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Preparation, Characterization and Electrochemical Properties of Mg-based Nanocomposite Particles

Author: GuoDaoYuan
Tutor: DongXingLong
School: Dalian University of Technology
Course: Materials Physics and Chemistry
Keywords: Mg-based hydrogen storage alloy hydrogen plasma DC-arc method nanoparticles Surface modification electrochemical performance
CLC: TB383.1
Type: Master's thesis
Year: 2011
Downloads: 26
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Abstract


Mg-based hydrogen storage alloys are considered as one of the most promising hydrogen storage alloys, offering the combination of great hydrogen storage capacity, low density, abundant resource and low cost. However, due to the bad oxidation resistance ability and stability in electrolyte, the Mg-based alloy was difficulty in practical applications, as well as poor hydrogen absorption and desorption properties. In order to overcome these shortcomings, the people have conducted massive modification studies, hoped that enhances the oxidation resistance ability and the electrochemistry stability in electrolyte of magnesium and Mg-based alloy through the superficial modification.In this work, Mg-based nanoparticles are fabricated by hydrogen plasma DC-arc method, and the microstructure and electrochemistry properties are explored by various analytical techniques. Ours work mainly includes three aspects:(1) prepared Mg nanoparticles under various reaction atmospheres, to investigate the nanoparticel’s characteristic which fabricated by arc discharge under various atmospheres, determination the influence of atmospheres on Mg-based nanoparticles. (2) fabricated Mg/Oxide (La2O3,CaO) composite nanoparticles, to study the influence of oxide on nanoparticel’s structure, appearance and performance. (3) using La2O3 to modified Mg-Ni nanoparticles, to study the influence of La2O3 on nanoparticel’s structure, appearance and electrochemical properties.Various Mg-nanoparticles were prepared by hydrogen plasma DC-arc method under various atmospheres (Ar, Ar+H2, Ar+N2 and Ar +CH4) using bulk Mg as precursors. The strcture and properties are explored by means of X-ray diffraction, transmission electron microscopy (TEM) and differential scanning calorimetry (DSC) analysis. It is shown that the Mg nanoparticles have obvious difference in composition and microscopic appearance.The particles produced in Ar or Ar+H2 atmosphere contain Mg and a little amount of MgO, with lrge particle’s sizes and the hexagon shapes. Meanwhile, the particles produced in Ar+N2 atmosphere contains Mg and Mg3N2,without MgO.The particles produced in Ar+CH4 atmosphere contains Mg and a little of C and MgO, with small particle’s sizes and the Sphere shapes.Mg/oxide (La2O3, CaO) nanocomposite particles were prepared by the same method using mixture compacts containing Mg and oxides as precursors. It was found that the nanocomposite particles had the "core/shell" type microstructure with an oxide shell and a metallic Mg core. It is noticed that the shape changes from the hexagon of pure Mg nanoparticles to the sphere for Mg/oxide nanocomposite particles, with smaller size compared to the Mg nanoparticles, the performance of oxidation resistance and anti-corrosion in the strong alkali electrolyte is also improved by oxide shell in the nanocomposite particles. Vapor-Liquid-Solid (V-L-S) mechanism is successfully adopted to explain the forming of nanoparticles.Based on the rare earth oxide’s good performance on electrocatalysis and the chemical stability, we used La2O3 to modify Mg-Ni alloy nanoparticels. It is found that, compared to Mg-Ni alloy nanoparticels, Mg-Ni/La2O3 composite nanoparticels have less MgO, better performance of oxidation resistance and anti-corrosion in the strong alkali electrolyte, higher first-discharge capacity and the circulation stability.

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