Structure And Electrochemical Properties Of Ab_n(n=3.3,3.5) Hydrogen Storage Alloys

In this thesis, previous research works on La-Mg-Ni system alloys have been extensively reviewed. On this basis, the La-Mg-Ni based A2B7-type hydrogen storage electrode alloys was selected as the subject of this study.By means of XRD, EPMA Rietveld analysis and the electrochemical test methods, the lower Mg hydrogen storage alloys,which were substituted by different atom radis'rare earth elements, were investigated systemically.Hydrogen storage alloys La0.83Mg0.17Ni2.8Co0.2Al0.2Zn0.1 were obtained by induction melting followed by annealing and the effect of rare earth R(Ce, Pr, Nd, Gd, Y and Sc) substitution for La on the structure and electrochemical properties was investigated. X-ray diffraction (XRD) analysis and EPMA show that La0.83Mg0.17Ni2.8Co0.2Al0.2Zn0.1 mainly consists of CaCus-type phase as matrix and Ce2Ni7and PuNi3-type as the secondary phase. The addition of elements Ce, Pr, Nd and Sc has no significant influence on the microstructures of the alloys. However, CaCu5-type phase decreases and Ce2Ni7-type phase increase obviously with the addition of Gd, the Ce2Ni7-type phase abundence reaches 79.03%, Meanwhile, the addition elements of Y and Sc leads to an disappear of Gd2Co7-type phase. The electrochemical measurements show that the activation performance has the minor influence but the discharge capacities have been developed more or less by the addition of elements Nd, Gd, Y, Sc. At the same time, replaced by Nd,Gd, the cyclic stability of the alloys has been improved obviously,the maximum discharge capacity reach 93.0% and 95.1%.Otherwise, the alloy of Sc replaced shows the best high rate discharge ability.Above all, AB3.5 alloy was selected as the subject of study. The non-Al La0.63Gd0.2Mg0.17Ni3.2Co0.3 and La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1 alloys,as far as the La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1 and La0.5Gd0.2Mg0.3Ni3.1Co0.3Al0.1 alloys,were investigated of structure and electrochemical properties. Experiment results showed that,La0.63Gd0.2Mg0.17Ni31Co0.3Al0.1 alloy is nearly composed of Ce2Ni7-type, phase abundence reaches 93.99%. Meanwhile,it shows good overall electrochemical properties, the discharge capacity of the alloy is 396.2mAh/g and S100 reachs to 95.8 %.The other alloys are mostly composed of Ce2Ni7/Gd2Co7,Pr5Co19,PuNi3 and CaCu5 phase,and which phase abundence of CaCu5 is very low. Compared with the Lao.63Gdo.2Mgo.17Ni3.2Coo.3 alloy, the Pr5Co19 and PuNi3 alloys of La0.5Gd0.2Mg0.3Ni3.1Co0.3Al0.1 are increased obviously. In addition, The high-rate dischargeability (HRD) of La0.63Gd0.2Mg0.17Ni3.2Co0.3 has good performance, HRD900 reaches 88.6%.