Electrochemically Induced CO <sub>2</sub> Capture Enabled by Aqueous Quinone Flow Chemistry
Yan Jing, Kiana Amini, Dawei Xi, Shijian Jin, Abdulrahman M. Alfaraidi, Emily F. Kerr, Roy G. Gordon, Michael J. Aziz
Abstract
Electrochemically driven CO 2 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–CO 2 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 CO 2 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 CO 2 molecules per quinone from 1-bar CO 2 –N 2 mixtures, for which the CO 2 partial pressure is as low as 0.05 bar, or the applied current density is as high as 100 mA/cm 2, or the organic concentration is as high as 0.4 M. The energetic cost ranges from 48 to 140 kJ/mol CO 2 . In a crude simulated flue gas composed of 3% O 2, 10% CO 2, and 87% N 2, 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 O 2 tolerance, demonstrating a substituent position effect on the reactivity of isomers with CO 2 and O 2 . The results provide fundamental insight into electrochemical CO 2 capture with aqueous quinone flow chemistry and suggest that the oxygen tolerance of reduced quinones may be significantly advanced through molecular engineering.