Effects of PuNi3-and Ce2Ni7-type phase abundance on electrochemical characteristics of La-Mg-Ni-based alloys

In order to study the effects of PuNi3-and Ce2Ni7-type phase abundance on electrochemical characteristics of La-Mg-Ni-based alloys, four alloys were prepared by powder sintering different molar ratios of LaNi5 alloy to LaMgNi4 alloy (x) (x = 0.56, 0.67, 0.74, 0.89). Rietveld refinement analysis showed that when x was 0.56, the alloy had a PuNi3-type single phase structure. While all the other alloys were composed of PuNi3-and Ce2Ni7-type double phases. The peritectic reaction between LaNi5 and PuNi3-type phases accounted for the formation of Ce2Ni7-type phase whose abundance increased with further increasing x. P-C isotherms indicated that all alloys exhibited single plateau, which was due to the similar super-stacking structures of both phases. In addition, the equilibrium pressure gradually rose as the Ce2Ni7-type phase abundance increased. Electrochemical studies showed that the discharge capacity first increased and then decreased with increasing amount of Ce2Ni7-type phase, while higher Ce2Ni7-type phase abundance favored the cycling stability. Besides, the x = 0.74 alloy electrode with the ratio of PuNi3-to Ce(2)Ni(7)type phase abundance close to 1:1 possessed superior high rate dischargeability and kinetic performances. This was attributed to more phase boundaries, which provided more tunnels for diffusion of hydrogen atoms. (C) 2013 Elsevier B.V. All rights reserved.