The proposed ambipolar flow cell (AFC) is a low-cost, modular, and scalable electrodialysis technology for direct removal of carbon dioxide from seawater with drastic operation voltage reduction of >60%compared with bipolar membrane electrodialysis (BPMED) technology. The AFC is a three-chamber flow cell (Figure.1.) that utilizes H2/H+ through hydrogen oxidation/evolution (HOR/HER) at two separate half-cells to convert the HCO3-and CO32- ions in the center seawater stream into dissolved CO2. The AFC capitalizes on the highly reversible HOR/HER to achieve the salt splitting, resulting in a low theoretical cell voltage of 0.24 V (dependent on pH at each electrode). Figure 1 shows the three-chamber configuration of an AFC cell, in which a proton exchange membrane will be used to electronically separate the anode and the center compartment while the center compartment and cathode will be electronically separated by a sodium ion exchange membrane. These two membranes will provide ionic conductivity, proton at the anode|center interface while Na+ ion at the center|cathode interface, to complete the circuit. When in operation, fresh seawater (pH~8.1) will be circulated through the center compartment and cathode half-cell. The hydrogen will be oxidated at anode half-cell when a voltage is applied across the cell to release two protons (Equation 1) that will be transported though proton exchange membrane (e.g. Nafion 212 or other low-cost non-perflorinated cation exchange membrane (CEM)) to center compartment, where proton will react with HCO3- to produce acidified seawater and CO2 gas (Equation 2-4). As protons are consumed, the charge neutrality of the center-chamber will be maintained by transporting Na+ ions to the cathode half-cell, where hydrogen in water will be reduced, resulting in the generation of hydrogen gas that will be circulated back to the anode half-cell, and the formation of NaOH through the reaction of Equation 5. During the operation, the acidified seawater at center chamber will flow through cathode chamber where acidified seawater will react with NaOH to increase pH of the seawater. Figure 2. The applied voltage vs current density Figure 2 shows the preliminary performance of an unoptimized AFC flow cell. The cell voltage is only ~0.42 V at the current density is 2 mA/cm2, indicating a very low energy consumption of 40 kJ/molCO2 could be achieved to remove CO2 from seawater. The seawater measured at the outlet of the center chamber has a pH value of 6.03, indicating acidification and thus successful removal of the CO2. This results also corroborates with the observed basification of the cathode half-cell due to the HER (Equation 5), in which an increase of pH value was observed from 6.03 to ~8. We also successfully developed a hydrolytic softening assisted EHL (HS-EHL) to extract CO2 from seawater. Figure 3 shows the schematic description of the (HS-EHL) flow cell. The hydrolytic softening process (Equation 6) that can produce CaCO3 is integrated into EHL system that can provide acidified water solution to react with CaCO3. Comparing to EHL, sodium form cation exchange membrane is replaced by calcium form cation exchange membrane because CaCl2 solution will flow through center chamber instead of seawater. When in operation, CaCl2 solution and decalcified seawater will be circulated through the center compartment and cathode half-cell, respectively. The oxidation of hydrogen at anode of HS-EHL will release two protons (Equation 1) that will be transported though proton exchange membrane to acidify the CaCl2 solution at center compartment, the acidify CaCl2 will react with CaCO3 to get neutral CaCl2 solution and release CO2 gas. The charge neutrality of the center-chamber will be maintained by transporting Ca2+ ions to the cathode half-cell, where hydrogen in water will be reduced, resulting in the generation of hydrogen gas that will be circulated back to the anode half-cell. It is noted here that the pH of seawater at cathode chamber is maintained at ~9.5 to prevent the formation of Mg(OH)2 precipitate. After mixing with fresh seawater in the separated chamber, Ca(OH)2 will react with Ca(HCO3)2 in the fresh water to finish hydrolytic softening process. Ca(HCO3)2 + Ca(OH)2 -----2CaCO3 + 2H2O (Equation 6) Figure 3. the schematic description of HS-EHL system