Mg(NH2)2的合成以及Mg(NH2)2-LiH的储氢性能研究

Synthesis of Mg (NH2)2 and Hydrogen Storage Properties of Mg (NH2)2–LiH System

摘要:

通过机械球磨的方法，将MgH2粉末与高纯NH3球磨反应后在300 ℃下热处理晶化，制备出了高纯度的Mg(NH2)2。在150~240 ℃的温度范围内，对Mg(NH2)2+2.2LiH（摩尔比）储氢体系的储氢性能进行了研究，结果发现，在系统脱氢后的产物为Li2Mg(NH)2。放氢动力学揭示了该系统在200~240 ℃时可逆储氢量可达4.5%（质量分数）左右。该系统在150 ℃开始脱氢，在动力学数据的基础上可以计算出其活化能为51.7 kJ/mol。此外，脱氢反应的焓变和熵变可由P-C-T曲线得到，其值分别为42.8 kJ/mol H2和149.2 J·K-1/mol H2。

Abstract:

Mg(NH2)2 was synthesized first by high energy milling MgH2 powder in a 99.995% NH3 atmosphere and then via crystallization heat treating at 300 ℃, and the hydrogen storage properties of Mg(NH2)2+2.2LiH (molar ratio) were investigated in the temperature range of 150~240 ℃. It is found that mechanical milling of Mg(NH2)2 and LiH with molar ratio 1:2.2 followed by heat treatment under static hydrogen pressure and dehydrogenating at 208.5 ℃ yields the desired reversible hydrogen storage phase:Li2Mg(NH)2. Desorption kinetics reveal that the reversible hydrogen capacity for the system can reach 4.5wt% in the temperature range of 200~240 ℃.The system starts to dehydrogenate at 150 ℃ and the Arrhenius activation energy Ea of desorption reaction can be determined to be 51.7 kJ/mol H2 based on the data of kinetics. Additionally, the dehydrogenating reaction enthalpy (△H) and entropy (△S) are calculated to be 42.8 kJ/mol H2 and 149.2 J·K-1/mol H2, respectively, by P-C-T measurements.