Structural phase transformation and electrochemical features of La-Mg-Ni-based AB₄-type alloys

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• 作者：Yumeng Zhao^a ; ^b ; Shumin Han^a ; ^b ; ^{hanshm@ysu.edu.cn" class="auth_mail" title="E-mail the corresponding author} ; Yuan Li^b ; Jingjing Liu^b ; Lu Zhang^b ; Shuqin Yang^b ; Juan Cao^b ; Zeru Jia^b
• 关键词：La&ndash ; Mg&ndash ; Ni-based hydrogen storage alloy ; Metal hydride electrode ; AB4-type structure ; Phase transformation ; Electrochemical properties
• 刊名：Electrochimica Acta
• 出版年：2016
• 出版时间：10 October 2016
• 年：2016
• 卷：215
• 期：Complete
• 页码：142-149
• 全文大小：2129 K

文摘

In this work, we studied the structural phase transformation and electrochemical characteristics of AB₄-type La–Mg–Ni-based alloys through zoning annealing of La_0.78Mg_0.22Ni_3.90 polymorphic alloy. The as-cast La_0.78Mg_0.22Ni_3.90 alloy contained two phases of LaNi₅ (50.8 wt.%) and (La,Mg)₂Ni₇ (49.2 wt.%). When annealed at 1173 K, solid LaNi₅ phase reacted with a liquid phase from (La,Mg)₂Ni₇ converting into the (La,Mg)₅Ni₁₉ phase. Increasing temperature to 1223 K, the residual LaNi₅ phase continued to react with a liquid phase from (La,Mg)₅Ni₁₉ forming a new (La,Mg)₆Ni₂₄ phase in the alloy. Field-emission scanning electron microscope (FE-SEM) analysis found that the (La,Mg)₆Ni₂₄ phase showed diffuse distributing in the alloys and this particular morphology provided plenty of phase boundaries which offered more hydrogen diffusion routes. The high rate dischargeability (HRD) of the alloy electrodes increased with higher (La,Mg)₆Ni₂₄ phase abundance. When the abundance of (La,Mg)₆Ni₂₄ phase raised to 62.0 wt.%, the HRD of the alloy electrode at a discharge current density of 1500 mA g⁻¹(HRD₁₅₀₀) reached 68.0%. Meanwhile, the surface exchange current density (I₀) and hydrogen diffusion coefficient (D) increased to 360.35 mA g⁻¹ and 2.450 × 10⁻¹¹ cm² s⁻¹, respectively.