Effect of rapid quenching on the microstructures and electrochemical performances of Co-free AB5-type hydrogen storage alloys

In order to compare the effects of the preparation techniques on the electrochemical performances of Co-free AB5-type hydrogen storage alloys, the Co-free AB5-type LaxMm1-x(NiMnSiAlFe)4.9(x=0,0.45,0.75,1.0) hydrogen storage alloys were prepared by casting and rapid quenching. The phase structures and microstructures of the as-cast and quenched alloys were analyzed by XRD, SEM and TEM. The effects of the rapid quenching on the microstructures and electrochemical performances of the specimen alloys were investigated in detail. The obtained results show that, when the amount of the La substitution x=0.75, the discharge capacity of the as-quenched alloy with quenching rate of 10 m/s is 292 mA h/g with charge-discharge current density of 60 mA/g, the capacity retaining rate (Rh) is 61.2% after 300 charge-discharge cycles with current density of 300 mA/g. When the amount of the La substitution x=1, the discharge capacities of the as-quenched alloy with quenching rate of 10 and 16 m/s are 300 and 292 mA h/g, and the capacity retaining rates (Rh) are 62.3% and 65.0%, respectively.