Study On Purification Of Rare Earth Hydrogen Storage Materials

LaNi₅alloy can absorb and desorb hydrogen in the equilibrium process according to the designed temperature and pressure,and can be used for hydrogen separation and purification by virtue of the strong absorption and selective adsorption of hydrogen by its hydride.However,LaNi₅alloy is easy to be poisoned by impurity gas and fail.In order to meet the practical application needs,the anti-poisoning performance of LaNi₅alloy should be improved.Based on this,the doping modification of rare earth elements and the surface modification on hydrogen absorption and poisoning resistance of LaNi₅alloy were studied in this paper.（1）La_0.75Ce_0.25Ni_5-xMn_x（x=0,0.1,0.2,0.3）series alloys doped with rare earth are all composed of single-phase LaNi₅phase.With the increase of Mn substitution for Ni,the volume of the alloy cell increases,the plateau pressure of the alloy decreases,the hysteresis decreases,but the hydrogen storage capacity remains unchanged.The hydrogen absorption rate of the alloy can be saturated within 200s,and the hydrogen absorption rate increases with the increase of Mn content.It is proved that Mn doping can realize the regulation of the plateau pressure of the alloy without affecting the hydrogen storage capacity and kinetics of the alloy.（2）The effect of substituting Co,Mn and Al on hydrogen storage properties of Lai5alloy was investigated.The main phase of the rare-earth doped LaNi_4.25（Co、Mn、Al）_0.75alloy is LaNi₅phase,the volume of the alloy cell increases with the increase of the atomic radius,and the platform pressure is LaNi_4.25Al_0.75<LaNi_4.25Mn_0.75<LaNi_4.25Co_0.75<LaNi_5.At 383 K,the hydrogen storage capacity of LaNi_4.25Co_0.75and LaNi_4.25Mn_0.75alloys can reach 1.34 wt.%,while the hydrogen storage capacity of LaNi_4.25Al_0.75alloy is relatively small,which can only reach about 1.08wt.%.LaNi_4.25Mn_0.75alloy has the highest hysteresis and slope factors.The hydrogen absorption rate of LaNi_4.25Al_0.75and LaNi_4.25Mn_0.75alloys is faster,while LaNi_4.25Co_0.75alloys have the best pulverization resistance.（3）In the presence of O₂,the effects of different doping elements,different oxygen concentration and different temperature on the anti-poisoning properties of LaNi₅alloy were studied.In hydrogen containing 1000ppm O₂impurity gas,LaNi₅and LaNi_4.25（Co,Mn,Al）_0.75alloys adsorbed not only H₂but also impurity O₂during the poisoning process,and a certain amount of O₂in the atmosphere was converted into H₂O.In 17 poisoning cycles,LaNi_4.25Mn_0.75alloy showed better anti-poisoning performance than LaNi_4.25Co_0.75alloy.Compared with 1000ppm O₂,5000ppm O₂has more obvious degradation on hydrogen absorption performance of the alloy.At 110℃,the anti-poisoning effect of the alloy is the best.（4）The effects of surface modification on hydrogen storage and anti-poisoning properties of LaNi_4.25Co_0.75alloy by ball milling after mixing with 5wt%MXene were studied.It was found that the ball milling had no effect on the alloy phase transformation,but the hydrogen storage of MH/MXene alloy was lower with the increase of the ball milling time.In the hydrogen containing 300ppm CO,the hydrogen storage capacity of the original alloy LaNi_4.25Co_0.75decreased by 84.5%after being poisoned,while the surface modified alloy with MXene after being ball milled for 10h and 15h only decreased by12.6%and 9.9%after being poisoned,and the hydrogen absorption rate increased significantly.SEM and EDS images showed that MXene was uniformly loaded on the surface of the alloy particles,indicating that the MXene phase loaded on the surface of the alloy played a role in the resistance to CO poisoning.