Electrochemical CO2 Capture with pH-Independent Redox Chemistry

Capturing anthropogenic carbon dioxide is essential to meet the climate targets. Despite the progress in decarbonizing the grid and transportation, some sectors remain difficult to decarbonize, and carbon capture is necessary to reach carbon neutrality. The incumbent technology for carbon capture utilizes amine sorbents to scrub CO₂ using thermal stimuli; however, the thermodynamic penalty for CO₂ capture and release is high and the heating of non-active water solvent with high heat capacity contribute to the high energy cost. As a result, current energy input needed is an order-of-magnitude larger than the theoretical minimum free energy associated with the entropy change. Alternatively, electrochemical carbon capture using redox-active sorbents has recently been gaining attention. Electrochemical activation specifically targets active materials, circumventing energy loss to substrate heating. Among various electrochemical CO₂ capture methods, electrochemical modulation of pH is a promising strategy that leverages the dependence of inorganic carbon solubility on pH.<br/>In this work, we present a pH-independent redox chemistry for energy efficient CO₂ capture. Our method is based on modulating the pH by changing the activity coefficient of H⁺. By circumventing direct modulation of H⁺ concentration, we can swing the pH without associated entropic penalties in the redox reaction. This minimizes the thermodynamic energy input for pH swing and CO₂ capture and release, which we demonstrate in a flow cell. Through molecular dynamics and density functional theory simulations, we find that H⁺ activity is modulated by polarizing water molecules. We demonstrate with in-situ infrared spectroscopy that bicarbonates and formed and released through redox reactions and electrochemical modulation of the pH.