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The Effects of Alloy Composition on the Phase Structure and Electrochemical Properties of La-Mg-Ni-Co-Mn-Al-based Hydrogen Storage Electrode Alloys

Author: MaShuai
Tutor: PanHongGe
School: Zhejiang University
Course: Materials Science
Keywords: Hydrogen storage electrode alloys La-Mg-Ni-Co-Mn-Al -based alloy Element substitution Crystal structure Electrochemical properties Cycle stability
CLC: TG139.6
Type: Master's thesis
Year: 2006
Downloads: 104
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Abstract

The the comprehensive overview home and abroad AB ₃-type hydrogen storage alloys research progress on the basis of determining the La-Mg-Ni-Co-Mn-Al Department of La _0.7 Mg < sub> 0.3 Ni _2.45 Co _0.75 Mn _0.1 the Al _0.2 hydrogen storage electrodes alloy as a research object XRD analysis and Rietveld method structure refinement materials analysis methods, as well as a constant current charge and discharge, electrochemical impedance spectroscopy (EIS), linear polarization, anodic polarization and constant potential step electrochemical techniques, respectively, on the part of Nd for La alternative, the partial substitute partial substitute Cr Pr of La Ni La _0.7 Mg _0.3 Ni _2.45 Co _0.75 Mn _0.1 Al _0.2 alloy phase structure and electrochemical properties of a thorough and systematic study. Reveal the composition of the alloy, the phase structure and electrochemical properties of the relationship, and strive to further improve the electrochemical performance of La-Mg-Ni-Co-Mn-Al Department of hydrogen storage electrode alloys composition optimization, developed a combination of high capacity and long life of the new rare earth based hydrogen storage electrode alloys. In order to improve the overall performance of the alloy, Nd La _0.7 Mg _0.3 Ni _2.45 Co _0.75 Mn _0.1 Al _0.2 alloy La the partial substitution system studied La _0.7-x Nd _x Mg _0.3 Ni _2.45 Co _0.75 Mn _0.1 Al _0.2 (x = 0.0-0.30) alloy phase structure and electrochemical hydrogen storage properties. The results showed that all alloys are mainly by the oblique hexahedral PuNi _{-type structure (La, Mg) the Ni ₃}-type phase and the six-party CaCu _{structure the LaNi ₅ phase composition, the Rietveld structure refinement found, as Nd replace the increase in the amount of two main phases in the alloy a c-axis parameters and cell volume gradually decreases. The simultaneously (La, Mg) Ni _{, 3} phase abundance decreased from x = 0.00 when 69.39wt% to x = 0.30 when 49.58wt% (x = 0.30), corresponding to the LaNi ₅ phase abundance when x = 0.00 30.61wt% to x = 0.30 when 50.42wt% (x = 0.30). Electrochemical performance tests show that as the value of x increases, the maximum discharge capacity of the alloy electrode is gradually decreased, and improved cyclic stability of the alloy electrode, the capacity retention ratio after 100 cycles (S ₁₀₀ up to x = 0.30 when 80.9%) from x = 0.0 to 73.2%. Alloy electrodes high rate discharge capability, electrochemical reaction impedance spectroscopy, linear polarization, anodic polarization and potentiostatic order the more research shows that high rate discharge capacity of the alloy electrode electrochemical reaction impedance exchange current density, the limit current density, the diffusion coefficient of hydrogen in the alloy were first increased and then decreased with the increase of the value of x law. This indicates that the with the Nd replace the amount of increase, the performance of electrochemical kinetics of the alloy electrodes showing a decreasing trend in the first increase. Comprehensive comparison found that, when Nd substitution quantity x = 0.10, the alloy has good overall electrochemical performance, the maximum discharge capacity as 372.7mAh / g, the activation times is 2, in a high discharge current density of 1000mA / g rate discharge ability (HRD ₁₀₀₀) of up to 70.1% after 100 charge-discharge cycle capacity retention rate (S ₁₀₀) of 78.4%. On the basis of this study, further research Pr La _0.7 Mg _0.3 Ni _2.45 Co _0.75 Mn < sub> 0.1} Al _0.2 partial substitute alloy La La _0.7-x the Pr _x Mg (0.3) Ni < sub> 2.45 Co _0.75 Mn _0.1 Al _0.2 (x = 0.0-0.30) alloy phase structure and electrochemical hydrogen storage properties. The results show that the above alloy still mainly controlled by the (La, Mg) Ni ₃ phase and LaNi ₅ phase composition, the two-phase unit cell parameters and cell volume with x values decreases with an increase. The simultaneously (La, Mg) Ni _{, 3} relative abundance from x = 0.00 when 69.48wt% reduced to x = 0.30 when 40.52wt% (x = 0.30), corresponding

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