Effects of Boron Addition on Structural and Electrochemical Properties of La-Mg-Ni-Co System Hydrogen Storage Electrode Alloys

The structural and electrochemical properties of La0.7Mg0.3Ni2.65Co0.75Mn0.1Al0.2Bx (x=0-0.08) hydrogen storage electrode alloys were investigated systematically. The results from XRD show that all of the alloys consist of a (La, Mg)Ni-3 phase and a LaNi5 phase. With the increase of B content, the abundance of the (La, Mg)Ni-3 phase increases, accordingly that of the LaNi5 phase decreases, and the cell volumes of the two phases decrease. Electrochemical studies indicate that B addition can effectively improve the high rate dischargeability (HRD) of the alloy electrode, and the optimal value of HRD1000 reaches 57.1% as x being 0.04. With the addition of small amount of B, the cycling stability and activation properties of the alloy electrodes keep almost unchanged, but the maximum discharge capacity (C-max) decreases. In addition, the electrochemical kinetics investigations including the linear polarization and anodic polarization were also performed in detail.