CO₂ capture by hybrid ultramicroporous TIFSIX-3-Ni under humid conditions using non-equilibrium cycling

Pyrazine-linked hybrid ultramicroporous materials (HUMs) have a pore size < 7 Å and are benchmark physisorbents for trace CO₂ capture. However, their affinity for H₂O decreases their carbon capture performance in humid environments. We present results of a study on the co-adsorption of H₂O and CO₂ in a high CO₂-affinity HUM, i.e. TIFSIX-3-Ni. Through a combination of ab initio modeling with dynamic column breakthrough measurements and in situ infrared spectroscopy, we find that slow H₂O sorption kinetics can enable CO₂ uptake/release with retention of up to 90% of the dry CO₂ uptake when using shortened adsorption cycles. The binding sites and sorption mechanisms of this co-adsorption environment reveal that the H₂O and CO₂ molecules cohabitate the same ultramicropore, made possible through favorable interactions between them at low water loading. At higher water loading, an energetically favored water network starts to displace CO₂ molecules. Our results offer bottom-up design principles and insight into co-adsorption of CO₂ and H₂O that is relevant for carbon capture sorbents to address the challenges posed by gas capture and sequestration in humid environments.