快速凝固钛钒系贮氢合金电化学性能研究

研究了快速凝固处理对钛钒系贮氢电极合金Ti0.8Zr0．2V2．4Mn0．48Cr0．72Ni0．9的相结构、特别是电化学性能的影响规律。XRD研究表明：合金主要由六方结构的C14 Laves相和体心立方结构的钒基固溶体相所组成，快速凝固减少了合金中C14 Laves相的含量。电化学性能分析表明：快速凝固降低了合金电极的最大放电容量，增加了电极的活化次数，提高了电极表面的反应阻抗，恶化了电极的动力学性能，但是却大大改善了合金电极的循环稳定性。     

Ti—Ⅴ基多相贮氢电极合金的电化学吸放氢机理研究

采用XRD的Rietveld全谱拟合技术以及利用储氢合金吸氢量与其体积膨胀成线形关系的原理，研究了Ti—Ⅴ基贮氢电极合金的电化学吸放氢机理．结果表明，铸态合金Ti0.8Zr0.2V1.867Mn0．373Cr0．56Ni0.7由C14型Laves相和Ⅴ基固溶体相构成在充电过程中，充电时间由3．33增至120min时，Laves相的晶胞体积膨胀率△Ⅴ／Ⅴ分别由0．301％增加到2．719％，而Ⅴ基固溶体相的△Ⅴ／Ⅴ由0．011％增至1．685％．在放电过程中，放电时间从0min增加到165min时，Laves相的△Ⅴ／Ⅴ从14．542％降到8．119％；而Ⅴ基固溶体相的△Ⅴ／Ⅴ从8．117％减小到6．248％．说明电化学吸氢时，氢首先被Laves相吸收，然后再扩散进入Ⅴ基固溶体；电化学放氢时，Ⅴ基固溶体中的氢首先扩散进入Laves相然旨再释放．因此，该合金中，Laves相既是吸氢相又是催化相，提高合金中Ⅴ基固溶体相的利用率，从而使Ti—Ⅴ基贮氢合金具有较好的综合电化学性能。     

Ti-V基多相贮氢电极合金的电化学吸放氢机理研究

采用XRD的Rietveld全谱拟合技术以及利用储氢合金吸氢量与其体积膨胀成线形关系的原理,研究了Ti-V基贮氢电极合金的电化学吸放氢机理.结果表明,铸态合金Ti0.8Zr0.2V1.867Mn0.373Cr0.56Ni0.7由C14型Laves相和V基固溶体相构成.在充电过程中,充电时间由3.33增至120 min时,Laves相的晶胞体积膨胀率ΔV/V分别由0.301％增加到2.719％,而V基同溶体相的ΔV/V由0.011％增至1.685％.在放电过程中,放电时间从0 min增加到165 min时,Layes相的ΔV/V从14.542％降到8.119％;而V基固溶体相的△V/V从8.117％减小到6.248％.说明电化学吸氢时,氢首先被Laves相吸收,然后再扩散进入V基固溶体;电化学放氢时, V基固溶体中的氢首先扩散进入Laves相然后再释放.因此,该合金中,Laves相既是吸氢相又是催化相,提高合金中V基固溶体相的利用率,从而使Ti-V基贮氢合金具有较好的综合电化学性能.     

Ti_（0.10）Zr_（0.15）V_（0.35）Cr_（0.10）Ni_（0.30）-10% LaNi_3复合物的电化学储氢特性及协同效应

为了改善钛钒基固溶体合金的电催化活性和动力学性能,采用两步电弧熔炼法制备储氢复合合金Ti0.10Zr0.15V0.35Cr0.10Ni0.30–10%LaNi3,利用X-射线衍射、场发射扫描电镜-能谱、电化学阻抗谱和恒流充放电测试技术系统研究该储氢复合合金电极的电化学性能与协同效应。结果表明：该复合合金的主相是BCC结构的钒基固溶体相和六方结构的C14Laves相,在复合过程中生成了第二相;复合合金电极的综合电化学性能较母体合金有显著改善;复合合金电极的活化周期为5周,最大放电容量为362.5mA·h/g,在233K时放电能力为65.84%;在活化、复合、任意循环及高、低温和高倍率放电过程中,该储氢复合合金电极的放电容量均存在协同效应;该复合合金电极的电荷转移电阻和交换电流密度均存在协同效应。     

