Effects of annealing treatment on phase structures, hydrogen absorption–desorption characteristics and electrochemical properties of a V 3TiNi 0.56Hf 0.24Mn 0.15Cr 0.1 alloy

Abstract

The effects of annealing treatment on the phase structures, hydrogen absorption–desorption characteristics and electrochemical properties of the V 3TiNi 0.56Hf 0.24Mn 0.15Cr 0.1 alloy have been studied. It is found that both the as-cast and annealed alloys consist of a main phase with b.c.c. structure and a C14-type secondary phase with hexagonal structure. With increasing annealing temperature, the lattice parameters of two phases decrease and the volume fraction of the main phase increases slightly. The present results indicate that annealing treatment decreases the maximum hydrogen desorption capacity, which could be attributed to a decrease in stability of alloy hydride due to the decrease in cell volume of the alloy phases. Furthermore, increasing annealing temperature decreases the high rate capability and deteriorates the durability of the alloy electrode in the alkaline electrolyte during charging–discharging cycles, which would be associated with the change in composition of the secondary phase and the grain growth of the main phase.