镁基储氢材料的改性及其性能研究

发布时间：2019-01-01 19:12

【摘要】：镁基储氢材料以其储氢量高(7.6wt.%)、资源丰富、成本低廉的特点,被认为是最具有发展前景的储氢材料之一,但是其高的吸放氢温度、缓慢的吸放氢动力学性能阻碍了它的实际工业化应用。本文以Mg粉为初始原料研究了高温高压氢化工艺对样品中Mg H2含量的影响,进一步选择Cs F、Ti C、Ni F2对Mg H2进行复相球磨改性,此外,还研究了Mg H2+Li Al H4复合体系的放氢性能。本文利用p-C-T测试仪在高温高压的条件下制备得到了Mg H2储氢合金。确定了较优的制备工艺,Mg粉的球磨参数为:球料比40:1,转速300r/min,球磨时间6h,氩气;氢化参数:氢压4MPa,温度653K,两次氢化时间分别为48h、24h。通过分析发现采用上述工艺制备得到的样品中Mg H2的含量达到了98wt.%左右。进一步通过复相球磨的方式制备得到了Mg H2+M(M:Cs F、Ti C、Ni F2)的储氢试样。吸放氢性能及XRD测试结果表明,三种添加物对Mg H2的吸放氢动力学性能均有很好的催化促进作用,但其催化的机理不尽相同。Ti C在系统的吸放氢过程稳定存在,没有与基质Mg H2发生反应,是以传统催化剂的形式对Mg H2产生了表面改性的效果,从而提高了Mg H2的吸放氢性能。而Cs F、Ni F2则是因为在吸放氢过程中分别与基体发生了2Cs F+Mg H2→2Cs H+Mg F2、Ni F2?4H2O+7Mg H2→Mg2Ni H4+Mg F2+4Mg O+9H2的反应,从而促进了Mg H2的吸放氢过程。对于Cs F和Ti C,均在添加量为5wt.%时表现出最好的催化效果,而Ni F2添加2wt.%时性能较好。综合比较,其中Cs F的催化作用较为突出,当其添加量在5wt.%时,573K下的放氢量达到了7.06wt.%,可逆吸氢容量为7.09wt.%,在473K时的吸氢量也达到了6.33wt.%。同样采用球磨的方式制备的Mg H2+Li Al H4、Mg H2+Li Al H4+5wt.%Ti C复合体系,其放氢性能测试及XRD结果表明,Mg H2+Li Al H4的放氢性能明显优于Mg H2,Mg H2+Li Al H4在较低温度(473K以下)时,只表现为Li Al H4的单方面放氢行为,当温度达到523K时产生了协同放氢效应,这一协同效应表现为Li Al H4分解产生的Al原子降低了Mg H2的稳定性,产生了两种新相Mg2Al3和Mg17Al12,从而改变了Mg H2放氢过程;在Mg H2+Li Al H4的基础上添加Ti C所带来的细化作用,增加了Mg H2与Li Al H4之间的相界面,有利于它们之间的这种协同放氢效应,进一步提高了系统的放氢动力学性能。
[Abstract]:Magnesium based hydrogen storage materials are considered as one of the most promising hydrogen storage materials due to their high hydrogen storage capacity (7.6 wt.%), rich resources and low cost, but their high hydrogen absorption and desorption temperatures. The slow kinetics of hydrogen absorption and desorption hinders its practical industrial application. In this paper, the effect of high temperature and high pressure hydrogenation on the content of Mg H2 in the sample was studied by using Mg powder as the initial raw material. Furthermore, the Cs FFU Ti Ni F 2 was selected to modify Mg H2 by multiphase ball milling. The hydrogen desorption properties of Mg H2 Li Al H 4 composite system were also studied. In this paper, Mg H2 hydrogen storage alloys were prepared by using p-C-T tester under high temperature and high pressure. The optimum preparation process was determined. The milling parameters of Mg powder were as follows: ratio of ball to material 40: 1, rotational speed 300 r / min, milling time 6 h, argon gas, hydrogenation parameter: hydrogen pressure 4 MPA, temperature 653 K, twice hydrogenation time 48 h and 24 h, respectively. It is found that the content of Mg H2 in the sample prepared by the above process is about 98 wt.%. Furthermore, the hydrogen storage samples of Mg H 2M (M:Cs FN Ti Ni F 2) were prepared by multiphase ball milling. The results of hydrogen absorption and desorption and XRD test showed that the three additives had a good catalytic effect on the hydrogen absorption and desorption kinetics of Mg H2, but the mechanism of their catalytic mechanism was different, and. Ti C existed stably in the process of hydrogen absorption and desorption. There was no reaction with Mg H2, which resulted in the surface modification of Mg H2 in the form of traditional catalyst, which improved the hydrogen absorption and desorption performance of Mg H2. However, the reaction of 2Cs F Mg H 2 + 2Cs H Mg F 2N Ni F2?4H2O 7Mg H 2 Mg2Ni H 4 Mg F 2 4Mg O 9H2 with the matrix occurred during the hydrogen absorption and desorption process of Cs F 2 Ni F 2, which promoted the hydrogen absorption and desorption process of Mg H 2. For Cs F and Ti C, both showed the best catalytic effect at the addition amount of 5wt.%, while the performance of Ni F2 was better when adding 2wt.%. Compared with each other, the catalytic activity of Cs F is more prominent. When the addition amount of Cs F is 5 wt.%, the hydrogen release capacity at 573K reaches 7.06wt.and the reversible hydrogen absorption capacity is 7.09wt.and the hydrogen absorption capacity at 473K reaches 6.33wt. The hydrogen release properties of Mg H 2 Li Al H 4 O mg H 2 Li Al H 4 5wt.%Ti C prepared by ball milling were tested and XRD results showed that Mg H 2 Li Al H 4 was superior to Mg H 2. At low temperature (under 473K), Mg H _ 2 Li Al H _ 4 exhibits only the unilateral hydrogen release behavior of Li Al H _ 4. When the temperature reaches 523K, there is a synergistic hydrogen release effect. The synergistic effect is that the Al atoms produced by the decomposition of Li Al H4 decrease the stability of Mg H2, and produce two new phases, Mg2Al3 and Mg17Al12, which change the process of Mg H2 dehydrogenation. The addition of Ti C on the basis of Mg H2 Li Al H4 increases the phase interface between Mg H2 and Li Al H4, which is beneficial to the synergistic dehydrogenation effect between Mg H2 and Li Al H4, and further improves the dehydrogenation kinetics of the system.
【学位授予单位】：重庆大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34

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