## 3 Results and Discussion
### Cellular Porous Carbon  
As mentioned above, lower electrolysis temperature and higher cell voltage/current density are beneficial for increasing the specific surface area of solid carbon-based products. Based on the above studies, Li\({}_{2}\)CO\({}_{3}\) + Na\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\) electrolyte is selected as the primary electrolyte for the best process factors to synthesize carbon materials with high specific surface area. The results are shown in the following SEM pictures. In Li\({}_{2}\)CO\({}_{3}\) + Na\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\) system (mass fraction 61%:22%:17%), nickel-chromium alloy is used to replace nickel as the anode material and galvanized iron as the cathode. The effective area of the cathode and anode are both 5 cm\({}^{2}\). And the current density of 100, 200, 400 or 500 mA/cm\({}^{2}\) is applied for constant current electrolysis at different temperatures. Unlike the previously reported butterfly wing carbon sheet, the honeycomb structure shows a high degree of regularity, and its content is more than 80%, as displayed in Figure 5a-d. The aperture distribution of the honeycomb structure is broad, ranging from the nanometer to micron level. Honeycomb carbon, formed by stacking sheets of carbon together, has a compact structure and high specific surface area. According to BET, the specific surface area of cellular porous carbon, separated from the electrolysis product at 450 \({}^{\circ}\)C with 500 mA/cm\({}^{2}\) in Li\({}_{2}\)CO\({}_{3}\) + Na\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\) electrolyte, is up to 198 m\({}^{2}\)/g. The surface area of carbon material with honeycomb structure can be further improved by decreasing the electrolysis temperature or applying higher current density. In addition, honeycomb-like carbon materials with high specific surface area have essential applications in gas adsorption and material transportation. Under this electrolytic condition, the cell voltage is about 3.2 V, considerably higher than the theoretical deposition potential of Li\({}^{+}\), Na\({}^{+}\) and K\({}^{+}\). Consequently, at such high cell voltages, the carbon products deposition process is accompanied by an alkali metal deposition reaction. It is inferred that the co-deposition of alkali metals is a crucial factor in forming the honeycomb-like structure of carbon. A Raman spectrometer is employed to detect the graphite crystal degree of cellular porous carbon, and the result is shown in Figure 6a. The Raman peak at 1340 cm\({}^{-1}\) (D band) corresponds to the defects and disorder-induced peaks in carbon materials. Another Raman peak at 1590 cm\({}^{-1}\) (G band) is produced by the stretching motion of sp\({}^{2}\) atom pairs in a carbon ring or long chain. The intensity ratio of the D band to the G band (\(I_{D}/I_{G}\)) is an important parameter to evaluate graphitization of carbon materials. For the cellular porous carbon obtained in the system of Li\({}_{2}\)CO\({}_{3}\) + Na\({}_{2}\)CO\({}_{3}\) + K\({}_{2}\)CO\({}_{3}\), the \(I_{D}/I_{G}\) value is about 0.8, indicating a high graphitization degree of the synthesized honeycomb carbon. An X-ray diffractometer is used to characterize the crystallinity to further reveal the structural features of the obtained carbon materials, and the result is displayed in Figure 6b. As the figure shows, there is a high intensity and sharp characteristic peak at 26(002), indicating that the graphite hexagonal crystal in honeycomb carbon is more regular and highly crystalline. Therefore, the carbon atoms in the obtained materials are mainly sp\({}^{2}\) hybridized. The electric capacity of carbon material with fewer defects is only about 360 mA\(\cdot\)h/g [33]. It is inferred that the carbon material with higher sp\({}^{2}\) content is difficult to combine with Li\({}^{+}\) in a mechanism similar to embedding, resulting in lower capacitance. As a new CO\({}_{2}\) utilization technology, molten salt electrochemical technology has attracted more attention in the field of carbon material synthesis.