Rare Earth Fluoride Preparation And Performance Study Of The Catalytic Magnesium-based Hydrogen Storage Alloy

Recently, Mg-based hydrogen storage alloy have been widely studied around the worldbecause they have merits of higher gravimetric and volumetric hydrogen storage density,lowerprice,no pollute to the environment compared to traditional methods of storage the hydrogen ina bottle with a high press,or make the hydrogen become into liquid and solid. However,most ofhydrides of Mg-based hydrogen storage alloy are very stable,and have a badhydrogenation-dehydrogenation kinetics, especially the high dehydrogenation temperature,which limit the application in public. For example,the reaction of hydride about Mg need ahigh temperature,and last a long time. Then, people made some methods to improve itshydriding/dehydriding skinetics and circle life by some extent. Such as element substitute,compound,and catalyze.Based on the previous studies,I have mixed the Rare earth fluoride with Mg-basedhydrogen storage alloy to modify its hydriding/dehydriding properties. The results are asfollows:In this article,the hydriding/dehydriding capacitiesof La_1.8Ca_0.2Mg₁₄Ni₃,La₂Mg₁₆Ni_0.5Co_0.5have been investigate in different conditions,which as-cast and after ball-milling in toluene.Theresults showed that, the absorbed activate speed of La_1.8Ca_0.2Mg₁₄Ni₃is quicker thanLa₂Mg₁₆Ni_0.5Co_0.5. The former's first absorbed hydrogen only have1.5wt.%at473K under4MPa H2. After four times cycle, it can absorbed4.3wt.%of hydrogen at473K,and the wholeprogress completed in250s; the latter can absorbed4.35wt.%of hydrogen respectively in500s.For the desorbed progress at613K under1atm H2, both of the two alloy's first two timesdesorbed progress are basically the same. From the third times, the former's initial desorbedspeed is more quickly than the latter.The La₂Mg₁₆Ni_0.5Co_0.5exhibited highest hydriding-dehydriding capacities after milled intoluene for20hours. After milled in toluene for20hours,It absorbed4.8wt%of hydrogen at473K under4MPa H2. Compared with the as-cast alloy at the same condition,its hydridingcapacities have improved0.3wt.%. And,the highest desorbed of hydrogen is4.98wt.%,at613K under0.1MPa H2. the alloy absorbed4.95wt%of hydrogen at600K under4MPa H2. TheXRD and SEM analysis indicated that after milling the particle size of the alloy becomes smaller, and parts of the alloy is amorphized to some extent, which made the alloys more easilyto be activated. Furthermore, toluene can modified magnesium-based La_1.8Ca_0.2Mg₁₄Ni₃alloyby formation of the EDA (electro donor-acceptor) complexes when milling. These factorsaltogether made the alloy show much better hydrogen storage properties after being modifiedby ball milling in toluene for20h.First,made some high-effective rare earth fluoride as catalyst by hydrothermal process.Such as LaF₃,YF₃,CeF₃,TbF₃,YbF₃,SmF₃,GdF₃,NdF₃,DyF₃and so on. In order to modifyhydrogen storage alloy's hydriding/dehydriding properties,we mixed this catalyst with hydrogenstorage alloy according to the percentage of3wt.%. The results showed that GdF₃had the bestcatalytic properties,which can improve the hydrogenation-dehydrogenation kinetics to the best,drop the react-temperature.Then mixed GdF₃to hydrogen storage alloy with different percentage by ball-milling.Whenthe percentage is5wt.%,we found the composite have the best hydrogenation-dehydrogenationkinetics. According to the study,the GdF₃have the best catalyze properties because of its thinand short nanowire,and dispersed very good. Then make the alloy particle very small,improveits surface area,increased the hydrogen absorbing channel and catalyze the decomposition ofLa_1.8Ca_0.2Mg₁₄Ni₃.