水熱法合成的過渡金屬化合物摻雜對Li-Mg-B-H儲氫體系的改性研究
發(fā)布時間：2019-03-08 14:09
【摘要】：硼氫化鋰(LiBH4)因其18.4wt%的高儲氫容量而被認為是一種有潛力的儲氫材料。但是,LiBH4分子內(nèi)部的強鍵合作用使其具有較高的熱力學(xué)穩(wěn)定性,從而導(dǎo)致放氫溫度過高,吸放氫動力學(xué)緩慢,以及吸放氫反應(yīng)的可逆性較差,因而極大地限制了它的實際應(yīng)用。針對LiBH4吸放氫性能的改善已經(jīng)提出了多種解決方法。其中,LiBH4與MgH2復(fù)合可構(gòu)成一個具有較高儲氫容量,吸放氫動力學(xué)性能優(yōu)良的可逆儲氫體系。為進一步優(yōu)化該體系的儲氫性能,我們通過水熱反應(yīng)合成了納米棒狀La(OH)3和Zr02,以及鈦酸鹽納米管和納米片,并將它們作為催化劑前驅(qū)體加入到2LiH+MgB2復(fù)合物(2LiBH4+MgH2的放氫態(tài))中,研究它們對2LiBH4+MgH2復(fù)合儲氫材料吸放氫反應(yīng)的催化效果和機理。納米棒狀La(OH)3的摻雜對2LiH+MgB2的放氫動力學(xué)和循環(huán)吸放氫性能有著良好的改善效果。XRD測試結(jié)果表明,La(OH)3在第一次吸氫過程中轉(zhuǎn)化成為LaB6,而LaB6可以作為MgB2的形核中心,從而縮短了MgB2形核的孕育期,加速了第二步放氫反應(yīng)的進行。納米棒狀Zr02摻雜的2LiH+MgB2體系表現(xiàn)出更為優(yōu)異的吸放氫動力學(xué)性能和循環(huán)穩(wěn)定性。通過XRD, SEM和HRTEM等分析測試發(fā)現(xiàn),納米棒狀ZrO2在第一次吸氫過程中轉(zhuǎn)化為5nm大小的ZrB2納米顆粒。由于ZrB2與MgB2具有相同的結(jié)構(gòu)和極相近的晶胞常數(shù),ZrB2納米顆粒成為MgB2極佳的形核劑,因此放氫動力學(xué)性能得到了極大的提高。另外,ZrB2納米顆粒在高溫條件下具有很好的熱穩(wěn)定性和化學(xué)穩(wěn)定性,從而保證了Zr02摻雜的2LiH+MgB2復(fù)合物體系具有優(yōu)異的循環(huán)穩(wěn)定性。此外,我們還通過水熱反應(yīng)方法制備了鈦酸鹽納米管(TNTs)和鈦酸鹽納米片(TNS),并將二者作為催化劑加入到2LiH+MgB2復(fù)合物體系中。結(jié)果表明,TNTs和TNS均可顯著改善2LiH+MgB2復(fù)合物體系的放氫動力學(xué)性能,并且TNTs的催化效果比TNS更好。但TNTs摻雜的2LiH+MgB2復(fù)合物體系隨著吸放氫循環(huán)次數(shù)的增加,儲氫容量有所衰減。當前的研究工作表明,通過改變催化劑前驅(qū)體的納米結(jié)構(gòu)和大小可以控制原位生成的催化劑的納米結(jié)構(gòu),從而進一步改善體系的儲氫性能,這為改善Li-Mg-B-H體系儲氫性能提供了一條新的途徑。同時,通過比較不同成分的催化劑前驅(qū)體所產(chǎn)生的不同的催化作用,有助于理解Li-Mg-B-H體系的吸放氫反應(yīng)機理。
[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.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB34
本文編號：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.
【學(xué)位授予單位】：浙江大學(xué)
【學(xué)位級別】：碩士
【學(xué)位授予年份】：2015
【分類號】：TB34
【參考文獻】
相關(guān)期刊論文 前1條
1 詹亮,李開喜,朱星明,宋燕,呂春祥,凌立成;超級活性炭儲氫性能研究[J];材料科學(xué)與工程;2002年01期
，本文編號：2436884
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