ACTIVATION OF AB_2 TYPE Zr-BASED HYDRIDE ELECTRODES

1.IntroductionABcLavesphasehydrideelectrodes(i.e.Zr--Cr--NiandZr--Mn--Nibasedhydrogenstoragealloys)havepromisingelectrochemicalperformancesuchashighdischargecapacity,excellentoxidationresistanceandtherebydurablecyclingstabilityetc.forNi/MHbatteryapplication[1].Thedensesurfaceoxidelayeralsoinducesthepoorcharging/dischargingkineticsandthedifficultyintheirinitialactivatingprocesses.RecentlymanyresearchersareworkinghardonmodifyingtheactivationpropertiesoftheZr--basedABZtypeLavesphasehydridee…     

热处理对低Co贮氢合金Ml(NiCoMnAlFe)_5电化学性能的影响

系统研究了热处理对低Co贮氢电极合金Ml(NiCoMnAlFe) 5 电化学性能的影响。结果表明 ,铸态合金的放电容量为 2 97mA·h/g ,经 2 68次充放电循环后的容量保持率为 68% ;经热处理后 ,合金的放电容量提高至30 2mA·h/g ,2 68次充放电循环后的容量保持率提高至 80 % ,热处理提高了合金的放电容量和循环稳定性 ;同时发现热处理会导致合金高倍率放电特性的恶化。XRD测试表明 ,热处理降低了晶格应力与晶格缺陷 ,改善了合金的成分均匀性 ,从而提高了合金的放电容量和循环稳定性。     

Hydrogen absorption properties of the slurry system composed of liquid C6H6 and F-treated Mg2Ni

The hydrogenation characteristics of the slurry composed of the NH₄F solution treated Mg₂Ni and liquid C₆H₆ were studied. The F-treatment results in a net-shaped MgF₂ surface and higher nickel content in the sub-layer. It is found that the hydride of the NH₄F treated alloy has a much higher activity for the hydrogenation of benzene. The catalytic activity for hydrogenation of the alloy depended strongly on the surface properties of the catalyst. At 483 K and under a hydrogen pressure of 4.0 MPa, the alloy absorbed hydrogen first, transformed into hydride and then the benzene was hydrogenated to cyclohexane with the hydride as the catalyst. The hydrogen absorption capacity of slurry system composed of 20 wt.% treated alloy and benzene reached 6.4 wt.% and the hydrogenation completed in 20 min. Results of X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM) analysis on the crystal structure, surface composition and surface morphology of the untreated and treated alloy are presented and discussed.     

Ni-B-C对La0.94Mg0.06Ni3.49Co0.73Mn0.12Al0.20储氢合金电化学性能的影响研究

为提高新型AB₃型储氢合金La_0.94Mg_0.06Ni_3.49Co_0.73Mn_0.12Al_0.20的电化学性能,将球磨法制备的Ni-B-C粉末按不同重量比添加到合金中。采用X-射线粉末衍射仪(XRD)和扫描电子显微镜(SEM)分析合金的相结构和表面形貌,添加Ni-B-C粉末后,合金相结构没有变化,仍由LaNi₅相和La₂Ni₇相两个相组成,但合金表面出现了细小颗粒。添加Ni-B-C粉末后,合金电极的最大放电容量和放电容量保持率均提高。当添加重量百分比为10%的Ni-B-C粉末后,电极的最大放电容量从346 mAh/g增加到363 mAh/g,50个循环后的放电容量保持率从70%提高到77%,交换电流密度I₀与极限电流密度I_L分别为106 mA/g和987 mA/g。动电位极化测试表明,电极的抗腐蚀能力也有所增强。研究结果表明,Ni-B-C可以提高AB₃型储氢合金的综合电化学性能。     

保压时间对储氢合金电极电化学性能的影响

在不同保压时间下制备了Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3储氢合金电极,研究了保压时间对合金电极的活化性能、最大放电容量、放电特性和循环稳定性的影响规律和机制。结果表明,保压时间对合金电极的活化性能基本无影响,而合金电极的其他电化学性能随着保压时间的增大均呈现出先变好后变坏的变化规律,保压时间为15min时,合金展示了最佳的综合电化学性能,电化学性能的改善主要归因于合金电极的电荷转移速度加速和内阻减小。     

