ELECTROCHEMICAL HYDROGEN STORAGE KINETICS OF THE AS-MELT La_(0.75-x)M_xMg_(0.25)Ni_(3.2)Co_(0.2)Al_(0.1) (M=Zr, Pr; x=0-0.2) ALLOYS APPLIED TO Ni-MH BATTERY

摘要

The electrochemical hydrogen storage kinetics of an alloy has been considered to be one of the most important properties for the practical application of hydride electrode in Ni/MH power battery. In order to improve the electrochemical characteristics of the La-Mg-Ni system A2B7-type electrode alloys, the partial substitution of M (M=Zr, Pr) for La has been performed. The La_(0.75-x)M_xMg_(0.25)Ni_(3.2)Co_(0.2)Al_(0.1) (M=Zr, Pr; x=0-0.2) electrode alloys were prepared by melt spinning technology. The influences of the melt spinning and substituting La with M (M=Zr, Pr) on the structures and the electrochemical hydrogen storage kinetics of the alloys were investigated. The results reveal that the as-cast and spun alloys hold a multiphase structure, containing two main phases (La, Mg)_2Ni_7 and LaNi_5 as well as a residual phase LaNi_2. The as-spun (M=none, Pr) alloy displays an entire nanocrystalline structure while an amorphous-like structure is detected in the as-spun (M=Zr) alloy, suggesting that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurement indicates that the high rate discharge ability (HRD) of the (M=Zr) alloys monotonously decreases while that of the (M=Pr) alloys first mounts up and then falls with the rising of spinning rate. Furthermore, the electrochemical impedance spectrum (EIS), the Tafel polarization curves and the potential-step measurements all indicate that the electrochemical kinetics of the (M=Zr) alloy always drop whereas those of the (M=Pr) alloy first mount up and then go down with the spinning rate growing.