In an attempt to improve the cyclic stability of La-Mg-Ni-based A2B7-type electrode alloys, La0.8Mg0.2Ni3.3Co0.2Six (x = 0−0.2) electrode alloys were fabricated by casting and annealing, and the effects of annealing temperature on the structures and electrochemical hydrogen storage performances of the alloys were systematically investigated. The results indicate that the as-cast and annealed alloys exhibit multiple structures that contain two major phases, (La,Mg)2Ni7 with a Ce2Ni7-type hexagonal structure and LaNi5 with a CaCu5-type hexagonal structure; and one residual phase, LaNi3. Both the lattice constants and cell volumes of the two major phases increase with the increasing annealing temperature. Instead of altering the phase composition, the annealing treatment causes the abundances of these two major phases to vary. Based on electrochemical measurements, the cycle stabilities of the alloys are found to be considerably improved by annealing, and the alloy’s discharge capacity yields a maximum value with the increasing annealing temperature due to the variation in phase abundance and the homogenization of the composition, respectively. The influence of the annealing treatment on the electrochemical kinetics of the alloys is associated with the alloy’s composition; the electrochemical kinetics of the Si-free alloy become slower with the increasing annealing temperature, whereas those of the Si-added alloys first mount up and then go down under the same conditions.
Effects of Annealing Temperature on the Electrochemical Hydrogen Storage Behaviors of La-Mg-Ni-Based A2B7-Type Electrode Alloys
2015
10 Seiten
Article (Journal)
English
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