超化学计量比Ti-Zr-V-Mn-Cr-Ni贮氢电极合金相结构及电化学性能研究

研究了超化学计量比对钛基贮氢合金相结构及电化学性能的影响。XRD及EDS分析表明，超化学计量比贮氢合金（Ti0.8Zr0.2)(V0.533Mn0.107Cr0.16Ni0.2)x(x=2,3,4,5,6)均主要由六方结构的C14型Laves相和体心立方结构的钒基固溶体相构成。随着x值的增大，两相的晶胞参数及晶胞体积均减小。电化学性能测试表明，当x的值在2－5范围内时，随着x值的增大，合金的最大放电容量、放电电位、高倍率放电性能（HRD）、循环稳定性、交换电流密度I0以及极限电流密度IL均提高。但继续增大x值后，除放电电位、高倍率放电性能和循环稳定性继续有所提高外，最大放电容量、交换电流密度I0以及极限电流密度IL均减小。此外，随着化学计量比的增大，合金电极的活化渐趋困难。     

球磨制备Ti_(0.8)Zr_(0.2)V_(2.7)Mn_(0.5)Cr_(0.7)Ni_(1.75)-15wt%A_2B_7复合储氢材料及其电化学性能研究

采用球磨和表面改性方法制备了复合储氢材料Ti0.8Zr0.2V2.7Mn0.5Cr0.7Ni1.75-15wt%La1.5Mg0.5Ni6.7Al0.3。研究和分析表明,钒基Ti0.8Zr0.2V2.7Mn0.5Cr0.7Ni1.7铸态合金由bcc结构固溶体相和六方晶系C14型Laves相构成三维网状组织,球磨改性后钒基合金与La1.5Mg0.5Ni6.7Al0.3之间并未发生合金化反应。电化学性能研究表明,经球磨改性后复合材料Ti0.8Zr0.2V2.7Mn0.5Cr0.7Ni1.75-15wt%La1.5Mg0.5Ni6.7Al0.3能明显增加合金的电极放电容量。铸态钒基合金和球磨复合材料均具有良好的电化学循环稳定性,其中球磨1h后电极最大放电容量为300.1mA/g,经100次循环后的电化学容量保持率为97.2%,球磨5h后试样的循环稳定性高达99%。     

Ti-V基固溶体/La-Mg基合金复合储氢材料的结构与电化学性能

两步电弧熔炼法制备Ti0.10Zr0.15V0.35Cr0.10Ni0.30+1%La0.85Mg0.25Ni4.5Co0.35Al0.15复合储氢合金,XRD、SEM、EDS分析结果表明,复合储氢合金的主相是体心立方结构的钒基固溶体相和六方结构的C14Laves相。电化学研究表明:复合过程中存在明显的协同效应;与母体合金电极相比,复合合金电极的P-C-T特性、活化性能、最大放电容量、循环稳定性、低温放电能力和高倍率放电性能均有了显著改善;复合合金电极的电荷转移电阻较小,交换电流密度和氢的扩散系数较大,这些改善可能与第二相的形成有关。     

元素Ti对贮氢合金ZrMn0．7V0．2CO0．1Ni1．2相结构和电化学性能的影响

研究了元素Ti对贮氢电极合金ZrMn0.7V0.2Co0.1Ni1.2的相结构、相组成以及电化学性能的影响。结果表明，对于合金Zr1-xTix(Mn0.7V0.2Co0.1Ni1.2)，其母体合金的主相为C15型Laves相，并含有少量的非Laves相Zr7M10；但随着掺Ti量的增加，合金中出现C14型Laves相，而且其含量逐渐增加；在x=0．1～0．2时，合金中还出现少量的TiNi相，而在x=0．4～0．5时，非Laves相Zr7M10和TiNi相全部消失，说明元素Ti大量的掺杂抑制了第二相的产生：而且随着Ti含量的增加，合金中的C15型和C14型Laves相的晶格常数逐渐减小。电化学测试结果发现，当含Ti量x=0．2时，合金有最大放电容量Cmax为354mAh／g，在放电电流为300mAh／g条件下，高倍率放电性能比母体合金提高了15％。     

