Polyamines with reactive CO₂ diffusion for carbon capture: the obvious and the unexpected

Polyamines have emerged as a leading materials platform for sorbents in direct air capture (DAC) of CO₂ and membranes for post-combustion capture (PCC) due to their reactions with CO₂. Such reactions compete with hydrogen bonding among amine groups, are sensitive to temperature and water content, and can self-limit the further diffusion and sorption of CO₂ in polyamines. These unique characteristics give rise to interesting, often conflicting phenomena in DAC sorbents and PCC membranes, which have not been resolved at the molecular level. Herein, we highlight the imbalanced effects of substrates on amine efficiency for CO₂ sorption, the complex interplay of temperature and time on pseudo-equilibrium CO₂ sorption, and the intricate effects of water vapor on CO₂ sorption and desorption in DAC. For PCC membranes, both facilitated and hindered CO₂ transport are critically reviewed with an integrated experimental and simulation approach. We elucidate the role of CO₂-reactive diffusion in both sorbent and membrane applications, providing cohesive guidance for designing polyamine-based systems to enhance CO₂ capture performance.