Carbon Nanotubes Synthesis from CO₂ Based on the Molten Salts Electrochemistry: Effect of Alkaline Earth Carbonate Additives on the Diameter of the Carbon Nanotubes

Molten carbonate electrolysis demonstrates a feasible approach for the direct transformation of CO 2 into reusable carbonaceous substance. In this work, in addition to previously commonly used expensive Li 2 CO 3 , alkaline earth carbonates of CaCO 3 , SrCO 3 and BaCO 3 which are abundant in nature and of much lower price are employed to combine with Li 2 CO 3 and contribute to the production of valuable carbon nanotubes. Structural features of the synthetic carbon nanotubes are characterized by scanning electron microscope, transmission electron microscope, high resolution transmission electron microscope and X-ray diffractometer. The results demonstrate that galvanostatic electrolysis in pure or alkaline-earth-carbonate-included Li 2 CO 3 provides a high yield of valuable carbon nanotubes production. Alkaline earth carbonate additives produce thicker carbon nanotubes than pure Li 2 CO 3 case, but the lattice distances of the carbon nanotubes electro-deposited in different electrolytes exhibit a good consistency with the standard data of multi-walled carbon nanotubes. Thermodynamic calculations are conducted in order to figure out why alkaline earth carbonate additives prefer thicker carbon nanotubes production. Summarily, this work discloses a rich understanding of how alkaline earth carbonates impact the size of carbon nanotubes and should be helpful to the future size control study.