Group The Proportion Of Ml: For Mm On The Pct Properties And Electrochemical Performance Of Hydrogen Storage Alloy

The rare earth based hydrogen storage alloys Mm_xMl_1-xNi_3.55Co_0.75Mn_0.4Al_0.3(x=0⁰.5) were investigated in this work. The influences of Ml:Mm ratio on theelectrochemical and thermodynamics properties were analyzed by means ofelectrochemical measurements and XRD analyses.The results indicate that plateau pressure and slope of the PCT curvesincrease, while plateau width of the PCT curves and the highest hydrogenconcentration decrease, with the increasing of Mm content in the alloys. Boththe -ΔH^θand -ΔS^θvalue decrease with increasing of Mm content, it indicatesthat the thermodynamics stability of the alloys decreases. The electrochemicaltests show that the discharge capacity of the alloys decreases and the number ofactivation increases with increasing of Mm content. The cycle stability and thehigh rate discharge ability are improved remarkably. The XRD analyses indicatethat the main phase of all alloys is LaNi5 and the crystal lattices constants ofLaNi5 are changed with increasing of Mm content, i.e, a-axis decrease, c-axis aswell as axis ratio increase and the nonlinear of crystal volume decrease. Thecrystal volume of the alloy with x=0.3 is larger than the others. There is secondphase AlLaNi4 in alloys with x≥0.25 and the AlLaNi4 content increase withincreasing of x value.By comparison with the others, the alloy with x=0.3 can be used in praticewith optimal Ml:Mm ratio for its better electrochemical and thermodynamicsproperties.