Effects of substituting Ni with Cu on the microstructures and electrochemical characteristics of the as-cast and quenchedelectrode alloys

The La–Mg–Ni-based PuNi 3 -type La 0.7 Mg 0.3 Ni 2.55 - x Co 0.45 Cu x ( x = 0 , 0.1 , 0.2 , 0.3 , 0.4 ) hydrogen storage alloys were prepared by casting and rapid quenching. Ni in the alloy was partly substituted by Cu in order to improve the cycle stabilities of the alloys. The effects of the substitution of Cu for Ni on the microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure which is composed of two main phases (La, Mg) Ni 3 and LaNi 5 as well as a residual phase LaNi 2 . The substitution of Cu for Ni leads to an obvious increase of the LaNi 2 phase in the as-cast alloys, and it also helps the formation of a desired amorphous phase in the as-quenched alloy. The results of the electrochemical measurement indicate that the substitution of Cu for Ni obviously decreases the discharge capacities of the as-cast and quenched alloys, but it significantly improves their cycle stabilities. The substitution of Cu for Ni slightly improves the discharge potential characteristics and the activation capabilities of the as-cast alloys, but it leads to reversal results for the as-quenched alloys.