DEGRADATION BEHAVIORS OF NEW TYPE TiV-BASED HYDROGEN STORAGE ELECTRODE ALLOYS

The degradation behaviors of the TiV-based multiphase hydrogen storage alloy Ti0.8,Zr0.2V3.2Mn0.64 Cr0.96Ni1.2 during electrochemical cycling in alkaline electrolyte have been studied by XRD, SEM, EIS and AES measurements. XRD analysis indicates that the alloy consists of a C14-type Laves phase and a V-based solid solution. The lattice parameters of both phases are increased after discharged with cycling, which indicates that more irreversible hydrogen remains not discharged in the alloy. It should be responsible for the decrease of discharge capacity. SEM micrographs show that after 10 electrochemical cycles, a large number of cracks can be observed in the alloy, existing mainly in the V-based solid solution phase. Moreover, after 30 cycles, the alloy particles are obviously pulverized due to the larger expansion and shrinkage of cell volumes during hydrogen absorption and desorption, which induces the fast degradation of the TiV-based hydrogen storage alloys. EIS and AES measurements indicate that some passive oxide film has been formed on the surface of alloy electrode, which has higher charge-transfer resistance, lower hydrogen diffusivity, and less electro-catalytic activity. Therefore it can be concluded that the pulverization and oxidation of the alloy are the main factors responsible for the fast degradation of the TiV-based hydrogen storage alloys.     

NaCl包覆/氢化脱氢联合法制备超细钛粉及其性能

以海绵钛为原料,采用经过氢化破碎、阻止剂包覆、真空脱氢以及阻止剂脱除的方法制备超细钛粉。采用TEM、SEM以及激光粒度测试等手段研究制备过程中工艺参数对钛粉形貌、粒度及氧含量的影响,探讨阻止剂的晶粒长大抑制机理。结果表明:海绵钛在700℃、2 h渗氢后经过球磨5 h,粉末中位径(D50)达到2.61μm,以NaCl为阻止剂对氢化粉末进行包覆,经630℃、2 h脱氢并脱除阻止剂后,制得的超细钛粉呈不规则形状,中位径达6.16μm,氧含量为0.89%(质量分数);阻止剂的引入造成钛粉氧含量的微量增加;通过阻止剂包覆,在粉末颗粒表面形成厚度为5~10 nm的隔离层,阻碍了加热过程中Ti颗粒表面的原子扩散,从而阻止加热脱氢过程中粉末颗粒的长大。     

TZM合金电化学腐蚀行为研究

采用粉末冶金和轧制工艺制备出TZM合金和稀土镧掺杂的La-TZM合金,通过动电位极化研究合金电化学腐蚀行为,扫描电子显微镜(SEM)观察、能谱定量(EDS)分析表征腐蚀产物显微结构特征。保持Cl-浓度不变分别探讨合金在中性、酸性、碱性介质中耐侵蚀能力。结果表明,TZM合金在中性和碱性介质中抗腐蚀性能优于La-TZM合金,而在酸性介质中La-TZM合金抗腐蚀性能优于TZM合金,两类合金抗腐蚀性均表现为酸性介质强于中性介质,碱性介质最弱。Cl-有效破坏腐蚀表面形成的钝化膜,OH-和Cl-双重侵蚀促使两类合金晶间腐蚀加剧、粉末冶金制备的TZM合金及La-TZM合金对酸性介质具有良好的耐蚀性。     

保压时间对储氢合金电极电化学性能的影响

在不同保压时间下制备Mm0.3Ml0.7Ni3.55Co0.75Mn0.4Al0.3储氢合金电极,研究保压时间对合金电极的活化性能、最大放电容量、放电特性和循环稳定性的影响规律和机制。结果表明,保压时间对合金电极的活化性能基本无影响。合金电极的其它电化学性能随保压时间的增加均呈现出先变好后变坏的变化规律,保压时间为15min时,合金展示了最佳的综合电化学性能,电化学性能的改善主要归因于合金电极的电荷转移速度加速和内阻减小。     

