Some Studies On The Relative Electrode Processes Of Direct Electro-Reduction Of Metal Chlorides In Ionic Liquids

Ionic liquids have received increasing research and commercial interests all over the world in recent years. They are regarded as one of the most promising solvents that may lead to a breakthrough in solving industrial problems related with pollution and safety The development of science and technology based on ionic liquids really took off as these liquids were envisaged as lower-temperature electrolytes. As to application in electro-deposition, ionic liquids provide an advantageous alternative to conventional electrolytes based on water, organic solvents, and molten salts. For example, they have a wide potential window, high electrical-conductivity. Compared to high temperature molten salt, the property of ionic liquids being liquid at room temperature can decrease the thermal energy input and meliorate corrosion problem at a higher temperature. Recently, more studies on preparing metals by electrodeposition of metal ions in ionic liquid have been performed in the new coming non-chloroaluminate ionic liquids due to its water-stability. However, the low solubility of metal chlorides in the Lewis neutral non-chloroaluminate ionic liquid limits its application. In this thesis, a novel method for electrochemical preparation of nano-metal powder, direct electro-reduction of solid metal chlorides in non-chloroaluminate ionic liquid, was proposed and investigated for the first time, and the anodic reaction has also been studied. The main results are summarized as follows.Firstly, this thesis summarizes some existing problems in synthesizing and purifying non-chloroaluminate ionic liquids. In the quaternization reaction, the experitmental conditions become milder from chloroalkanes to bromoalkanes. In the case of anion-exchange reaction, Lewis acid was found to be a better raw material than salts, especially to the synthesis of water-immiscible ionic liquid, such as [BMIM]PF6, due to the absence of solid byproduct and the low-cost of acids. The [BMIM]PF₆ was choosen as the electrolyte for the futher study in this thesis for its satisfying electrochemical performance as well as the simpler synthesis procedure.Secondly, this thesis presents investigation results from the direct electro-reduction of solid metal chlorides in non-chloroaluminate ionic liquids. It was found for the first time that nano-copper powder can be prepared by the method in the potential region of -1.2—1.8V (vs. Ag+/Ag)in [BMEVI]PF6. The average size of obtained copper powder particle is in the range of 1-1 Onm, while the size of the metal cluster is in the range of 30²00nm. More importantly, the obtained nano-copper showed an excellent antioxidability. The influence of potential and temperature on the morphology has also been studied. Furthermore, it is believed that this process can be developed as a general and promising method for preparing ultra-fine metal powder in the non-chloroalumina ionic liquids based on the electrochemical investigation of other metal chlorides in the electrolyte.Finally, the thesis examines the anodic behavior of chloride ion in [BMIM]PF6 ionic liquid. The unusual observation was that during constant potential or current electrolysis, the oxidation of the chloride ions did not lead to chlorine gas evolution. Investigation by cyclic voltammetry and UV-Vis spectrometry revealed that the anodic products of electrolysis, including CI2 and C13^, were retained in the ionic liquid.