Carbon dioxide (CO2) must be removed from the atmosphere to mitigate the negative effects of climate change. However, the most scalable methods for removing CO2 from the air require heat from fossil-fuel combustion to produce pure CO2 and continuously regenerate the sorbent. Bipolar-membrane electrodialysis (BPM-ED) is a promising technology that uses renewable electricity to dissociate water into acid and base to regenerate bicarbonate-based CO2 capture solutions, such as those used in chemical loops of direct-air-capture (DAC) processes, and also in direct-ocean capture (DOC) to promote atmospheric CO2 drawdown via decarbonization of the shallow ocean. However, a lack of understanding of the mechanisms of reactive carbon species transport in BPMs has precluded industrial-scale deployment of BPM-ED. In this study, we develop an experimentally-validated 1D model for the electrochemical regeneration of CO2 from bicarbonate-based carbon capture solutions and seawater using BPM-ED. Our experimental and computational results demonstrate that out-of-equilibrium buffer reactions within the BPM drive the formation of CO2 at the BPM/electrolyte interface with energy-intensities of less than 150 kJ mol-1. However, high rates of bubble formation increase the energy intensity of CO2 recovery at current densities >100 mA cm−2. Sensitivity analyses show that optimizing the BPM and bubble removal could enable CO2 recovery from bicarbonate solutions at energy intensities <100 kJ mol−1 and current densities >100 mA cm−2. These results provide design principles for industrial-scale CO2 recovery using BPM-ED.
Supporting Information for "Exploring Bipolar Membranes for Electrochemical Carbon Capture"
Computational Methods, Table of Parameters Employed in Model, Schematic of Experimental Cell for BPM Measurement, Supplemental Profiles, Definition of Water Dissociation Efficiency, Zoomed Inset of Coulombic Efficiency and Energy Intensity for i < 10 mA cm–2, Note on Inflection Point in CO2 Regeneration Rate, Supplementary Note on Catholyte Equilibrium and Inflection Point in CO2 Regeneration Rate Curve, Fluxes and Efficiencies of Sorbent Regeneration within the AEL, Effect of pH Gradient Operation on Polarization Curve and Efficiencies, Effect of Boundary Layer Thickness on Polarization Curve and CO2 Bubbling, Experimental Analysis of Flow Rate Effects, Supplementary Experimental Methods for Flow Rate Experiments, Effect of Bubbling on Polarization Curve and CO2 Generation, Sensitivity Analysis, Supplementary Note on “Optimal BPM” Simulations, Theoretical Analysis of Performance in a BPM-ED Stack