Study On The Characteristics Of Rare Earth Based AB₃-Type Hydrogen Storage Electrode Alloys

The RE-based AB₃-type hydrogen storage alloys have been concerned widely for their higher discharge capacity, easier activation and better hydrogen pressure. However, the cycle stabilities of these alloys are rather poor, which resists their commercial application. In this paper, the RE-based AB₃-type hydrogen storage electrode alloys were prepared. Then the effects of Mg and rare earth on the hydrogen storage properties and electrochemical performances have been discussed by X-ray diffraction, electrochemical charge/discharge, cyclic voltammetry (CV) and Pressure-composition-isotherm analysis.The results are shown in the followings:1.La_0．7Ca_0．3Ni_2．8-xMg_x (x=0.l, 0.2,0.3,0.4) alloys were prepared by vacuum inductionlevitation. XRD analysis, electrochemical experiment and PCT analysis show that each sample contains at lease two phases. The main phase is LaNi₅ with a hexagonal CaCu₅-type structure when x is 0.1 or 0.3 and LaNi₂ with AB₂-type laves phase when x is 0.2 or 0.4 Electrochemical experiment results show that the maximum discharge capacities of the electrodes alloy are 244.7(x=0.1), 140.8(x=0.2), 257.6(x=0.3) and 164(x=0.4) mAh/g, respectively. The maximum hydrogen absorption capacity ofLa_0．7Ca_0．3Ni_2．7Mg_0．1 alloy is 1.1wt.% under a hydrogen pressure of 2MPa at 25℃.2.La₃(Ni_0．80Co_0．15Al_0.05)₉ alloy was prepared by induction melting under Ar₂ gas. Theingot was mixed with Mg. And then the mixture was pressed into pellet and sintered at800℃for 5 h. The structure investigation shows that all the alloys mainly consist of theLa₂Ni₇, the La(Al, Ni)₅ phase. Electrochemical analyses show that all the alloys are easy activating. The capacity decreased by increasing Mg content.3.The (La_0．9Re_0．1)₃(Ni_0．80Co_0．15Al_0．05)₉ (Re=La, Ce, Pr, Nd) alloys and(La_1-xNd_x)₃(Ni_0．80Co_0．15Al_0．05)₉(x=0．1～0．4) hydrogen storage electrode alloys were obtainedby inductive melting. The hydrogen storage properties and electrochemical characteristicwere studied systematically. The result shows that (La_0．9Nd_0．1)₃(Ni_0．80Co_0．15Al_0．05)₉ alloy hasthe best hydrogen storage capacity and absorption-desorption kinetic property relatively. The maximum hydrogen storage capacity of the alloy is 1.34wt.% H₂ at 40℃, the maximum discharge capacity of the alloy electrode is up to 237.4mAh/g.