Sm对La0.5Nd0.35-xSmxMg0.15Ni3.5合金晶体结构和储氢性能的影响

Crystallographic and electrochemical hydrogen storage properties of Sm substitute Nd for La0.5Nd0.35-xSmxMg0.15Ni3.5 alloys

金属Sm替代La0.5Nd0.35Mg0.15Ni3.5合金中的Nd用以提高合金性价比。通过多种研究手段分析了La0.5Nd0.35-xSmxMg0.15Ni3.5合金的相结构、合金形貌以及电化学储氢性能。所制备合金为A2B7、A5B19主相和AB5残余相组成的多相结构。随着Sm替代量增加(x值由0增加至0.3),相丰度的变化规律为主相A2B7和A5B19先升高后降低,而AB5残余相相丰度呈相反的变化趋势。合金最大放电容量由334.6 mA·h/g (x=0)升高至346.5 mA·h/g(x=0.20),当x=0.30时,最大放电容量为331.1 mA·h/g。高倍率放电性能(HRD2000)由41.4%(x=0)升高至63.8%(x=0.20),当x=0.30时,HRD2000为52.1%。100周期容量循环保持率呈单调上升趋势,由65.6%(x=0)升高至69.2%(x=0.30)。

The Nd in the La0.5Nd0.35Mg0.15Ni3.5 alloy has been substituted with Sm to improve the performance to price ratio.Herein,the phase structures,morphologies,and hydrogen storage properties of the La0.5Nd0.35−xSmxMg0.15Ni3.5 alloys are studied using different methods.The Rietveld analysis pattern showed that the phase composition of the alloys containing multiphase structures,including the major phases(i.e.,A2B7 and A5B19)and the residual phase(i.e.,AB5),remained unchanged after the partial substitution of Sm instead of Nd.Increasing the content of the substituted Sm(x=0-0.30)changes the phase abundance,causing the A2B7 and A5B19 phases to increase before decreasing,whereas the AB5 phase showed the reverse trend.The a-axis parameter,c-axis,and unit cell volume of the major phases and the residual phase gradually decreased with the increasing Sm content.Further,the electrochemical properties of the alloy electrodes were improved by substituting Nd with Sm.The maximum discharge capacity of the alloy electrodes initially increased from 334.6 mA·h/g(x=0)to 346.5 mA·h/g(x=0.20).Then,it decreased to 331.1 mA·h/g(x=0.30).The high-rate dischargeability at a discharge current density of 2000 mA/g(HRD2000)initially increased from 41.4%(x=0)to 63.8%(x=0.20).Subsequently,it decreased to 52.1%(x=0.30).The cycling capacity retention rate at the 100th cycle monotonically increased from 65.6%(x=0)to 69.2%(x=0.30),which should be attributed to the improvement in corrosion resistance of the alloy electrodes during the charge-discharge cycle.