Evaluating Quinone Redox Chemistry for CO ₂ Capture in Aqueous Solvents under Flue Gas Conditions

Electrochemical quinone-mediated CO2 capture offers a promising strategy for mitigating global carbon emissions. However, many quinone studies are conducted in organic solvents, and the CO2-quinone redox chemistry is less explored under application-relevant conditions, such as aqueous solvent and flue gas concentration. To address this gap, we investigated the effect of aromaticity and the electronic structure of different quinones on their CO2 binding and release under aqueous flue gas conditions. Cyclic voltammetry studies revealed that quinones with smaller aromatic systems exhibited stronger CO2 binding, which was attributed to their higher nucleophilicity. However, in CO2 capture and release studies, the quinone with the highest binding constant did not lead to the best capture performance. Among the quinones studied, 1,2-naphthoquinone-4-sulfonic acid (NQS), an intermediate-sized quinone, exhibited the highest performance. At 10 mA/cm2 under a 20% CO2 feed, NQS achieved a CO2 release rate of 227 μmol/h, maintaining 45% electron utilization over 16 h. Electrochemical impedance spectroscopy analysis shows that NQS maintains a similar charge-transfer resistance during both CO2 capture and release, which is consistent with its superior performance relative to the other quinones studied. These findings reveal a clear structure–property relationship and highlight the need for an optimal balance between CO2 binding strength and redox reversibility.