Effect of Co content on the structural, and electrochemical properties of the La0.7Mg0.3Ni3.4-xMn0.1Cox hydride alloys I.: The structure and hydrogen storage

In this paper, the structural, hydrogen storage and electrochemical studies were performed on the La0.7Mg0.3Ni3.4-xMn0.1Cox (x = 0.00, 0.30, 0.60, 0.75, 0.90, 1.05, 1.15, 1.30, 1.45, 1.60) hydrogen storage alloys. The phase structures were identified by X-ray diffraction (XRD) and Rietveld analyses showing that all alloys consist mainly of two phases: the (La,Mg)Ni-3 phase with the rhombohedral PuNi3 -type structure and the LaNi5 phase with the hexagonal CaCu5 -type structure besides a small amount of LaNi phase. Both a and c parameters of the (La,Mg)Ni-3 phase and the LaNi5 phase increase with increasing Co content and a subsequent expansion of the cell volumes owing to the atomic radius of Co (1.67Angstrom) being somewhat larger than that of Ni (1.62Angstrom). Moreover, the abundances of the (La,Mg)Ni-3 phase and the LaNi5 phase are changed relatively. P-C isotherms indicate that the equilibrium pressure for absorption/desorption hydrogen depresses steadily due to the expansion of the cell volume and the hydrogen storage capacity first increases and then decreases with increasing x from 0.00 to 1.60. Moreover, the absorption/desorption pressure hysteresis decreases and the plateau slope increases with the increase in Co content. (C) 2003 Elsevier B.V. All rights reserved.