Effect of AB2-based alloy addition on structure and electrochemical properties of La0.5Pr0.2Zr0.1Mg0.2Ni2.75Co0.45Fe0.1Al0.2 hydrogen storage alloy

The La_0.5Pr_0.2Zr_0.1Mg_0.2Ni_2.75Co_0.45Fe_0.1Al_0.2 (M₁) and Zr_0.65Ti_0.35(Mn_0.2V_0.2Cr_0.15Ni_0.45)_1.76 (M₂) hydrogen storage alloys were prepared by inductive melting. In addition, the M₁+30 wt.%M₂ composites were successively prepared by using high-energy ball milling technology. From the X-ray diffraction (XRD) analysis, it was found that M₁ and M₂ alloys still retained their respective main phases in the M₁+30 wt.%M₂ composites. The scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) indicated that the decrease in discharge capacity of M₁ and M₂ alloy electrodes was ascribed to the oxidation-dissolution of La, Pr, Mg and Ti, Mn, V, Cr active elements, respectively. The electrochemical studies showed that the M₁+30 wt.%M₂ composite electrode ball milling for 5 min exhibited excellence cyclic stability (92.3%) after 80 charge/discharge cycles, which was higher than 77.7 % and 85.6% of M₁ and M₂ alloy electrodes, respectively. Moreover, at the discharge current density of 1200 mA/g, the high rate discharge ability (HRD) of the M₁+30 wt.%M₂ composite electrode increased from 61.5% (5 min) to 70.3% (10 min). According to the linear polarization, Tafel polarization and cyclic voltammograms (CV), the electrochemical kinetics of hydrogen reaction on the surface of the electrode and hydrogen diffusion rate in the bulk of alloy were also improved in the M₁+30 wt.%M₂ composite with increasing ball milling time.