## 3 Results and Discussion
### The Catholic Production of Carbon
In the electrolyte of Li\({}_{1.43}\)Na\({}_{0.26}\)K\({}_{0.21}\)CO\({}_{3}\) at certain conditions, as above-mentioned, the synthesis carbon comprises five elements (mole ratio): C (94%), O (5%), Na (0.3%), Au (0.3%), and Cl (0.3%). In particular, it needs to be explained that the peak of the Au element comes from the gold spraying operation before the SEM characterization. There is a predominant mole fraction (94%) of C to that of O in the solid black product, suggesting that the cathodic product is likely solid carbon, with a few oxygen-containing functional groups [34]. The small number of Na or Cl detected in the carbon products may come from the molten salts that have not been thoroughly cleaned. As in previous studies, the minimum theoretical electrolytic potential for carbon deposition is 1.65 V at 550 \({}^{\circ}\)C in a pure Li\({}_{2}\)CO\({}_{3}\) electrolyte. The working voltage was determined to be 2.5 V to ensure that the elemental carbon can be reduced on the cathode's surface. Considering the electrical resistance of molten salts and the corrosion resistance of electrolytic cells, 500 \({}^{\circ}\)C to 750 \({}^{\circ}\)C was selected to investigate the microstructure characteristics of carbon, and the SEM photographs are shown below in Figure 3a-d.  
Figure 2: (**a**) Cell-current curve and digital photos of the Fe cathode after different electrolysis times at 550 \({}^{\circ}\)C. (**b**) EDS analysis of the solid carbon obtained from the Li\({}_{1.43}\)Na\({}_{0.26}\)K\({}_{0.21}\)CO\({}_{3}\) electrolysis at 2.5 V.  
The carbon nanomaterial is a class of carbon material having at least one size less than 100 nm on the dispersed phase scale. The price of carbon nanomaterials is $10,000 to $400,000 per ton, approximately 10 to 400 times more than regular activated carbon. More importantly, the economic and application value of carbon nanomaterials is much higher than that of carbon dioxide material. It is evident from Figure 3a that amorphous carbon materials with unique microstructures can be obtained in an Li\({}_{2}\)CO\({}_{3}\)-Na\({}_{2}\)CO\({}_{3}\)-K\({}_{2}\)CO\({}_{3}\) electrolyte at 600 \({}^{\circ}\)C with 100 mA/cm\({}^{2}\). As can be seen intuitively in Figure 3b, a large number of spherical carbon particles with different diameters (micron scale) obtained at different cell voltages are irregularly stacked together, showing similar microstructures and appearing like aggregates of carbon nanoparticles. The main reason for producing carbon spheres is the interfacial effect of Cao and BaO, which is formed during electrolysis. The diameter of a carbon sphere product is approximately 200-300 nm. Honeycomb carbon is another product with a unique microscope morphology, which is generated via electrolysis in alkali carbonates at 450 \({}^{\circ}\)C with 450 mA/cm\({}^{2}\). By regulating the electrolysis temperature and current density, carbon materials with high surface area, up to 200 m\({}^{2}\)/g, can be separated from the cathode's surface. More importantly, carbon nanotubes (CNTs) are observed in the SEMs of products obtained in pure Li\({}_{2}\)CO\({}_{3}\) at 750 \({}^{\circ}\)C with 10 mA/cm\({}^{2}\), initially, and 100 mA/cm\({}^{2}\), finally. The purity of CNTs with a diameter of 50-80 nm is up to 80%, and their current efficiency can reach more than 85%. It has been demonstrated that molten salt electrochemical technology has the potential to electrochemically reduce CO\({}_{2}\) to high-value, carbon-based materials. An X-ray diffractometer (XRD) and Raman spectroscopy were employed to further characterize and analyze carbon nanotubes, which is shown in Figure 4. In the left of Figure 4, a significantly enhanced and narrow characteristic peak (red star) of carbon nanotubes is observed at 26\({}^{\circ}\) (002), indicating that the graphite hexagonal crystals in the CNTs are relatively regular and the degree of crystallization is high.