| Carbonaceous materials have attracted great attention in material science and engineering, since nano diamond, fullerene, carbon nanotube and graphene being successively discovered. In particular, carbon nanotube and graphene have been widely used in, the preparation of compound with metal, ceramic and conducting polymer, energy storge devices, sensor and display, for their excellent properties in mechanical, thermal and electrical performance. On one side, CO2 is a kind of greenhouse gas. But on the other side, it is an abundant, notoxic, non-flammable, easily available, environmentally friendly and renewable carbon source. So it is proposed that carbonaceous material can be extracted using CO2 as a feedstock. However, the biggest challenge for this process is the inherent thermodynamic stability and kinetic inertness of CO2. Molten salt, who has distinctive properties, such’as good ionic conductivity, wide electrochemical window and fast kinetic reactions, is widely used in electrochemical metallurgy. Therefore, molten salt can be an alternative for electrochemical processing of CO2.Molten CaCl2 has been widely used as the electrolyte, particularly in the famous FFC and OS processes, for its high solubility of oxygen ions and easy. availability. Oxygen ions are also regarded as capture agent for CO2. So the extraction of carbonaceous materials from CO2 has been realized in CaCl2 based molten salt and the main work is summarized as follows:(1) The RuO2-TiO2 composite anodes have been successfully prepared and owned an excellent physical and chemical stability, which were systematic evaluated by anodic polarization accompanied by an in situ analysis of anode gases using the mass spectra, proving the capability of the sustained evolution of oxygen at the TiO2*RuO2 anode during electrolysis, meaning that this oxides anode could be a potential candidate as inert anode in calcium chloride-calcium oxide melts for green metallurgical processes.(2) The capture abilities of CO2 in CaCh based molten salt have been evaluated. CaCl2 based molten salt showed a strong affinity to CO2 and CO2 can be fixed into CO32-.(3) The ultrathin graphite sheets have been successfully extracted from CO2 in CaCl2-CaO melt at 850 ℃, using RuO2-TiO2 pellet and stainless steel as inert anode and cathode, respectively. The reduction mechanism of CO32- was investigated by cyclic voltammetry and square wave voltammetry. Results demonstrated that there are two steps in electrochemical reduction of CO32-CO32-(â…£)+2e â†' CO22-(â…¡), CO32-(II)+2eâ†'C. The diffusion efficient is calculated to be 2.17x 10-5 cm2 s-1.(4) The graphene has been successfully extracted from CO2 in CaCl2-NaCl-CaO melt at 750 ℃ and 850 ℃, using RuO2-TiO2 pellet and stainless steel as inert anode and cathode, respectively. The morphology and structure was greatly influenced by the temperature, and the thickness of the graphite sheet decreased with the increasing temperature. In the same way, Ni, W and Cu have been employed as cathode, and graphene can also be obtained on Ni and Cu. The intrinsic nature for the formation of graphene can be ascribed to the catalysis of active Fe, Ni and Cu atom at the surface of the cathode and the microexplosion effect through evolution of CO in the interlayer space of graphite layer. The reduction mechanism of CO32- was investigated by cyclic voltammetry and square wave voltammetry. Results demonstrated that there are two steps in electrochemical reduction of CO32-:CO32-(â…£)+2e-CO22-(â…¡), CO32-(â…¡)+2e â†' C. The reduction potential shift toward the positive direction and the diffusion coneffcient increased with the increasing temperature.(5) In this section, the carbonaceous material has been employed as the cathode such as graphite and glassy carbon, where carbon sphere, carbon nanotube and graphite sheet were obtained. The morphology of carbon collected from graphite and glassy carbon are quite different at the same condition. Furthermore, to some extent, the morphologies of carbon on glassy carbon are influenced by the temperature. |
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