Influences of Ni addition on the structures and electrochemical properties of La 0.7Mg 0.3Ni 2.65+ xCo 0.75Mn 0.1 ( x = 0.0–0.5) hydrogen storage alloys

Abstract

In this paper, the effects of Ni addition on the structure, hydrogen storage and electrochemical properties of the La 0.7Mg 0.3Ni 2.65+ x Mn 0.1Co 0.75 ( x = 0–0.5) hydrogen storage alloys were studied systematically. The structural investigation shows that all the alloys mainly consist of the (La, Mg)Ni 3 phase and the LaNi 5 phase, and the abundance of the (La, Mg)Ni 3 phase and the LaNi 5 phase was relatively changed with increasing Ni content. Pressure–composition isotherms (P–C–T) indicate that, with increasing Ni content, the maximum hydrogen storage capacity and the hysteresis for hydrogen absorption/desorption decrease, but the plateau pressure increases. Electrochemical studies show that the maximum discharge capacity decreases from 395.1 ( x = 0) to 313.8 mAh/g ( x = 0.5). With increasing Ni content, the cyclic stability of alloy electrodes was not effectively improved. While x increases from 0 to 0.4, the electrochemical kinetic properties of the alloy electrodes were markedly improved due to the increase of the electrocatalytic activation of the surface and the increase of the hydrogen diffusivity in the alloy bulk.