Investigation On Hydrogen Storage Properties And Mechanism Of Mechanical Alloying CeMg₁₂ Alloy

At present, magnesium base hydrogen storage alloys, including La2Mg17, Mg-Ni, RE-Mg₁₂(RE=La, Ce, Pr, Nd) were considered to be one of the most promising materials for hydrogen storage, because of their low cost, highest hydrogen capacity and abundant natural resources. The emphasis of research was focused on reducing the alloy price, improving their electrochemical cycle stability and hydrogenation/dehydrogenation kinetic performance. Mechanical alloying (MA) is a new-type method to produce hydrogen storage alloys and these alloys possess a great quantity of nanocrystalline, microcrystal and amorphous structure, which can effectively enhance the cycle stability of alloy. In this work, magnesium base CeMg₁₂ series hydrogen storage alloys were prepared by MA. In the process of experiment, the change tendency of alloy hydrogen storage properties was investigated by adjusting ball-milling, the content of Ni powder and TiF₃.Prolonging the ball-milling time can enhance the glass forming ability in the CeMg₁₂+100%Ni+0%TiF₃ alloy, increase crystal defects (such as dislocations and grain boundaries) and strengthen the anticorrosion and antioxidition ability of milling alloy, which improve the electrochemical discharge and hydrogenation kinetic property. Optimum milling time will ameliorate dramatically electrochemical kinetic property of milled alloy. However, the increasing milling time reduces dehydrogenation kinetic performance.In milling process, the addition of TiF₃ significantly enhance amorphous formation ability of CeMg₁₂+100%Ni+Y%TiF₃(Y=0, 3, 5) alloy, improving the electrochemical discharge ability, cycle stability and hydrogenation kinetic property. Moderate TiF₃ can enhance electrochemical kinetic property. Nevertheless, the addition of TiF₃ will change the thermostability of milled alloy hydride, which makes dehydrogenation kinetic performance of alloy deteriorate.The increase of Ni powder content is conducive to the glass phase formation of CeMg₁₂+Y%Ni+0%TiF₃(Y=50, 100, 150) alloy. In the meantime, Ni powder has strong electrochemical catalysis activation. The two factors work together to ameliorate electrochemical properties and hydrogenation kinetic property of alloy. The addition of Ni powder changes the composition and heat stability of alloy hydride, which reduce the dehydrogenation kinetic property of milling alloy. Electrochemical discharge PCT(Pressure-Concentration-Tempreture) curves explains the differences of milled alloy electrochemical discharge property in the sight of thermodynamics.