La_(0.8-x)Ce_xMg_(0.2)Ni_(3.5)(x=0～0.20)贮氢合金电极的低温放电性能

Electrochemical Properties of La_(0.8-x)Ce_xMg_(0.2)Ni_(3.5)(x=0～0.20) Hydrogen Storage Alloy Electrode at 233 K

用冷坩埚磁悬浮熔炼炉制备La0.8-xCexMg0.2Ni3.5(x=0,0.05,0.10,0.15,0.20)贮氢电极合金,采用X射线衍射、三电极体系系统研究合金的微观结构和电化学性能。研究表明:合金为多相结构,主相均为Ce2Ni7型六方相,还包括CaCu5型六方相、PuNi3型菱方相;P-C-T曲线显示,随着Ce含量的增加,合金放氢平台区域变窄,平台压力升高。合金中各组成相单胞体积的减小是其主要原因。随着Ce含量的增加,合金常温最大放电容量逐渐减小并且循环稳定性有一定改善;低温最大放电容量则先增大后减小,合金的低温高倍率放电性能以及交换电流密度均随Ce含量的增加而增加,但氢扩散系数随着Ce含量的增加而减小。

In this paper, the effects of cerium content on the structural and electrochemical properties of the La0.8-xCexMg0.2Ni3.5（x=0～0.20） hydrogen storage alloys have been studied systematically. XRD analyses show that all these alloys consist of hexagonal Ce2Ni7-type main-phase, hexagonal CaCus-type phase, and rhombohedral PuNi3-type phase. The P-C isotherms curves show that the plateau pressure of the hydrogen desorption increases gradually and the plateau region becomes narrower with increasing the Ce content in the alloys. It is also found that with increasing the Ce content, the discharge capacity at 303 K decreases and the cycling life can be gradually improved, but the discharge capacity at 233 K increases firstly and then decreases. The high rate dischargeability （HRD） and the exchange current density 10 increase but the hydrogen diffusion coefficient D of the alloy electrodes decreases with the increase of Ce content at 233 K. These imply that the charge-transfer reaction on the surface of alloy electrodes is the rate-determining step at 233 K.