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)Ni3 phase and a LaNi5 phase. With the increase of B content, the abundance of the (La, Mg)Ni3 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 (Cmax) decreases. In addition, the electrochemical kinetics investigations including the linear polarization and anodic polarization were also performed in detail.