Influences of annealing heat treatment on phase structure and electrochemical properties of Zr(MnVNi)2 hydrogen storage alloys

Abstract

Abstract The influences of annealing treatment on the phase structure and the electrochemical properties of Zr(Mn 0.25 V 0.20 Ni 0.55 ) 2 and Zr(Mn 0.05 V 0.40 Ni 0.55 ) 2 hydrogen storage alloys were investigated by means of XRD analysis and electrochemical tests. As-cast alloys were comprised of Laves phases (i.e., C15 and C14) dispersed Zr–Ni phases (Zr 9 Ni 11 and ZrNi) and exhibited good overall electrochemical properties. When the as-cast alloys were annealed, the Zr–Ni phases and part of C14 phase decomposed completely with increasing annealing time. The thermodynamically stable phase structure of the annealed alloys was a mixture of C15 and C14 Laves phase. The decomposition of Zr–Ni phases and part of C14 phase resulted in a remarkable decrease in capacity and activation property as compared to those of the as-cast alloy. A synergistic effect due to the presence of Zr–Ni phases in the Laves phases is inferred. The deterioration in the overall electrochemical properties is attributed to the decomposition of the Zr–Ni phases.