Influences of molybdenum substitution for cobalt on the phase structure and electrochemical kinetic properties of AB 5-type hydrogen storage alloys

Abstract

The effects of the partial replacement of Co with Mo on the phase structure and electrochemical kinetic properties of La 0.35Ce 0.65Ni 3.54Co 0.80– x Mn 0.35Al 0.32Mo x ( x=0.00, 0.10, 0.15, 0.20, 0.25) hydrogen storage alloys prepared by arc-melting method were systematically studied in this paper. The X-ray diffraction (XRD) showed that after partial substitution of Mo for Co, the alloys remained a single LaNi 5 phase with a hexagonal CaCu 5-type structure. The P-C isotherms indicated that the equilibrium pressure gradually decreased with increasing of Mo content. Electrochemical studies showed that the substitution of Mo for Co could greatly increase discharge capacity, improve activation ability and reduce self-discharge of alloy electrodes. The alloy with x=0.25 exhibited a higher rate dischargeability (HRD 1200= 50.9%). Moreover, Mo is a vital element in favor of kinetic properties of AB 5-type hydrogen storage alloys. As Mo content increased, the exchange current density I 0, the hydrogen diffusion rate gradually increased.