La_(0.75)Mg_(0.25)Ni_(3.5)Si_(0.10)贮氢合金高温动力学性能的研究

Research on the dynamic characteristics of La_(0.75)Mg_(0.25)Ni_(3.5)Si_(0.10) alloy under high temperature

贮氢合金在高温下会表现出与常温不同的电化学特性,以La0.75Mg0.25Ni3.5Si0.10合金为研究对象,采用交流阻抗谱和电位阶跃方法,对其高温使用环境下(30～70℃)的高倍率放电特性和动力学性能进行了深入的研究。研究结果表明合金的动力学性能是由电化学反应与氢的扩散共同控制的,合金的电荷传递电阻随温度升高而减小,高温有助于电极表面电化学反应速度的提高;但对于La0.75Mg0.25Ni3.5Si0.10合金存在最佳氢扩散温度,当温度高于其最佳温度时,由于释氢等副反应的进行,以及氧化腐蚀反应的加剧等,使合金的扩散系数反而减小;在合金表面电化学反应速度与氢扩散系数共同作用下,La0.75Mg0.25Ni3.5Si0.10合金高倍率放电性能在45℃时最优异,当温度高于45℃时反而降低。

Hydrogen storage alloys will show especial characteristics under high temperature.In this paper,the high-rate discharge ability and dynamic characteristic of La0.75Mg0.25 Ni3.5 Si0.10 alloy under 30-70℃ has been researched,by using electrochemical impedance spectrum（EIS） and constant potential-step discharge technique.The results show： the dynamic characteristic of the alloy is controlled by both the electrochemical reaction rate and the speed of hydrogen diffusion.The charge transfer resistance is decreased with testing temperature,and the electrode surface electrochemical reaction rate is increased at high testing temperature.But for La0.75Mg0.25 Ni3.5 Si0.10 alloy,hydrogen diffusion coefficient will be decreased when the testing temperature is above the optimal temperature（45℃）,due to the escape of the finite hydrogen in alloys being accelerated and the oxide film becomes thicker at high testing temperature.The increase of electrochemical reaction rates and the decrease of hydrogen diffusion speed together determine the high-rate discharge ability of La0.75Mg0.25 Ni3.5 Si0.10 alloys gets its best at 45℃.