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 La0.70Ni2.45Co0.75Al0.30 was prepared by vacuum arc melting. La–Mg–Ni-based La0.70MgxNi2.45Co0.75Al0.30 hydrogen storage alloy has been synthesized by high-energy vibratory milling blending of the La0.70Ni2.45Co0.75Al0.30 as-cast alloy and elemental Mg, followed by an isothermal annealing. The microstructures and electrochemical properties of the La0.70Ni2.45Co0.75Al0.30 and La0.70MgxNi2.45Co0.75Al0.30 alloys were investigated by XRD, SEM and electrochemical measurements. The XRD analysis and Rietveld refinement showed that the as-cast La0.70Ni2.45Co0.75Al0.30 alloy consists of single LaNi5 phase, whereas the La0.70MgxNi2.45Co0.75Al0.30 alloys contain the LaNi5 and (La, Mg)2Ni7. The electrochemical measurements indicated that the maximum discharge capacity and discharge potential characteristic of the La0.70MgxNi2.45Co0.75Al0.30 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 La0.70MgxNi2.45Co0.75Al0.30 alloy with a smaller quantity of Mg is better than that of the alloy with a larger quantity of Mg.