# Analysis of Technologies for Carbon Dioxide Capture from the Air
## 2 DAC Technologies
### Electrochemical Method  
The first application of an electrochemical method was in the early 1970s to capture CO\({}_{2}\) in spacecraft cabins [115; 116]. In [PERSON] et al. [115], the system was able to capture 1.9 kgCO\({}_{2}\)/day without signs of deterioration after 260 days of working. Other studies have been reported in [PERSON] et al. [117] and [PERSON] et al. [118], considering a molten carbonate fuel cell at high temperatures. Substantially, in this method, CO\({}_{2}\) is captured using electrochemical reactions and an electrochemical cell operating in a fuel cell mode if electricity is provided or in a driving mode if electricity is consumed [119]. A fuel cell concentrator has been suggested by [PERSON] [23], as shown in Figure 8. In this system, hydrogen is used as the energy source to capture CO\({}_{2}\) and release it at a higher concentration. In addition, a filter-paper membrane is sandwiched between two gas diffusion electrodes (coated with carbon particle-support platinum catalyst) and is wetted by an electrolyte solution (a room-temperature ionic liquid) to support the transfer of ions between the electrodes, electrically connected with a variable resistive load. The stainless-steel current collector plates of the anode and cathode serve as gridded gas flow fields that deliver gases at known flow rates to the electrodes: H\({}_{2}\) at the anode and a combination of N\({}_{2}\), O\({}_{2}\) and CO\({}_{2}\) at the cathode. In the process, the cell temperature is kept at 298 K by using cooling water. The reactions that occur at the anode side are the following (see Equations (23)-(25)):  
\[H_{2}\to H^{+}+2e^{-} \tag{23}\]  
\[HCO_{3}^{-}+H^{+}\ \to H_{2}O+CO_{2} \tag{24}\]  
\[CO_{3}^{2-}+2H^{+}\to H_{2}O+CO_{2} \tag{25}\]  
while at the cathode side the following reactions occur (see Equations (26)-(28)):  
\[\frac{1}{2}O_{2}+H_{2}O+2e^{-}\to OH^{-} \tag{26}\]  
\[CO_{2}+OH^{-}\to HCO_{3}^{-} \tag{27}\]  
\[HCO_{3}^{-}+OH^{-}\ \to\ H_{2}O+CO_{3}^{2-} \tag{28}\]Essentially, the CO\({}_{2}\) provided at the cathode side reacts with OH\({}^{-}\) to form bicarbonate (HCO\({}_{3}\)\({}^{-}\)) (Equation (27)) and carbonate (CO\({}_{3}\)\({}^{2-}\)) ions (Equation (28)). After the diffusion of carbon ions at the anode side, these react with H\({}^{+}\) to produce more concentrated CO\({}_{2}\) and water. The Faradaic efficiency (the number of CO\({}_{2}\) molecules transferred over the total number of electrons transferred) and the energy consumption are, respectively, 23% and 350 kJ/molCO\({}_{2}\)[119]. Some disadvantages are present for this technology. As it is possible to see, the application of the electrochemical approach to CO\({}_{2}\) capture from the air has high energetic costs to deliver a large amount of air to the cell, due to the low CO\({}_{2}\) concentration, limitations in applicable current density and difficulties in generating a pure CO\({}_{2}\) stream [119]. However, some advantages of this methodology are the possibility of separating CO\({}_{2}\) in a single step; the continuous development; the lack of energy waste during the heating of the solvent or pressuring a gas feed, respectively, in the absorption and adsorption processes; the modularity able to capture CO\({}_{2}\) at different scale; and integration with a future electrified industry. Other studies have investigated the electrochemical approach. In recent years, [PERSON] and [PERSON] [120] have suggested a new kind of electrochemical method to capture CO\({}_{2}\) from the air or other gases, based on passing these on electrochemical plates working in charging and discharging modes and forming an interesting battery. The process is known as Faradaic electro-swing reactive adsorption for CO\({}_{2}\) capture.