Zr替代Ti对Ti19．5V40Mn16．2Cr9．8Ni14．5合金的影响结构及储氢性能

为改善Ti—V基固溶体型储氢合金的电化学性能，使用少量的Zr部分取代Ti19.5V40Mn16.2Cr9.8Ni14.5合金中的Ti，并采用XRD，SEM以及PCT等测试手段研究替代前后合金微观结构和储氢性能的变化情况。通过XRD和SEM分析表明，（Ti1-xZrx）19.5V40Mn16.2Cr9.8Ni14.5（x=0，0．1，0．15，0．2，0．25，0．3）合金均是由Ti-V基BCC相和C14 Laves相组成。但Zr的部分替代明显增加了C14 Laves相的含量，并使Ti-V基BCC相在减少的同时由树枝状变成了被C14 Laves相包围的岛状。PCT曲线显示：随着Zr替代量的增加。合金的吸放氢平台不断下降，而合金的吸放氢量先有所增加后又逐渐减小。这说明适量提高C14 Laves相的含量对增加Ti—V基固溶体型储氢合金的吸放氢能力有一定的促进作用。     

Cr部分替代Mn对Ti—Zr—V—Mn—Ni贮氢合金相结构、显微组织及电化学性能的影响

研究了Cr部分替代Mn对Ti-Zr-V-Mn-Ni贮氢合金相结合,显微组织及电化学性能的影响。结果表明,随着Cr的加入,合金电极的循环稳定性得到明显改善,但电极放电容量有所下降,XRD及EDS分析表明,合金主要由六方结构的C14Laves母相和立方结构的TiNi型第二相构成,Cr替代后,合金中出现了立方结构的V-Cr固溶相,金相显微组织显示,铸态和退火态合金均由连续的C14Laves相基体以及TiNi型树枝晶第二相组成。     

Effect of rapid solidification on the structural and electrochemical properties of the Ti–V-based hydrogen storage electrode alloy

The structural and electrochemical properties of the as-cast and rapidly solidified Ti_0.8Zr_0.2V_2.4Mn_0.48Cr_0.72Ni_0.9 alloys were studied. Both the as-cast and the rapidly solidified alloys were mainly composed of a C14 Laves phase matrix with hexagonal structure and a V-based solid solution phase with body centered cubic (BCC) structure. The V-based solid solution phase showed very fine dendrites in the rapidly solidified alloy instead of the large dendrites as observed in the as-cast alloy. In addition, the content of the C14 Laves phase in the alloy decreased greatly after rapid solidification. Electrochemical measurements indicated that the rapidly solidified alloy had a lower discharge capacity, a slower activation rate, a worse high rate dischargeability, a smaller exchange current density and limiting current density, but an improved cycle life compared with that of the as-cast alloy.     

Electrochemical properties of TiV-based hydrogen storage alloys

The electrochemical properties of the super-stoichiometric TiV-based hydrogen storage electrode alloys(Ti0.8Zr0.2)(V0.533Mn0.107Cr0.16Ni0.2)x(x=2,3,4,5,6)were studied.It is found by XRD analysis that all the alloys mainly consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with BCC structure.The lattice parameters and the unit cell volumes of the two phases decrease with increasing x.The cycle life.the linear polarization.the anode polarization and the electrochemical impedance spectra of the alloy electrodes were investigated systematically.The overall electrochemical properties of the alloy electrode are found improved greatly as the result of super-stoicfhiometry and get to the best when x=5.     

XRD study of the hydrogenation and dehydrogenation process of the two different phase components in a Ti–V-based multiphase hydrogen storage electrode alloy

Hydrogenation and dehydrogenation of two different phases in a multiphase Ti–V-based alloy Ti_0.8Zr_0.2V_1.867Mn_0.373Cr_0.56Ni_0.7, namely the C14 Laves phase with hexagonal structure and the V-based solid solution phase with body centered cubic (bcc) structure during electrochemical charging and discharging were investigated by X-ray powder diffraction (XRD) analysis. For the alloy investigated, the C14 Laves phase component, which had good surface electrochemical activity for decomposing water, was hydrogenated from the very beginning of the charging process and was providing hydrogen to both phase components throughout the entire electrochemical charging process. The V-based solid solution phase, which had no or very low surface electrochemical activity for decomposing water during electrochemical charging, could obtain hydrogen only from its neighboring C14 Laves phase component when the hydrogen content of which was high enough to build up an adequate pressure to feed hydrogen to its neighboring phase component. The V-based solid solution phase experienced a phase change when the hydrogen in it reached a definite level, namely from bcc to body centered tetragonal (bct) structure. Probably due to the high stability of bct hydride phase of the V-based solid solution phase, it did not revert back to the initial bcc structure during the electrochemical discharging process conducted in our experiment at the room temperature and atmospheric pressure.     

