The synthesis of new forms of carbon is of great use in the production of many new materials and comforts of modern life. The synthesis of carbon has previously been achieved through many paths, however a path that has been given some major interest in recent years as a medium temperature method of producing carbon products with interesting physical and electrochemical characteristics is the reduction of molten carbonate salts to form value-added carbon products [1]. Of these products, it has recently been noted that carbon nanofibers may form during the reduction of molten Li₂CO₃ in the presence of trace elements of transitional metals [2]. If carbon nanotubes can be formed through the reduction of molten carbonates it would be of great benefit for many fields, embodying a cheap, low energy cost method of producing these materials. This research investigates the formation of carbon tube structures from molten Li₂CO₃-K₂CO₃-Na₂CO₃ eutectic at 600°C-700°C using copper substrates (Figure 1). Findings suggest that optimal conditions for nanotube synthesis involve nucleation and growth steps, which occur concurrently with the formation of further carbon phases. The formed fibers are hollow tubes which may be capped unless broken, with two major size distributions, thick tubes and thin tubes. The thin tubes have diameters in the order of 300-400 nm.

[1] Hughes, M.A., J.A. Allen, and S.W. Donne, Carbonate Reduction and the Properties and Applications of Carbon Formed Through Electrochemical Deposition in Molten Carbonates: A Review. Electrochimica Acta, 2015. 176: p. 1511-1521.

[2] Ren, J., et al., One-Pot Synthesis of Carbon Nanofibers from CO2. Nano Letters, 2015. 15(9): p. 6142-6148.