Electrochemically Induced CO2 Capture Enabled by Aqueous Quinone Flow Chemistry

Electrochemically driven CO₂ capture processes utilizing redox-active organics in aqueous flow chemistry show promise for nonflammability, continuous-flow engineering and the possibility of being driven at a high current density by inexpensive, clean electricity. We show that deprotonated hydroquinone–CO₂ adducts, whose insolubility limits the utility of the quinone–hydroquinone redox couple, become soluble when alkylammonium cations are introduced. Consequently, we introduced alkylammonium groups to anthraquinone via covalent bonds, making the resulting bis[3-(trimethylammonio)propyl]anthraquinones (BTMAPAQs) soluble. We report the first aqueous quinone flow chemistry-enabled electrochemical CO₂ capture/release process, which occurs at ambient temperature and pressure, and show that it proceeds via both pH-swing and nucleophilicity-swing mechanisms. 1,5-BTMAPAQ reaches the theoretical capture capacity of two CO₂ molecules per quinone from 1-bar CO₂–N₂ mixtures, for which the CO₂ partial pressure is as low as 0.05 bar, or the applied current density is as high as 100 mA/cm², or the organic concentration is as high as 0.4 M. The energetic cost ranges from 48 to 140 kJ/mol CO₂. In a crude simulated flue gas composed of 3% O₂, 10% CO₂, and 87% N₂, 1,5-BTMAPAQ electrolyte reversibly captured and released 50% of the theoretical capacity during an exposure of over 4 h. It outperforms its isomeric counterparts 1,4-, and 1,8-BTMAPAQ in capture capacity and O₂ tolerance, demonstrating a substituent position effect on the reactivity of isomers with CO₂ and O₂. The results provide fundamental insight into electrochemical CO₂ capture with aqueous quinone flow chemistry and suggest that the oxygen tolerance of reduced quinones may be significantly advanced through molecular engineering.