An investigation on electrochemical and gaseous hydrogen storage performances of as-cast La1−xPrxMgNi3.6Co0.4 (x = 0-0.4) alloys

The as-cast RE-Mg-Ni-based AB2-type La1−xPrxMgNi3.6Co0.4 (x = 0-0.4) alloys were prepared by vacuum induction furnace with a high purity helium gas as the protective atmosphere. The phase composition and microstructure of the as-cast alloys were characterized by XRD, SEM equipped with EDS. The results indicate that the as-cast alloys consist of two phases of LaMgNi4 and LaNi5. The measurements of the electrochemical properties show that the discharge capacity of the alloys slightly decreases with Pr content rising. As the Pr content grows from 0 to 0.4, the maximum discharge capacity decreases from 347.0 to 310.4 mAh/g. However, the cycle stability and the high-rate dischargeability of the alloy obviously augment with the Pr content increasing. Furthermore, the measurements of the electrochemical hydrogen storage kinetics reveal that the limiting current density (IL) first increases then decreases whereas the exchange current density I0 of the alloys first decreases then increases with the rising amount of Pr substitution, which indicates that the electrochemical dynamic of the alloy electrode are jointly dominated by the charge-transfer resistance and diffusion ability of hydrogen atoms. The measuring of the gaseous hydrogen storage reveals two pressure plateaus appear on each pressure-concentration-isotherm (P-C-T) curve of the as-cast alloys, which correspond to the LaMgNi4 and LaNi5 phases. Furthermore, we note that the pressure plateau of the P-C-T curve visibly rises with Pr content increasing.