Effect of annealing temperature on microstructure and electrochemical performance of La_(0.75)Mg_(0.25)Ni_(3.5)Co_(0.2) hydrogen storage electrode alloy

摘要

To improve the cyclic stability of La-Mg-Ni system alloy, as-cast La0.75Mg0.25Ni3.5Co0.2 alloy was annealed at 1123, 1223, and 1323 K for 10 h in 0.3 MPa argon. The microstructure and electrochemical performance of different annealed alloys were investigated sys- tematically by X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), X-Ray Photoelectron Spectroscopy (XPS), and electro- chemical experiments. The results obtained by XRD and SEM showed that the as-cast and annealed (1123 K) alloys had multiphase structure containing LaNi5, (La, Mg)2(Ni, Co)7 and few LaNi2 phases. When annealing temperatures approached 1223 and 1323 K, LaNi2 phase dis- appeared. The annealed alloys at 1223 and 1323 K were composed of LaNi5, (La, Mg)2(Ni, Co)7 and (La, Mg)(Ni, Co)3 phases. With in- creasing annealing temperature, the maximum discharge capacity of the alloy decreased monotonously, but the cyclic stability was improved owing to structure homogeneity and grain growth after annealing, as well as the enhancement of anti-oxidation/corrosion ability and the sup- pression of pulverization during cycling in KOH electrolyte.