Impacts of Melt Spinning and Element Replacement on the Electrochemical Performances of the RE-Mg-Ni-based A_2B_7-type Electrode Alloys

摘要

The RE-Mg-Ni-based A_2B_7-type La_(0.75-x)Pr_xMg_(0.25)Ni_(3.2)Co_(0.2)Al_(0.1)(x = 0, 0.1, 0.2, 0.3, 0.4) electrode alloys fabricated by melt spinning technology. The impacts of the melt spinning and the replacement of La by Pr on the microstructures and electrochemical performances of the alloys were systematically investigated. The results indicate that the as-cast and spun alloys hold a compound phase structure, containing (La, Mg)_2Ni_7 and LaNi_5 phases as well as a residual phase LaNi_2. A notable grain refinement of the alloys without altering the phase structures of the alloys obtained by melt spinning. The discharge capacity of the alloy (x = 0.2) tend to first augments and then falls with the growing spinning rate. And the as-spun (10 m/s) alloy gains the maximum discharge capacity as Pr content augmenting in the alloys. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the high rate discharge ability (HRD), the hydrogen diffusion coefficient (D) and the limiting current density (IL) of the alloys first increase then decrease with the rising of the spinning rate and the amount of Pr substitution.