Electrochemical Regeneration of Spent Alkaline Absorbent from Direct Air Capture

CO₂ capture from the atmosphere (or direct air capture) is widely recognized as a promising solution to reach negative emissions, and technologies using alkaline solutions as absorbent have already been demonstrated on a full scale. In the conventional temperature swing process, the subsequent regeneration of the alkaline solution is highly energy-demanding. In this study, we experimentally demonstrate simultaneous solvent regeneration and CO₂ desorption in a continuous system using a H₂-recycling electrochemical cell. A pH gradient is created in the electrochemical cell so that CO₂ is desorbed at a low pH, while an alkaline capture solution (NaOH) is regenerated at high pH. By testing the cell under different working conditions, we experimentally achieved CO₂ desorption with an energy consumption of 374 kJ·mol^-1 CO₂ and a CO₂ purity higher than 95%. Moreover, our theoretical calculations show that a minimum energy consumption of 164 kJ·mol^-1 CO₂ could be achieved. Overall, the H₂-recycling electrochemical cell allowed us to accomplish the simultaneous desorption of high-purity CO₂ stream and regeneration of up to 59% of the CO₂ capture capacity of the absorbent. These results are promising toward the upscaling of an energy-effective process for direct air capture.