CO₂ Capture and Consecutive Conversion into Cyclic Carbonates in a Redox Flow

Electrochemical methods are promising for CO₂ mitigation due to their potential for high energy efficiency, adaptability to decentralized operations, and alignment with renewable energy sources. Among the two main approaches for electrochemical CO₂ mitigation—electrochemical CO₂ capture and electrochemical CO₂ reduction—the extended concept of redox-flow batteries often adopts the CO₂ capture approach. In these systems, cathode reactions generate alkaline species capable of capturing CO₂. Diluted CO₂ streams are treated by contact with an electrolyte containing these species, followed by oxidation reactions that facilitate CO₂ release, ultimately separating CO₂ from the feed gas. To achieve an energy-efficient capture process, research focuses on developing cell components, primarily redox-active species with high reversibility and facile reaction kinetics, such as quinones, bipyridines, and transition metal complexes.
While the use of separated CO₂ gas is addressed in other fields, integrating CO₂ capture and utilization processes can significantly reduce overall energy requirements. Thus, electrochemical systems that simultaneously generate bases and reduce CO₂ are under development. In these systems, electrons are introduced to chemisorbed CO₂ species such as carbamates and carbonates, yielding CO₂ reduction products and bases.
In this study, we propose a redox-flow system that captures CO₂ and subsequently converts it into cyclic carbonates. Our system integrates CO₂ capture and conversion through a series of domino reactions triggered by the electrochemical generation of organic bases. Unlike other redox flow systems that use redox-active species targeting highly reversible redox reactions for CO₂ capture, our system utilizes vicinal halohydrin molecules as precursors of alkaline species, which spontaneously undergo intramolecular cyclization reactions after capturing CO₂ and yield cyclic carbonates. Our method achieves a Faradaic efficiency of up to 100% for ethylene carbonate production, demonstrating highly selective sequential capture and conversion reactions. Additionally, it is expandable to the synthesis of various cyclic carbonates directly from diluted CO₂ sources.