熔盐电解固态混合物制备纳米空心材料的研究

Direct electro-reduction of solid compounds in molten salts is a simple and straightforward electrolytic metallurgical method. Large-scale deployment of the above approach in metallurgy is significantly retarded due to low energy efficiency and sluggish kinetics. However, many unusual interfacial processes exist in molten salt electrolysis, which might offer opportunities on high-efficient preparation of functional materials with high added value. It was demonstrated in our laboratory that hollow nanostructured Si-Ge alloys could form via direct electro-reduction of solid mixtures between SiO2 and GeO2 in molten salts. It was speculated that the formation of hollow nanostructured electrolytic products might be due to the presence of “Nanoscale Kirkendall effect”. Such an unprecedented phenomenon might result from the coupling between electrochemical process in cathode and solid diffusion in electrolytic products. Further to the preliminary results, the present project aims at deep understanding of the unheeded correlation between electrode kinetics and solid diffusion both in cathode during molten salt electrolysis of solid mixtures. To develop controllable preparation of hollow nanostructured materials with high added value, the present project would systematically investigate the fundamental principles of the process. It consists of: (1) interaction between solid cathode and molten salts; (2) electrode kinetics in cathode; (3) solid diffusion in cathode; (4) nucleation and growth of electrolytic products, and (5) application capability of electrolytic products in electrochemical energy storage/conversion devices. The results are therefore helpful to establishment of systems suitable for formation of hollow nanostructured materials by molten salt electrolysis of solid mixtures and specification of correlations among electrolysis conditions, energy efficiency of molten salt electrolysis, composition/microstructure of electrolytic products and functionalities of electrolytic products. The present study forms a solid scientific ground for developing cost-affordable and energy-efficient molten-salt-electrolysis preparation, which also opens a new avenue towards facile construction of hollow nanostructured materials.

熔盐电解固态化合物这一短流程电化学冶金技术虽在大规模冶金上尚存在能量效率低和动力学慢的不足，但其中蕴含诸多有待深入认识和可兹利用的特异界面过程，可能为高效制备高附加值的功能材料开辟新的途径。申请者在熔盐电解硅锗混合氧化物的研究中，观察到阴极中可能因为存在纳米柯肯达尔效应而形成具有纳米空心结构的硅锗合金这一特异现象，并推测这是由于熔盐电解过程中电化学过程与产物固相扩散过程耦合的结果。本项目拟在此基础上，深入认识这一科学问题，并据此可控制备高附加值的纳米空心材料。拟通过研究熔盐与固态阴极的相互作用、阴极电极过程动力学、产物固相扩散规律、产物生长规律和产物的电化学能量转换与存储性能，建立适合熔盐电解制备纳米空心材料的体系，揭示电解条件-电解能量效率-电解产物成分和微结构-电解产物应用特性的相互影响规律，为发展经济高效的熔盐材料制备技术提供科学基础，并为纳米空心材料的合成提供新的思路。

熔盐电化学蕴含诸多有待深入认识和可兹利用的特异界面过程，可为高效制备高附加值的功能材料开辟新的途径。本项目围绕“熔盐电化学制备纳米空心材料”这一总体目标，通过深入系统研究熔盐电化学界面反应规律这一关键科学问题，成功开发出熔盐电解固态混合物、熔盐电解金属氧化物和有机质混合物、和熔盐电解二氧化碳这三种技术路线，实现了熔盐电化学制备纳米空心材料。项目进展如下：.（1）利用“电化学还原-固相扩散”原位耦合机制，通过熔盐电解固态混合氧化物实现了纳米空心硅基合金的短流程无模板制备。.（2）利用原位电沉积银诱导液固转化机制，通过熔盐电解固态二氧化硅和氯化银实现了硅纳米管无模板制备。.（3）将有机质熔盐热解碳化和熔盐电解金属氧化物有机结合，采用熔盐同步热解电解耦合策略处理有机质包裹的二氧化硅，有机质壳层热解碳化将电解硅胶囊化，实现了纳米空心硅碳的制备。.（4）利用熔盐电化学原位转化碳阳极上产生的二氧化碳，通过同槽耦合串联金属氧化物熔盐电解和熔盐电化学二氧化碳转化，实现了制备碳纳米管包裹金属。提供了碳材料升级转化的新思路，即碳阳极中的碳在阴极升级转化为高附加值碳纳米管。.（5）利用熔盐电化学二氧化碳还原中阴极气体的鼓泡效应成功制备了纳米空心碳。.上述对熔盐电化学界面反应规律的研究揭示了熔盐电化学是制备纳米空心材料的有力手段；同时制备纳米空心材料也是提高熔盐电化学冶金和熔盐电化学减碳的效率和产物附加值的实施途径。本项目为短流程低碳冶金技术提供了实施途径。

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