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An Investigation on the Preparation and Performance of the RE-Mg-Ni Based AB3.8 System Hydrogen Storage Alloys

Author: LiMeng
Tutor: ZhuLei
School: Beijing Nonferrous Metal Research
Course: Materials Science and Engineering
Keywords: high capacity hydrogen storage alloys phase structure cycling stability heat treatment nickel coating by chemical plating first principle
CLC: TG139.7
Type: Master's thesis
Year: 2011
Downloads: 95
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Abstract


Based on the review of research and development of RE-Mg-Ni system hydrogen storage alloys, A5B19-type alloys were selected as the subject of this work by means of ICP-AES, Rietveld, SEM, DSC and electrochemical tests, The paper introduced the influence and interaction of phase structure and electrochemical properties using the idea of heat-treatment and nickel coating in order to develop some kinds of A5B19-type hydrogen storage alloys, which is to invest a hydrogen storage alloy with high discharge capacity and good cycling stability.Firstly, Based on the composition optimization research, the microscopic structure, phase structure and electrochemical properties of (LaNdPrMg)(CoAl)3.8 alloy, the process of heat-treated alloys was studied,Overall electrochemical properties of the alloys annealed at 1323k for 5 hours and fast cooling are optimum. Cmax increased from 357.5mAh·g-1 to 400.9mAh·g-1, because the abundance of AB5-type phase decreased, A5B19-type phase increased. The cycling stability was improved with S100 increasing from 79.5% to 87.5% siganificantly.This paper studied the process of chemical coating on the (LaNdPrMg)(CoAl)3.g alloys after heat-treatment,The results of SEM showed that the density and cover rate of gilt have been obviously increased after nickel coating,The electrochemical results showed that although the maximum discharge capacity of (LaNdPrMg)(CoAl)3.8 alloys, after nickel coating, was reduced, the cyclic stability was some improved at the same time,What is more, it also showed that the thicker of the coating layer the better of the cyclic stability would be, According to the dynamical analysis, the sample which has been coated would expose lower electrochemical reaction resistance, higher electrochemical rate and exchange current of hydrogen diffusion in the electrode which can improve the high-rate discharge performance.As a consequence of the above, overall electrochemical properties of (LaNdPrMg)(CoAl)3.8 alloy annealed at 1323k for 5 hours after fast cooling and nickel coating by chemical plating(18%) were optimum. Cmax was 366mAh·g-1, Na was 3, the HRD1200 was 85%, the S100 was 85%.More over,the density functional GGA method and the full-potential linearized augmented plane wave were used to optimize the cell and internal parameters of hydrides LaNi5Hx (x=3,4,5).The equilibrium structure,density of state and charge density were worked out.This is a research which calculated using First principles.

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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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