Preparation and kinetic performances of single-phase PuNi3-, Ce2Ni7-, Pr5Co19-type superlattice structure La–Gd–Mg–Ni-based hydrogen storage alloys

Abstract

RE–Mg–Ni-based hydrogen storage alloys are new cathode materials of Nickel-metal hydride (Ni-MH) batteries and the improvement of their kinetic performance is meaningful for enhancing the output power of Ni-MH power batteries. In this work, La–Gd–Mg–Ni-based alloys with different type superlattice structures are obtained by a powder sintering method from LaMgNi4 and La0.60Gd0.15Mg0.25Ni3.60 alloys at a temperature of 1203 K. When the precursor ratio (LaMgNi4/La0.60Gd0.15Mg0.25Ni3.60) is 1.00, the alloy sample shows a single-phase Pr5Co19-type structure. The increased LaMgNi4 ratio promotes the formation of [A2B4] subunit, and a Ce2Ni7-type phase structure which is consisted by more [A2B4] subunits compared with the Pr5Co19-type structure emerges. As a consequence, a Ce2Ni7-type single phase is obtained at the ratio of 1.4, and with the further increase of LaMgNi4, a single-phase PuNi3-type structure forms at the ratio of 1.8. Reaction kinetic characterization shows that the exchange current density of the Pr5Co19-type electrode is high to 769 mA g−1 which represents a good charge-transfer rate. Electrochemical measurements show that the discharge capacity of the Pr5Co19-type electrode could reach 200 mAh g−1 at a current density of 1800 mA g−1. Pr5Co19-type RE–Mg–Ni-based alloys are considered prospective materials of high-power Ni-MH batteries.