Influence of current density on the erosion of a graphite cathode and electrolytic formation of carbon nanotubes in molten NaCl and LiCl

The electrochemical deposition of sodium and lithium from their respective molten chlorides onto a graphite cathode as the first step of carbon nanotube electrolytic production has been investigated. It has been shown that in the case of both sodium and lithium, as the cathodic current density increases, the cathode weight first increases and then decreases, i.e. the dependence of cathode weight change vs. cathodic current density passes through a maximum. The value of cathodic current density corresponding to the maximum increase in the cathode weight in the case of sodium is approximately 4 times as high as that in the case of lithium, which is explained by a higher solubility of sodium metal in molten sodium chloride compared to that of lithium metal in molten lithium chloride. The higher sodium metal solubility causes a higher electronic conductivity of the molten electrolyte, while the ratio of intercalated to dissolved sodium will be lower as compared to lithium. Curved multi-walled carbon nanotubes of an outer diameter of 20–50 nm with a wall thickness of 5–10 nm (molten NaCl) and of 20–100 nm with a wall thickness of 5–40 nm (molten LiCl) have been synthesized.