钆对La-Mg-Ni系A_2B_7型储氢合金微观结构和电化学性能的影响

Effects of Gadolinium on Microstructure and Electrochemical Properties of La-Mg-Ni Based A_2B_7-Type Hydrogen Storage Alloys

用高频感应熔炼方法制备了稀土系A2B7型La0.83-xGdxMg0.17N i3.05Co0.3A l0.15（x=0~0.5）储氢合金,在Ar气氛中和1173 K下对铸态合金进行退火处理,通过X射线衍射（XRD）、电子探针显微分析方法（EPMA）和电化学测试等分析方法系统研究了稀土Gd部分替代La元素对合金微观组织和电化学性能的影响规律。研究结果表明,合金退火组织主要由Ce2N i7型、Gd2Co7型、Pr5Co19型、PuN i3型和CaCu5型相组成,稀土Gd元素能有效减少和抑制退火组织中CaCu5型相的形成,随Gd含量x增加,合金相组成中A2B7型（Ce2N i7和Gd2Co7型）相丰度呈先增加后减小的规律,当x=0.2时其相丰度最大（91.0%）。合金的PCT吸氢平台压随Gd含量的增加而升高,x=0.5时吸氢平台压力接近0.1 MPa,x=0.2时合金的吸氢量达到最大值1.34%。电化学测试分析表明,随Gd含量x的增加,合金电极最大放电容量和容量保持率均呈先增加后减小的规律,适量的Gd元素可明显改善合金的综合电化学性能。当x=0.2时,合金电极放电容量达到最大值392.9 mAh.g-1,经100次充放电循环后其电极容量的保持率S100为91.2%,具有较好的综合电化学性能。

La0.83-xGdxMg0.17Ni3.05Co0.3Al0.15（x=0~0.5） hydrogen storage alloys were prepared by induction melting followed by annealing treatment at 1173 K in Ar atmosphere.The effect of Gd on the microstructure and electrochemical properties of La0.83-xGdxMg0.17Ni3.05Co0.3Al0.15（x=0~0.5） were investigated systematically by means of X-ray diffraction（XRD）,electron probe micro-analysis（EPMA） and electrochemical measurements.The results showed that all these alloys mainly consisted of Ce2Ni7-type＋Gd2Co7-type,Pr5Co19-type,PuNi3-type and CaCu5-type phase.The substitution of La by Gd element led to a significant decrease in CaCu5-type phase abundance and an increase in Ce2Ni7-type phase abundance.Meanwhile,with increasing Gd content,Ce2Ni7-type phase abundance first increased and then decreased and the maximum phase abundance obtained was 91.0% when x was 0.2.The plateau pressure of PCT curves rose gradually and became flatter when x increased.The maximum hydrogen storage capacity of alloys was about 1.34% when x was 0.2.The electrochemical measurements showed that all these alloys had a good activation performance,and then the discharge capacity of the alloys first increased and then decreased with the increase of Gd,and also the maximum discharge capacity of the alloys reached 392.9 mAh · g-1 when x was 0.2.After 100 charge-discharge cycles,the discharge capacity retention rate S100 of the alloy electrode（x=0.2） reached 91.2%.Among the alloys studied,the La0.63Gd0.2Mg0.17Ni3.05Co0.3Al0.15 alloy possessed the best electrochemical properties.