Mixed Rare Earth La-mg-ni The Department Puni <sub> 3 </ Sub> Type Hydrogen Storage Alloy Structure And Electrochemical Properties

In this paper, previous research works on sorts of hydrogen storage alloys have been extensively reviewed. On this basis, the La-Mg-Ni based PuNi3-type hydrogen storage electrode alloys were selected as the subject of this study.This work aims to improve the cycling number and high-rate capacity of PuNi3-type hydrogen storage alloys mainly through optimizing the rare earth composition of La side combined with appropriated alloys preparated method and annealing at high temperature, By means of XRD, SEM, EDS analysis and the electrochemical test methods such as galvanostatic charge- dischar -ge, linear polarization, potentialstatic discharge and EIS etc, the phase structure, electro -chemical properties and cycling capacity degradation mechanism of PuNi3-type alloys were studied systematically, and we drow some useful conclusion.The study shows that there is a clear relationship between the alloy's comprehensive electrochemical properties of PuNi3-type hydrogen storage alloys and their thermodynam -ic, and kinetic characteristics. The rare earth composition can significantly influence the high-rate capability of PuNi3-type hydrogen storage alloys, which is mainly through incresing the velocity of the electrochemistry reaction and hydrogen diffusion rate in the alloys. Besides, the addition of rare earth composition can improve the cycle number of PuNi3-type hydrogen storage alloys due to reducing their high cell expansion on hydriding and corrosion of the alloys.From the research on the substitution of the rare earth elements for La in La₀.67Mg₀.33Ni₃.0 AB₃-type hydrogen storage alloys, the electrochemical capacity of Ce-rich rare earth composition is very low(under 200mAh/g ) because of the high absorbation flat, but the electrochemical capacity of La-rich rare earth composition is moderate(hyper 320mAh/g), in this basis, we adopt rare earth composition La₀.7Ce₀.1Pr_x Nd₂-x(x=0,0.1,0.2) to substitute La in La₀.67Mg₀.33Ni₃.0 AB3-type hydrogen storage alloys, compared with La₀.67Mg₀.33Ni₃.0, The substitution alloys has no significant influence on microstructures of the alloys and the microstructures of the alloys are similar to that of La₀.67Mg₀.33Ni₃.0, PuNi₃ phase with LaMgNi₄ is as second phase, but the cell volume of the PuNi₃ decreases and the anisotropy of the PuNi₃ structure increases, a to decrease, c and c/a to increase. In (La₀.7Ce₀.1PrxNd₀.2-x) ₀.67Mg₀.33Ni₃.0 alloys, the electrochemical properties of the alloy are improved obviously when x=0, 0.1, 0.2, compared with La₀.67Mg₀.33Ni₃.0, the discharge capacities of the alloys decrease few; but the cycling stability can be obviously improved, after 100 cycle, the capacity holding increases from 64% to 82.8%, 83%, 82.6%; the high rate dischargeability (HRD) increases from 78.4% to 89.4%, 91.1%, 90.1%; and the electrode kinetics (include the exchange current density I₀, the impedance and the hydrogen diffusion coefficient D of the alloy electrodes) are also improved greatly.Orthogonal experimental design is used to research the substitution of the rare earth elements for La in La₁.5Mg₀.5Ni₇.0A₂B₇-type hydrogen storage alloys, the influence of rare earth elements Ce Pr Nd and their interaction on La₁.5Mg₀.5Ni₇.0 hydrogen storage alloys is researched systemly, the addition of elements Pr, Ce reduce the alloy's electrochemical capacity greatly, but the influence of Nd is small; the addition of elements Pr, Nd improve the alloy's cycle number greatly, but Ce also reduce reduce he alloy's cycle number; the addition of elements Pr, Nd improve the alloy's high rate dischargeability by incresing the velocity of the electrochemistry reaction and hydrogen diffusion rate in the alloys;by orthogonal experimental design, (La₀.66Ce₀.04Pr₀.15Nd₀.15)₁.5 Mg₀.5Ni₇.0 alloys is found which has high comprehensive electrochemical, the electro -chemical capacity of the alloy is 368.2mAh/g, after 100 cycle, the capacity holding is 89.66%, and the rate dischargeability at 900mA/g is 91.86%.