The effects of partial substitution of Mn by Cr on the phase structure, microstructure and electrochemical properties of Ti-Zr-V-Mn-Ni hydrogen storage alloys

AB(2) type Ti-Zr-V-Mn-Ni-based Laves phase hydrogen storage alloys have a very high initial electrochemical discharge capacity, but the capacity decreases drastically within several charging-discharging cycles in KOH electrolyte which impede their applications as the negative electrode materials in Ni-MH batteries. In is work, Mn was partially substituted by Cr in the Ti-Zr-V-Mn-Ni hydrogen storage alloy and the effects of Cr substitution on the phase structure, microstructure and electrochemical properties of the alloys have been investigated. It is found that the cycle durability of the alloy electrodes have been greatly improved with Cr substitution despite the decrease of discharge capacities. Based on the XRD and EDS analysis, the alloys are mainly composed of C14 Laves phase matrix with hexagonal structure and TiNi type secondary phase with bcc structure. With Cr substitution, another V-Cr solid solution with bee structure appears. The metallographic observation shows that both the as cast and annealed alloys consist of a continuous C14 Laves phase matrix and TiNi type secondary phase with dendritic structure.