Microstructures And Electrochemical Properties Of The As-milled La_2-xPr_xMg₁₆Ni?x=0.1?0.4?+Y Wt.%Ni Hydrogen Storage Alloys

In this paper,as-cast alloy La2-xPrxMg16Ni(x=0.1,0.2,0.3,04)was prepared by vacuum induction melting.The composite hydrogen storage alloy powder was prepared by grinding the as-cast alloy by 200 mesh screen with 0,100,150 and 200 wt.%Ni powder for 10 h,20 h,30 h and 40 h,respectively.The phase structure of the composite hydrogen storage alloy powder was analyzed by XRD and the morphology of the composite hydrogen storage alloy powder was observed by SEM electron microscope.The life,capacity,full charge and half charge of alloy electrode were measured by LAND battery tester.The open circuit potential,charge transfer impedance(Rct)limit current density(IL)and hydrogen diffusion coefficient(D)of the alloy were measured by SI 1280B multifunction electrochemical workstationThe effects of Pr substitution on the microstructure,electrochemical and kinetic properties of La2-xPrxMg16Ni+200 wt.%Ni(x=0.1,0.2,0.3,0.4)alloy after ball milling for 20 h were studied.The results show that the microstructure of the ball-milled alloy La2-xPrxMg16Ni+200 wt.%Ni(x=0.1,0.2,0.3,0.4)is composed of the Ni main phase and a small amount of Mg2Ni secondary phase.The substitution of Pr for La contributes to the formation of amorphous phase.The electrochemical measurements show that the discharge capacity,cycle stability both increase with the increase of Pr substitution and then At Pr(x=0.2),the maximum values are 1009.7 mAh/g and 50.99%,respectively.And the kinetic measurements show that HRD,the limit current density IL and the hydrogen diffusion coefficient D both increase with the increase of Pr substitution and then decrease.At Pr(x=0.2),the maximum values are 72.8%,2439 mA/g and 9.6×10-11 cm2/s,respectively.With the increase of the substitution amount of Pr,the discharge potential characteristics of the alloy were obviously improved.The change trend of electrochemical impedance spectroscopy is that the electrochemical impedance(Rct)of alloy surface decreases first and then increases.When the substitution of Pr is 0.2,the open circuit potential is the most positive and has strong corrosion resistanceThe effect of Ni content on microstructure,electrochemical properties and kinetic properties of La1.8Pr0.2Mg16Ni+y wt.%Ni(y=0,100,150,200)alloy after ball milling for 20 h were studied in this paper.The results show that the microstructure of ball-milled alloy La1.8Pr0.2Mg16Ni+y wt.%Ni(y=0,100,150,200)is composed of La2Mg17,Mg2Ni and Ni phases.With the increase of Ni content,the La2Mg17 phase and Mg2Ni phase gradually disappear,and the nano/amorphous phase is obvious.The electrochemical and kinetic measurements show that the maximum discharge capacity increases 55 times from 18.5 mAh/g to 1009.7 mAh/g when the Ni content increases from 0 wt.%to 200 wt.%;the capacity retention rate of the alloy increased from 43.34%to 84.47%for 50 cycles,high rate discharge performance of HRD1500 increased from 55.02%to 72.9%,the limiting current density(IL)is from 396 mA/g to 2439 mA/g,and the hydrogen diffusion coefficient(D)is from 4.67×10-11 cm2/s to 9.60×10-11 cm2/s.The change trend of electrochemical impedance spectroscopy is that the electrochemical reaction impedance(Rct)on the alloy surface increases gradually,that is,the charge transfer resistance increases.The effects of milling timelO h,20 h,30 h,40 h on the microstructure,electrochemical properties and kinetic properties of ball-milled La1.8Pr0.2Mg16Ni+200 wt.%Ni alloy were studied.The results show that the micro structure of the ball-milled La1.8Pr0.2Mg16Ni+200 wt.%Ni alloy is composed of the Ni main phase and a small amount of Mg2Ni secondary phase.It is found that the grain refinement of the alloy is obvious,and the milling time is helpful to the formation of amorphous phase.The electrochemical measurements show that the discharge capacity and cycle stability both increase with the increase of ball milling time and then decrease.Ball milling for 20 h.,the maximum values are 1009.7 mAh/g,55.15%,respectively.And the kinetic measurements show that HRD,the limit current density IL and the hydrogen diffusion coefficient D both increase with the increase of ball milling time and then decrease.Ball milling for 20 h.,the maximum values are 72.70%,2439 mA/g and 9.60×10-11 cm2/s,respectively.The change trend of electrochemical impedance spectroscopy is that the electrochemical impedance(Rct)of alloy surface decreases first and then increases.After ball milling for 20 h,the electrochemical impedance(Rct)of the alloy surface is minimum,that is to say,the charge transfer ability of the alloy electrode surface is increased.