Investigation of Electrochemical Hydrogen Storage Kinetics of Melt Spun Nanocrystalline and Amorphous Mg2Ni-type Alloy

The Mg2Ni-type Mg2Ni1−xCox (x=0, 0.1, 0.2, 0.3, 0.4) alloys were prepared by melt-spinning technique. The structures of the as-cast and spun alloys were characterized by XRD, SEM and TEM. The electrochemical hydrogen storage kinetics of the as-spun alloy ribbons was tested by an automatic galvanostatic system. The hydrogen diffusion coefficients in the alloys were calculated by virtue of potential-step method. The electrochemical impedance spectrums (EIS) and the Tafel polarization curves were plotted by an electrochemical workstation. The results show that the as-spun Co-free alloy exhibits a typical nanocrystalline structure, while the as-spun (x=0.4) alloy displays a nanocrystalline and amorphous structure, confirming that the substitution of Co for Ni facilitates the glass formation in the Mg2Ni-type alloy. The amorphization degree of the as-spun alloys substituted by Co visibly increases with the increase in the amount of Co replacement. The Co replacement for Ni notably improves the electrochemical hydrogen storage kinetics of the alloys. With a growth in the amount of Co replacement from 0 to 0.4, the high rate discharge ability of the as-spun (25 m/s) alloy increases from 65.3% to 75.3%, the hydrogen diffusion coefficient (D) from 2.22 to 3.34 cm2/s and the limiting current density IL from 247.8 to 712.4 mA/g, respectively.