Aqueous Capture of Atmospheric CO2 Enabled by a Hemoglobin-like Dynamic, Cooperative Polymer

Abstract The reversible capture of atmospheric CO2 is essential for artificially closing the carbon cycle but is fundamentally constrained by a materials paradox: achieving sufficient affinity at ultradilute concentrations (<1000 ppm, or <0.1 vol %) conflicts with the need for low-energy sorbent regeneration, especially in aquatic environments. Here, we report a bioinspired polymer that circumvents this trade-off by undergoing a hemoglobin-like state switch in water. Upon exposure to atmospheric-level CO2 (e.g., 400 ppm, and down to 100 ppm, in N2), the polymer chain collapses uniformly, triggering positive cooperativity that enhances the effective binding affinity by nearly 5-fold. This dynamic mechanism enables efficient capture (1.04 mmol g–1 at 400 ppm of CO2 in N2) with mild, complete release. Crucially, the captured CO2 is stored predominantly as dissolved CO2(aq), allowing the spent solution to serve directly as an efficient electrolyte for electrochemical CO2 reduction and boosting the Faradaic efficiency for formate to 57.3% under 400 ppm of CO2, a performance comparable to that of a polymer-free system using pure CO2. This work establishes a dynamic, cooperative capture paradigm that can integrate molecular sequestration and conversion, offering a practical route to energy-lean carbon cycling.