The Structure And Hydrogen Storage Properties Of New Hydrogen Storage Alloys Containing Magnesium

In this thesis, based on the review of the research and development of the La-Mg-Nibased hydrogen storage alloys and Mg-based amorphous hydrogen storage alloys havebeen extensively reviewed. On this basis, the La-Mg-Ni based AB_3.5-type hydrogen storagealloys and Mg₆₃Ni₂₂Pr₁₅ bulk metallic glass were selected as the subject of this study. Bymeans of XRD(Rietveld), SEM, DSC, PCT and galvanostatic charge-discharge etc, the effectof elemental substitution on the phase structure and electrochemical properties at normaltemperature and high temperature of the La-Mg-Ni based AB_3.5-type hydrogen storagealloys, and the structure, hydrogenation effects and hydrogen storage properties ofMg₆₃Ni₂₂Pr₁₅ bulk metallic glass were studied systematically. The purpose of suchinvestigation is to get some basic data and understanding about the electrochemicalproperties and hydrogenation of the new hydrogen storage alloys containingmagnesium. The result stated:1. It is found that the La_0.7Mg_0.3Ni_3.5-xM_x alloys mainly consist of the LaNi₅ phasewith the CaCu₅-type structure, the LaMgNi₄ phase with the AuBe₅-type structure and thephase with the PuNi₃-type structure, the abundance of the LaNi₅ phase was increased andthe abundance of the LaMgNi₄ phase was decreased by the elemental substitution. Thedischarge capacity of the alloys were markedly improved by the elemental substitution. Mnelemental substitution was propitious to improving the discharge capacity of the alloys atnormal temperature. Cu elemental substitution made for improving the discharge capacityof the alloys at high temperature. La_0.7Mg_0.3Ni_3.5 has the best high-ratedischargeability(HRD₁₂₀₀ above 72.087ï¼…) at normal temperature and high temperature. Alelemental substitution improves the cycle stability of the alloys. The electrochemicalproperties of the alloys were markedly affected by elemental substitution andtemperature, the synthesis properties of the alloys have to be further improved.2. It is found that the La_0.7Mg_0.3Ni_2.8Co_0.5Fe_0.2 alloy mainly consist of the LaNi₅ phasewith the CaCu₅-type structure, the LaMgNi₄ phase with the AuBe₅-type structure and thephase with the PuNi₃-type structure; the doping boron mainly consist of the LaNi₅ phasewith the CaCu₅-type structure, the LaMgNi₄ phase with the AuBe₅-type structure, theLaMg₂Ni₉ phase with the PuNi₃-type structure and the LaCo₄B phase. With the improvingof the temperature, the discharge capacity of La_0.7Mg_0.3Ni_2.8Co_0.5Fe_0.2 decrease from312mAh/g to 247.4mAh/g.The doping boron also decreases the discharge capacity(just 230.3mAh/g at normal temperature); High temperature make for the big electric currentdischarge.The doping boron exhibits much better cycle stability(S₇₂=70.777%, 71.69%) atnormal temperature and high temperature.3. Bulk amorphous alloys have a high hydrogen storage, endure causticity and highglass forming ability, Mg₆₃Ni₂₂Pr₁₅ metallic glasses were produced by a single rollermelt-spinning technique. By means of PCT and galvanostatic charge-discharge etc, thehydrogenation effect and hydrogen storage properties were researched at first. Thehydrogen absorption and desorption capacities were respectively 0.38 wt.% and 0.14 wt.%at 313 K and 333K, respectively. The hydrogenated Mg₆₃Ni₂₂Pr₁₅ metallic glass keep asingle glassy phase and the characteristic broad maxima of the amorphous state shift tolower scattering angles in comparison to the as-quenched ribbons. The glass transitiontemperature T_g, the onset crystallization temperature T_x, the crystallization temperature T_pof the hydrogenated Mg₆₃Ni₂₂Pr₁₅ metallic glass was 550, 570 and 577K, respectively, much higher than the corresponding value of 440, 470 and 499K of the as-quenchedsample. This means that dramatic enhancement of thermal stability. Mg₆₃Ni₂₂Pr₁₅ metallicglasses have a low discharge capacity (28.8mAh/g) at 298K, but shows a excellentactivation properties and cycle stability with S₇₅=69.44%.