Investigations On Hydrogen Storage Properties Of The2LiNH₂-MgH₂Composite Material

The Li-Mg-N-H complex hydrides are a very promising hydrogen storage system for application because of thire favorable reversible hydrogen capacity. This thesis mainly studies the effect of ball-milling time and different kinds of additives on this composite material. The initial material is a mixture of LiNH2and MgH2in a molar ratio of2:1. In experiments, samples were prepared by ball-milling method and the performances of samples were tested by the X-ray diffraction, absorption/desorption kinetics and thermal analysis means.The sample which was milled for3h could absorb hydrogen3.89wt.%in total and complete90%of its maximum hydrogen absorption capacity in135s and its desorption amount was3.95wt.%. After considering both the hydrogen absorption and desorption properties of samples milled for different time,3h was finally selected as the optimal ball-milling time and in subsequent experiments all the samples were milled for3h.The samples with5wt.%titanium and its compounds (Ti、TiH2、TiF3、TiCl3、TiO2) had lower decomposition temperature and faster hydrogen sorption rate. The sample with Ti owned the maximum hydrogen desorption capacity of4.32wt.%while the admixing of TiF3led to the largest amount of hydrogen absorption. It could absorp hydrogen4.01wt.%in isothermal test and5.4wt.%in non-isothermal test. In subsequent experiments the percent of Ti and TiF3were altered and the results showed that the added amount of additives was suitable when between2.5wt.%and5wt.%and when to7.5wt.%the reversible hydrogen capacity of samples showed a declining trend.The samples with5wt.%metal oxide (V2O5、CuO、Nb2O5、Cr2O3、ZrO2) had lower decomposition temperature and slower hydrogen sorption rate. The sample with Nb2O5owned the maximum hydrogen desorption capacity of5.02wt.%while the admixing of ZrO2led to the largest amount of hydrogen absorption. It could absorp hydrogen4.24wt.%in isothermal test and5.45wt.%in non-isothermal test. In subsequent experiments the percent of Nb2O5and ZrO2were altered and the results showed that the added amount of additives was suitable when between2.5wt.%and5wt.%and when to7.5wt.%the reversible hydrogen capacity of samples showed a declining trend.