An Investigation On Hydrogen Storage Properties Of Li-N-H Series Newly Hydrogen Storage Materials

As development of varied alloy hydrogen storage material becoming riper day by day, development of higher quality/volume percentage hydrogen storage material become the new subject. For its high hydrogen density, much attention has paid to metal complex and some new-type inorganic compound materials in recent years. Li-N-H series material have a theory hydrogen density of 10.4wt%, it is one of the research hotspot about the hydrogen storage field in the world at present. However, in our country, except Yong Chen etc of Shenyang National Laboratory for material science had research on hydrogen desorption performance of LiNH₂/MgH₂, there is no relevant article report any more. In this thesis, the synthetic factor of initial Li₃N material is studied;then through XRD phase qualitative analysis and hydrogen absorption quantitative analysis, hydrogen absorption properties of Li₃N under different temperature were studied, condition of absolute hydrogenated to LiNH₂ +2LiH is confirmed;P-C-T curve test and TG/DTA thermal analysis were used to carry on the research of hydrogen desorption performance of LiNH₂ +2LiH;and compared the hydrogen storage properties of ball milled and catalyst-added sample. The detailed resluts are as follows.1. Under certain nitrogen pressure and different temperature, influences of synthesisLi₃N were compared. It is shown that temperature level only reflects on reaction time needed, not do any to phase composed. While temperature is relatively high, time needed is relatively short, and slightly in difference, therefore, 200 ℃ of litter higher than the Li melting points was selected for reaction temperature.2. On the basis of Li₃N synthesized, hydrogen absorption performances were studied. P-C-T curve test were carried under lower hydrogen pressure, the result shown that, for lower pressure and temperature, absorption curve of Li₃N only appeared one platform, and maximum absorption amount was 3.24wt% at 250℃ reaction temperature. While under 4⁵MPa hydrogen pressure and different temperature, XRD phase qualitative analysis and weighted quantitative analysis revealed that, hydrogen absorption amount just reach 1.87wt% at 200℃;9.5wt% at 400℃, in which state reaction was complete, and the difference to the theory quantity was resulted from existing of LiOH and Li₂O impurities. When Li₃N was been ball milled, the impurity of stainless steel composition took shape, the probable phase was AlCo, AINi, Fe₂₄N₁₀, Fe₂SiTi and Fe₃N, existence of which had influence onreaction kinetics greatly;and after ball milling, the crystal space group changed P6/mmm into P63/mmc, results in declination of structure stability;also there was small amount of T1N0.9 formed while add Ti for ball milling.3. U3N was fully hydrogenated into LiNH2+2LiH, then its hydrogen desorption performance in different reaction terms were studied. High-temperature P-C-T curve tests have shown that, amount of about 2.75wt% hydrogen can released in 400°C after 72h reaction;and up to 3.33wt% in 300°C while after 108h reaction. This indicated that it was still incomplete to release all of hydrogen though reaction time enough long, poor reaction kinetics may have certain relations with vacuity. TG/DTA thermal analysis results indicated, while rising from room temperature to 400 °C with the heating rate of 3k/min and 8k/min respectively and kept the 400 °C temperature for lh, the total weight losses (that is hydrogen released) were all larger than 6.5%;the initial endothermic temperature were at 270 °C approximately and the endothermic peak were above 350°C. Corresponding to the first step in hydrogen desorption reaction of LiNH2+2LiH. The second step of reaction was more difficult to proceed for its low platform.4. Compared the influence of all ball milled process to hydrogen storage properties;we can learned that impurities of stainless steel were produced in all the cases. For existence of these impurities, in P-C-T testing process, hydrogen absorption of U13N and hydrogen desorption of LiNH^/LiH become more difficult to occur;TG/DTA thermal analysis results indicated that ball milling caused grain of powder sample decreased greatly. In the thermal analysis figure, instability and weight increase appeared in different degrees. Hydrogen amount dehydrogenated decreased to some extent, however, initial endothermic/desorption temperature diminished remarkably, amplitude up to more than 50°C. Intermittence ball milling was adopted, kept the total milling time not change, shorten each time of milling could reduce temperature rising and benefit to prevent harmful heat effect. Amount of hydrogen desorption increased, initial endothermic/desorption temperature reduced also. And when Ti-added in ball milling process, its hydrogen desorption performance improved greatly. When the way of Ti-added changed, weight increase can be diminished, and hydrogen desorption amount increased much more.