Study of Electrodeposition Method to Produce Carbon Nanotubes

Abstract

Since its first observation, Carbon Nanotubes (CNT) has drawn considerable research interest. Numerous investigations revealed outstanding properties for this unique form of carbon. Its remarkable characteristics include its electronic properties, thermal conductivity, and mechanical properties offer tremendous new opportunities and applications, often described as technological marvels. Nevertheless, like other new materials, CNT faces the transfer phenomenon from marvel material to market driven by its profitability or marketability. From the market perspective, the need for carbon nanotubes increases each year, while in the manufacturing view, production is plateauing. Therefore the gap between supply and demand exists, and the commercial viability of CNTs seems assured. However, the market's growth will depend on the efficiency in tackling dominant factors such as price to be competitive. No matter how excellent new materials are, the requirement of cheap to produce, consistent quality, easy handle and toxicity tolerance were always the rule. This study presents the Electrodeposition method as an alternative method to producing Multiwalled Carbon Nanotubes (MWCNT) utilising CO2 as carbon feedstock. Four approaches are discussed in this thesis: Literature review, Molecular dynamics, and experiments using Taguchi and OFAT (One Factor at a Time). Electrodeposition is a method that utilises molten salt, atmospheric CO2, and electrodes that can perform without catalyst preparations. At the same time, the requirements of well-established methods such as Arc Discharge, Laser Ablation, and Chemical Vapour Deposition result in a less cost-effective product and are challenging to scale up. In arc discharge, pure graphitic carbon soot can be utilised to synthesise CNT, but the addition of catalysts and preparation is required to produce a large amount of CNT. However, the electrode size and high current proportion are limited even with the extra preparation process. Laser ablation produces high-quality CNT with the limitation of its laser power requirement, while preparing catalyst in CVD also adds time or labour cost. The literature review in this study concludes that Electrodeposition can produce carbon nanotubes in an uncomplex way due to preparation ease. Electrodeposition does not have the limitation of the previous process and is arguably easier to scale up. However, this method has some challenges that need to be addressed, most related to synthesis parameters. In the previous research, the study is conducted partially and comparing the result is sometimes unusable since each investigator weighs in some value over another. For example, yield is measured in the purity or weight of the end product, and other research considers the CNT growth area or catalyst-CNT ratio in the system. In this research, Molecular dynamics, Taguchi and OFAT (One Factor at a Time) methods counter the challenges by providing a thorough study. Molecular dynamics determine the base behaviour expected from variables, focusing only on parameter changes that affect the carbon bonds formed in the electrodeposition system. Furthermore, Taguchi and OFAT are used to optimise variables and examine the end-product properties of each variable on an experiment basis. From molecular dynamics, it is found that the carbon bond created is affected by the total energy in the system, while total energy depends on variable value. Under the theoretical models used in the simulation, increasing parameters value which includes temperature, external potential, Carbon number in the system, and synthesis time, increases the carbon bond created in the system. Furthermore, changing the cathode from Ni to Cu decreases the carbon bond formed. Using the Taguchi method L25 design with five parameters, optimisation was conducted. The optimisation result is not as linear as the expectations of the Molecular dynamic and revealed that other factors, such as the Expansion of molten salt, conductivity gain, current instability, and excessive carbon debris, play roles in the system. The use of metal alloys was essential to promote CNT, as suggested in the previous investigation, which is supported in this thesis. Further evidence of better performance electrode metal alloys is found in Taguchi and OFAT, in which Zn alloys dominated early research. The OFAT also present the end-product characterisation under parameter changes utilising XRD, FTIR, Raman SEM, and EDX analysis. Using the Taguchi method L25 design with five parameters, optimisation was conducted. The optimisation result is not as linear as the expectations of the Molecular dynamic and revealed that other factors, such as the Expansion of molten salt, conductivity gain, current instability, and excessive carbon debris, play roles in the system. The use of metal alloys was essential to promote CNT, as suggested in the previous investigation, which is supported in this thesis. Further evidence of better performance electrode metal alloys is found in Taguchi and OFAT, in which Zn alloys dominated early research. The OFAT also present the end-product characterisation under parameter changes utilising XRD, FTIR, Raman SEM, and EDX analysis.