Investigation on structures and electrochemical characteristics of the as-cast and quenched La0.5Ce0.2Mg0.3Co0.4Ni2.6−xMnx (x=0–0.4) electrode alloys

Abstract

Abstract The La–Mg–Ni system PuNi 3 -type La 0.5 Ce 0.2 Mg 0.3 Co 0.4 Ni 2.6− x Mn x ( x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and quenching. Ni in the alloy was partially substituted by Mn in order to improve the electrochemical characteristics of the alloys. The effects of the substitution of Mn for Ni and rapid quenching on the structures and electrochemical characteristics of the alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the alloys have multiphase structures which are composed of two major phases (La, Mg)Ni 3 and LaNi 5 as well as a residual phase LaNi. The substitution of Mn for Ni leads to an obvious increase of the LaNi 5 phase and an decrease of the (La, Mg)Ni 3 in the alloys. The electrochemical measurements indicate that the discharge capacities of the as-cast and quenched alloys first increase and then decrease with growing Mn content. The substitution of Mn for Ni clearly improves the high rate discharge abilities (HRDs) and the activation capabilities of the as-cast and quenched alloys, but it slightly impairs the cycle stabilities of the alloys. The rapid quenching significantly improves the cycle stabilities of the alloys, and the discharge capacities and HRDs of the alloys have the maximum values with the variety of the quenching rate.