Enhancement of the electrochemical properties of rare earth-based alloy by doping with CoZnB alloy

•A new composite of La0.7Mg0.3Ni3.5–CoZnB was prepared.•Cmax of 487.5 mAh/g and HRD800 of 93.1% were achieved for composite electrode.•Hydrogen diffusion inside the composite electrode was accelerated.

With the purpose of improving the electrochemical hydrogen storage properties of the alloys containing rare earth elements, an amorphous CoZnB was introduced into a La0.7Mg0.3Ni3.5 alloy to form a novel composite by ball milling. Electrochemical measurements demonstrated that both the high-rate dischargeability (HRD) and the maximum discharge capacity (Cmax) of the composite electrodes were significantly improved. Cmax of the composite electrodes could reach 487.5 mAh/g, which is much higher than that of pristine La0.7Mg0.3Ni3.5 alloy electrode (343.9 mAh/g). Moreover, HRD at a current density of 800 was increased to 93.1%. The electrochemical reaction kinetics was also investigated by linear polarization, anodic polarization, electrochemical impedance spectroscopy and potential-step discharge. It was found that, compared to pristine La0.7Mg0.3Ni3.5 alloy electrode, doping with CoZnB could give rise to a decrease of exchange current density and an increase of hydrogen diffusion coefficient, limiting current density and charge-transfer resistance.