## 3 Results and Discussion  
### Li\({}_{2}\)CO\({}_{3}\) Splitting and CO\({}_{2}\) Transformation  
In electrochemical study, liquid molten salt has become one of the most promising media in the electrochemical field because of its high conductivity, wide temperature range, low vapor pressure and excellent mass transfer and heat storage. Theoretically, all the carbonates can be used as electrolytes to produce carbon materials by CO\({}_{2}\) electrolysis. However, compared with other carbonates, monovalent cation carbonates (Li\({}_{2}\)CO\({}_{3}\), Na\({}_{2}\)CO\({}_{3}\) and K\({}_{2}\)CO\({}_{3}\)) have higher conductivity, better heat and mass transfer performance at the same temperature, which is conducive to promoting CO\({}_{2}\) reduction and reducing the reaction energy consumption. The electrochemical reduction reaction of carbonate and hydroxide will occur at high temperature, and the thermal decomposition reaction will inevitably occur at the same time. As a competitive electrolytic reaction, the occurrence of thermal decomposition reactions will reduce the conversion of the target product and lead to energy independent loss. There has been some research reporting that the thermal stability of carbonates decreased with increasing temperature as Equation (1) describes [23; 24]. As is shown in the picture, the weight of Li\({}_{2}\)CO\({}_{3}\) is almost constant under an open atmosphere (-0.03% CO\({}_{2}\)), but dropped significantly over 800 \({}^{\circ}\)C. Thus, it indicates that the thermal decomposition reaction of Li\({}_{2}\)CO\({}_{3}\) will not occur below 800 \({}^{\circ}\)C. Another obvious pattern is that prolonged reaction time leads to a more severe decrease in the weight of Li\({}_{2}\)CO\({}_{3}\). It is evident that the weight decreases from 97.1% at the 6 h point to 85.9% at the 24 h point under 900 \({}^{\circ}\)C. According to the principle of chemical equilibrium, the reaction can be prevented from proceeding in the positive direction by increasing the concentration of the products in the system. It is indicated by the green line that the weight of Li\({}_{2}\)CO\({}_{3}\) shows hardly any change, only 0.2% at 1000 \({}^{\circ}\)C after 6 h. Therefore, it is suggested that excess CO\({}_{2}\) rapidly combines with newly generated Li\({}_{2}\)O in molten salts and produces Li\({}_{2}\)CO\({}_{3}\) again from the decreased weight loss. Similarly, we tried to increase the concentration of another product, Li\({}_{2}\)O to further slow the thermal decomposition of Li\({}_{2}\)CO\({}_{3}\). Proof by the navy blue and the purple point in Figure 1, that Li\({}_{2}\)O can not only slow down the mass loss of Li\({}_{2}\)CO\({}_{3}\) at high temperature, but also capture more CO\({}_{2}\) into the molten salt system (Equation (2)). Li\({}_{2}\)CO\({}_{3}\) thermal decomposition:  
\[\text{Li}_{2}\text{CO}_{3}=\text{Li}_{2}\text{O}+\text{CO}_{2} \tag{1}\]  
\(\text{CO}_{2}\) dissolution:  
\[\text{Li}_{2}\text{O}+\text{CO}_{2}=\text{Li}_{2}\text{CO}_{3} \tag{2}\]  
The experiment further verified the promotion effect of lithium oxide on the absorption of carbon dioxide in molten carbonates. No weight loss is observed in Li\({}_{2}\)CO\({}_{3}\) + Li\({}_{2}\)O (90:10, weight ratio) at 800 \({}^{\circ}\)C for 6 h. More significantly, the purple point in Figure 1 shows an apparent mass gain in the system of 80% Li\({}_{2}\)CO\({}_{3}\) + 20% Li\({}_{2}\)O. As further presented, the metal oxide can act as an absorber of CO\({}_{2}\), but Li\({}_{2}\)O shows a more excellent property. It is suggested that molten carbonates, represented by Li\({}_{2}\)CO\({}_{3}\), can transform CO\({}_{2}\) into carbon-based products and regenerate rapidly. Molten Li\({}_{2}\)CO\({}_{3}\) has over 10 moles of feedstock carbon per liter for electrochemical reaction at 750 \({}^{\circ}\)C. However, there is only 0.03-0.04% CO\({}_{2}\) in the air, about only 10\({}^{-5}\) moles of reducible carbon per liter.