Microstructures and electrochemical performances of La 2Mg(Ni 0.85Co 0.15) 9[formula omitted] ( [formula omitted], Cr, Ti; [formula omitted]) electrode alloys prepared by casting and rapid quenching

Abstract

The La–Mg–Ni-based (PuNi 3-type) La 2Mg(Ni 0.85Co 0.15) 9 M x ( M = B , Cr, Ti; x = 0 , 0.1 ) hydrogen storage electrode alloys were prepared by casting and rapid quenching. The microstructures and electrochemical performances of the as-cast and quenched alloys were analyzed and measured. The effects of B, Cr, Ti and rapid quenching on the microstructures and electrochemical properties of the alloys were investigated in detail. The obtained results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni 3 phase (PuNi 3-type structure) and the LaNi 5 phase as well as the small amount of the LaNi 2 phase. A trace of the Ni 2B phase exists in the as-cast alloy containing boron, and the Ni 2B phase in the alloy nearly disappears after rapid quenching. The relative amount of each phase in the alloys depends on the composition of the alloys and the quenching rate. The addition of B, Cr enhances the cycle stability of the as-cast alloys, while the addition of Ti reduces the cycle stability of the as-cast alloy. The addition of B, Cr, Ti decreases the discharge capacities of the alloys. Rapid quenching increase the cycle lives of the alloys, but the effect of rapid quenching on the discharge capacity of the alloys is different. Except the alloy containing boron, the capacities of the alloys decrease monotonously with the increase of the quenching rate. The capacity of the alloy containing boron has a maximum value with the increase of the quenching rate. The as-cast and quenched alloys have an excellent activation performance.