Electrochemical properties of as-cast La2-xYxMg16Ni (x = 0, 0.1, 0.2, 0.3, 0.4) alloys

Abstract

Hydrogen storage alloys of La2-xYxMg16Ni (x = 0, 0.1, 0.2, 0.3, 0.4) were smelted by vacuum induction melting furnace. The microstructure of the cast alloys were observed by scanning electron microscope, and the alloys structure were analyzed by X-ray Diffractometer (XRD) before and after hydrogen absorption. The electrochemical capacity, cyclic stability, high-rate discharge, potentiodynamic polarization curves, and constant potential crossing curves were tested. Besides, the limited current density and diffusion coefficient were calculated. The results show that the main phase of the as-cast alloy is La2Mg17, and a little amount of the second phase Mg2Ni exist. In addition, LaH3 and MgH2 and a small amount of Mg2NiH4 phases were formed in the alloy after saturated hydrogen absorption. With the increasing of La element substituted by Y element in La2Mg16Ni alloy, the discharge specific capacity of alloy shows a decreasing tendency, it's unconspicuous, though. The cyclic stability and high rate discharge of hydrogen storage alloys increase first and then decrease with the increasing of La element substituted by Y element in La2Mg16Ni alloy. When S50 is 34.01%, the cyclic stability of La1.8Y0.2Mg16Ni alloy is best. Both the limited discharge current density and hydrogen diffusion coefficient of the alloy increase first and then decrease with the increasing of the La element of La2Mg16Ni alloy replaced by Y element. The maximum current density of La1.8Y0.2Mg16Ni alloy is IL = 325.11 mA/g, and the maximum diffusion coefficient is D = 1.849 × 10−8 cm2/s.