Carbonate Dynamics and Opportunities With Low Temperature, Anion Exchange Membrane-Based Electrochemical Carbon Dioxide Separators

Fossil fuel power plants are responsible for a significant portion of anthropogenic atmospheric carbon dioxide (CO₂) and due to concerns over global climate change, finding solutions that significantly reduce emissions at their source has become a vital concern. When oxygen (O₂) is reduced along with CO₂ at the cathode of an anion exchange membrane (AEM) electrochemical cell, carbonate and bicarbonate are formed which are transported through electrolyte by migration from the cathode to the anode where they are oxidized back to CO₂ and O₂. This behavior makes AEM-based devices scientifically interesting CO₂ separation devices or “electrochemical CO₂ pumps.” Electrochemical CO₂ separation is a promising alternative to the state-of-the-art solvent-based methods because the cells operate at low temperatures and scale with surface area, not volume, suggesting that the industrial electrochemical systems could be more compact than amine sorption technologies. In this work, we investigate the impact of the CO₂ separator cell potential on the CO₂ flux, carbonate transport mechanism, and process costs. The applied electrical current and CO₂ flux showed a strong correlation that was both stable and reversible. The dominant anion transport pathway, carbonate versus bicarbonate, undergoes a shift from carbonate to mixed carbonate/bicarbonate with increased potential. A preliminary techno-economic analysis shows that despite the limitations of present cells, there is a clear pathway to meet the U.S. Department of Energy (DOE) 2025 and 2035 targets for power plant retrofit CO₂ capture systems through materials and systems-level advances.