水热法合成的过渡金属化合物掺杂对Li-Mg-B-H储氢体系的改性研究
发布时间：2019-03-08 14:09
【摘要】：硼氢化锂(LiBH4)因其18.4wt%的高储氢容量而被认为是一种有潜力的储氢材料。但是,LiBH4分子内部的强键合作用使其具有较高的热力学稳定性,从而导致放氢温度过高,吸放氢动力学缓慢,以及吸放氢反应的可逆性较差,因而极大地限制了它的实际应用。针对LiBH4吸放氢性能的改善已经提出了多种解决方法。其中,LiBH4与MgH2复合可构成一个具有较高储氢容量,吸放氢动力学性能优良的可逆储氢体系。为进一步优化该体系的储氢性能,我们通过水热反应合成了纳米棒状La(OH)3和Zr02,以及钛酸盐纳米管和纳米片,并将它们作为催化剂前驱体加入到2LiH+MgB2复合物(2LiBH4+MgH2的放氢态)中,研究它们对2LiBH4+MgH2复合储氢材料吸放氢反应的催化效果和机理。纳米棒状La(OH)3的掺杂对2LiH+MgB2的放氢动力学和循环吸放氢性能有着良好的改善效果。XRD测试结果表明,La(OH)3在第一次吸氢过程中转化成为LaB6,而LaB6可以作为MgB2的形核中心,从而缩短了MgB2形核的孕育期,加速了第二步放氢反应的进行。纳米棒状Zr02掺杂的2LiH+MgB2体系表现出更为优异的吸放氢动力学性能和循环稳定性。通过XRD, SEM和HRTEM等分析测试发现,纳米棒状ZrO2在第一次吸氢过程中转化为5nm大小的ZrB2纳米颗粒。由于ZrB2与MgB2具有相同的结构和极相近的晶胞常数,ZrB2纳米颗粒成为MgB2极佳的形核剂,因此放氢动力学性能得到了极大的提高。另外,ZrB2纳米颗粒在高温条件下具有很好的热稳定性和化学稳定性,从而保证了Zr02掺杂的2LiH+MgB2复合物体系具有优异的循环稳定性。此外,我们还通过水热反应方法制备了钛酸盐纳米管(TNTs)和钛酸盐纳米片(TNS),并将二者作为催化剂加入到2LiH+MgB2复合物体系中。结果表明,TNTs和TNS均可显著改善2LiH+MgB2复合物体系的放氢动力学性能,并且TNTs的催化效果比TNS更好。但TNTs掺杂的2LiH+MgB2复合物体系随着吸放氢循环次数的增加,储氢容量有所衰减。当前的研究工作表明,通过改变催化剂前驱体的纳米结构和大小可以控制原位生成的催化剂的纳米结构,从而进一步改善体系的储氢性能,这为改善Li-Mg-B-H体系储氢性能提供了一条新的途径。同时,通过比较不同成分的催化剂前驱体所产生的不同的催化作用,有助于理解Li-Mg-B-H体系的吸放氢反应机理。
[Abstract]:Lithium borohydride (LiBH4) is considered as a potential hydrogen storage material because of its high hydrogen storage capacity of 18.4 wt%. However, the strong bonding of LiBH4 molecules makes it have high thermodynamic stability, which leads to high temperature of hydrogen desorption, slow kinetics of hydrogen absorption and desorption, and poor reversibility of hydrogen absorption and desorption reaction, which greatly limits its practical application. In view of the improvement of hydrogen absorption and desorption performance of LiBH4, a variety of solutions have been put forward. Among them, the composite of LiBH4 and MgH2 can form a reversible hydrogen storage system with high hydrogen storage capacity and excellent kinetic properties of hydrogen absorption and desorption. In order to further optimize the hydrogen storage performance of the system, nanorods of La (OH) 3 and Zr02, titanate nanotubes and nanotubes were synthesized by hydrothermal reaction. They were added to the 2LiH MgB2 complex (2LiBH4 MgH2) as catalyst precursors to study their catalytic effect and mechanism for the hydrogen absorption and desorption reaction of 2LiBH4 MgH2 composite hydrogen storage materials. The doping of nanorod La (OH) 3 has a good effect on the hydrogen desorption kinetics and cycle hydrogen absorption and desorption performance of 2LiH MgB2. XRD results show that, La (OH) 3 is converted into LaB6, during the first hydrogen absorption process. However, LaB6 can be used as the nucleation center of MgB2, which shortens the gestation period of MgB2 nucleation and accelerates the second step of hydrogen release reaction. The nanorod-like Zr02-doped 2LiH MgB2 system exhibits better hydrogen absorption and desorption kinetics and cycle stability. It was found by XRD, SEM and HRTEM that nanorod-like ZrO2 was transformed into 5nm-sized ZrB2 nanoparticles during the first hydrogen absorption process. Because ZrB2 and MgB2 have the same structure and close cell constant, ZrB2 nanoparticles become the best nucleating agent for MgB2, so the kinetic properties of hydrogen release have been greatly improved. In addition, ZrB2 nanoparticles have good thermal stability and chemical stability at high temperature, thus ensuring the excellent cycle stability of Zr02-doped 2LiH MgB2 composite system. In addition, titanate nanotubes (TNTs) and titanate nanoparticles (TNS),) were prepared by hydrothermal reaction and added into the 2LiH MgB2 composite system as catalysts. The results showed that both TNTs and TNS could significantly improve the kinetics of hydrogen release of 2LiH MgB2 complex, and the catalytic effect of TNTs was better than that of TNS. However, the hydrogen storage capacity of TNTs-doped 2LiH MgB2 complex decreases with the increase of hydrogen absorption and desorption cycles. The present research shows that the nano-structure of in-situ formed catalyst can be controlled by changing the nanostructure and size of the catalyst precursor, so as to further improve the hydrogen storage performance of the system. This provides a new way to improve the hydrogen storage performance of Li-Mg-B-H system. At the same time, it is helpful to understand the mechanism of hydrogen absorption and desorption in Li-Mg-B-H system by comparing the different catalytic effects of catalyst precursors with different components.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34
