Direct Air Capture Using Electrochemically Regenerated Anion Exchange Resins

Direct air capture (DAC) aims to remove CO₂ directly from the atmosphere. In this study, we have demonstrated proof-of-concept of a DAC process combining CO₂ adsorption in a packed bed of amine-functionalized anion exchange resins (AERs) with a pH swing regeneration using an electrochemical cell (EC). The resin bed was regenerated using the alkaline solution produced in the cathodic compartment of the EC, while high purity CO₂ (>95%) was desorbed in the acidifying compartment. After regenerating the AERs, some alkaline solution remained on the surface of the resins and provided additional CO₂ capture capacity during adsorption. The highest CO₂ capture capacity measured was 1.76 mmol·g^-1 dry resins. Moreover, as the whole process was operated at room temperature, the resins did not show any apparent degradation after 150 cycles of adsorption-desorption. Furthermore, when the relative humidity of the air source increased from 33 to 84%, the water loss of the process decreased by 63%, while CO₂ capture capacity fell 22%. Finally, although the pressure drop of the adsorption column (5 ± 1 kPa) and the energy consumption of the EC (537 ± 33 kJ·mol^-1 at 20 mA·cm^-2) are high, we have discussed the potential improvements toward a successful upscaling.