Study on the Complex Li-N-H Hydrogen Storage System

Nowadays the developments of clean energy technologies become more and more necessary andimportant. Hydrogen-powered vehicles are a promising alternative to the current fossil fuel basedvehicle infrastructure. However, so far there is still no hydrogen storage material which can fit thestandards for an on-board hydrogen storage system. On this background, this work deals with the development of a hydrogen storage material. The focus isput on the Lithium amide + Lithium hydride (LiNH$_{2}$+LiH) hydrogen storage system because of its hightheoretical capacity and relatively low desorption temperature. Moreover, Lithium amide + Magnesiumhydride (LiNH$_{2}$+MgH$_{2}$) as an alternative system was also briefly studied. The aims of this work are to achieve a deeper understanding of the reaction mechanism with the help ofmicrostructural and thermodynamic studies, building a model to describe the sorption process and thento improve the system properties. As the desorption from LiNH$_{2}$ particles is the first step of the desorption process of the LiNH$_{2}$+LiH system, the properties and sorption behavior of LiNH$_{2}$ sample materials were studied separately first. Sothe work in this thesis can be mainly divided into two parts: LiNH$_{2}$ samples and LiNH$_{2}$+LiH samples. Inorder to activate the sample materials, both dry ball milling and wet ball milling (with tetrahydrofuran)methods were used. Boron nitride was mainly applied as catalyst. Furthermore, titanium tetrachloride was also used as an alternative additive. The sorption behaviors were studied with the help of avolumetric and a gravimetric system. Further investigation methods include X-ray Diffraction (XRD) method, Scanning Electron Microscope (SEM), Brunauer–Emmett–Teller (BET) method, DifferentialThermal Analysis (DTA)/ Thermo Gravimetric Analysis (TGA)/ Mass Spectrometry (MS), and others.The results obtained in this work show that no obvious microstructure differences have been foundbetween the wet ball milled and dry ball milled samples. Boron nitride (BN) as additive has improved therecyclability of the LiNH$_{2}$+LiH system clearly. The activation energy of the desorption reaction of wetanddry ball milled samples have been reduced with BN as additive. BN did neither influence thecrystallite sizes nor the particle sizes of both of the LiNH$_{2}$ and LiNH$_{2}$+LiH as milled samples clearly. However, it has been found that BN can stabilize the crystallite sizes of LiNH$_{2}$+LiH samples during thehigh temperature desorption and absorption processes. Titanium tetrachloride as alternative additive had also improved the recyclability of LiNH$_{2}$+LiH samples. However, the resulted system pressure wasnot as high as that of the LiNH$_{2}$+LiH samples with BN as additive. BN did not improve the recyclability ofthe LiNH$_{2}$+MgH$_{2}$ samples. Apart from the experimental work, a model to describe the desorption behavior of LiNH$_{2}$ particles was developed to understand the desorption process