CO₂ Capture by Hybrid Ultramicroporous TIFSIX-3-Ni under Humid Conditions Using Non-Equilibrium Cycling

Although pyrazine-linked hybrid ultramicroporous materials (HUMs, pore size <7 Å) are benchmark physisorbents for trace carbon dioxide (CO₂) capture under dry conditions, their affinity for water (H₂O) mitigates their carbon capture performance in humid conditions. Herein, we report on the co-adsorption of H₂O and CO₂ by TIFSIX-3-Ni—a high CO₂ affinity HUM—and find that slow H₂O sorption kinetics can enable CO₂ uptake and release using shortened adsorption cycles with retention of ca. 90 % of dry CO₂ uptake. Insight into co-adsorption is provided by in situ infrared spectroscopy and ab initio calculations. The binding sites and sorption mechanisms reveal that both CO₂ and H₂O molecules occupy the same ultramicropore through favorable interactions between CO₂ and H₂O at low water loading. An energetically favored water network displaces CO₂ molecules at higher loading. Our results offer bottom-up design principles and insight into co-adsorption of CO₂ and H₂O that is likely to be relevant across the full spectrum of carbon capture sorbents to better understand and address the challenge posed by humidity to gas capture.