Microstructure and electrochemical performances of La0.7Mg0.3Ni2.55-xCo0.45Cux (x=0-0.4) hydrogen storage alloys prepared by casting and rapid quenching

La-Mg-Ni system (PuNi3-type) La0.7Mg0.3Ni2.55-Co0.45CUx (x=0, 0.2, 0.4) hydrogen storage electrode alloys were prepared by casting and rapid quenching. The effects of substituting Ni with Cu and rapid quenching on microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The microstructures of the as-cast and quenched alloys were systematically determined by XRD, SEM and TEM. The obtained results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni-3 phase and the LaNi5 phase as well as the LaNi2 phase. The substitution and the rapid quenching do not have a large influence on the phase compositions of the alloys, but both changed the phase abundances of the alloys obviously. The results obtained by the electrochemical measurement indicate that the substitution decreased the discharge capacities of the as-cast and quenched alloys, whereas it improved the cycle stability and discharge voltage characteristic of the as-cast and quenched alloys. The rapid quenching significantly enhanced the cycle stability of the alloys, but it notably decreased the discharge capacity of the alloys. (c) 2005 Elsevier B.V. All rights reserved.