CO2 Capture via Crystalline Hydrogen-Bonded Bicarbonate Dimers

Abstract

Summary Limiting global temperature rises is increasingly dependent on the development of energy-efficient carbon-capture methods. Here, we report a simple CO2-separation cycle using an aqueous bis(iminoguanidine) (BIG) sorbent that reacts with CO2 and crystallizes into an insoluble bicarbonate salt. X-ray diffraction analysis of the bicarbonate crystals revealed “anti-electrostatic” hydrogen-bonded (HCO3−)2 dimers, stabilized by guanidinium cations and water. Mild heating of the crystals releases the CO2 and regenerates the BIG sorbent quantitatively, thereby closing the CO2-separation cycle. Experimental and computational investigations support a CO2-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 CO2 and H2O 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 CO2, which is 24% lower than the regeneration energy of monoethanolamine, a benchmark industrial sorbent.