Evaluating 4-Stage Aqueous Electrochemical CO 2 Separation with Dissolved Quinone Derivatives

State-of-the-art carbon capture primarily relies on amine-based thermal-swing systems, in which temperature controls carbon dioxide (CO 2 ) binding to and release from amines. However, these systems face challenges such as Carnot efficiency limits, substantial energy demand for solvent regeneration, 1 and progressive amine degradation over time and cycling. 2 These constraints motivate exploration of alternative approaches. Electrochemical CO 2 separation may enable higher energetic efficiencies because faradaic reactions can selectively activate only the capture species, driving CO 2 absorption or desorption. 3 In particular, aqueous CO 2 -capture media—where proton-coupled electron-transfer reactions generate a pH gradient across an electrochemical cell—enable capture in alkaline conditions and release in acidic conditions, providing environmental, safety, and cost advantages as compared to non-aqueous electrolytes. 4,5 In this presentation, we investigate the separation capability and stability of different water-soluble quinone derivatives in a 4-stage system designed for continuousCO 2 capture and release. The 4-stage system utilizes an absorber and flash tank to separate CO 2 capture and release from the cathodic activation and anodic deactivation of the capture species in the electrolytic cell. We experimentally assess the durational performance of 4-stage system as a function of inlet gas composition (including oxygen), electrolyte formulation, volumetric flow rate, and applied current. To isolate the CO 2 capture and release behavior, we also operate the system in a batch-mode configuration analogous to a redox flow battery, cycling the quinone derivatives and quantifying the separation performance. Complementary electrochemical diagnostics are employed to assess ohmic, charge-transfer, and mass-transfer contributions to cell resistance, as well as self-discharge and decomposition processes in both batch and continuous operation modes. The insights gained from these studies can be used to inform the molecular engineering of capture species and to assess the feasibility of different operating approaches for electrochemical CO 2 separation. References [1] Herzog H. J. 2018. Carbon Capture; The MIT Press Essential Knowledge Series; The MIT Press. [2] Gouedard, C., Picq, D., Launay, F. and Carrette, P.L., 2012. Amine degradation in CO 2 capture. I. A review. International journal of greenhouse gas control, 10, pp.244-270. [3] Clarke, L.E., Leonard, M.E., Hatton, T.A. and Brushett, F.R., 2022. Thermodynamic modeling of CO 2 separation systems with soluble, redox-active capture species. Industrial & Engineering Chemistry Research, 61(29), pp.10531-10546. [4] Wenger, S.R. and D'Alessandro, D.M., 2025. Aqueous Electrochemical Direct Air Capture Using Alizarin Red S. ChemSusChem, 18(3), p.e202401315. [5] Ripley, K.M. and Brushett, F.R., 2024. Modeling and Comparative Analysis of CO 2 Absorption Columns in Electrochemical and Thermochemical Carbon Capture Systems. Industrial & Engineering Chemistry Research, 63(49), pp.21479-21504.