Moisture-Driven CO2 Sorbents

An energy-saving system containing ion-exchange or nanoporous materials and carbonate ions is proposed, which is capable of capturing CO2 from ambient air simply by controlling the amount of water (moisture) in contact with the sorbent. The system binds CO2 from the air when the surrounding is dry, whereas it desorbs CO2 when it is wet. A design of such CO2 sorption and desorption systems is investigated using quantum mechanics simulations and is verified by experiments. Its working mechanism is revealed as the free energy change of the chemical reaction of the carbonate ions and water molecules; the free energy change decreases when the number of water molecules in the materials decreases. The influence of pore size, spacing of cations, and surface hydrophobicity of the sorbents on CO2 capture efficiency are elucidated. The study sheds light on ways to optimize an efficient direct air capture system and therefore contributes to the development of “negative emission technologies.” © 2020 Elsevier Inc.An energy-saving sorbent is proposed to capture CO2 from ambient air simply by controlling the amount of water (moisture) in contact with it. The system binds CO2 from the air when the surrounding is dry, whereas it desorbs CO2 when it is wet. Various microporous and ion-exchange materials can be employed in subsequent studies. The study sheds light on ways to optimize an efficient direct air capture system and therefore contributes to the development of “negative emission technologies.” © 2020 Elsevier Inc.Moving the energy infrastructure away from fossil fuels to renewable energies to stop global warming is a challenging task. In the transition, CO2 capture and storage (CCS) from point sources could reduce CO2 emission. However, the objective of stabilizing atmospheric CO2 at 450 ppm cannot be achieved by CCS alone. Here, the urgency of the development of CO2 capture from ambient air, or “direct air capture” (DAC) is demonstrated. A successful sorbent for DAC must (1) have fast reaction kinetics, (2) be low in cost, and (3) be able to regenerate with a low energy barrier to complete the whole CO2 capture-release cycle. Most CO2 sorbents failed in the third category as they had to overcome a large energy barrier to regenerate. This study presents an energy-saving sorbent to capture CO2 simply by controlling the water quantities on it. We report the effects of parameters of the sorbents on CO2 capture efficiency. The study can lead the way toward the optimization of sorbents for DAC. © 2020 Elsevier Inc.