CO2 Capture via Crystalline Hydrogen-Bonded Bicarbonate Dimers

Summary Limiting global temperature rises is increasingly dependent on the development of energy-efficient carbon-capture methods. Here, we report a simple CO 2 -separation cycle using an aqueous bis(iminoguanidine) (BIG) sorbent that reacts with CO 2 and crystallizes into an insoluble bicarbonate salt. X-ray diffraction analysis of the bicarbonate crystals revealed “anti-electrostatic” hydrogen-bonded (HCO 3 − ) 2 dimers, stabilized by guanidinium cations and water. Mild heating of the crystals releases the CO 2 and regenerates the BIG sorbent quantitatively, thereby closing the CO 2 -separation cycle. Experimental and computational investigations support a CO 2 -release mechanism consisting of surface-initiated low-barrier proton transfer from guanidinium groups to bicarbonate anions with the formation of carbonic acid dimers, followed by CO 2 and H 2 O release in the rate-limiting step, with a measured activation energy of 102 ± 12 kJ/mol. The minimum energy required for sorbent regeneration is 151.5 kJ/mol CO 2 , which is 24% lower than the regeneration energy of monoethanolamine, a benchmark industrial sorbent.