Abstract: Mg1.95RE0.05Ni (RE=La, Ce, Pr, Nd, Y), REMgNi4 (RE=La, Ce, Pr, Nd) and REMg2Ni9(RE=Pr, Nd) compounds were prepared by ball-milling of mixed powder of Mg, Ni, RENi (or RE) followed by sintering in pure Ar. XRD analysis showed that Mg1.95RE0.05Ni compounds are all single-phase with a crystal structure same as Mg2Ni. The lattice constants (a, c, c/a) were calculated. It was suggested that rare earth substitution leads to a slight increase in the values of a and c compared with Mg2Ni. Electrode properties of these compounds were evaluated by means of a simulated battery test. The effectiveness in improving the discharge capacity resulted from the addition of RE increased in the following order: Mg1.95Pr0.05Ni>Mg1.95Nd0.05Ni>Mg1.95Ce0.05Ni>Mg1.95La0.05Ni>Mg1.95Y0.05Ni. For REMgNi4 compounds, a slight increase in the discharge capacity was observed in the following order: NdMgNi4>PrMgNi4>La- MgNi4>CeMgNi4. The maximum discharge capacity of NdMgNi4 compound was about 200 mAh/g. The discharge capacities of both NdMg2Ni9 and PrMg2Ni9 compounds were less than 100 mAh/g.

Key words: Mg-Ni-RE compounds, Hydrogen storage, Discharge capacity