Studies On Preparation And Hydrogen Generation Performance Of High Capacity Al-Based Composites（Al-Li₃AlH₆/Al-NaMgH₃）

In this paper, materials with high capacity of H₂ generation have been successfully prepared by ball milling Al with home-made fresh Li₃AlH₆, home-made fresh NaMgH₃ powder and other additives, the specific research contents are as follows:The Al-Li₃AlH₆-CaO composite has been synthesized by ball milling. The influence of CaO on the corrosion resistant of the Al-Li₃AlH₆ is investigated. The result shows added 35 wt% CaO into Al-Li₃AlH₆, the Al-Li₃AlH₆-CaO exhibits well corrosion resistant performance. Its hydrogen yield only decreases by 18.8% placing the material in the air for 30 days. However, the hydrogen yield of the Al-Li₃AlH₆ drops by 45.4% at the same condition for 5 days. Meanwhile, the results also indicate that the increase of the amount of added CaO can enhance the hydrogen generation yield. The yield increases by 40.1% when the amount of added CaO is 30 wt%, These are attributed to the CaO can prevent the Al powder contact with O2 and ware vapor in the air; and produce Ca（OH）₂ of the alkaline environment as meets water, which is conducive to the Al-H₂ O reaction.Al-NaMgH₃ Composite has prepared by high energy ball-milling method. Results show that the hydrogen production performance of Al-NaMgH₃ is obviously enhanced by increasing the content of NaMgH₃. When the content of NaMgH₃ is 20 wt%, the weight ratio of ball to material is 60:1 and the ball-milling time is 7 h, prepared material has the best performance of hydrogen generation. The hydrogen generation properties of Al-15 wt%NaMgH₃ composite are studied at different temperatures. It indicates that doping NaMgH₃ in Al power can reduce activation energy and enhance the reaction activity of system. The mechanism study shows that NaMgH₃ can react with water itself to release H₂ and increase the H₂ generation capacity of the material. At the same time, releasing heat and producing alkaline environment promote the Al-H₂ O reaction as NaMgH₃ reacts with water. But, Mg（OH）₂ produced by hydrolysis of NaMgH₃ can form new compound with Al（OH）₃ on the surface of Al. The new compound Mg4Al2（OH）14 can impede the proceeding of the Al-H₂ O reaction. This leads to H₂ generation yield is low for Al-NaMgH₃ Composite.Ternary system has been prepared by ball milling the mixture of Al, NaMgH₃ and different metal power. Result obtained show that Bi have the best effect for the ternary composites. Al-20 wt%NaMgH₃-10 wt%Bi can produce 1057.6 m L/g with H₂ yield of 85.2%. Comparing to Al-NaMgH₃, the yield of Al-20 wt%NaMgH₃-10 wt%Bi increases by 41.5%. Based on the research of ternary composite, we prepared the quaternary systems by doping mineral salt or metal hydride. Li₃AlH₆ has the best performance between the new additives. Result shows that Al-20 wt%NaMgH₃-5 wt%Bi-5 wt%Li₃AlH₆ can produce 1379.8 m L/g with conversion efficiency closing to 100%.