Effect of substituting B for Ni on electrochemical kinetic properties of AB5-type hydrogen storage alloys for high-power nickel/metal hydride batteries

In this paper, the structure and electrochemical kinetic properties of MmNi3.70−xMn0.35Co0.60Al0.25Bx (x = 0.00, 0.10, 0.15, 0.20, 0.25) hydrogen storage alloys prepared by inductive melting have been systematically studied. The X-ray diffraction (XRD) shows that the alloys with B have not only LaNi5 phase, but the secondary phase with CeCo4B-type structure. The amount of the secondary phase and the plateau pressure of pressure-composition (P-C) isotherms gradually increase with the increase of B content. As x increases from 0.00 to 0.25, the high-rate dischargeability (HRD) of alloy electrodes first increases and then decreases. When x = 0.20, the HRD value reaches the maximum-63.1% at 1500 mA/g discharge current density. Electrochemical kinetic measurements indicate that the superior HRD of alloy electrodes is ascribed to their high surface electrocatalytic activity and fast hydrogen transfer in the bulk of alloys. The substitution of Ni with B in suitable amount could improve the kinetic properties of rare earth-based AB5-type alloys because of the formation of the secondary phase.