Microstructure and electrochemical performances of La0.7Mg0.3Ni2.55−xCo0.45Alx (x = 0–0.4) hydrogen storage alloys prepared by casting and rapid quenching

In order to improve the cycle stability of La–Mg–Ni system (PuNi3-type) hydrogen storage alloy, Ni in the alloy was partly substituted by Al, and La0.7Mg0.3Ni2.55−xCo0.45Alx (x = 0, 0.1, 0.2, 0.3, 0.4) hydrogen storage alloys were prepared by casting and rapid quenching. The effects of substituting Ni with Al and rapid quenching on the microstructures and electrochemical performances of the as-cast and quenched alloys were investigated in detail. The results obtained by XRD show that the as-cast and quenched alloys have a multiphase structure, including the (La, Mg)Ni3 phase, the LaNi5 phase and the LaNi2 phase. The substitution of Al for Ni increases the amount of the LaNi2 phase in the as-cast alloys, but it has an inappreciable influence on the abundance of the LaNi2 phase in the as-quenched alloy. The results obtained by the electrochemical measurement indicate that the capacities of the as-cast and quenched alloys monotonously decrease and their cycle stabilities significantly increase with the increase of Al content. Rapid quenching leads to the decrease of the capacity and an obvious improvement of the cycle stability of the alloys.