Effect of Mg substitution for La on microstructure, hydrogen storage and electrochemical properties of La_1−xMg_xNi_3.5 (x=0.20, 0.23, 0.25 at%) alloys

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• 作者：Wei Lv ; Yufan Shi ; Wanpeng Deng ; Jianguang Yuan ; Youhua Yan ; Ying Wu ; ^{yingwu2000@hotmail.com" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Hydrogen storage alloy ; Mg substitution for La ; Electrochemical property
• 刊名：Progress in Natural Science
• 出版年：2016
• 出版时间：April 2016
• 年：2016
• 卷：26
• 期：2
• 页码：177-181
• 全文大小：1517 K

文摘

The effect of Mg substitution for La on microstructure, hydrogen storage and electrochemical properties of the annealed La_1−xMg_xNi_3.5 (x=0.20, 0.23, 0.25 at%) alloys have been studied. All the samples were mainly composed of (LaMg)₂Ni₇, (LaMg)Ni₃, and LaNi₅ phases. Mg substitution for La changed the phase abundance, but did not change the constitution of all phases, which is confirmed by the results of back-scattered SEM images and EDS analysis. The P–C isotherms indicated that the La_1−xMg_xNi_3.5 alloys reversibly absorbed and desorbed hydrogen smoothly at 298 K. The hydrogen absorption cyclic stabilities of La_0.77Mg_0.23Ni_3.5 alloy after 5 hydrogen absorption/desorption cycles reached the maximum values of 91.9% and 96.0% at 298 K and 323 K, respectively. The hydrogen desorption capacity and plateau pressure for the La_0.77Mg_0.23Ni_3.5 alloy reached the maximum values of 1.055 H/M and 0.074 MPa, respectively. The desorption capacities of La_0.77Mg_0.23Ni_3.5 reached 0.193 H/M and 0.565 H/M in the first minute at 298 K and 323 K, respectively. Electrochemical property measurement indicated that La_1−xMg_xNi_3.5 (x=0.20, 0.23, 0.25 at%) alloys possessed excellent activation capability and were completely activated within 3 cycles. Discharge capacities of La_1−xMg_xNi_3.5 alloys reached 378.2 mA h/g (x=0.20 at%), 342.7 mA h/g (x=0.23 at%), and 369.6 mA h/g (x=0.25 at%), respectively. Moreover, energy density of La_0.77Mg_0.23Ni_3.5 alloy was much larger than that of La_0.80Mg_0.20Ni_3.5 alloy and nearly approaches the maximum value of La_0.75Mg_0.25Ni_3.5. Thus, the La_0.77Mg_0.23Ni_3.5 alloy exhibits optimum comprehensive properties of hydrogen storage and electrochemistry.