Phase Structure And Electrochemical Performances Of The As-cast And Quenched (Mg_2.4Ni)_100-x RE_x(RE=La, Ce; X=0-20) Hydrogen Storage Alloys

In order to improve its hydrogen storage properties, the Mg_2.4Ni type hydrogen storage alloys were selected as the object of this work based on the review of the research and development of the Mg₂Ni system alloys both from home and abroad. The multi-component Mg_2.4Ni type hydrogen storage alloys were prepared by medium induction furnace under vacuum. The (Mg_2.4Ni)_100-xREx(RE=La,Ce; x=0,5,10,15,20) alloys were designed. The high purity helium with a pressure of 0.04 MPa was used as protecting atmosphere to prevent the volatilization of magnesium during the melting. The amorphous ribbon with the length of consecutive, thickness 25-35um, and the width of 3-10mm was obtained by single-roll rapid quenching. The structure and morphology were observed and analyzed by XRD and SEM. The electrochemical properties of alloys were measured by electrochemical tester. The crystallization temperature of the amorphous phase was measured by DSC. The influence of the alloy composition and quenching techniques on the amorphous phase thermal stability was analyzed. The obtained results are as follows:The addition of rear earth element La into the alloys can greatly increase the formation capability of the amorphous phase in the (Mg_2.4Ni)_100-xLa_x(x=0,5,10,15,20) alloys. The phase structure change obviously with the addition of La, and the main Mg₂Ni phase change to LaNi₃+LaMg3 phase with increasing La content. The activation performance of the cast and as-cast alloys is favorable, but the maximum discharge capacity changes complicatedly. The kinetics of hydriding is worsen and the amount of hydrogen absorption is lessen, the main reason is the hydrogen capacity of the LaNi₃ phase decrease after quenching. The addition a bit of rear earth element La into the alloys is beneficial on the electrochemical cycle stability, which is consistent with the alloy electrode open circuit potential. The high rate discharge properties of the alloy,Whether as-cast alloy or fast quenching state alloy ,are decreased with La increased ,which is consistent with a trend alloy electrode dynamic performance .For the (Mg_2.4Ni)_100-xCex(x=0,5,10,15,20)alloys, the phase structure changes obviously with the addition of Ce. The phase structure change obviously with the addition of Ce, and the main Mg₂Ni phase change to CeMg3+Ce7Ni₃ phase with increasing Ce content. The maximum capacity increases with rising Ce content of the cast alloys, and the maximum capacity of the as-cast alloys decreases with rising Ce content. The maximum discharge capacity and the amount of hydrogen absorption decrease after quenching; the main reason is the Ce content and quenching techniques lead the phase composition and phase structure to change. The addition earth element Ce into the alloys is unfavorable on the electrochemical cycle stability, which is consistent with the alloy electrode open circuit potential. The high rate discharge properties of the alloy,Whether as-cast alloy or fast quenching state alloy ,are improved with Ce increased ,which is consistent with a trend alloy electrode dynamic performance .