Effect of various temperatures and voltage variation on electro-deposition of carbon using CaCO3-Li2CO3-LiCI salt
Demand in carbon materials for various applications i.e. energy storage, biosensors and etcetera, calls the need to produced carbon materials especially nano-sized carbon. The microstructure, size and structure of the carbon materials are important in determining its possible application. One of the...
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| Format: | Thesis |
| Language: | English English |
| Published: |
2018
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| Subjects: | |
| Online Access: | https://eprints.ums.edu.my/id/eprint/42181/1/24%20PAGES.pdf https://eprints.ums.edu.my/id/eprint/42181/2/FULLTEXT.pdf |
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| Summary: | Demand in carbon materials for various applications i.e. energy storage, biosensors and etcetera, calls the need to produced carbon materials especially nano-sized carbon. The microstructure, size and structure of the carbon materials are important in determining its possible application. One of the potential process to produced carbon materials is electrolysis of molten salt. Electro-deposition process is a preparation of solid carbon via electrolysis process using molten salt as electrolyte. The molten salt electrolyte has high melting temperature thus not economical. Furthermore, the electrolysis parameters; temperature and voltage play important role in determining the quantity and quality of carbon produced. Therefore, the aims of this research were to formulate salt mixture to obtain low melting temperature, to investigate the effects of electrolysis temperature and voltage on the amount of carbon, microstructure, purity, and carbon structure, and to determine the energy usage for electrolysis process. In this study, carbonate and chloride-based salts were properly selected to formulate a mixture with low melting temperature and with low electrochemical stability to ensure successful deposition of solid carbon via electrolysis process. Molten salt mixture containing CaCO3, Li2CO3 and LiCl was successfully formulated with mole ratio of CaCO3:Li2CO3:LiCl = 0.09:0.28:0.63 (m.p. = 495°C), that has much lower melting temperature compared to CaCO3 (decomposes at 825°C), Li2CO3 (m.p. = 726°C) and LiCl (m.p. = 610°C) individually. In the electro-deposition process, electrolysis process was carried in two-electrode cell using AISI 304 stainless steel electrodes under CO2 gas environment, with voltage 4 – 6V and temperature of 550, 650 and 750°C. The CO2 gas was captured and electro-converted to solid carbon which then deposited on the cathode surface. Solid carbon was successfully deposited using the newly formulated salt mixture. For further understanding and comparison, electrolysis processes were also carried out for the individual salt electrolyte; CaCO3, Li2CO3 and LiCl. It was found that only Li2CO3 and LiCl were able to deposit solid carbon. SEM images of solid carbon prepared in Li2CO3 electrolyte consisted of particles and tubes with diameter ranging from 0.05 to 0.2μm, whereas LiCl produced large flakes and small particles with size 0.5 to 6.5μm range. Carbon prepared in CaCO3–Li2CO3–LiCl salt mixture revealed five dominant microstructures: grape-like, tubes, thread-like, spheres, and flakes. Nanotubes structures of 13 – 90nm outer diameter was also detected under TEM analysis. The size of the carbon microstructures decreased with elevation of temperature and enlarged when cell voltage increased. Elemental analysis had confirmed that electro-deposited products prepared in the newly formulated salt at various temperature and voltages have 69 – 82% carbon content. The XRD analysis had revealed carbon with amorphous structure for all carbon produced in various temperature and voltage. Electrolysis efficiency were calculated for processes carried out at 550°C (70 – 85%), 650°C (28 – 46%) and 750°C (59 – 79%) and had shown peculiar trend where 550°C give the highest efficiency, followed by 750°C and 650°C process. Higher electrolysis efficiency uses less energy thus the equivalent trend in the amount of energy usage was observed; electrolysis at 550°C (62 – 85kW.h/kg) uses lowest energy followed by electrolysis at 650°C (186 – 554kW.h/kg) and 750°C (70 – 126kW.h/kg). |
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