氧化物—空气半燃料电池用贮氢合金电极的烧结制备及其电化学特性

研究了应用在空气－氢化物半燃料电池上的制备配套金属氢化物厚型电极烧结技术，将贮氢合金与细镍粉和一定的添加剂形成浆料涂覆在泡沫镍基体，测试不同烧结参数对贮氢合金电极的电化学性能的影响，烧结电极合金的电化学活化特性和高倍率放电能力与传统的粘结式电极有较大的提高，为设计适合电动车用高能量密度空气－氢化物燃料电池，分别选用冲孔镍箔带，冲孔铜箔带和铜编织网作为集流体进行比较实验。结果表明，选定冲孔铜箔带是适宜于设计空气－氢化物燃料电池用厚型氢化物电极。     

AZ91D镁合金微弧氧化膜的腐蚀行为研究

利用双向全波脉冲电源对AZ91D镁合金在硅酸盐体系中进行了微弧氧化处理,通过电化学阻抗谱(EIS)测试、极化曲线分析并结合XRD和SEM等分析方法对微弧氧化处理的镁合金腐蚀行为进行了研究.结果表明,微弧氧化膜表面分布着几微米的微孔,微弧氧化膜中主要含有MgF2,Mg2SiO4和Al2O3.AZ91D镁合金经过微弧氧化处理之后,耐蚀性能明显提高,自腐蚀电流密度降低3个数量级,自腐蚀电位高出约300 mV,阻抗值高出3个数量级,研制的微弧氧化膜对镁合金具有很好的防腐保护性能.     

无机成膜型缓蚀剂对铝合金缓蚀作用的研究

通过电化学实验和扫描电子显微镜（SEM）观察,系统地研究了四种无机缓蚀剂对铝合金在3．5％氯化钠溶液中的缓蚀作用。实验结果表明,这些无机缓蚀剂对铝合金具有较好的缓蚀效果。它们主要是通过在铝合金的表面形成一种化学转化膜来实现其缓蚀作用的。同时,由于这层转化膜的存在,明显地提高了铝合金在氯化钠溶注中的抗点蚀的能力。     

化学镀镍对A2B7型贮氢合金电极电化学性能的影响

本文对气态粉化后A2B7型贮氢合金La0.75Mg0.25Ni3.44Al0.06进行化学镀不同厚度Ni包覆处理.通过SEM观察,结果表明,包覆处理后镀层镍为球形颗粒且均匀弥散于合金表面.电化学测试结果表明,表面包覆镍处理的A2B7型合金电极放电容量有所降低,而循环稳定性有所提高.线性极化扫描和电化学阻抗谱等分析结果表明,表面包覆Ni处理后增大了合金电极的交换电流密度(I0),减小了电化学阻抗,改善了合金电极的动力学性能.     

铝合金防护涂层老化动力学研究

在紫外/盐雾加速综合环境条件下,研究了铝合金试样上聚酰胺清漆老化过程。采用环境扫描电子显微镜观察了防护涂层表面形貌的变化,采用电化学阻抗(EIS)分析了涂层的老化过程,同时还测量了光泽度、颜色、表面电阻和体积电阻在涂层老化过程中的变化。结果表明：在涂层老化过程中,涂层孔隙率增加,而体积电阻、表面电阻则降低, EIS给出了在涂层老化的不同阶段的特征。采用光泽度、颜色、表面电阻和体积电阻以及电化学阻抗数据作为性能参数,建立了涂层老化动力学方程,并给出了涂层失效判据,并对涂层老化动力学的参数进行了讨论,认为采用体积电阻或低频阻抗模值作为性能参数描述涂层老化动力学过程更为合理。     

表面处理对储氢合金电化学性能的影响研究

通过电化学方法,研究了储氢合金碱化处理及碱液中加入KBH4对合金电极的电催化活性和高倍率放电性能的影响.结果表明:处理后合金颗粒分布均匀,表面变得粗糙.两种处理方法均增加了合金表面的电催化活性,降低了合金电极的极化电阻,从而提高了高倍率放电能力.尤其在900mA/g放电时,处理前合金电极不能放电,单一碱处理合金电极和加入还原剂碱处理合金电极仍具有较高的高倍率放电能力,分别为69.2%和83.4%.在单一碱溶液中加入还原剂KBH4处理后,合金电极的电化学性能明显高于单一碱处理合金电极.     