Pulverization mechanism of the multiphase Ti–V-based hydrogen storage electrode alloy during charge/discharge cycling

Pulverization is an important key factor for the electrochemical cycle stability of many hydrogen storage alloys. In this paper, the pulverization mechanism of the multiphase Ti–V-based hydrogen storage alloy which mainly consists of a V-based solid solution phase with the BCC structure and a C14 Laves phase is studied based on a sample material of the Ti_0.8Zr_0.2V_2.7Mn_0.5Cr_0.6Ni_1.25Fe_0.2 alloy. The microstructure of the alloy and the morphology change of the alloy electrode during the charge/discharge process were observed by transmission electron microscope, scanning electron microscope and atomic force microscope, etc. The effect of mechanical properties of the V-based phase and the C14 Laves phase on the pulverization behavior of the Ti–V-based alloy is discussed. The results show that microcracks initially occur at the phase boundary of the V-based phase and the C14 Laves phase and then extend to the C14 Laves phase in the charge/discharge process. The phase boundary is composed of a Ti segregated amorphous layer with a thickness of about 90 nm, mismatching with the crystallized V-base phase and C14 Laves phase. The toughness of the C14 Laves phase is much lower and the hardness is higher than that of the V-based phase. The weak bonding strength of the phase boundary, the lower toughness of the C14 Laves phase and the large volume expansion/contraction of the C14 Laves phase during charge/discharge cycling are the main factors that cause the pulverization of the Ti–V-based alloy.     

Structure and electrochemical properties of the Fe substituted Ti–V-based hydrogen storage alloys

To elucidate the effects of Fe on the Ti–V-based hydrogen storage electrode alloys, the Ti_0.8Zr_0.2V_2.7−xMn_0.5Cr_0.8Ni_1.0Fe_x (x = 0.0–0.5) alloys were prepared and their structures and electrochemical properties were systematically investigated. XRD results show that all the alloys consist of a C14 Laves phase with hexagonal structure and a V-based solid solution phase with bcc structure. With increasing Fe content, the abundance of the C14 Laves phase gradually decreases from 43.4 wt% (x = 0.0) to 28.5 wt% (x = 0.5), on the contrary, that of the V-based solid solution phase monotonously increases from 56.6 wt% to 71.5 wt%. In addition, SEM observation finds that the grain size of the V-based solid solution phase is first gradually reduced and then enlarged with increasing x. Electrochemical investigations indicate that the substitution of Fe for V markedly improves the cycling stability and the high rate dischargeability of the alloy electrodes, but decreases the maximum discharge capacity and the activation performance. Further electrochemical impedance spectra, the linear polarization curve and the potentiostatic step discharge measurements reveal that the electrochemical kinetics of the alloy electrodes should be jointly controlled by the charge-transfer reaction rate on the alloy surface and the hydrogen diffusion rate in the bulk of the alloys. For the alloy electrodes with the lower Fe content (x = 0.0–0.2), the hydrogen diffusion in the bulk of the alloys should be the rate-determining step of its discharge process, and while x increases from 0.3 to 0.5, the charge-transfer reaction on the alloy surface becomes to the rate-determining step, which induces that the electrochemical kinetics of the alloy electrodes is firstly improved and then decreased with increasing Fe content.     

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.     

Ti掺杂ZrV2合金的相组成及贮氢性能研究

利用真空感应熔炼的方法制备出(ZrTi)V2合金,在950℃下对合金进行长时间的退火处理,对合金的相结构及吸氢性能进行测试。结果表明:(ZrTi)V2合金主要由C15Laves相、α-Zr相、Zr3V3O相和V基固溶体相组成,热处理使得α-Zr相及V基固溶体相减少;该合金经400℃,1h除气之后,再经过一次吸放氢循环即可达到最佳的活化效果;根据Van’tHoff关系外推出室温下该合金的平衡压力为8.1×10-14Pa。     

热处理对包含正二十面体准晶相Ti1.4V0.6Ni合金电极的电化学性能的影响（英文）

研究了热处理前后Ti1.4V0.6Ni合金的结构和电化学性能。采用X射线粉末衍射(XRD)方法分析合金的结构。电化学特性包括放电容量、循环稳定性和高倍率放电性能等。XRD衍射分析表明,在590°C热处理30min的合金,主要包含正二十面体准晶相、Ti2Ni(FCC)相、V基固溶相(BCC)和C14Laves相(Hex)。电化学测试显示,热处理后在30°C和放电电流密度为30mA/g的条件下,合金电极的最大放电容量可达330.9mA·h/g,并且循环稳定性和高倍率放电性能也得到改善。此外,通过电化学阻抗和合金内部氢的扩散系数研究了合金电极的动力学性能。