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The Phase Structures and Electrochemical Properties of La-Mg-Ni-Co Based AB3-type Hydrogen Storage Alloys

Author: TuDeZhou
Tutor: LeiYongQuan
School: Zhejiang University
Course: Materials Science
Keywords: La-Mg-Ni-Co -based AB3 type alloy Annealing Element substitution Phase structure Electrochemical properties
CLC: TG139.7
Type: Master's thesis
Year: 2006
Downloads: 110
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Abstract


In this paper, on the basis of a comprehensive overview of the research progress of the domestic and international rare earth based non AB 5 -type hydrogen storage alloy, determine the La-Mg-Ni-Co-based AB 3 type alloy as the object of study, XRD analysis and constant current charge and discharge, and electrochemical techniques such as linear polarization, potentiostatic step discharge systematically studied La 0.7 Mg 0.3 < / sub> the (Ni 0.85 Co 0.15 ) x (X = 3.1-3.6) phase structure and electrochemical properties of the alloy, and from screening the one with a higher capacity and better overall performance, La 0.7 Mg 0.3 (Ni 0.85 Co 0.15 ) 3.4 alloys. On this basis, further study of the annealing of La 0.7 Mg 0.3 (Ni 0.85 Co 0.15 ) 3 .4 alloy phase structure and electrochemical properties of Cu on Ni partial substitution of La 0.7 Mg 0.3 (Ni 0.85-x Co 0.15 Cu x ) 3 .4 (x = 0-0.03) alloy phase structure and electrochemical properties the impact of rules and mechanisms, and strive to further enhance the comprehensive electrochemical properties of the alloy. Of La 0.7 Mg 0.3 (Ni 0.85 Co 0.15 ) x (X = 3.1-3.6) alloy XRD analysis shows, the all alloy are the one kind PuNi 3 -type structure (La Mg) Ni , 3 main phase and a small amount of LaNi 5 phase and LaNi 2 phase. However, with increasing values ??of x, (La, Mg), Ni alloys 3 abundance of the main phase increased slightly, and X = 3.4, the maximum value (77.5%), and then decreased with the increase in the value of X, hydrogen absorbing alloy volume expansion ratio (△ V / V) is reduced by X = 3.1 to 24.7% X 23.2% = 3.4. The electrochemical tests show that with the increase in the value of X, the maximum discharge capacity of the alloy, high-rate discharge performance and cycle stability have been enhanced, and there is a great value in the X = 3.4, and then with the further increase of the value of X large decrease. Studied alloys, better overall performance alloy to X = 3.4, its maximum discharge capacity for 403.2mAh / g activated for two times, high rate discharge performance 1200mA / g discharge current conditions HRD < sub> 1200 = 84.6%, and low alloy capacity retention after 100 cycles (S 100 : 36.8%). La 0.7 Mg 0.3 (Ni 0.85 Co 0.15 ) 3 .4 alloy studies have shown that the annealing (1073K-1223K × 9h), the cast and annealed alloys still a PuNi 3 -type structure (La, Mg) Ni 3 main phase and a small amount of impurity phase (LaNi 2 and LaNi 5 ), but annealed alloys (La, Mg) Ni 3 main relative abundance than those cast alloy increased, and at an annealing temperature of 1123K when the maximum value (84.1%), and have lower hydrogen-absorbing volume expansion coefficient (T = 1123K when △ V / V was 20.1% ). The electrochemical tests show that annealing increased the maximum discharge capacity of the alloy, cycle stability has been significantly improved, but the alloy's high rate discharge performance than cast alloy decreased. The study found that improve the alloy of the the annealed alloys discharge capacity of the main phase abundance increases closely related, the alloy cycle stability improvement is mainly due to the annealed alloys with lower hydrogen absorption volume expansion rate and better alloy composition uniformity, while the catalytic activity of the electrodes of the annealed alloys, and the rate of diffusion of hydrogen in the alloy compared with the cast alloy has been reduced is the main reason for the high rate discharge performance degradation. Studied alloy after 1123K annealing treatment after the alloy better overall performance, the maximum discharge capacity as 414.4mAh / g, the activation times is 2, in the high rate discharge performance 1200mA / g discharge current conditions HRO 1200 = 75.4%, after 100 cycles, the capacity retention rate (S 100 ) was 59.2%.

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CLC: > Industrial Technology > Metallurgy and Metal Craft > Metallurgy and Heat Treatment > The alloy learn with a variety of properties of alloys > Other special nature of the alloy > Hydrogen storage alloy
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