The morphology and electrochemical properties of La1-xMgxNi3.4Al0.1 (x = 0.1–0.4) hydrogen storage alloys

In view of the importance of Mg in R-Mg-Ni-type alloys (R generally represents rare earth elements), the effect of Mg on the morphology and electrochemical performance of the as-cast La_1-xMg_xNi_3.4Al_0.1 (x = 0.1, 0.2, 0.3 and 0.4) hydrogen storage alloys were studied in this work. The samples possess multiphase structures, including Gd₂Co₇-, Ce₂Ni₇-, Pr₅Co₁₉-and CaCu₅-type, PuNi₃-and MgCu₄Sn-type phases. It is found that reasonably increasing Mg contents can promote the formation of Gd₂Co₇-and Ce₂Ni₇-type phase as well as Mg contents have important effects on phase morphology. Furthermore, fine-dispersed LaNi₅ structure in (La, Mg)₂Ni₇ matrix is beneficial to facilitate the hydrogen diffusion and exert the electrochemical properties for the alloys.The EIS results indicate that the charge transfer resistance decreases nonlinearly with increase of (La, Mg)₂Ni₇ phase content and presents approximately linear relationship with LaNi₅ phase content. When x equals to 0.2, the alloy displays more optimal comprehensive electrochemical properties, i.e. the discharge capacity reaches 357.4 mA/g, the high rate dischargeability at 1200 mA/g 60.1% and the cycling performance 74.5%.