Electrochemical hydrogen storage characteristics of La_(0.75-x) M_xMg_(0.25)Ni_(3.2)Co_(0.2)Al_(0.1)(M=Zr,Pr;x=0,0.1) alloys prepared by melt spinning

摘要

In order to ameliorate the electrochemical hydrogen storage performances of La-Mg-Ni system A_2B_7-type electrode alloys, the partial substitution of M (M = Zr, Pr) for La was performed. The melt spinning technology was used to fabricate the La_(0.75-x)M_xMg_0.25Ni_3.2Co_0.2Al_0.1 (M = Zr, Pr; x = 0, 0.1) electrode alloys. The influences of the melt spinning and substituting La with M (M = Zr, Pr) on the structures and the electrochemical hydrogen storage characteristics of the alloys were investigated. The analysis of XRD, SEM, and TEM reveals that the as-cast and spun alloys have a multiphase structure composed of two main phases (La, Mg)_2Ni_7 and LaNi_5 as well as a residual phase LaNi_2 . The as-spun (M = Pr) alloy displays an entire nanocrystalline structure, while an amorphous-like structure is detected in the as-spun (M = Zr) alloy, implying that the substitution of Zr for La facilitates the amorphous formation. The electrochemical measurements exhibit that the substitution of Pr for La clearly increases the discharge capacity of the alloys; however, the Zr substitution brings on an adverse impact. Meanwhile, the M (M = Zr, Pr) substitution significantly enhances its cycle stability. The melt spinning exerts an evident effect on the electrochemical performances of the alloys, whose discharge capacity and high rate discharge ability (HRD) first mount up and then fall with the growing spinning rate, whereas their cycle stabilities monotonously augment as the spinning