【作者】 刘述丽；

【导师】 张轲；

【作者基本信息】 沈阳师范大学 ， 应用化学， 2011， 硕士

【摘要】 日益严峻的能源危机和环境污染,使得发展清洁的可再生能源备受关注。氢能源以其可再生性和环保性好成为未来最具发展潜力的能源载体。在氢能的应用中最关键的问题是氢气的存储。在固态储氢材料中,碱金属和碱土金属-氮-氢体系拥有储氢容量高、可逆性好等优点,被认为是最有前景的储氢材料之一。本文对球磨和球磨-加热法制备高纯度LiNH2和Mg(NH2)2储氢材料的工艺进行了系统的研究,并测试了它们的热分解性能以及探讨了Mg(NH2)2-LiH储氢系统的储氢性能,得出以下结论：(1)球磨法合成LiNH2时,提高球磨罐内氨气压力和延长球磨时间均能提高合成产物LiNH2的相对纯度,最佳合成工艺为球磨罐内氨气压力0.3MPa,球磨时间为2h；按最佳工艺合成的LiNH2红外光谱图显示LiNH2的两个N-H键红外吸收峰的位置在波数为3259cm-1和3312 cm-1；XRD图谱未显示出反应物LiH的衍射峰,且其相对纯度已达到98%；其初始分解温度约在340—370℃之间,分解反应的活化能为75 kJ/mol左右。(2)球磨法+热处理合成Mg(NH2)2时,加热时氨气压力、温度、保温时间对Mg(NH2)2的合成没有明显的影响作用,而球磨时间对Mg(NH2)2的合成具有显著影响,最佳合成工艺为球磨时氨气压力为5atm,球磨8h,后处理为在3atm氨气压力下300℃热处理3h使其晶化；按最佳工艺合成的Mg(NH2)2红外光谱图显示Mg(NH2)2的两个N-H键的红外吸收分别在波数为3274cm-1和3700 cm-1处与XRD的结果相吻合。其初始分解温度在350—360℃。(3)PCT测试仪研究表明Mg(NH2)2+2.2LiH储氢系统的初始脱氢温度约为150℃,200℃以上的可逆储氢量为4.6wt%。随着温度的升高,该系统的脱氢平衡压增大,平衡压与系统组成满足范特霍夫公式,并计算其脱氢焓变和熵变分别为ΔH=42.8kJ/molH2和ΔS=149.2JK-1/molH2,自由能为ΔG=(42800-149.2×T) J/molH2。(4)吸放氢动力学研究表明该储氢系统具有较快的动力学,特别是脱氢反应在200℃以上时可在1h内结束,脱氢产物为Li2Mg(NH)2,从脱氢反应动力学可计算得到其活化能约为Ea=51.7kJ/mol。更多还原

【Abstract】 Due to serious problems caused by energy crisis and environmental pollution, much attention is focused on developing clean renewable energy. Hydrogen, for its renewable and pollution free characteristics, has become the most potential energy carrier. An important issue for the utilization of hydrogen energy is the hydrogen storage and transportation. In the solid hydrogen storage materials, alkali metals and alkaline earth metals-nitrogen-hydrogen (metal-N-H) systems possess quite high hydrogen storage capacity and good reversibility so that they are viewed as one of the most promising hydrogen storage materials. In this study, we carried out a systematic study of LiNH2 and Mg(NH2)2 prepared by ball milling, and TG analysis were employed to investigate thermo-decomposition of the two amides. Additionally, hydrogen storage properties of Mg(NH2)2-LiH system were also investigated. the results showed that:(1) When LiNH2 was synthesized by ball milling, with increasing the milling tank NH3 pressure and extending the ball milling time, the relative purity of ball milling product LiNH2 is increased. The optimization technique of synthesis Lithium amide is in condition of 0.3Mpa milling tank NH3 pressure,2h milling time. FTIR analysis showed that infrared absorption wave numbers of LiNH2 two N-H bonds are 3259cm-1 and 3312 cm-1 respectively, and no LiH but LiNH2 diffraction peak is detected in final synthesis product. At last, initial decomposition temperature of LiNH2 is within the limits of 340-370℃, and the apparent activation energy of the decomposition reaction is calculated and the value is about 75 kJ/mol;(2) When Mg(NH2)2 was prepared by two step method (ball milling then post heat-treatment), NH3 pressure, temperature and heating time in the post heat-treatment have not obvious influence on the synthesis of magnesium amide, but ball milling time has a obvious influence on the final product amide. The optimization technique of synthesis magnesium amide is in condition of 5atm primal milling NH3 pressure,8h primal milling time, and in 3atm NH3 pressure at 300oC for 3h post heat-treatment to crystallization. FTIR analysis showed that infrared absorption wave numbers of Mg(NH2)2 two N-H bonds are 3274cm-1and 3700 cm-1 respectively and this is consistent with XRD results. Finally, initial decomposition temperature of the magnesium amide is within the limits of 350-360℃.(3) Hydrogen storage performance of Mg(NH2)2-LiH (mol ratio 1:2.2) materials system was studied by an equipment of PCT(pressure-composition-Temperature).The results showed that initial dehydrogenation temperature of Mg(NH2)2-LiH Hydrogen Storage system is at about 150℃and its reversible hydrogen storage capacity is 4.6wt.% at above 200℃. Dehydrogenation equilibrium pressure of the hydrogen storage system is increasing with the increase of temperature. Equilibrium pressures and system compositions at different temperature meet the Van’t Hoff equation, therefore, enthalpy and entropy of the dehydrogenation reaction could be calculated based on the Van’t Hoff equation, and their value areΔH=42.8kJ/molH2,ΔS=149.2JK-1/molH2, and Gibbs free energyΔG= (42800-149.2×T) J/molH2 respectively.(4) Kinetics of hydrogen absorption and desorption showed that the Mg(NH2)2-LiH hydrogen storage system possess relatively fast kinetics, especially in dehydrogenation process desorption can be completed within 1 hour at above 200℃, and XRD result showed that hydrogenation products is Li2Mg(NH)2. Based on principle of kinetics, the apparent activation energy of the dehydrogenation reaction can be calculated by kinetics data of hydrogen desorption, and its value is 51.7kJ/mol.更多还原