The nanocrystalline and amorphous Mg2Ni-type Mg2–xLaxNi (x=0,0.2) hydrogen storage alloys were synthesized by melt-spinning technique.The as-spun alloy ribbons were obtained.The microstructures of the as-spun ribbons were characterized by X-ray diffraction (XRD),high resolution transmission electronic microscopy (HRTEM) and electron diffraction (ED).The hydrogen absorption and desorption kinetics of the alloys were measured using an automatically controlled Sieverts apparatus,and their electrochemical kinetics were tested by an automatic galvanostatic system.The electrochemical impedance spectrums (EIS) were plotted by an electrochemical workstation (PARSTAT 2273).The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method.The obtained results showed that no amorphous phase was detected in the as-spun La-free alloy,but the as-spun alloys substituted by La held a major amorphous phase,con-firming that the substitution of La for Mg markedly intensified the glass forming ability of the Mg2Ni-type alloy.The substitution of La for Mg notably improved the electrochemical hydrogen storage kinetics of the Mg2Ni-type alloy.Furthermore,the hydrogen storage kinetics of the experimental alloys was evidently ameliorated with the spinning rate growing.
Aiming at the improvement of the cyclic stability of La-Mg-Ni system (PuNi3-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Fe. The electrode alloys of La0.7Mg0.3Co0.45Ni2.55-xFex (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 elec- trochemical 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)Ni3 and LaNi5 as well as an impurity phase LaNi2. Rapid quenching helped the formation of an amorphous-like structure in Fe containing alloys.
