## 3 Results and Discussion
### Co\({}_{2}\) Mechanism  
In this work, primary or secondary amines are considered to absorb CO\({}_{2}\). The amine will act as a nucleophile and bind the CO\({}_{2}\) via an electrophilic addition. The principle of electrochemical regeneration is to put this amine-CO\({}_{2}\) bond in competition with an amine-metal cation bond. One must therefore find the metal cation that interacts more strongly with the amine than with the CO\({}_{2}\). Metal cation was chosen so that the amine-metal cation complexation would be thermodynamically favored with respect to the amine-CO\({}_{2}\) reaction. For the metal complex to be thermodynamically favored over the amine-CO\({}_{2}\) bond, the constant for the formation of the metal complex must satisfy the following equation:  
\[log(\beta)\geq n_{ligand}\times log\big{(}K_{CO_{2}}\big{)} \tag{6}\]  
where \(\beta\) represents the global formation constant of the metal complex, \(n_{ligand}\) is the number of ligands complexing the metallic cation, and \(K_{CO_{2}}\) is the equilibrium constant of the amine-CO\({}_{2}\) reaction.  
\[M^{m+}+n\ amine=[M(amine)_{n}]^{m+} \tag{7}\]  
\[\beta=\frac{[M(amine)_{n}]^{m+}}{[M^{m+}][amine]^{m}} \tag{8}\]  
\[CO_{2}+amine=amine-CO_{2} \tag{9}\]  
\[K_{CO2}=\frac{[amine-CO_{2}]}{[CO_{2}][amine]} \tag{10}\]  
The amine selected in this work is ethylenediamine (EDA), and the metal cation is Fe\({}^{3+}\). This amine was chosen for its chelating properties. Iron forms octahedral complexes. This means that it forms six coordination bonds with its ligands. Ethylenediamine can form coordination bonds with its lone pairs on its two amine functions. Because ethylenediamine has two lone pairs, it is a bidentate ligand. Thus, to form its octahedron, an Fe\({}^{3+}\) cation binds with three molecules of ethylenediamine. The absorption cycle of CO\({}_{2}\) is illustrated in Figure 4.  
The amine solution, rich in absorbed gases, is sent to the anode compartment of an electrochemical cell (electrolyte, see Figure 2), and a potential difference (voltage) is imposed on the electrodes to carry out redox reactions. The electrolyzer consists of two  
Figure 4: The absorption cycle of CO\({}_{2}\).  
electrodes. The first is an anode where the oxidation reaction takes place; this is the positive pole of the electrolyzer. The second is a cathode where the reduction reaction occurs; this is the negative pole. If several redox reactions can happen at the anode and/or at the cathode, then at the anode, the oxidation reacting at lower potential will first and foremost occur and, conversely, at the cathode, the reduction reacting at higher potential will first and foremost take place. Here, the anode is iron, and it is oxidized to form Fe\({}^{3+}\) ions. These will compete with the CO\({}_{2}\) to interact with the amine. They complex with the amine and therefore release CO\({}_{2}\). This solution is then sent to a flash drum to shift the equilibrium and extract the CO\({}_{2}\) from the liquid phase to the vapor phase. Finally, this solution rich in metal cations and poor in CO\({}_{2}\) is sent to the cathode compartment of the electrochemical cell. Fe\({}^{3+}\) ions will be reduced to elemental iron with an iron cathode. Finally, this regenerated solution can be recycled and sent to the absorption column for a new cycle. The leads to the following overall reaction equation:  
\[M^{m+}+n\;amine(CO_{2}) = \left[M(amine)_{n}\right]^{m+}+n\;CO_{2(g)} \tag{11}\] \[Fe^{3+}+3\;EDA(CO_{2}) = \left[Fe(EDA)_{3}\right]^{3+}+3\;CO_{2(g)} \tag{12}\]