Effect of the cerium content on the structural and electrochemical properties of the La 0.7− xCe xMg 0.3Ni 2.875Mn 0.1Co 0.525 ( x=0–0.5) hydrogen storage alloys

Abstract

In this paper, the effect of the cerium content on the structural and electrochemical properties of the La 0.7− x Ce x Mg 0.3Ni 2.875Mn 0.1Co 0.525 ( x=0–0.5) hydrogen storage alloys has been studied systematically. It is found by XRD Rietveld analysis that all these alloys mainly consist of two phases: the La(La,Mg) 2Ni 9 phase with the rhombohedral PuNi 3-type structure and the LaNi 5 phase with the hexagonal CaCu 5-type structure. The abundance of the La(La,Mg) 2Ni 9 phase increases with increasing cerium content. The P– C isotherms curves show that with increasing Ce content in the alloys, the plateau pressure of the hydrogen absorption and desorption increases steeply and the plateau region becomes narrower and steeper. It is found that with increasing Ce content the discharge capacity decreases and the cycling life can be gradually improved. The high rate dischargeability (HRD), the exchange current density I 0, and the limiting current density I L of the alloy electrodes increases from x=0 to 0.3 and then decreases with the increase of Ce content.