Electrochemically Induced CO2 Capture Enabled By Aqueous Quinone Flow Chemistry
Authors: Jing Yan , Amini Kiana , Xi Dawei , Jin Shijian , Alfaraidi Abdulrahman , Kerr Emily F. , Gordon Roy G. , Aziz Michael J. 
Published: December 2024

Climate change caused by the accumulation of anthropogenic CO2 emissions motivates the development and deployment of cost-effective, scalable, modular, and energetically efficient techniques to capture CO2 from point or diffuse sources. Electrochemically-driven CO2 capture processes utilizing redox-active organics in aqueous flow chemistry and operating at ambient temperature and pressure show promise for nonflammability, continuous-flow engineering, and the possibility of being driven at high current density by inexpensive, clean electricity.[1-2]

We show that the deprotonated hydroquinone-CO2 adducts, whose insolubility limits the utility of the quinone-hydroquinone redox couple, become soluble when alkylammonium cations are introduced. Consequently, we introduce alkylammonium groups to anthraquinone via covalent bonds, making the resulting bis[3-(trimethylammonio)propyl]-anthraquinones (BTMAPAQs) soluble.[3] We report the first aqueous quinone flow electrochemistry induced CO2capture/release process, which occurs at ambient temperature and pressure. We show that the electrochemically reduced BTMAPAQs are both Lewis bases and Brønsted bases, thus capturing CO2 via both a pH-swing and a nucleophilicity-swing mechanism. Among the 1,4-, 1,5-, and 1,8-BTMAPAQ isomers, 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/molCO2. In a crude simulated flue gas composed of 3% O2, 10% CO2, and 87% N2 with a flow rate of ~12 mL/min, 1,5-BTMAPAQ electrolyte reversibly captured and released 50% of the theoretical capacity during an exposure of over 4 hours. 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 CO2 capture with aqueous quinone flow electrochemistry. The oxygen tolerance of reduced quinones may be significantly advanced through molecular engineering by introducing steric and/or electronic effects, intra-molecular interactions, elevating or lowering the oxidation potentials of reduced quinones.
[1] Jin, S.; Wu, M.; Gordon, R. G.; Aziz, M. J.; Kwabi, D. G. pH swing cycle for CO2 capture electrochemically driven through proton-coupled electron transfer, Energy Environ. Sci., 2020, 13, 3706-3722.
[2] Jin, S.; Wu, M.; Jing, Y.; Gordon, R. G.; Aziz, M. J. Low energy carbon capture via electrochemically induced pH swing with electrochemical rebalancing, Nature Communications, 2022, 13, 2140.
[3] Jing, Y.; Amin, K.; Xi, D.; Jin, S.; Alfaraidi, A.; Kerr, E.F.; Gordon, R.G.; Aziz, M.J, Electrochemically induced CO2 capture enabled by aqueous quinone flow chemistry, ChemRxiv, 2023, DOIs:10.26434/chemrxiv-2023-nfg6z-v2; 10.26434/chemrxiv-2023-nfg6z.