An electrochemical study of La0.4Ce0.3Mg0.3Ni2.975-xMnxCO0.525 (x=0.1-0.4) hydrogen storage alloys

In this paper, the structural and electrochemical properties of La0.4Ce0.3Mg0.3Ni2.975-xMnxCo0.525 (x = 0.1 - 0.4) hydrogen storage alloys have been studied systematically. It can be found by XRD Rietveld analysis that all these alloys mainly consist of two phases: the La(La, Mg)(2)Ni-9 phase with the rhombohedral PuNi3-type structure and the LaNi5 phase with the hexagonal CaCu5-type structure. The XRD analysis results also reveal that with increasing manganese content in the alloys, the La(La, Mg)(2)Ni-9 phase content decreases and the LaNi5 phase content increases and both the lattice parameters and the cell volume of La(La, Mg)(2)Ni-9 and LaNi5 phase increase. The P-C isotherms show that with increasing manganese content in the alloys the hydrogen storage capacity (H/M) changes very little and the plateau pressure for hydrogen absorption and desorption decreases evidently. The electrochemical studies show that the discharge capacity increases with increasing manganese content. The high rate dischargeability and the exchange current density I-0, and the limiting current density I-L of all alloy electrodes increase as x increases from 0.1 to 0.3 and then decrease when x increases further. (C) 2004 Elsevier B.V. All rights reserved.