本文编号：2436884
[Abstract]:Lithium borohydride (LiBH4) is considered as a potential hydrogen storage material because of its high hydrogen storage capacity of 18.4 wt%. However, the strong bonding of LiBH4 molecules makes it have high thermodynamic stability, which leads to high temperature of hydrogen desorption, slow kinetics of hydrogen absorption and desorption, and poor reversibility of hydrogen absorption and desorption reaction, which greatly limits its practical application. In view of the improvement of hydrogen absorption and desorption performance of LiBH4, a variety of solutions have been put forward. Among them, the composite of LiBH4 and MgH2 can form a reversible hydrogen storage system with high hydrogen storage capacity and excellent kinetic properties of hydrogen absorption and desorption. In order to further optimize the hydrogen storage performance of the system, nanorods of La (OH) 3 and Zr02, titanate nanotubes and nanotubes were synthesized by hydrothermal reaction. They were added to the 2LiH MgB2 complex (2LiBH4 MgH2) as catalyst precursors to study their catalytic effect and mechanism for the hydrogen absorption and desorption reaction of 2LiBH4 MgH2 composite hydrogen storage materials. The doping of nanorod La (OH) 3 has a good effect on the hydrogen desorption kinetics and cycle hydrogen absorption and desorption performance of 2LiH MgB2. XRD results show that, La (OH) 3 is converted into LaB6, during the first hydrogen absorption process. However, LaB6 can be used as the nucleation center of MgB2, which shortens the gestation period of MgB2 nucleation and accelerates the second step of hydrogen release reaction. The nanorod-like Zr02-doped 2LiH MgB2 system exhibits better hydrogen absorption and desorption kinetics and cycle stability. It was found by XRD, SEM and HRTEM that nanorod-like ZrO2 was transformed into 5nm-sized ZrB2 nanoparticles during the first hydrogen absorption process. Because ZrB2 and MgB2 have the same structure and close cell constant, ZrB2 nanoparticles become the best nucleating agent for MgB2, so the kinetic properties of hydrogen release have been greatly improved. In addition, ZrB2 nanoparticles have good thermal stability and chemical stability at high temperature, thus ensuring the excellent cycle stability of Zr02-doped 2LiH MgB2 composite system. In addition, titanate nanotubes (TNTs) and titanate nanoparticles (TNS),) were prepared by hydrothermal reaction and added into the 2LiH MgB2 composite system as catalysts. The results showed that both TNTs and TNS could significantly improve the kinetics of hydrogen release of 2LiH MgB2 complex, and the catalytic effect of TNTs was better than that of TNS. However, the hydrogen storage capacity of TNTs-doped 2LiH MgB2 complex decreases with the increase of hydrogen absorption and desorption cycles. The present research shows that the nano-structure of in-situ formed catalyst can be controlled by changing the nanostructure and size of the catalyst precursor, so as to further improve the hydrogen storage performance of the system. This provides a new way to improve the hydrogen storage performance of Li-Mg-B-H system. At the same time, it is helpful to understand the mechanism of hydrogen absorption and desorption in Li-Mg-B-H system by comparing the different catalytic effects of catalyst precursors with different components.
【学位授予单位】：浙江大学
【学位级别】：硕士
【学位授予年份】：2015
【分类号】：TB34
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相关期刊论文 前1条
1 詹亮,李开喜,朱星明,宋燕,吕春祥,凌立成;超级活性炭储氢性能研究[J];材料科学与工程;2002年01期
，本文编号：2436884
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