Research On Ball Milling Process And Modification Of Mg₂Ni Hydrogen Storage Alloy Prepared By High Energy Ball Millin

Hydrogen energy systems are considered a potential alternative to current fossil fuel energy systems.With the development of hydrogen fuel cell vehicles,the requirements for hydrogen storage materials are increasing.Mg-based hydrogen storage materials have the advantages of high mass hydrogen storage density,good reversibility of hydrogen absorption and desorption,abundant resources,high safety and non-toxicity,and they have shown great potential in solid-state hydrogen storage applications.However,the high hydrogen absorption and desorption reaction temperature of Mg and the slow rate of hydrogen absorption and desorption reaction lead to great challenges in preparing high-performance hydrogen storage materials suitable for room temperature.In order to solve the above problems,Mg2Ni hydrogen storage alloy was prepared by mechanical alloying.Through XRD,SEM,TEM,PCT and other characterization methods,the effects of ball milling process parameters,transition metal element doping and carbon source composite on the composition,morphology and properties of Mg2Ni alloy were studied.The main research contents and results are as follows:(1)The ball milling process parameters for the preparation of Mg2Ni hydrogen storage alloy by mechanical alloying method were studied.It was found that a highperformance Mg2Ni hydrogen storage alloy with a partially amorphous structure could be obtained after 4 h at ball milling speed of 1000/1100 rpm and a molar ratio of Mg to Ni of 2:1(an additional 4 wt.%of Mg was added to compensate for the loss of Mg).The hydrogen storage reached 3.6 wt.%;In order to meet the demand for on-board hydrogen storage,in the study of the addition parameter of Mg,it was found that the alloy had the best hydrogen storage performance when an additional 12 wt.%Mg was added when the molar ratio of Mg and Ni was 2:1,and the hydrogen storage capacity reached 4.4 wt.%.(2)The effect of transition metal doping on the hydrogen storage performance of Mg2Ni alloy was studied.The partial substitution of the Ni side alloy by Cr and Mn was carried out to improve the hydrogen storage performance of Mg2Ni,it was found that the hydrogen storage performance was the best at 10 wt.%Cr substitution.The hydrogen absorption reached 3.7 wt.%,the thermodynamic properties were significantly improved,and the hydrogen absorption temperature was reduced by about 50 K.However,excessive Cr addition will reduce the hydrogen storage performance of the alloy.The substitution amount of Mn improved the hydrogen storage performance of Mg2Ni alloy at 20 wt.%.It can effectively reduce the activation energy to improve the kinetic properties of Mg2Ni alloy,and the addition of Mn can effectively improve the cycle performance of Mg2Ni alloy.After 20 cycles of hydrogen absorption and desorption,the maximum hydrogen storage capacity is still maintained at 3.7 wt.%.(3)The effect of carbon source(graphene and MWCNTs)composite on the hydrogen storage performance of Mg2Ni alloy was studied.It was found that the addition of carbon source had a certain improvement on the kinetics and cycling properties of Mg2Ni alloy,compared with the modification effect of graphene was better than that of MWCNTs,and the addition of graphene could effectively improve the agglomeration and welding phenomenon during the ball milling process,refine the grain and increase the specific surface area.When 3 wt.%graphene was added,the first hydrogen absorption activation time was only 20 min,which was about 70%lower than that of Mg2Ni alloy,and the hydrogen absorption was 3.65 wt.%.