Toward Low-Energy Direct-Air Capture by Reversible Proton-Intercalation Mediated Alkalization

Mitigation strategies to avoid climate change impacts rely on direct air capture (DAC) of CO2. We demonstrate CO2 capture at 400 ppm and release using solid proton-intercalation electrodes to swing the pH of an alkaline electrolyte with 1.68 GJ/tonne energy use that extrapolates to less than 2.74 GJ/tonne when compressed to 1 bar. An electrochemical cell with symmetric potassium-stabilized alpha-phase manganese dioxide (α-K0.05MnO2) electrodes was used to (de)intercalate protons from two separate electrolyte streams, thereby swinging dissolved inorganic carbon (DIC) solubility in an asynchronous cycle wherein electrochemical steps occur in sequence with CO2 transfer steps. Mixing among aqueous streams is shown by theory to reduce CO2 transfer, where the retention of DIC concentration during alkalizing/dealkalizing steps is affected by mixing more so than the generation of an alkali-ion concentration swing. Energy use is shown to further reduce by pre-mixing post-capture and -release electrolytes prior to alkalizing/dealkalizing steps.