Influence of rapid quenching on cyclic stability of La-Mg-Ni system (AB 3-type) electrode alloys

Abstract

Aiming at the improvement of the cyclic stability of La-Mg-Ni system (PuNi 3-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Fe. The electrode alloys of La 0.7Mg 0.3Co 0.45Ni 2.55- x Fe x ( x=0, 0.1, 0.2, 0.3, 0.4) were prepared by casting and rapid quenching. The influence of the quenching on cyclic stability as well as structure of the alloys was investigated in detail. The results of electrochemical measurement indicated that rapid quenching significantly improved cyclic stability. When the quenching rate rose from 0 (As-cast was defined as a quenching rate of 0 m/s) to 30 m/s, the cyclic life of Fe-free alloy ( x=0) increased from 81 to 105 cycles, and for alloy containing Fe( x=0.4), it grew from 106 to 166 cycles at a current density of 600 mA/g. The results obtained by XRD, TEM and SEM revealed that the as-cast and quenched alloys had multiphase structures, including two major phases (La, Mg)Ni 3 and LaNi 5 as well as an impurity phase LaNi 2. Rapid quenching helped the formation of an amorphous-like structure in Fe containing alloys.