Effects of rapid quenching on microstructures and electrochemical properties of La 0.7Mg 0.3Ni 2.55Co 0.45B x( x=0−0.2) hydrogen storage alloy

Abstract

In order to improve the electrochemical performances of La-Mg-Ni based electrode alloys with PuNi 3-type structure, a trace of boron was added in La 0.7Mg 0.3Ni 2.55Co 0.45 alloy. The La 0.7Mg 0.3Ni 2.55Co 0.45(x=0, 0.05, 0.1, 0.15 and 0.2) alloys were prepared by casting and rapid quenching. The electrochemical performances and microstructures of the as-cast and quenched alloys were investigated. The effects of rapid quenching on the microstructures and electrochemical performances of the above alloys were investigated. The results show that the as-cast and quenched alloys are composed of (La, Mg)Ni 3 phase, LaNi 5 phase and LaNi 2 phase. A trace of the Ni 2B phase exists in the as-cast alloys containing boron, and the Ni 2B phase in the B-contained alloys nearly disappears after rapid quenching. Rapid quenching increases the amount of the LaNi 2 phase in the B-free alloy, but it decreases the amount of the LaNi 2 phase in the boron-containing alloys. The effects of rapid quenching on the capacities of the boron-containing and boron-free alloys are different. The capacity of the B-free alloy monotonously decreases with increasing quenching rate, whereas the capacities of the B-contained alloys have a maximum value with the change of the quenching rate. The rapid quenching can improve the stability of La-Mg-Ni based electrode alloy but lowers the discharge plateau voltage and decreases the plateau length. The effect of rapid quenching on the activation capabilities of the alloys was complicated.