添加Co对AB3.5型储氢合金结构及性能影响的理论与实验研究

摘要

基于密度泛函理论,采用总能量平面波赝势方法,设计了Lao.75 Mg0.25Ni3.5-xCox(x=0、0.25、0.5、0.75)系列合金,并研究了其晶体及电子结构,计算结果显示随着Co含量的增加,La原子上的电荷转移先增大后保持不变,在Co含量为0.5时达到最大；费米能级处的态密度值先增加后稍减小,Co含量在0.5时达到最大.利用悬浮感应熔炼法制备了该系列合金La0.75Mg0.25Ni3.5-xCox (x=0、0.3、0.5、0.7).对熔炼所得合金进行了结构和性能表征,XRD结果显示,随着Co含量的增加,合金的主相均为Ce2Ni7型AB3.5相；电化学测试显示,x=0.5时,合金的放电容量和循环性能均较好,为398.5 mAh/g,容量保持率S250为62％; PCT结果表明,在室温条件下合金的吸氢平台在0.04～0.09 MPa之间,当x=0.5时,吸氢平台压最低,为0.04 MPa,同时吸氢量最大,为1.587wt％.综合分析计算和实验的结果,AB3.5合金性能随Co添加量的变化趋势符合第一性原理计算的预测.%The structures and electronic properties of designed alloys La0.75Mg0.25Ni3.5-xCox (x=0, 0.25, 0.5, 0.75) were theoretically investigated by using density functional theory (DFT) of plane wave pseudopotential method. Calculation results showed that, with the increasing Co content, the charge transfer on La atom and the number of states at Fermi level (N(EF)) first increase and then slightly decrease, reaching maximum values at x=0.5. Meanwhile, La0.75Mg0.25Ni35-xCox (x=0, 0.3, 0.5, 0.7) alloys were prepared through induced melting method. The effects of substitution Co for Ni on the structure and properties of the alloys were systematically investigated. X-ray diffraction results show that the majority phase in the alloys is Ce2Ni7-type AB3.5 phase. The electrochemical analysis shows that both the discharge capacity and the cycling stability of the alloys reach the maximum values at x=0.5. It is observed from PCT measurements that the alloys can absorb hydrogen under 0.04 - 0.09 MPa hydrogen pressure at room temperature. Both the lowest absorption pressure of 0.04 MPa and the highest storage capacity of 1.587wt% were obtained with Co content of 0.5. The results clearly show that the property change of AB3.5 alloys with Co content can be predicted by first principle based theoretical calculations.