Oxygen-tolerant CO₂ capture using protected redox-driven reverse bias bipolar membrane electrodialysis

Electrochemical methods for carbon capture potentially have the advantage of low cost and low energy consumption. The practical applicability of pH-swing carbon capture processes driven by proton-coupled redox-active molecules has been limited by the sensitivity of reduced molecules to oxidation by O₂. In those CO₂ capture processes, the molecules are reduced, basifying the electrolyte; the electrolyte containing the reduced molecules is exposed to air or flue gas containing CO₂ but also containing enough O₂ to oxidize the molecules. O₂ sensitivity would not be problematic if the electrolyte that captures CO₂ contains the oxidized form of the molecule instead; this can be accomplished by switching from an electron-driven system to an ion-driven system. We report the development and performance of a two-chamber flow cell incorporating a reverse-bias bipolar membrane (BPM) and non-proton-coupled redox-active molecules for ion-driven pH-swing. When using ferri/ferrocyanide electrolytes in this cell with a BPM, the cell pH can be spatially swung with the oxidized side basified for CO₂ capture and the reduced side acidified for release. Buffering agents and cell rebalancing mediators improved the efficiency and stability of the system. This work points out an alternative way of employing redox couples for electrochemically-powered pH swings.