the as-cast was defined as the spinning rate of 0 m/s) to 40 m/s brings on the hydrogen absorption saturation ratio(R_5~a)(a ratio of the hydrogen absorption quantity in 5 min to the saturated hydrogen absorption capacity) increasing from 36.9% to 91.5% and the hydrogen desorption ratio(R_(1 0)~d)(a ratio of the hydrogen desorption quantity in 10 min to the saturated hydrogen absorption capacity) rising from 16.4% to 47.7% for the(x=10) alloy, respectively.     

Effect of VFe addition on hydrogen storage behavior of TiMn1.5-based alloys

The hydrogen absorption and desorption behavior of TiMn1.25Cr0.25 alloys with VFe substitution for partial Mn was investigated at 273, 293 and 313 K. It is found that VFe substitution increases their hydrogen storage capacity, decreases the plateau pressure and the hysteresis factor of their pressure-composition-temperature (PCT) curves. After annealing treatment at 1223 K for 6 h, TiMn0.95Cr0.25(VFe)0.3 alloy exhibits a lower hydrogen desorption plateau pressure (0.27 MPa at 313 K) and a smaller hysteresis factor (0.13 at 313 K); the maximum and effective hydrogen storage capacities (mass fraction) are 2.03% and 1.12% respectively, which can satisfy the demand of hydrogen storage tanks for proton exchange membrane fuel cells (PEMFC).     

Co部分替代Ni对La_(0.4)Er_(0.4)Mg_(0.2)Ni_(3.3-x)Co_xAl_(0.2)(0.1≤x≤0.4)储氢合金结构和电化学性能的影响

为了改善储氢合金La0.4Er0.4Mg0.2Ni3.3-xCoxAl0.2(0.1≤x≤0.4)的结构和综合电化学性能,采用Co部分替代Ni的方法,实验采用高频感应炉制备La0.4Er0.4Mg0.2Ni3.3-xCoxAl0.2(0.1≤x≤0.4)储氢合金。通过X射线衍射技术和电化学测量方法研究储氢合金的晶体结构和电化学性能。XRD图谱显示样品储氢合金主要由LaNi5和La2Ni7相组成,电化学实验表明,随着Co含量的增高,储氢合金电极的最大放电容量和50次循环后的容量保持率S50基本呈现增加状态,放电容量从x=0.1时的225mA·h/g升高到x=0.4时的254.9mA·h/g,容量保持率S50从57.11%(x=0.1)增加到66.10%(x=0.4),但高倍率性能不断下降。通过交流阻抗(EIS)和线性扫描(LS)对Co替代Ni的合金动力学性能分析发现,Co替代Ni后合金的表面电荷转移能力先降低后升高。     

Al-Ce-TM（Fe,Co,Ni）非晶铝合金在NaCl溶液中的耐腐蚀性

使用单辊旋淬技术制备非晶态Al88Ce6TM6（Fe,Co,Ni）薄带,并研究了非晶态铝合金Al88Ce6TM6（Fe,Co,Ni）在中性NaCl溶液的电化学腐蚀行为.采用XRD和TEM对非晶合金的微观结构进行表征.使用直流和交流的电化学分析方法研究非晶态合金在中性0.6M NaCl溶液中的耐腐蚀性,并与纯Al进行比较.结果发现：使用单辊旋淬技术制备的铝基合金Al88Ce6TM6（Fe,Co,Ni）为完全非晶结构,铝基非晶合金在阳极活化过程中均发生了明显的钝化现象,在中性NaCl溶液中铝基非晶合金Al88Ce6TM6（Fe,Co,Ni）均发生点蚀.与纯Al相比,3种非晶合金有更高的抗腐蚀能力和抗点蚀能力.3种铝基非晶合金中Al88Ce6Fe6的耐蚀性最好.     

Gaseous and electrochemical hydrogen storage kinetics of as-quenched nanocrystalline and amorphous Mg2Ni-type alloys

The nanocrystalline and amorphous Mg₂Ni-type Mg₂Ni_1?x Co _x (x = 0, 0.1, 0.2, 0.3, 0.4) alloys were synthesized by melt quenching technology. The structures of the as-cast and quenched alloys were characterized by XRD, SEM and HRTEM. The gaseous hydrogen storage kinetics of the alloys was measured using an automatically controlled Sieverts apparatus. The alloy electrodes were charged and discharged with a constant current density in order to investigate the electrochemical hydrogen storage kinetics of the alloys. The results demonstrate that the substitution of Co for Ni results in the formation of secondary phases MgCo₂ and Mg instead of altering the major phase Mg₂Ni. No amorphous phase is detected in the as-quenched Cofree alloy, however, a certain amount of amorphous phase is clearly found in the as-quenched alloys substituted by Co. Furthermore, both the rapid quenching and the Co substitution significantly improve the gaseous and electrochemical hydrogen storage kinetics of the alloys, for which the notable increase of the hydrogen diffusion coefficient (D) along with the limiting current density (I _L ) and the obvious decline of the electrochemical impedance generated by both the Co substitution and the rapid quenching are basically responsible.     

Effects of Si and Ce on the microstructure and hydrogen storage property of Ti_(26.5)Cr_(20)V_(45)Fe_(8.5)Ce_(0.5) alloy

In this paper, the effects of Si and Ce on the microstructure and hydrogen storage property of Ti26.5 Cr20V45Fe8.5Ce0.5 alloy were studied, respectively. First of all, effects of Si on the microstructure and hydrogen storage properties of Ti26.5Cr20(V45Fe8.5)1?xSixCe0.5 (x = 0, 0.5, 1.0, 1.5 and 2.0 at%) alloys were studied by X-ray diffraction, scanning electron microscopy and P-C isotherm measurements. As the Si addition increases, the hydrogen absorption capacities of alloys decrease but the equilibrium pressure increases, due to the formation of Laves phase. Secondly, the effect of Ce on Ti26.5Cr20 (V45Fe8.5)0.98Si2 alloy was studied. It was found that Ce addition is an effective way to eliminate the effect of Si on the hydrogen storage properties of the alloy.     

Effects of alloying side B on Ti-based AB2 hydrogen storage alloys

Ti-based AB2-type hydrogen storage alloys are a group of promising materials, which will probably replace the prevalent rare earth-based AB5-type alloys and be adopted as the main cathode materials of nickelmetal hydride (Ni-MH) batteries in the near future. Alloying in side B is a major way to improve the performance of Ti-based AB2-type alloys. Based on recent studies, the effects of alloying elements in side B upon the performance of Ti-based AB2-type hydrogen storage alloys are systematically reviewed here. These performance sare divided into two categories, namely PCI characteristics, including hydrogen storage capacity (HSC), plateau pressure (PP), pressure hysteresis (PH) and pressure plateau sloping (PPS), and electrochemical properties, including discharge capacity (DC), activation property ( AP), cycling stability (CS) and high-rate dischargeability (HRD). Furthermore, the existing problems in these investigations and some suggestions for future research are proposed.