稀土含量对La_(0.7))(Pr_(0.75)Nd_(0.25))_xMg_(0.3)Ni_(3.3)(Co_(0.7)Al_(0.3))_(0.3)(x=0.0～0.3)合金电极电化学性能影响

Effects of Rare-Earth Content on Electrochemical Properties of La_(0.7))(Pr_(0.75)Nd_(0.25))_xMg_(0.3)Ni_(3.3)(Co_(0.7)Al_(0.3))_(0.3)(x=0.0,0.1,0.2,0.3) Alloy Electrodes

在氩气保护条件下用高频感应悬浮熔炼法制备La0.7(Pr0.75Nd0.25)xMg0.3Ni3.3(Co0.7Al0.3)0.3(x=0.0,0.1,0.2,0.3)合金,研究混合稀土含量对合金储氢和电化学性能的影响。合金XRD相分析结果表明,合金相主要由LaNi5,(La,Pr)Mg2Ni9,(La,Nd)2Ni7和LaNi3相组成。随着Pr和Nd含量的增加,合金吸氢量先增加后减小,最大吸氢量为1.42%(质量分数)(x=0.2),放氢平台变短坪斜增加。合金电极电化学测试表明,电极最大放电容量为378 mAh·g-1(x=0.2),放电容量保持率S100从53.2%(x=0.0)增加到56.2%(x=0.3),增加Pr和Nd的含量可以提高电极的循环稳定性。合金电极电化学阻抗谱、线性极化、Tafel极化和循环伏安特性研究表明,添加适量的Pr和Nd可以提高电极动力学性能。当x=0.1时,合金电极电荷传递电阻Rct和极化电阻Rp较小,交换电流密度I0、极限电流密度IL以及阳极峰电流密度Ip较大,合金电极动力学性能较好。

The La0.7（Pr0.75Nd0.25）xMg0.3Ni3.3（Co0.7Al0.3）0.3（x=0.0,0.1,0.2,0.3） hydrogen storage alloys were prepared by magnetic levitation melting under Ar atmosphere,and the effects of Pr and Nd on the hydrogen storage and electrochemical properties were systematically investigated.X-ray diffraction（XRD） results showed that the alloy phases were mainly consisted of LaNi5,（La,Pr）Mg2Ni9,（La,Nd）2Ni7 and LaNi3 phases.The hydrogen storage capacity first increased and then decreased,the plateau region of the hydrogen desorption became narrower and steeper with the increasing Pr and Nd content in the alloys,the maximum hydrogen storage capacity of alloys reached to 1.42%（mass fraction）（x=0.2）.The electrochemical measurements showed that the maximum discharge capacity of the alloy electrodes was 378 mAh · g-1（x=0.2）.After 100 charge/discharge cycles,the capacity retention rate of the alloys was enhanced from 53.2%（x=0.0） to 56.2%（x=0.3）,and the cycling durability of the alloy electrodes was improved with the increases of Pr and Nd contents.The electrochemical impedance spectra（EIS）,linear polarization,Tafel polarization and constant potential-step method measurement results showed that appropriate Pr and Nd content could improve the electrochemical kinetics of alloy electrodes.When x=0.1,the charge-transfer resistance（Rct） and the polarization resistance（Rp） of electrode was smaller,and the exchange current density I0,limiting current density IL and anodic peak density Ip larger than others,and the electrode showed better electrochemical kinetic characteristic.