Electrochemical hydrogen storage behaviors of as-cast and spun RE–Mg–Ni–Co–Al-based AB₂-type alloys applied to Ni–MH battery

Preparation of La–Mg–Ni–Co–Al-based AB₂-type alloys La_0.8−xCe_0.2Y_xMgNi_3.4Co_0.4Al_0.1 (x = 0, 0.05, 0.10, 0.15, 0.20) was performed using melt spinning technology. The influences of spun rate and Y content on structures and electrochemical hydrogen storage characteristics were studied. The base phase LaMgNi₄ and the lesser phase LaNi₅ were detected by X-ray diffraction (XRD) and scanning electron microscope (SEM). The variations of spinning rate and Y content cause an obvious change in phase content, but without altering phase composition, namely, with spinning rate and Y content growing, LaMgNi₄ phase content augments while LaNi₅ content declines. Furthermore, melt spinning and the replacing La by Y refine the grains dramatically. The electrochemical tests show a favorable activation capability of the two kinds of alloys, and the maximum discharge capacities are achieved during the first cycle. Discharge capacity firstly increases and subsequently decreases with spinning rate rising, while cycle stability is ameliorated and discharge capacity decreases with Y addition increasing. It is found that the amelioration of cycle stability is due to the enhancement of anti-pulverization, anti-corrosion and anti-oxidation abilities by both replacement of La with Y and melt spinning. Moreover, with the increase of Y addition and/or spinning rate, the electrochemical kinetics that contain charge transfer rate, limiting current density (I_L), hydrogen diffusion coefficient (D) and the high rate discharge ability (HRD) firstly augment and then reduce.