Mg-Co基储氢电极合金的制备、结构与电化学性能

发布时间：2018-01-22 04:23

本文关键词： 镍氢电池镁-钴基储氢合金电极机械合金化体心立方结构电化学性能　出处：《东南大学》2017年硕士论文　论文类型：学位论文

【摘要】：镁基储氢合金是一种高容量、低成本的储氢材料。其中镁钴系储氢合金因其具有低温吸氢性能,成为近些年研究的热点。先前报导的镁-钴体系储氢合金具有体心立方结构,且晶粒在纳米尺度时具备有良好的吸氢性能。但是镁-钴基合金即使是在真空条件下也难以放出储存的氢气。对此,本研究将探索电化学条件下镁-钴基合金的可逆储氢(充放电)性能。本论文以机械合金化的方法,制备了 Mg-Co二元合金,添加5 at.%Pd的Mg-Co三元合金,Mg50Co50 替代不同元素的 Mg45M5Co50(M = Zr,Ti,Pd)、Mg50CO45Pd5三元合金,以及Mg侧替代不同含量Pd元素的Mg67-xP(xCo33 =1,3,5,7)三元合金。通过X射线衍射及透射电镜分析,证实除了 Mg67CO33和短时间球磨的Mg67Co33-5 at.%Pd以外的所有合金的主相结构均为单一的体心立方结构,且晶粒已细化至纳米尺度。合金电极的充电放电测试显示,随着Mg含量的增加,二元Mg-Co合金的首次放电容量先增加后减小,循环稳定性逐渐降低;对于Mg-Co-5 at.%Pd三元合金,容量逐渐升高,循环稳定性逐渐降低。对于部分合金化的Mg67Co33,其容量仅有14.7mAhg-1;添加5at.%Pd后,随着球磨时间增加,容量逐渐升高,循环稳定性增强;Mg侧替代不同含量的Pd元素,其容量随着Pd含量的增加先升高后降低,循环稳定性逐渐增强。Mg64Pd3Co33的容量为所有合金中最高,达到624.3 mAh g-1。对合金电极进行线性极化、恒电位阶跃等电化学动力学的测试,结果显示合金的动力学性能随着Mg含量的增加而升高,添加Pd或者替代元素,均能提升合金的动力学性能。对合金电极进行塔菲尔极化的测试,得到腐蚀电流密度的结果,表明合金的耐腐蚀性能随着Mg含量的增加而降低,添加Pd或者替代元素,能够提高合金的耐腐蚀性能。对五次循环后的合金粉末进行X射线衍射和X射线光电子能谱的测试,结果表明合金粉末表面有氢氧化物生成,Pd元素能有效抑制Mg的腐蚀。对五次循环后的电解液进行电感耦合等离子体质谱的测试结果表明,电解液中有Mg离子存在,且随着Pd元素含量的增加而减少。因此可以认为合金的容量损失来自表面氢氧化物的形成,表面活性降低,以及Mg的溶解。
[Abstract]:Magnesium based hydrogen storage alloy is a kind of high capacity hydrogen storage materials with low cost. The cobalt magnesium based hydrogen storage alloys because of its hydrogen absorption properties of low temperature, become the focus of research in recent years. Previously reported magnesium cobalt system hydrogen storage alloy has a body centered cubic structure, and the grain size in the nano scale with hydrogen good. But the absorption properties of magnesium - cobalt alloy even difficult to release hydrogen storage under vacuum conditions. In this regard, this study will explore the reversible hydrogen storage under the condition of electrochemical magnesium cobalt based alloy (discharge) performance. This method on mechanical alloying of Mg-Co alloy was prepared two yuan 5, add at.%Pd Mg-Co three alloys, Mg50Co50 substitution of different elements Mg45M5Co50 (M = Zr, Ti, Pd, Mg50CO45Pd5) three yuan alloy, and Mg substitution with different content of Pd element Mg67-xP (xCo33 =1,3,5,7) three alloy. By X ray diffraction and transmission electron microscopy analysis confirmed. In addition to all the alloys except Mg67CO33 and Mg67Co33-5 short milling time of at.%Pd main phase structure are single bcc structure, and the grain has been refined to nanometer scale. The charge and discharge test alloy electrode shows that with the increase of Mg content, two yuan for the first time the discharge capacity of Mg-Co alloy increased first and then decreased, the cycle stability decreased; at.%Pd three yuan for the Mg-Co-5 alloy, the capacity gradually increased, the cycle stability decreased gradually. For some alloying of Mg67Co33, its capacity is only 14.7mAhg-1; after the addition of 5at.%Pd, with the increase of milling time, capacity gradually increased, the cycle stability enhancement; Pd Mg side instead of different content of elements of its capacity, with the increase of Pd content increased first and then decreased, the cycle stability gradually increased the capacity of the.Mg64Pd3Co33 is the highest in all alloys, up to 624.3 mAh g-1. linear polarization on the alloy electrode, constant power One step electrochemical kinetics test results show that the dynamic performance of the alloy increases with the increase of Mg content, add or replace the Pd elements, can improve the dynamic performance of both alloys. The Tafel polarization on the alloy electrode test, obtained results show that the corrosion current density and corrosion resistance of the alloys decrease with the increase of Mg content the addition of Pd or substitution elements can improve the corrosion resistance of alloy. X ray diffraction and X ray photoelectron spectroscopy test on the alloy powder after five cycles. The results show that the surface of the alloy powder with hydroxide formation, corrosion of Pd elements can effectively inhibit the Mg. Test results of inductively coupled plasma mass spectrometry the electrolyte after five cycles showed that Mg ions in the electrolyte, and decreases with the increase of Pd content. It can be concluded that the capacity of the alloys. The loss comes from the formation of the surface hydroxides, the decrease of the surface activity and the dissolution of the Mg.

【学位授予单位】：东南大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG139.7

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