Preparation and electrochemical properties of La0.70MgxNi2.45Co0.75Al0.30 (x = 0, 0.30, 0.33, 0.36, 0.39) hydrogen storage alloys

Abstract The as-cast alloy with the composition of La 0.70 Ni 2.45 Co 0.75 Al 0.30 was prepared by vacuum arc melting. La–Mg–Ni-based La 0.70 Mg x Ni 2.45 Co 0.75 Al 0.30 hydrogen storage alloy has been synthesized by high-energy vibratory milling blending of the La 0.70 Ni 2.45 Co 0.75 Al 0.30 as-cast alloy and elemental Mg, followed by an isothermal annealing. The microstructures and electrochemical properties of the La 0.70 Ni 2.45 Co 0.75 Al 0.30 and La 0.70 Mg x Ni 2.45 Co 0.75 Al 0.30 alloys were investigated by XRD, SEM and electrochemical measurements. The XRD analysis and Rietveld refinement showed that the as-cast La 0.70 Ni 2.45 Co 0.75 Al 0.30 alloy consists of single LaNi 5 phase, whereas the La 0.70 Mg x Ni 2.45 Co 0.75 Al 0.30 alloys contain the LaNi 5 and (La, Mg) 2 Ni 7 . The electrochemical measurements indicated that the maximum discharge capacity and discharge potential characteristic of the La 0.70 Mg x Ni 2.45 Co 0.75 Al 0.30 alloys increases first and then decreases with increasing x . The maximum discharge capacity and discharge potential characteristic of alloy reaches the optimum when x is 0.36. The cyclic stability of the La 0.70 Mg x Ni 2.45 Co 0.75 Al 0.30 alloy with a smaller quantity of Mg is better than that of the alloy with a larger quantity of Mg.