Co元素对La-Y-Ni系A_(2)B_(7)型储氢合金的微观结构及电化学性能的影响

Effect of Co element on the microstructure and electrochemical properties of La-Y-Ni based A_(2)B_(7)-type hydrogen storage alloys

用真空电弧熔炼方法制备La-Y-Ni系A_(2)B_(7)型La_(0.3)Y_(0.7)Ni_(3.25-x)Co_(x)Mn_(0.15)Al_(0.1)(x=0~1.5)合金,并在高纯Ar气氛下进行1023 K+24 h退火处理,通过X射线衍射(XRD)、扫描电子显微镜(SEM)、能量分散谱(EDS)和电化学测试等方法,系统研究了Co部分替代Ni对La-Y-Ni系A_(2)B_(7)型合金微观组织、相结构及电化学性能的影响规律。结果表明,退火后合金的物相由Ce2Ni7型相、Gd_(2)Co_(7)型相、Ce_(5)Co_(19)型相、Pr_(5)Co_(19)型相及CeNi_(5)型相组成,其中A_(2)B_(7)型(2H-Ce_(2)Ni_(7)型与3R-Gd_(2)Co_(7)型)为主相;随Co含量逐渐增加,A_(2)B_(7)型主相含量的相丰度呈先减小后增大规律,晶胞体积VA_(2)B_(7)也随之逐渐增大。当Co逐渐含量增加时,合金电极的放电容量和充放电循环稳定性整体呈先增加后减小规律,其中最大放电容量C_(max)和最佳循环稳定性S100分别为386.0 mAh/g(x=0.2)与85.0%(x=0.7)。适量加入Co元素能明显提高合金电极容量和循环稳定性。

La_(0.3)Y_(0.7)Ni_(3.25-x)Co_(x)Mn_(0.15)Al_(0.1)(x=0~1.5)alloys of La-Y-Ni based A_(2)B_(7)-type were prepared by vacuum arc melting method and annealed at 1023 K for 24 h under high purity Ar atmosphere.The effect of Co element replacing Ni on the microstructure,phase structure and electrochemical properties of La-Y-Ni based A_(2)B_(7)-type alloys were systematically investigated by XRD,SEM,EDS and electrochemical methods.The results showed that the annealed alloys had multiphase structure of Ce_(2)Ni_(7)-type,Gd_(2)Co_(7)-type,Ce_(5)Co_(19)-type,Pr_(5)Co_(19)-type and CeNi_(5)-type,among which the main phase of A_(2)B_(7) type were consisted of Ce2Ni7-and Gd_(2)Co_(7)-type.With the increase of Co content,the phase abundance of A_(2)B_(7)-type main phase increased first and then decreased,but the unit cell volume VA2 B7 increased continuously.With the increase of Co element,the charge-discharge cycle stability and discharge capacity of the alloy electrode increased first and then decreased.The maximum discharge capacity and the optimal cycle stability of the alloy electrode were 385.9 mAh/g(x=0.2)and 82.3%(x=1.0)respectively.Proper addition of Co element can significantly improve the capacity and cycle stability of the alloy electrodes.