Hydrogen absorption studies of an over-stoichiometric zirconium-based AB_2 alloy

摘要

The hydrogen absorption characteristics and the electrochemical behavior of the Zr_(0.9)Ti_(0.1)Mn_(0.66)V_(0.46)Ni_(1.1) alloy were studied. The pressure-composition isotherms for the alloy show a high hydrogen storage capacity and a steep slope with a slight plateau instead of the horizontal plateau corresponding to the two-phase equilibrium. This feature is attributed to the presence of small amounts of secondary phases due to microsegregation of alloying elements during solidification. The plateau tendency is enhanced upon homogenization annealing of the alloy. The activation of the Zr_(0.9)Ti_(0.1)Mn_(0.66)V_(0.46)Ni_(1.1) alloy electrode in alkaline solution at 30℃ was evaluated by using the cyclic voltammetry technique. For comparison, the Zr_(0.9)Ti_(0.1)CrNi alloy was also studied. The discharge capacities are about 330 mAh/g for both as-melted alloys, but the activation is faster for Zr_(0.9)Ti_(0.1)Mn_(0.66)V_(0.46)Ni_(1.1) than for Zr_(0.9)Ti_(0.1) CrNi, indicating that the substitution of Cr by Mn and V enhances the rate of activation due to the formation of metal surface oxides that can be reduced more easily, which increases the reaction surface area. For the annealed Zr_(0.9)Ti_(0.1)Mn_(0.66)V_(0.46)Ni_(1.1) alloy, large charge-discharge overpotentials and a significant decrease in discharge capacity are observed, which is ascribed to the disappearance of catalytic secondary phases present in the as-melted alloy.