Unexpected Oversolubility of CO 2 Measured at Electrode–Electrolyte Interfaces

High Resolution Image Download MS PowerPoint Slide Enhancements in gas solubility in pore-confined liquids─termed oversolubility─can drastically influence gas separation and catalytic efficiency in confined environments; however, they remain poorly understood in electrochemical CO 2 capture and reduction systems. While previous investigations of oversolubility have emphasized the importance of mesoporosity and incomplete pore saturation by the solvent, in this work, we report an unprecedented 30-fold oversolubility effect for CO 2 in solely microporous activated carbons saturated with 1 M Na 2 SO 4(aq) . The oversolubility effect occurs regardless of the activated carbon’s functional groups and level of disorder and is enhanced for smaller pore sizes. Oversolubility is quantified using solid-state 13 C nuclear magnetic resonance spectroscopy (NMR), enabling differentiation between in-pore and ex-pore CO 2 and HCO 3 – . Atomistic modeling of the system, based on a machine-learning model delivering first-principles accuracy, suggests that the effect is driven by an adsorption-like mechanism underpinned by favorable interactions between CO 2 and the pore walls. Our findings demonstrate the unexpected importance of oversolubility for gas uptake in microporous, solvent-saturated carbon electrodes, an effect with direct relevance for improving electrochemical CO 2 capture and conversion technologies.