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 by using an H2-recycling electrochemical cell. A pH gradient is created in the electrochemical cell so that CO2 is desorbed at low pH, while 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 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 towards the upscaling of an energy-effective process for direct air capture.