Effect of annealing time on the structure and electrochemical properties of La0.72Nd0.08Mg0.2Ni3.4Al0.1 hydrogen storage alloys

Abstract: The effect of annealing time on the structure and electrochemical properties of La0.72Nd0.08Mg0.2Ni3.4Al0.1 hydrogen storage alloys was investigated. The alloys were annealed at 1173K for different time, and the results of Rietveld refinement for the XRD data showed that the alloys were composed of Gd2Co7-type, Ce2Ni7-type, Pr5Co19-type, PuNi3-type, LaNi5-type and MgCu4Sn-type phases. Lengthening annealing time obviously promoted the formation of Gd2Co7-type phase which possessed high hydrogen storage capacity, and the largest content of Gd2Co7-type phase was obtained when the alloys were annealed for 20h. The maximum discharge capacity increased from 365.0 (as-cast) to 389.6mAh/g (annealed for 20h), which was ascribed to Gd2Co7-type phase abundance increasing from 35% (as-cast) to a maximum (81.71%, annealed for 20h). Also, the discharge capacity retention over 180 cycles at charge/discharge current density of 300mA/g was remarkably heightened from 56.6% (as-cast) to 80.5% (annealed for 20h). In addition, annealing treatment at 1173K for 6h can enhance high rate discharge ability. [Copyright &y& Elsevier]