Study On The Hydrogen Storage Performance And Microstructure Of NaAlH₄and LiAlH₄Doping With Rare Earth Oxides

Solid hydrogen storage alloys such as complex hydrides have been explored widely dueto their high hydrogen amount, volume density and conveniences, especially NaAlH₄andLiAlH₄. In the present studies, the focus has been on NaAlH₄and LiAlH₄with addingcatalysts in order to improve their hydrogen storage capability better.This experiment choseNaAlH₄and LiAlH₄as the main raw materials, and several kinds of rare earth oxides such asLa₂O₃, CeO₂, Y₂O₃, Nd₂O₃and Gd₂O₃as catalysts to study the hydrogen storage performanceon the basis of a comprehensive description of the Complex hydrides of NaAlH₄and LiAlH₄according to current researches. All the raw stuff have been used are supplied by Industrialwithout further purification so as to have a simple and economy process. Meanwhile, we usethe method of single doped. In the experiment, we first prepared samples using a PlanetaryBall Mill. Then monitored the hydrogen desorption performance of all samples inpressure-composition-temperature（PCT） apparatus and studied the microstructure of allsamples before and after hydrogen desorption in scanning-electron-microscope（SEM）.The study of NaAlH₄doping with rare earth oxides display that1mol%CeO₂-NaAlH₄and1mol%Gd₂O₃-NaAlH₄show the best catalytic effect, and the amount of hydrogendesorption reach5.94wt%and5.92wt%, respectively. Simultaneously, different kinds ofcatalysts have a similar effect trend on the hydrogen desorption performance that themaximum dehydrogenation amount and the maximum dehydrogenation rate increase first andthen decrease under the same conditions with the increasing of catalysts concentration.Besides, all the doping samples exert the larger dehydrogenation rate than the originalNaAlH₄and there are two peaks which represents the maximum dehydrogenation rate foreach sample. In addition, the time of the hydrogen desorption decrease visibly. For example,to achieve the same hydrogen amount about5.50wt%of the theoretical value of NaAlH₄, it isproved that1mol%Nd₂O₃-NaAlH₄and1mol%Gd₂O₃-NaAlH₄samples lower thedehydrogenation time97and75min than NaAlH₄,respectively. The SEM images reveal thatthe crystalline morphology of power particles of the samples after ball milling are bulky anduneven with different size and shape forming flocculent structure. The effect of catalysts and different doping amount on microstructure are not very clear.The study of LiAlH₄doping with rare earth oxides manifest1mol%Y₂O₃-LiAlH₄and0.5mol%Y₂O₃-LiAlH₄have the best catalytic effect and the amount of hydrogen desorptionreach7.23wt%and6.73wt%. Besides, different kinds of catalysts have a similar effect trendon the hydrogen desorption performance of LiAlH₄, it is that the maximum dehydrogenationamount and the maximum dehydrogenation rate increase first and then decrease under thesame conditions with the increasing of catalysts concentration from0mol%to6mol%.Moreover, all the samples doped with catalysts lower the dehydrogenation time about10-40min. The SEM images reveal that the crystalline morphology the samples after ball millingare bulky and uneven with different size and shape forming flocculent structure, and there arebroken course including a lot of pore structure. The microstructure of the samples underheating manifests a kind of porous structure like honeycomb visibly. It is the same withNaAlH₄,the microstructure of samples of LiAlH₄can not display obvious regular change withthe increase of the catalysts.