Study On Microstructure And Electrochemical Properties Of Ball-milled PrMg₁₂ Hydrogen Storage Alloy

Environmental pollution accelerates the exploration of hydrogen energy,and hydrides are the first choice for hydrogen storage.RE-Mg-based alloys become the most promising hydrogen storage materials because of their high hydrogen storage capacity and electrochemical theoretical capacity.They can not only store hydrogen through gaseous hydrogenation,but also participate in electrochemical reactions to expand the development of power batteries.In this paper,different Ni and graphene contents were added in the PrMg₁₂2 during the ball milling process to test the microstructure,electrochemical properties such as discharge capacity,cyclic stability,high rate discharge performance and so on,limiting current density,hydrogen diffusion coefficient and other dynamic properties were also tested.Firstly,PrMg₁₂2 alloy was prepared by melting,and then ball milled with 50 wt.%,100 wt.%,150 wt.%and 200 wt.%Ni respectively.The phase composition and microstructure of the alloy were analyzed by XRD and HRTEM.The results showed that the main phase of the alloy was Ni phase,the secondary phase were Mg₂Ni and PrMg₁₂2 phase after adding Ni.As the milling time increased to 40h,PrMg₁₂2 phase disappears.The electrochemical properties of the alloy showed that Ni can improved the maximum discharge capacity and reach the optimum value when the amount of Ni was200 wt%.When the milling time was 10h-40h,the maximum discharge capacity was 47mAh/g,280 mAh/g,680 mAh/g and 730 mAh/g respectively,and the cycle stability and high rate discharge performance were improved.The results showed that under the same milling time,the maximum current density of each component alloy was 0.058mA/g,0.175 mA/g,0.293 mA/g and 0.352 mA/g,respectively.when the amount of Ni was 200 wt.%,which effectively promotes the diffusion of hydrogen and improves the effect obviously.Secondly,the effects of different milling time?10h?20h?30h and 40h?on the microstructure,electrochemical and dynamic properties of the alloy were studied.The results showed that with the increase of milling time,the main phase of the alloy was Ni phase,and the secondary phase changes from Mg₂Ni and PrMg₁₂2 phase to Mg₂Ni phase.In the process of x=50 rising to 200,the maximum discharge capacity was 19 mAh/g,92 mAh/g,340 mAh/g and 730 mAh/g respectively;the discharge capacity was 0.065wt.%,1.22 wt.%,3.72 wt.%and 3.78 wt.%respectively.The high rate discharge performance,limiting current density and hydrogen diffusion coefficient of the alloy were also the best at 40 h.Finally,PrMg₁₂+200wt.%Ni+y wt.%graphene?y=3?6?9?12?hydrogen storage alloy was prepared by adding graphene with better Electrocatalytic Property.The results showed that with the increase of graphene,the phase structure of the alloy changes from Ni and Mg₂Ni phase to Ni phase as the main phase and Mg₂Ni phase and graphene phase as the secondary phase.The maximum discharge capacity and high rate discharge performance of the alloy first increased and then decreased.When y=6 wt.%,the maximum discharge capacity of the alloy was 979 mAh/g and the best high rate discharge performance was 49.9%.