Abstract: The microstructures and electrochemical properties of the as-cast and quenched alloys MmNi3.8Co0.4Mn0.6Al0.2Bx(x=0, 0.1, 0.2, 0.3, 0.4)were analyzed and measured. The effect of boron additive on the microstructures and electrochemical properties of the as-cast and quenched alloys MmNi3.8Co0.4Mn0.6Al0.2 were investigated comprehensively. The experimental results show that the microstructure of as-cast alloys MmNi3.8Co0.4Mn0.6Al0.2Bx(x=0, 0.1, 0.2, 0.3, 0.4) is composed of CaCu5-type main phase and a small amount of CeCo4B-type secondary phase. The abundance of secondary phase increases with the increase of boron content. The rapid quenching technology was used in the preparation of the alloys. The amount of secondary phase in the alloys decreases with the increase of quenching rate. The electrochemical tests show that the addition of boron modifies the activation properties and dramatically enhances the cycle lives, but lead to the decrease of the capacities of the as-cast and quenched alloys. The influences of boron addition on the electrochemical properties of as-quenched alloys are much stronger than that of as-cast alloys, because boron strongly promotes the formation of amorphous phase in as-quenched alloy.
Effect of boron additive on microstructures and electrochemical properties of rare earth-based AB5 hydrogen storage alloy
Abstract:
The microstructures and electrochemical properties of the as-cast and quenched alloys MmNi3.8(Co0.4-)(Mn0.6Al0.2Bx)(x=0, 0.1, 0.2, 0.3, 0.4were analyzed and measured. The effect of boron additive on the microstructures and electrochemical properties of the as-cast and quenched alloys MmNi3.8Co0.4Mn0.6Al0.2 were investigated comprehensively. The experimental results show that the microstructure of as-cast alloys MmNi3.8Co0.4Mn0.6Al0.2Bx(x=0, 0.1, 0.2, 0.3, 0.4 is composed of CaCu5-type main phase and a small amount of CeCo4B-type secondary phase. The abundance of secondary phase increases with the increase of boron content. The rapid quenching technology was used in the preparation of the alloys. The amount of secondary phase in the alloys decreases with the increase of quenching rate. The electrochemical tests show that the addition of boron modifies the activation properties and dramatically enhances the cycle lives, but lead to the decrease of the capacities of the as-cast and quenched alloys. The influences of boron addition on the electrochemical properties of as-quenched alloys are much stronger than that of as-cast alloys, because boron strongly promotes the formation of amorphous phase in as-quenched alloy.
Fig.1 Relationship between cycle number and discharge capacity for as-cast and quenched alloys (a)—As-cast; (b)—As-quenched(22 m/s)
图2 硼含量x与电化学容量的关系
Fig.2 Relationship between boron content x and maximum discharge capacity for as-cast and quenched alloys (a)—Charge-discharge current density of 60 mA/g; (b)—Charge-discharge current density of 300 mA/g
Fig.5 Morphologies of as-cast and quenched alloys (a) and (b)—Morphologies of as-cast alloys(B0 and B4); (c) and (d)—Morphologies of as-quenched alloys(B0 and B4, 22 m/s)
图6 快淬B0和B4合金的TEM组织和选区电子衍射谱(22 m/s)
Fig.6 TEM microstructures and SAED of as-quenched alloys(22 m/s) (a) and (c)—Morphologies of B0 and B4 alloys; (b) and (d)—Diffraction patterns of B0 and B4 alloys