## 3 Results and Discussion
### Amorphous Carbon  
In the synthesis process of new carbon-based materials, the carbon products obtained by electrolytic melting of \(\text{Li}_{2}\text{CO}_{3}+\text{Na}_{2}\text{CO}_{3}+\text{K}_{2}\text{CO}_{3}\) under conventional conditions are mainly amorphous carbon. Figure 3a-f shows the micromorphology of carbon products obtained in the carbonate system of \(\text{Li}_{2}\text{CO}_{3}+\text{Na}_{2}\text{CO}_{3}+\text{K}_{2}\text{CO}_{3}\) with an Fe cathode and  
Figure 2: (**a**) Picture of Fe cathode surface after electrolysis; (**b**)carbon products after purification; (**c**) SEM of carbon at 750 \({}^{\circ}\)C under 200 mA/cm\({}^{2}\); (**d**) EDS result of the obtained carbon product.  
Ni anode at current density of 50, 100 or 200 mA/cm\({}^{2}\). As the picture below shows, the obtained carbon products are all amorphous carbon.  
The operating temperature and current density/cell voltage have significant effects on the specific surface area of the prepared carbon materials. Lower operating temperature and higher current density/cell voltage are beneficial to increase the specific surface area of carbon-based materials. The results of carbon materials' specific surface area are displayed in Table 1. The specific surface area of obtained carbon is 127 m\({}^{2}\)/g at 450 \({}^{\circ}\)C under 100 mA/cm\({}^{2}\) but drops sharply to 37.1 m\({}^{2}\)/g at 550 \({}^{\circ}\)C under the same current density. The reason is that the increase in electrolysis temperature accelerates the carbon deposition reaction and promotes the formation of a dense carbon structure, which leads to a prominent decreasing specific surface area of carbon material. Besides, the top-down deposition rate of the cathode product slows down at low temperatures, resulting in a porous structure and a large specific surface area. For Li\({}_{2}\)CO\({}_{3}\) + Na\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\) (61: 22:17, weight ratio) system electrolyzed at 750 \({}^{\circ}\)C, the specific surface area of formed carbon  
Figure 3: Carbon products obtained from molten eutectic carbonates from 450 \({}^{\circ}\)C to 750 \({}^{\circ}\)C.  
is 28.2 m\({}^{2}\)/g at 50 mA/cm\({}^{2}\) and increases to 51.7 m\({}^{2}\)/g at 200 mA/cm\({}^{2}\). The reason for this structural change may be that the increase in current density leads to a higher voltage in the electrolysis cell. And the deposition of alkali metals on the carbon surface at higher cell voltage promotes the metal cation intercalation reaction, which is conducive to forming a loose and porous structure. The comparison of the products produced by a series of molten salt electrolytes with different compositions (NO.4, NO.7, NO.9) shows that the surface area of the carbon product is also affected by the composition and proportion of the electrolyte. The surface area of amorphous carbon generated from Li\({}_{2}\)CO\({}_{3}\) + Na\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\) (33: 33: 33, weight ratio) is up to 412 m\({}^{2}\)/g, but only 13.4 in Li\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\) (50%:50%). The reason is that under the same electrolysis temperature, the fluidity and conductivity of molten salt formulations are different, influencing the carbon deposition process. Different from the previously reported pure Li\({}_{2}\)CO\({}_{3}\) electrolysis [27; 28], carbon materials with a larger surface area are synthesized in a molten salt media containing less Li\({}_{2}\)CO\({}_{3}\). More importantly, carbon materials with high surface area and large pore volume also have important applications in adsorption and material transport. From what has been discussed above, carbon materials with different specific surface areas can be synthesized by changing the electrolytic temperature, cell voltage/current density, electrolyte composition and ratio to meet diverse needs.