Direct air capture (DAC) of CO2, as opposed to point source capture, is a negative emissions technology that not only has the potential to help achieve carbon neutrality, but also to reach net negative emissions. However, DAC technology is limited in application due to its high cost, which primarily stems from the relatively low partial pressure of CO2 with respect to uptake by an absorber. In this study, we evaluate two approaches for DAC based on chemical absorption by a solvent: an electroswing (i.e. direct binding of CO2) and a pH swing. In the electroswing approach, the final active site is a quinone molecule, which requires tuning the CO2 binding energy to the solvent to be strong enough to absorb but lower than that of the quinone. On the other hand, in the pH swing approach, the solvent is the final active site, and quinones are used as proton carriers to tune the pH for enhanced CO2 loading and CO2 release (i.e., solvent regeneration). In this approach, the quinone must be tuned to have a high pKa as well as a high solubility in the carbon capture solvent. To address these challenges, we have used highly accurate quantum chemical calculations to screen libraries of both quinones and carbon capture solvents in order to identify promising solvent/quinone pairs, develop structure-property relationships for both approaches and determine the mechanistic details of captured CO2 and intermediates.

Computational design of quinones for direct air capture of CO2

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