含锂盐、钾盐铝电解质体系的电化学原位Raman光谱研究

Aim at the situation of enrichment of lithium salts and potassium salts in electrolysis cell in a lot of Chinese aluminum company, electrochemical in situ Raman spectra study in aluminum electrolyte containing lithium salts and potassium salts is planned to be studied. Structural characteristics of the molten salts during the electrolysis process and the mechanism of electrode process are planned to be analyzed deeply and the effect of lithium salts and potassium salts is planned to be investigated. The applied range of Raman spectroscopy will therefore be extended. Firstly, a sample cell and furnace sysytem used for in situ Raman spectra study of high-temperature molten fluoride is planned to be prepared; secondly, the coupling measuring conditions of electrochemical experiment and Raman spectra scan will be studied. On that basis, in situ Raman spectra of the melts between the two electrodes and materials in the electrode district are planned to be scanned during the potentiostatic electrolysis, cyclic voltammetry, and potential step process. Structural characteristics of the molten salts under the electrical field will be analyzed, and the law of moving and transferring of the related complexes will be studied. Elementary step and dynamic process of the electrode reaction will be researched, and the mechanism of electrode process and anodic passivation are hoped to be obtained. In the whole study planned above, the effect of lithium salts and potassium salts on each researching part will be emphatically investigated. The whole study are hoped to provide basic information for optimizing the electrolysis process, increasing current efficiency, and decreasing energy consumption for aluminum electrolysis cells containing lithium salts and potassium salts.

本项目针对我国许多铝厂电解槽出现的锂盐、钾盐富集的情况，以深入探析铝电解过程中熔盐结构特征和电极过程机理，考察锂盐和钾盐对电解过程的影响，并拓展Raman光谱的应用范围为目标，进行含锂盐、钾盐铝电解质的电化学原位Raman光谱研究。 首先进行适合于高温氟化物熔盐电化学原位Raman光谱测定用热台和样品池系统的制备，并研究熔盐电化学原位Raman光谱测定的耦合测试条件；在此基础上，进行恒电位电解、循环伏安法、阶跃电位法等电化学测试过程中含锂盐、钾盐铝电解质两极间和电极区物质结构的原位Raman光谱研究。分析电场条件下铝电解熔盐的结构特征，探索相关结构基团的迁移和转化规律；研究电极反应的基元步骤和动力学过程，力图揭示电解电极过程机理和阳极钝化机理。着重考察锂盐和钾盐对上述研究过程的影响。为优化富集锂盐、钾盐电解槽的生产过程，提高电流效率，降低铝电解能耗奠定基础。

本项目针对我国许多铝厂电解槽出现的锂盐、钾盐富集的情况，进行了铝电解质的电化学原位Raman 光谱研究，首先制备了适用于高温挥发性熔盐电化学原位Raman光谱研究用的显微热台和样品池成套系统，能够获得较好的实验效果，并发展了高温铝电解熔盐电化学原位Raman光谱测定的综合分析方法。之后，通过计算机模拟和实际测定相结合的方式，测定了不同组成的MF-AlF3和MF-AlF3-Al2O3熔盐中络合离子团的存在形式和转化规律，得到了相关的Al-F、Al-O-F络合离子团的优化结构参数，并分析得到了阳离子对络合离子团的结构和电荷分布的影响规律。最后，研究了LiF-KF和NaF-AlF3-Al2O3熔盐中的石墨阳极过程，揭示了碳质电极在铝电解熔盐中发生电化学氟化与钝化机理，认为在LiF-KF体系中，石墨电极发生电化学氟化的电极反应为：xF−+C→CFx+xe−，这个电极反应的机理模式为完全不可逆电子传递机理模式，熔盐中石墨电极上生成CFx的电极反应的电子传递系数为0.27；在NaF-AlF3-Al2O3熔盐中，石墨阳极过程发生四个电极反应，按反应电位从低到高分别为生成CO2、CF4、CFx和F2的电极反应，生成CO2的电极反应的机理模式为耦合后置自催化化学反应的完全不可逆电子传递机理模式，该电极过程包含两个电子传递步骤，并且生成中间产物CxO；在NaF-AlF3-Al2O3熔盐中，Al-F络合阴离子团在高电位下与碳放电生成CFx，认为铝电解“阳极效应”发生的根本原因是由于阳极表面形成致密的CFx层阻塞传质过程。.本项目拓展了光谱电化学在熔盐结构研究领域中的应用；同时，通过对项目研究获得的“阳极效应”机理进行分析，认为可望从抑制CFx的生成或加速CFx的分解展开进一步研究，消除或抑制“阳极效应”发生。