Characterization and corrosion studies of ceria thin film based on fluorinated AZ91D magnesium alloy

The CeO₂ thin film was prepared via sol-gel method on fluorinated AZ91D magnesium alloy surfaces. The surface morphology, composition and the corrosion resistance of the film were investigated in details using scanning electron microscope, X-ray photoelectron spectroscopy and electrochemical impedance spectroscopy as well as potentiodynamic polarization tests. It was found that small amount of MgO and MgF₂ were encapsulated in CeO₂ thin film. The electrochemical measurement results demonstrated that the CeO₂ thin film on fluorinated AZ91D magnesium alloy could improve the corrosion resistance approximately by two orders of magnitude compared with that of the bare substrate.     

电力系统用LF21铝合金的电化学腐蚀行为

采用Tafel直线外推法、电化学阻抗谱和中性盐雾腐蚀试验研究了电力系统用LF21铝合金在5%NaCl溶液中的电化学腐蚀行为,利用SEM和EDS表征材料的腐蚀形态与腐蚀产物组成,并探讨腐蚀机理.结果表明,LF21铝合金在5%NaCl溶液中耐蚀性很差.随着电解液温度升高,铝合金的自腐蚀电位负移,腐蚀速率变大.电化学阻抗谱显示其容抗减小,膜电容下降,合金表面的保护膜被破坏.LF21铝合金在NaCl介质中的腐蚀主要以点蚀为主,形成较深的腐蚀坑,点蚀部位O含量明显增高.     

Mg-Li合金表面浅绿色超疏水复合膜层的制备及耐蚀性能研究

通过微弧氧化着色技术在Mg-Li合金表面生成浅绿色类陶瓷膜层,并在着色膜表面有机镀膜复合改性。用蒸馏水在镀膜表面的静态接触角以及动电位极化曲线和电化学阻抗谱测试,分别研究复合改性前后润湿性及耐蚀性。结果表明,微弧氧化着色表面通过有机镀膜生长了一层有机薄膜,接触角由近0°变为169.2°,实现了超亲水到超疏水的功能转化。Mg-Li合金基体经微弧氧化着色改性后,耐蚀性能明显提高,经复合改性后耐蚀性能进一步提高;与基体相比,超疏水复合膜在0.1 mol/L NaCl溶液中的动电位极化腐蚀电流密度减小3个数量级,电化学阻抗提高3个数量级。     

Effect of passive film on the galvanic corrosion of titanium alloy Ti60 coupled to copper alloy H62

Ti alloys exhibit high potential because of the compact passive film. However, the effect of passive film on galvanic corrosion is not clear. On the one hand, the great potential difference can accelerate the galvanic corrosion of other metals with low potential. On the other hand, the passive film can hinder the electrochemical reactions, inhibiting the galvanic corrosion. To clarify this question, the galvanic corrosion of titanium alloy Ti60 coupled to copper alloy H62 was studied using zero‐resistance ammeter, scanning vibrating electrode technique, scanning electron microscopy, and potentiodynamic polarization measurements. The chemical composition and electrical properties of the passive film on Ti60 were detected using X‐ray photoelectron spectroscopy and Mott‐Schottky plots. The results indicate the galvanic corrosion of Ti60‐H62 coupling is ignorable in spite of the great galvanic potential difference between them. It can be attributed to the low electron donor density of passive film, which inhibits the electron charge transfer process at the film/solution interface, causing the slow cathodic reaction rate on Ti60.     

真空电子束原位合成碳化物技术

通过真空电子束原位合成技术在低碳钢表面局部区域合成碳化物,用以改善金属表面的耐磨性能.在试验中将配比不同的Fe粉,Cr粉,C粉末均匀混合,直接涂敷或制备成试样放于低碳钢钢板表面,应用真空电子束作为热源,以旋转线扫描加热方式对金属粉末表面进行加热,使粉末发生化学反应.通过对生成的化合物进行X射线衍射分析发现在金属表面生成了碳化物Cr7C3,且金相分析也证明了表面有聚集成块的碳化物增强项.结果表明,试样表面由于生成了碳化物增强相使得表面的硬度远远大于其基体的硬度,从而可以改善金属表明的耐磨性能.原位合成技术被证明是可以实现金属表面改性的一种较好的方法.＃