Ion pairing enhances hydroquinone stability toward oxygen in aqueous electrochemical carbon dioxide capture.

The use of redox-active organic molecules for aqueous electrochemical carbon dioxide capture is limited by their tendency to undergo reversible oxidation by oxygen. Here we show that a naphthoquinone derivative, when reduced in the presence of tetraalkylammonium countercations, displays enhanced stability toward oxygen while maintaining carbon dioxide binding ability. By combining structural modification with control of non-covalent interactions, we mitigate a previously observed trade-off between carbon dioxide capture performance and resistance to aerobic oxidation. In situ spectrophotometry and comparative voltammetry indicate that ion pairing stabilizes the reduced quinone both by shifting its redox potential and by promoting carbon dioxide adduct formation. Among the cations tested, tetraethylammonium provides the most favorable balance, supporting efficient capture and release cycle with 87 % Coulombic efficiency and an energy cost of 157 kilojoules per mole of carbon dioxide from a gas mixture containing carbon dioxide, oxygen, and nitrogen. These findings illustrate how molecular design combined with electrolyte engineering can improve the durability of aqueous quinone-based electrochemical carbon capture systems and may inform the development of more robust and energy-efficient approaches for sustainable carbon management.