Study on the structural and electrochemical properties of Ti-based multiphase hydrogen storage alloys

The multi-component, multiphase Ti-based hydrogen storage alloys (Ti_0.8Zr_0.2)(V_0.533Mn_0.107Cr_{0.1 6}Ni_0.2)_x (x=6, 6.5, 7) have been studied systematically in this paper. It is found by XRD and EDS analysis that all the alloys mainly consist of two phases: a C14 Laves phase with hexagonal structure and a V-based solid solution phase with b.c.c. structure. In addition, a small amount of TiNi-rich phase is also found precipitated in both phases, probably due to the compositional segregation during solidification. The lattice parameters and unit cell volumes of the C14 Laves phase and the V-based solid solution all decrease when x is increased. Electrochemical measurements show that with x increasing, the maximum discharge capacity of the alloy electrode decreases and the activation properties also worsen, while the cyclic durability and the high rate dischargeability are all improved. Furthermore, the exchange current density I₀ of the alloy decreases and the limiting current density I_L of the alloy increases with increasing x, respectively.