Electrochemically Induced Carbon Dioxide Capture from Air with an Aqueous Fluoflavine Molecule

Redox sorbent-based electrochemically induced direct air capture (DAC) holds great promise, as it operates at ambient conditions and requires substantially lower energy inputs. However, the oxygen sensitivity of redox sorbents limits their practical implementation. Here, we developed an aqueous-soluble oxygen-tolerant fluoflavine disulfonate (FFDS) sorbent for DAC. Electrochemical characterizations, spectroscopic studies, along with theoretical calculations, reveal that FFDS undergoes proton-coupled electron transfer and exhibits a redox potential higher than the two-electron transfer oxygen reduction potential. When exposed to simulated flue gas containing 10% O2, FFDS demonstrates reversible CO2 capture and release with an average CO2/e molar ratio of 0.88. Implemented for both indoor and outdoor DAC, FFDS sorbent shows stable cycling performance over 40 days with a three-day DAC under the normal discharge–charge mode, and exhibits an enhanced CO2 capture capacity and a Coulombic efficiency exceeding 99% with an accelerated overnight DAC under the deep discharge–charge mode. Doubling the concentration of FFDS leads to a 2-fold increase in CO2 capture/release capacity. The energy cost for CO2 release and sorbent regeneration ranges from 58 to 190 kJ mol–1 CO2, depending on the applied current densities and discharge–charge modes.