双氰胺基离子液体低温电解制备稀土金属镧的基础研究

The present critical situation of energy shortage and increasing aggravation of greenhouse effect requires the preparation of rare-earth metals with lower energy consumption, lower cost and environmental- friendly, however, to produce metal lanthanum, the current high-temperature molten salt electrolysis process suffers from high energy consumption, low efficiency, enormous quantities of exhaust emissions as well as severe corrosion of the equipment issues. This project focuses on investigation of the low-temperature electrolytic preparation of rare-earth metal lanthanum from dicyanamide anion-based ionic liquids (ILs) based on the high chemical and thermal stability, good thermal and ionic conductivity, wide electrochemical windows and environmental- friendly characteristics of ILs. The dissolve coordinated behavior of lanthanum chloride in ILs, solvated structure as well as the most stable configuration of La(Ⅲ) ions in ILs will be studied. And an electrochemical kinetic model on the cathode/ILs interface where the reaction of the metallic complexes happened will be established to demonstrate the electrode reaction kinetics, explore the charge transfer mechanism, and then reveal the electrochemical reduction mechanism of La(Ⅲ) complexes in ILs. Furthermore, the effect of electrolytic parameters on the current efficiency, power consumption and cathodic products, and the interrelation between the electrodeposition conditions and the electrodeposited lanthanum products will be used to identify the nucleation and growth regulatory mechanism of metal lanthanum in ILs. Finally, the corresponding technology prototype will be proposed. The findings by this project research will provide both scientific foundation and technical support for the electrochemical processes of metal lanthanum preparation in an energy conservation and environmental-friendly manner.

面临能源短缺和环境恶化的双重压力，开发低能耗、低成本、绿色化的稀土金属制备新方法日渐成为人们研究的重点。本项目针对离子液体性质稳定、导热导电性良好、电化学窗口宽和环境友好等特点，提出采用双氰胺基离子液体为电解质，开展稀土金属镧的低温电解制备。研究LaCl3在双氰胺基离子液体中的溶解配位行为，分析离子液体中La(Ⅲ)的溶剂化结构与最稳定配位构型；建立金属配合物在阴极/离子液体界面上的电化学反应动力学模型，开展反应动力学研究，探讨其电荷转移机制，揭示离子液体中La(Ⅲ)配合物的电化学还原机理；分析电解参数对电流效率、电耗及阴极产物的影响规律，探索电沉积条件与金属镧产物间的关联性规律，确定离子液体中金属镧的形核与生长规律及调控机制，提出相应的技术原型。研究工作为发展金属镧的节能减排和绿色生产新技术提供科学依据和技术支撑。

现行的高温融盐电解法在制备金属镧时存在能耗巨大、效率低、废气排放量高且设备腐蚀严重等不足。本项目针对离子液体性质稳定、导热导电性良好、电化学窗口宽和环境友好的特点，提出采用双氰胺基离子液体为电解质，开展稀土金属镧的低温电解制备。. 项目系统研究了具有不同阳离子与DCA-阴离子组合所得双氰胺基离子液体中LaCl3的溶解配位行为；333 K时，LaCl3在咪唑型-[BMIM]DCA、吡啶型-[BMP]DCA 和季铵型-[Me3NBu]DCA 三种不同类型双氰胺基离子液体中的溶解度分别为2.82，3.63和2.35 g/100g-ILs，满足电沉积的需求；确定了离子液体中La(Ⅲ)的稳定配位构型为[La(DCA)4]-，其还原为受扩散控制的准可逆过程，333 K条件下，扩散速率为1.17 × 10-10 cm2 s-1；选取惰性阳极，恒电位沉积可在铂基体上得到金属镧沉积层。通过控制电位可得到不同纳米结构的金属镧，随着沉积电位的负移，其晶粒细化，形貌从均匀纳米颗粒向蓬纳米多孔、海绵状结构转变。但由于纳米构型金属镧活性很高，极易氧化，不利于获得高纯金属镧。双氰胺基离子液体[BMP]DCA中，通过诱导电沉积引入碱金属Ni可实现Ni-La合金共沉积，成功稳定了纳米构型的金属La，抑制其氧化；333 K，-1.30 V vs.Ag /AgCl恒电位沉积控制电量密度为1.5 C cm-2可得到纳米颗粒组装的多孔状构型的合金薄膜。合金中La与Ni的协同作用不仅引发形貌重组并修饰了Ni-La合金表层Ni原子的电子结构，进一步激发了单质Ni的本征催化活性和稳定性，获得了具有高催化析氢性能的Ni-La合金薄膜材料。研究工作为低温电沉积制备金属镧及其合金提供了一种新途径，具有较好的应用前景。. 低共熔离子液体可替代双氰胺基离子液体用于电沉积制备镍基-稀土合金薄膜材料，在Ethaline中，分别以NiCl2和Ce(NO3)3为镍和铈盐前驱体，控制-0.85 V vs.Ag/AgCl电量密度5 C cm-2条件下，可得到具有优异催化析氧性能的Ni-Ce合金薄膜材料。将低共熔离子液体作为电解质用于电沉积制备纳米镍基-稀土复合催化电极材料，为寻找贵金属电催化剂替代物提供了新方向。