## 3 Results and Discussion  
### Reaction Mechanism of Single CO\({}_{2}\) and CO\({}_{2}\) and H\({}_{2}\)O  
It is well known that the traditional CO\({}_{2}\) activation and conversion methods are limited by the high stability and low conversion of CO\({}_{2}\). Under standard conditions, only 1.3 \(\times\) 10\({}^{-5}\) moles of carbon per liter of air are available for the reaction. As high as 28.5 moles o reducible CO\({}_{3}^{2-}\), nearly seven orders of magnitude more than the air, is in one liter of molten Li\({}_{2}\)CO\({}_{3}\) at 723 \({}^{\circ}\)C. The results show that the reducible carbon concentration of carbonate anions is much higher than that of airborne or dissolved carbon dioxide, which improves the mass transfer efficiency.  
The movement, reduction, and absorption of carbon dioxide are carried out by the electrolysis of tetravalent carbon to zero-valent carbon or other carbon-based fuels on the cathode's surface [20,21]. There is a general belief that the electrochemical reaction of CO\({}_{2}\) in molten salts occurs in two different reaction mechanisms: the direct path and the indirect path [20]. As shown in the below equations, more authors are inclined to recognize that elemental carbon is generated indirectly in molten salt by CO\({}_{2}\) through CO\({}_{3}^{2-}\). Alkali or alkaline earth metals, such as Li, Na, and K, are represented by M. The most apparent difference between the reduction mechanisms is the first step, the transformation from CO\({}_{2}\) to charged CO\({}_{3}^{2-}\) (Equation (4)). Then, the newly formed CO\({}_{3}^{2-}\) from the CO\({}_{2}\) and the original ionized CO\({}_{3}^{2-}\) from the electrolytes can be reduced to elemental C or bivalent CO and oxide ions via Equation (5) or (6). There are two different reaction trends for O\({}^{2-}\) that is formed simultaneously with the reduction products. One part of the O\({}^{2-}\) moves to the anode, where it loses two electrons and converts into O\({}_{2}\) (Equation (7)) [22]. The rest of the O\({}^{2-}\) further acts as an absorbent for CO\({}_{2}\), allowing the regeneration of molten carbonate electrolytes (Equation (7)) [23]. The H\({}_{2}\)O is also transformed into H\({}_{2}\) and O\({}_{2}\) through the process that resembles that of CO\({}_{2}\)[24,25].  
First Step: absorption of CO\({}_{2}\) in molten salts  
\[\rm M_{2}O+CO_{2}=M_{2}CO_{3} \tag{4}\]  
Second Step: reduction of CO\({}_{3}^{2-}\) to CO or C  
\[\rm CO_{3}^{2-}+2e^{-}=CO+2O^{2-} \tag{5}\]  
\[\rm CO_{3}^{2-}+4e^{-}=C+3O^{2-} \tag{6}\]  
Oxidation of O\({}^{2-}\)  
\[\rm O^{2-}=O_{2}+4e^{-} \tag{7}\]  
Regeneration of CO\({}_{3}^{2-}\):  
\[\rm CO_{2}+O^{2-}=CO_{3}^{2-} \tag{8}\]  
In this study, the electrochemical reduction of a single CO\({}_{2}\) or CO\({}_{2}\) and H\({}_{2}\)O is driven by applying an external electric field to the sealed reaction electrolyzer. The electrical energy consumed in this process can be replaced by sustainable energy sources, including solar, wind, and tidal power. As shown in Scheme 1, the environmental contaminant CO\({}_{2}\) is transformed into solid carbon or co-electrolyzed with convenient H\({}_{2}\)O to generate syngas or CH\({}_{4}\) by high efficiency and selectivity on the cathode's surface. As mentioned above, the electrolyte can be regenerated through the rapid absorption capacity of the intermediates (metal oxides) for CO\({}_{2}\) and H\({}_{2}\)O, completing the construction of the circulatory system.