Microstructure and electrochemical properties of Ti–V-based multiphase hydrogen storage electrode alloys Ti0.8Zr0.2V2.7Mn0.5Cr0.8-xNi1.25FexTi0.8Zr0.2V2.7Mn0.5Cr0.8-xNi1.25Fex(x=0.0–0.8)(x=0.0–0.8)

The effects of Fe substitution for Cr on the microstructures and electrochemical properties of the electrode alloys Ti0.8Zr0.2V2.7Mn0.5Cr0.8-xNi1.25FexTi0.8Zr0.2V2.7Mn0.5Cr0.8-xNi1.25Fex(x=0.0–0.8)(x=0.0–0.8) were studied systematically. The microstructures of the alloys were characterized by XRD and SEM. The electrochemical properties including the maximum discharge capacity, the cyclic stability and the high rate dischargeability, etc. were tested. The results show that all of the alloys mainly consist of two phases, the C14 Laves phase with three-dimensional network and the dendritic V-based solid solution phase. Further, the lattice parameters of the two phases decrease with the increase of the content of Fe substitution. The content of the C14 Laves phase increases and accordingly that of the V-based solid solution phase decreases with increasing xx from 0.0 to 0.8. The maximum discharge capacity of the alloy electrodes displays a decrease tendency with the increase of the content of Fe substitution, whereas the cyclic stability and the high rate dischargeability increase firstly and then decrease with increasing xx. The optimal values of C200/CmaxC200/Cmax and R600R600 are 69.24% and 65.12%, corresponding to xx being 0.4 and 0.3, respectively. In addition, the electrochemical kinetics of the alloy electrodes were also studied by electrochemical impedance spectroscopy and by means of the exchange current density (I0)(I0), the limiting current density (IL)(IL) and the hydrogen diffusion coefficient (D)(D).