【作者】 张宏亮；

【导师】 朱敏；

【作者基本信息】 华南理工大学 ， 材料加工工程， 2010， 硕士

【摘要】 随着全球经济的高速发展和对能源需求的日益增加,人类面临着化石能源枯竭和生态环境恶化的双重压力,因此开发绿色新能源意义重大。氢能是理想的能源载体,而储氢技术是实现氢能规模化应用的前提和基础。本论文首先综述了储氢材料的发展历史和研究现状,LiBH4和MgH2为代表的配位氢化物和金属氢化物因其较高的氢容量,是具有重要应用前景的储氢材料。但是这二类材料的吸放氢条件苛刻,动力学性能差的问题尚待解决。本论文针对MgH2和LiBH4存在的问题开展研究。首先采用高能球磨法及添加不同催化剂制备LiBH4-MgH2复合材料。进而研究了球磨工艺、催化剂种类及催化剂的添加量对LiBH4-MgH2复合体系放氢性能的影响。采用储氢性能测试仪测定了其放氢性能;运用X射线衍射、扫描电镜等方法表征材料在球磨及放氢后的组织结构。研究结果表明,LiBH4-MgH2复合体系的颗粒度随着球磨时间的增加而逐渐减小,使得放氢量和放氢动力学逐渐提高,但是当球磨时间增加到10小时后,LiBH4-MgH2复合体系的颗粒尺寸没有继续降低,反而有所增大,放氢量和放氢动力学也有所降低。在相同的球粉比和球磨时间下,振动式球磨比行星式球磨对提高LiBH4-MgH2复合体系的放氢动力学有更好的效果。对不同摩尔比的LiBH4-MgH2复合体系放氢性能的研究表明,其放氢量和放氢动力学随着MgH2含量的增加而增加。其放氢分为两个阶段进行,第一阶段主要为LiBH4放氢,第二阶段主要为MgH2放氢。而且放氢前后都有LiBH4存在,说明LiBH4第一步分解反应没有完全进行。过渡族金属单质Ni和Nb,氧化物TiO2和Nb2O5,以及氯化物NiCl2、FeCl2和YCl3均能改善LiBH4-MgH2复合体系的放氢性能。在本论文研究的催化剂中,Nb2O5和YCl3催化效果最好,使得LiBH4和MgH2的分解反应能够同步进行。Ni和Nb对LiBH4-MgH2复合体系的放氢量的催化效果不明显,而TiO2和Nb2O5对放氢量有相同的催化效果,YCl3的催化效果较明显,放氢量提高了2%。稀土氯化物LaCl3、CeCl3、NdCl3、SmCl3均能不同程度地提高LiBH4和MgH2的放氢量和放氢速率。LaCl3、CeCl3、NdCl3、SmCl3对MgH2放氢动力学的催化效果基本相同。就放氢量来说,NdCl3的催化效果要优于LaCl3、CeCl3、SmCl3。MgH2的放氢量和放氢速率随着温度的升高而增大。当温度达到350℃,其放氢量为7.5%,接近MgH2的理论储氢量。采用活性炭负载NdCl3能够有效提高NdCl3的分散度及提高NdCl3与MgH2的接触面积,从而有利于提高NdCl3对MgH2的催化作用。添加20wt%的NdCl3对不同摩尔比的LiBH4-MgH2复合体系都有较好的催化作用,摩尔比为1:2的LiBH4-MgH2在330℃下、1小时内能放出其理论氢容量的80%。而且,随着MgH2含量的增加,LiBH4的放氢量增加。更多还原

【Abstract】 With the rapid development of the global economy and growing energy demand, our society is faced with the problems of fossil energy depletion and ecological environment deterioration. Thus, developing new green energy and researching materials for energy conversion have great significance. Hydrogen is the ideal energy in the future. However, hydrogen storage technology is a prerequisite for large-scale applications and infrastructure of hydrogen energy. In this paper, the history and the current state of the research on LiBH4 and MgH2 have been summarized. LiBH4 and MgH2, as the representations of complex hydrides and metal hydrides, respectively, are promising hydrogen storage materials due to their higher hydrogen storage capacity. However, the harsh condition and poor kinetics of their hydriding and dehydriding are need to be further studied.Improving the kinetics of LiBH4 and MgH2 is the significance of this thesis. Firstly, high energy ball milling and catalyst doping are used to obtain LiBH4-MgH2 composite materials. Secondly, the effects of ball milling process and catalysts on the hydrogen storage properties were investigated. Furthermore, the X-ray diffraction (XRD) and scanning electron microscopy (SEM) were used to characterize the structure of LiBH4-MgH2 system after ball milling and dehydriding.It was found that with increase of the milling time, the particle size of LiBH4-MgH2 was decreased markedly while the dehydrogenation capacity and kinetics were also improved. However, the sample milled more than 10 hours could not lead to smaller particle size and better dehydrogenation properties. It was also found that vibration ball milling have the better effect than the planetary milling on the dehydriding kinetics of LiBH4-MgH2 with the same milling time and ratio of ball to powder.With respect to the LiBH4-MgH2 composite with different mole ratios, the capacity and the kinetics of dehydrogenation was enhanced with increase of the MgH2 content. The dehydrogenation was composed of two steps while the first step is decomposition of LiBH4 and the second is MgH2. However, the decomposition of LiBH4 is not fully carried out in the first step.It was found that the transition metal elemental Ni and Nb, oxides TiO2 and Nb2O5, chlorides NiCl2, FeCl2 and YCl3 all can improve the dehydrogenation property of LiBH4-MgH2. Nb2O5 and YCl3 have the best catalytic effect, which lead to the simultaneous decomposition of MgH2 and LiBH4. The catalytic effects of Ni and Nb on dehydriding capacity of LiBH4-MgH2 were not obvious. The TiO2 and Nb2O5 have similar catalytic effect. However, the YCl3 has better catalytic effect, which increased 2wt% of the dehydrogenation capacity.LaCl3, CeCl3, NdCl3 and SmCl3 all can enhance the dehydriding capacity of LiBH4 and MgH2, in which the NdCl3 has the best effect to enhance the dehydrogenation capacity of MgH2. With the temperature increasing, the dehydriding capacity of MgH2 increased. The dehydrogenation capacity reached 7.5wt% at 350℃, which closes to the theoretical hydrogen storage capacity of MgH2. Dispersion of NdCl3 in activate carbon increase the contact area of NdCl3 and MgH2 and thus enhance the catalytic effect of NdCl3 on dehydriding kinetics of MgH2.The addition of 20wt% of NdCl3 has better catalytic effects on the LiBH4-MgH2 composite with different mole ratios. LiBH4-MgH2(molar ratio 1:2) can release 80% hydrogen of their theoretical capacity at 330℃. Moreover, with the increasing of the content of MgH2, the dehydriding capacity of LiBH4 increased.更多还原