Effect of stoichiometric ratio upon electrochemical properties of AB5-type alloys
(1.北京有色金属研究总院 分析测试中心, 北京 1000882.北京市北京有色金属研究总院分析测试中心3.北京市北京有色金属研究总院能源材料与技术研究所4.General Research Institute for Nonferrous Metals, Beijing 100088, China)
Abstract: In order to evaluate the effect of stoichiometric ratio upon electrochemical properties of AB5-type hydrogen storage alloys, a series of alloys Mm0.8La0.2(Ni4.0Mn0.5Al0.3Co0.37Fe0.13)a (a=0.90？1.08) were prepared and the electrochemical properties were tested. Mm0.8La0.2Ni4.0Mn0.5Al0.3Co0.37Fe0.13 was one of some new low cobalt AB5-type hydrogen storage alloys which had been researched to have good electrochemical properties. The results show that the stoichiometric ratio has great effects on the electrochemical properties of alloys. And the effects were investigated in detail. When stoichiometric ratio x＜5.3, the activation performances of alloys are all good. But when stoichiometric ratio x＞5.3, the activation performances are decreased evidently. When stoichiometric ratio x＜5.3, the discharge capacities of alloys are linearly increased with the increase of stoichiometric ratio. When stoichiometric ratio x＞5.3, the discharge capacities of hydrogen storage alloys decrease linearly rapidly by the raise of stoichiometric ratio. Overstoichiometry is good to the cycle lives of alloys. When stoichiometric ratio is between 4.8 and 5.4, voltage platforms of alloys tend to increase linearly with the increasing of x. When x＞5.4, the increase of stoichiometric ratio leads to the decrease of voltage platform of alloys.
Key words: hydrogen storage alloys; AB5; low cobalt; stoichiometric ratio; electrochemical properties