The Study On Hydrogen Storage And Electrochemical Propetries Of R-Mg-Ni Based A₅B₁9-type Hydrogen Storage Alloys

In this thesis, previous research works on R-Mg-Ni (R=La,Ce,Pr,Nd) systemalloys had been extensively reviewed. On this basis, the La-Mg-Ni based A₅B₁₉-typehydrogen storage electrode alloys was selected as the subject of this study. By meansof XRD, EPMA Rietveld analysis and the electrochemical test methods,thehydrogen storage alloys, which were substituted by rare earth elements, Mg elements,were investigated systemically.The effect of rare earth elements on the microstructure, hydrogen storageproperties and electrochemical properties ofLa_0.68M_0.2Mg_0.12Ni_3.3Co_0.3Al_0.1x;(M=La,Ce, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Yb, Sc, Y) were investigated systematically. Theresults showed that substitution of La by rare earth elements led to uniformdistribution of a variety of phases and the main phases also are Pr5Co19-type,Ce2Ni7(Gd₂Co₇)-type, CaCu5-type, PuNi3-type phases. The Pr5Co19-type phasesignificant increased when M=Nd, Gd, Dy and the maximum main phase abundancereached85.12wt.%when M=Dy. The plateau pressure of P-C-T curves rosegradually and became flatter when substitution of La by rare earth elements. Thehydrogen storage capacity of the La_0.68Yb_0.2Mg_0.12Ni_3.3Co_0.3Al0.1was1.37wt.%.Among the alloys studied, the La_0.68Gd_0.2Mg_0.12Ni_3.3Co_0.3Al0.1alloy possessed the bestelectrochemical properties,the maximum discharge capacity of the alloy reached371.4mAh/g and the discharge capacity retention rate S100reached85%after100charge-discharge cycles.Based on La_0.68M_0.2Mg_0.12Ni_3.3Co_0.3Al0.1alloys, the effects of Mg content onLa_0.8-xGd_0.2Mg_xNi_3.3Co_0.3Al_0.1(x=0-0.4) alloy structure, hydrogen storage propertiesand electrochemical properties were examined systematically. The results showedthat all the annealed alloys mainly consisted of Pr₅Co₁₉-type, PuNi₃-type,Ce₂Ni₇-type and CaCu₅-type phase. The main phase of Pr5Co19-type abundance firstincreased and then decreased with increasing Mg content, and the maximum mainphase abundance reached88.23wt.%when x was0.15. The equilibrium pressures ofhydrogen absorption rose gradually and became flatter when x increased. The lowestplateau pressure of the alloys was about0.02MPa and the hydrogen storage capacitywas1.334wt.%when x was0.15. The electrochemical measurements showed thatall the alloys had a superior activation capability and the discharge capacity of thealloys first increased and then decreased with the increase of Mg. Among the alloysstudied, the La0.65Gd_0.2Mg0.15Ni_3.3Co_0.3Al0.1alloy(x=0.15)possessed the bestelectrochemical properties,the maximum discharge capacity of the alloy reached377.9mAh/g and the discharge capacity retention rate S100reached9_0.2%after100charge-discharge cycles.