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The Effect Of Alloying On Microstructure And Electrochemical Property Of La-Mg-Ni Based A2B7-type Hydrogen Storage Alloys

Posted on:2011-07-26Degree:MasterType:Thesis
Country:ChinaCandidate:T WuFull Text:PDF
GTID:2121360305490460Subject:Materials Processing Engineering
Abstract/Summary:PDF Full Text Request
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, SEM, EPMA Rietveld analysis and the electrochemical test methods. Through the contrast AB3.5 alloy with AB3.3 alloy, no Co alloy,and no Gd alloy of microstructure and electrochemical properties, found that AB3.5 show it better integrated electrochemical properties.To do this, we focus on the effect of Co and Al element on the alloy of microstructure and electrochemical properties.Hydrogen storage alloys La0.63Gd0.2Mg0.17Ni3.35-xCoxAl0.15 (x=0~2.0) were obtained by induction melting followed by annealing and the effect of Co element on the microstructure and electrochemical properties were investigated was investigated by X-ray diffraction (XRD) and EPMA .The results show that La0.63Gd0.2Mg0.17Ni3.35-xCoxAl0.15 mainly consists of Ce2Ni7-type,Pr5Co19-type and CaCu5-type phase.The increase of Co leads to a significant decrease in Ce2Ni7- type phase abaundance and increase in CaCu5-type phase abundance. And the CaCu5- type phase abundance reaches 27.50% when x is 2.0. The electrochemical measurements show that all these alloys have good activation performance, but the discharge capacity of the alloys decrease with the increase of Co, the discharge capacity of the alloys reaches 392.92mAh/g when x is 0.3. The cyclic stability of the La0.63Gd0.2Mg0.17Ni3.35-xCoxAl0.15 alloy electrodes have been improved obviously. After 100 charge/discharge cycles, the discharge capacity retention rate S100=(C100/Cmax) of the alloy electrodes(x=1.0,1.5) respectively reach to 94.4% and 96.1%. Meanwhile, the increase of Co can obviously change the HRD, and the HRD is about 71.6~86.3% when x is from 0 to 1.5, however, the HRD reaches64.1% when x is 2.0.The effect of Al element on the microstructure and electrochemical properties of La0.63Gd0.2Mg0.17Ni3.2-xCo0.3Alx (x=0~0.4) hydrogen storage alloys were investigated. The results show that all these alloys mainly consist of Ce2Ni7-type/Gd2Co7-type,Pr5Co19-type,PuNi3-type and CaCu5-type phase. The increase of Al can obviously change the microstructure, and the CaCu5- type phase abundance is about 4~5% when x is from 0.1 to 0.2, however, CaCu5-type phase abundance reaches 66.65% when x is 0.4. The electrochemical measurements show that all these alloys have good activation performance, but the discharge capacity of the alloys decrease with the increase of Al, the discharge capacity of the alloys reaches 391mAh/g when x is 0.1. The cyclic stability of the La0.63Gd0.2Mg0.17Ni3.2-xCo0.3Alx alloy electrodes have been improved obviously. After 100 charge-discharge cycles, the discharge capacity retention rate S100=(C100/Cmax) of the alloy electrodes(x=0.1,0.2) respectively reach to 92.7% and 90.1%. Among the alloys studied, the La0.63Gd0.2Mg0.17Ni3.1Co0.3Al0.1 alloy possessd the best over electrochemical properties.
Keywords/Search Tags:La-Mg-Ni based A2B7 type hydrogen storge alloys, microstructure, electrochemical property, alloying
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